ADVANCED TECHNOLOGIES - turknorosirurji.org.trder the longus colli muscles after the dissection. The C2/3 disc space is identified after the blunt dissection and mar-ked with 2 mm

ADVANCED TECHNOLOGIES

Murat Cosar M.D. Ph.D., Larry T. Khoo M.D., Farbod Asgarzadie M.D.

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ally Invasive Procedures In Spine Surgery

CT BASED IMAGE GUIDANCE IN SPINE

SURGERYMurat Cosar M.D. Ph.D., Larry T. Khoo M.D., Farbod Asgarzadie M.D.

1.Introduction: The surgical approaches to the deformated, scolio-tic and upper cervical spine needs more experience for the spine surgeons because of relocated anatomi-cal marks, relationship with critical structures such as aorta, vertebral artery, spinal cord and other ne-ural structures. The various on the course of verteb-ral artery and difficulties for the localization of land-marks may increase the hazard of screw placement to upper cervical spine (1-3).

As the technology developes, the novel radiolo-gical tecniques and tools are added to facilitate the operative procedures and increase the confidence of spine surgery. The two dimentional systems such as fluoroscopy are used in spine surgery for many ye-ars. The three-dimensional (3D) anatomy of spine, especially the cranio-cervical, cervico-thoracic and lumbosacral junction is complex with critical structu-res and may present difficulties for most of the spine surgeons. These structures are limited to image in fluoroscopy due to its dense bone anatomy (4). The two-dimensional (2D) images of fluoroscopy make the surgeon to care on the 3D surgical anatomy. The use of biplanar fluoroscopy (may help to consider 3D) may cause to waste the operation time and need to respect to the surgical field sterilization (5).

The developing technology brought novel tools to the surgical technique and in recent years. There are a few developed and new developing 3D systems such as classical volumetric guided navigation (CT and/or MRI based), and fluoroscopic assisted nav-igation, etc. CT-based image-guided surgery (IGS) applications are added to spine surgical techniques which is adapted from the cranial surgery.

CT-based IGS system reformate the preopera-tive 2D images to 3D renderings and a navigation system is added to display in real time during ope-ration. CT-based IGS allows the surgeon to evalu-ate the patient’s anatomical structures before and during surgery. It helps to avoid the injury of neu-ral and vascular structures and limit the resection of anatomical structures. CT-based IGS can help to determine the surgical dissection, reduce fluorosco-pic x-ray exposure, facilitate the implant placement and localization (6).

Although the history of image guidance techno-logy depends on the stereotaxis, it was developed after the invent of CT and MRI. The first generation of CT-based IGS technology targetted the safely re-section of the deep-seated brain tumors with mini-mal trauma to the surrounding structures. Recently, development for the IGS technology allowed the surgeons to use it for cranial-based, upper cervical, cervico-thoracal junction and lumbosacral junction surgery. Although these developments, image gu-idance in spine surgery is more difficult compared to cranial surgery. The rigidly fixed skull to the ope-rating table makes the landmarks stable for cranial surgery, however the prone position of the patient on a mobile abdomen allow the movement of the spine and also landmarks during operation.

The increased operation time due to set up and registration, the cost and complex use of the equip-ment, the long preoperative time for image scanning, the need of re-registration during operation, additio-nal tools in the operation field are the disadvantages of CT-based IGS systems (5). For these reasons, it did not take place for routine use in spine surgery altho-ugh it increases the accuracy of spine surgery. The surgeon must take in mind that, IGS systems decre-

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ase the risk of damages but does not eliminate. Addi-tionally, at the beginning, the complex and high risk spinal procedures outweigh the disadvantages beca-use of the considerable learning curve of IGS.

Severeal studies showed that the image guidance is useful for the preoperative surgical planning and intraoperative guidance of C1-C2 transarticular screw placement (2,5,7). It reduces the risk of screw mispla-cement so, decrease the risk of neural and vascular structures. Additionally, image guidance increase the accuracy of transoral spinal procedures (2,8).

2. Indications: CT-based image guidance system can be used for the TSF of C1 and C2 and odontoid fixation, scoliotic and deformated spine, cervico-thoracal and lumbosacral junctions of the patients. Addition to these, it may be chosen for the guidance on tumor surgery to define limits and displaced anatomical structures.

3. Surgical Procedures:

3.a. Surgical Equipment:The preoperative CT images of the patient is neces-sary to transfer them to the work station. A computer workstation and monitor, a tracking system, a spine clamp with reference array, optical tracked instruments are the main parts of CT-based IGS system. The rou-tine minimally invasive surgical tools are also neces-sary for the surgical procedure (Figure 1a, b).

3.b. Operation room set-up:The work station computer and monitor is settled op-posite to the surgeon. The optical track instruments must come just opposite to the reference array spine clamp. The routine surgical tools and nurse are sett-led to the left side while the assistant is locating at the right side of the surgeon (Figure 2).

3.c. Patient positioning:The rigid fixation of the skull (Mayfield clamp) may help to decrease the re-registration of the IGS system during surgery which is caused by abdomi-nal movements and/or other positional problems. Prone position is chosen for C1-C2 transarticular fixation and posterior cervical, thoracal ans lum-bar aproaches while supine position with a slight

extension is chosen for anterior odontoid fixation (Figure 3a,b).

3.d. Surgical Technique:Prior to surgery, the CT image slices (1 mm slice thickness or smaller) of the upper cervical spine is obtained which can be converted to 3D configurati-ons. The images are transferred to the IGS compu-ter workstation and preoperative plan is performed by the surgeon at the workstation (Brain Lab, Medt-ronic, CA, USA). The converted 3D renderings allow the surgeon to understand the anatomical relations-hip with the diseased anatomical structure. The entry point, trajectory, and screw dimensions can be ma-nipulated and mapped preoperatively at the work-

Figure 1a, b: The basic tools of CT-based IGS system.


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station and stored to use later during operation. The common instructions of the CT-based IGS system is summarized in (Figure 4).

After these common processes of CT-based IGS system;

3.d.1. TSF of C1 and C2: A virtual centerpoint where the vertebral artery is closest to C2 and a virtual exit point out of C2 at the dorsal half of the upper joint surface of C2 are

selected at the workstation. The entry point is loca-ted by projecting this trajectory onto the dorsal sur-face of C2. In the same trajectory, the target point for drilling in C1 is found (Figure 5a,b). The diameter of the pars interarticularis is measured at the screw trajectory axis (2).

The patient is positioned prone as conventio-nal approach of TSF of C1 and C2 and the head was secured by a Mayfield clamp. After the clea-ning of surgical area, a standard midline approach

Figure 2: The operation room set up.

Figure 3a, b: The patients position.


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of C1 and C2 is performed, the reference array of CT-based IGS system is fixed to the spinous pro-cess of C2. The accurate of registration is important before using the IGS system for intraoperative na-vigation. The surface and surgical field are matc-hed with the virtual computer field by point-to-point registration.

After the registration, the drill guide inserted through a stab incision, which provided the dril-ling trajectory of the surgical plan. After drilling

period has finished, a 4.0-mm cannulated screw with a proper length as in virtual images is inser-ted under the guidance of computer images. After the screw is reached and grasped the C1, the si-milar procedure is performed to the other side (2). The authors declare that more than 5 mm screw insertion into C1 is adequate for stabilization (10). The routine closure of TSF of C1 and C2 is per-formed after removing the reference array of the IGS system.

Figure 4:

Preoperative CT Scan Transfer of images to the

workstation and reformations for anatomical structures

Selection of patient anatomical guidelines and registration with reformatted CT

Reference array is attached to a suitable location at the surgical field

Registration of probe touches of surgical points to the workstation

Verification of system by matching virtual and real probes

Three-dimensional anatomical are illlustrated on the workstation monitor

Figure 4: The common instructions of the CT-based IGS system is summarized.


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3.d.2. Odontoid Fixation: A virtual centerpoint at the corpus of C2 and a vir-

tual exit point at the fractured odontoid part C2 are se-lected at the work station. The entry point is located by

projecting this trajectory onto the anterior surface of C2/C3 disc space. The length of the virtual trajectory of the screw is mea-sured at the work station.

The head was secured by a Mayfield clamp after the patient is positioned supine as the traditional approach of odontoid fixation. The re-ference array was attached to the Mayfield clamp. A 6 cm li-near incision is centred on the C3/4 disc space after the pre-paration of the skin. The trans-verse retractors are placed un-der the longus colli muscles after the dissection. The C2/3 disc space is identified after the blunt dissection and mar-ked with 2 mm wire (9).

The accurate registration of CT-based IGS system is perfor-med with the reference array. The surface and surgical field are matched with the virtual computer field by point-to-point registration. After the registra-tion, the optimal drill entry po-int was identified at the inferior endplate of C2, and drilled to-wards the apical cortical surface of the odontoid process under the guidance of appropriate sur-gical trajectory plan.

After drilling period has finished, an appropriate sized odontoid screw is inserted un-der the guidance of IGS, after the screw crosses the fracture line, the threads engage the fragment and the lag effect of the screw reduces the disp-laced fragments. Slowly and smooth drill advancement and screw insertion is one of the most important points of this

technique. After the confirmation of stability, the ro-utine closure of is performed and then the reference array of the IGS system is removed.

Figure 5a, b: The CT based image guidance figures of C1-2 transarticular screwing

is seen.


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3.d.3. Posterior Pedicular Fixation: A virtual centerpoint at the pedicle of vertebra and a virtual exit point at the corpus of vertebra are se-lected at the work station. The entry point is located by projecting this trajectory onto the posterior sur-face of facet and transverse process intersection. The length of the virtual trajectory of the screw is mea-sured at the work station.

Mayfield clamp is used for maintaining the head for the cervico-thoral located cases in prone posi-tion. The reference array was attached to the May-field clamp. The reference array may be fixed to an apparatus which is connected to the operation table for the lumbar and spinal vertebrae cases.

After an adequate linear incision at the midline just over the spinous processes, the fascia and musc-les are retracted and an apropriate retractor is pla-ced. The facet joints are identified after a blunt di-section and marked with 2 mm wire.

The accurate registration of CT-based IGS system is performed with the reference ar-ray. The surface and surgical field are matched with the virtual computer field by point-to-point registration. After the registration, the optimal drill entry point was identified at the lateral of facet joints and drilled to-wards the pedicle and corpus of ver-tebra under the guidance of approp-riate surgical trajectory plan.

After drilling period has finished, an appropriate sized screw is inserted under the guidance of IGS. The screw crosses the pedicle and corpus of ver-tebra. Slowly and smooth drill advan-cement and screw insertion is one of the most important points of this tech-nique. After the confirmation of sta-bility, the routine closure of is perfor-med and then the reference array of the IGS system is removed.

4. Postoperative care and Avoiding Complications

The patient is taken to the recovery unit after the operation. Muscle relaxants and non-steroidal anti-inflammatory,

antibiotics can be performed after operation if it is ne-eded. The patients may be allowed to mobilize in the same day and discharged the day after surgery. The patient may return his job in 2 weeks after surgery if he is free from the postoperative problems.

Although it can not be eliminate and less than the classical approaches, the risk of vertebral artery and neural injury may decrease with the learning curve begun with cadaveric and neuranatomic studies.

5. Case Illustrations:

Case 1.The CT based image guidance figures of cervical pe-dicular screwing is seen in figure 6 a,b.

Case 2.The CT based image guidance figures of Thoracal pedicular screwing is seen in figure 7.

Figure 6a, b: The CT based image guidance figures of cervical pedicular screwing is seen.


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7. References:1. Fassett DR, Apfelbaum RI, Hipp JA. Comparison

of fusion assessment techniques: computer-assisted versus manual measurements. J Neurosurg Spine 2008; 8(6):544-7.

2. Weidner A, Wahler M, Chiu ST, Ulrich CG. Modifi-cation of C1-C2 transarticular screw fixation by im-age guided surgery. Spine 2000; 25: 2668-2674.

3. Wright NM, Lauryssen C. Vertebral artery injury in C1–2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. American Associ-ation of Neurological Surgeons/Congress of Neu-rological Surgeons. J Neurosurg 1998; 88: 634–640.

4. Maurer CR, Shahidi R, West JB, Kim DH. Image Guided Endoscopic and Minimally Invasive Spine Surgery. In: Kim DH, Fessler RG, Regan JJ. Endo-scopic Spine Surgery and Instrumentation. Thieme, New York, 2004, pp 361-378.

5. Eichholz KM, Nioguy S, Samartzis D, Jako RV, Per-ez-Cruet MJ. Applications of Image Guidance in

Minimally Invasive Spine Surgery. In: Perez-Cruet MJ, Khoo LT, Fessler RG. An Anatomic Approach to Minimally Invasive Spine Surgery. Quality Medi-cal Publishing, Inc. St. Louis Missouri, 2006, pp 207-213.

6. Klimo P, Rao G, Apfelbaum RI. Microsurgical Treat-ment of Odontoid Fractures.

7. Bloch O, Holly LT, Park J. Effect of frameless stereo-taxy on the accuracy of C1-2 transarticular screw placement. J Neurosurg Spine 2001; 95: 74-79.

8. Veres R, Bago A, Fedorcsak I. Early experiences with image-guided transoral surgery for the pathologies of the upper cervical spine. Spine 2001; 26: 1385-8.

9. Chibbaro S, Benvenuti L, Carnesecchi S, Marsella M, Serino D, Gagliardi R. The use of virtual fluo-roscopy in managing acute type II odontoid fracture with anterior single-screw fixation. A safe, effective, elegant and fast form of treatment. Acta Neurochir (Wien) 2005; 147: 735–739.

10. Madawi AA, Casey AT, Solanki GA. Radiological and anatomical evaluation of the atlantoaxial tran-sarticular screw fixation technique. J Neurosurg 1997; 86: 961–968.

Figure 7: The CT based image guidance figures of thoracal pedicular screwing

is seen.

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Larry T. Khoo M.D., Fred H. Geisler M.D. Ph.D., J.J. Abitbol M.D.

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LUMBAR DISC REPLACEMENTLarry T. Khoo M.D., Fred H. Geisler M.D. Ph.D., J.J. Abitbol M.D.

1. IntroductionMultiple intervertebral disc procedures have been de-veloped to deal with abnormalities in the interver-tebral disc. These include herniation of the nucleus pulposus, degenerative disc disease, and segmental instability. In recent years, the diagnostic accuracy and description of these abnormalities have been aided by the development of water-soluble myelography, MRI, provocative discogram, diagnostic blocks, and high resolution CT scan techniques with both intra-venous and intrathecal contrast. Over the past 15 years, multiple therapeutic advances have also oc-curred to aid in managing intervertebral disc disease. These have included rigid segmental pedicle screw fixation (which has been shown to enhance the fu-sion rate over a non-instrumented fusion), single fi-ber carbon cage, and allograft spacers placed in the anterior column to promote anterior column fusion, demineralized bone matrix, platelet derived autolo-gous growth factor (AGF), bone morphogenic proteins (BMP), and numerous bone graft extenders to elimi-nate or minimize iliac bone graft harvested during a lumbar fusion procedure. There has also been recog-nition over the last decade that interbody stabiliza-tion and arthrodesis, in addition to posterior instru-mentation and arthrodesis, enhances the total lumbar joint fusion rate. The interbody fusion can be accom-plished either anteriorly through a separate incision or posteriorly via a PLIF or TLIF approach. Laparo-scopic surgery has also been used in spinal surgery for anterior cage insertion and minimally invasive techniques posteriorly and posterolaterally have been developed. There are also several intradiscal thera-pies with internal decompression of the disc center or heating of the posterior annulus to minimize the

patient’s surgical discomfort while potentially reliev-ing some symptoms of low back disorder.

2. Advantages of an Artificial DiscAll of the above techniques, however, either patch over the true disease process or eliminate the joint motion and its normal physiological function. With lumbar artificial disc technology, we now have the ability to fix the problem and restore normal anatomy and physiologic motion rather than simply fuse the back (2,4,5,7). Fusion works in many instances because the motion itself of the joint causes pain through its inability to comfortably support the weight of the body. Thus, when it is fused, it no longer moves and hence the motion cannot cause pain. The fusion does, however, cause stress and increased motion in the joints adjacent to the fused level as a direct effect of eliminating motion at the fused level. The theory behind an artificial disc in the lumbar area would be to not only preserve the motion but additionally to correct the abnormal motion that would be pres-ent in the degenerative disc and to restore the disc height, lordosis and a normal instantaneous axis of rotation. By doing so, the joints adjacent to the dy-namically stable segment would not be subject to ab-normal loads and motions. It is hoped with this new technology of artificial lumbar disc that the good re-sults, which have followed the introduction of artifi-cial knees and hips, will likewise be seen in the lum-bar spine (1).

The advantage of the artificial lumbar disc com-pared with a lumbar fusion is that it reproduces the biomechanics of the normal disc. Additionally, it would reduce the mechanical forces transmitted to the adjacent segments. It has the promise of slowing

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or halting the degenerative changes at the adjacent levels. Performing a total discectomy eliminates the chance of a disc herniation and will hopefully retard spondylosis, stenosis, and instability at the dynam-ically stabilized segment. By restoring the anatomic disc height, the artificial disc would increase the ex-iting foraminal height and prevent compression on the exiting nerve roots at the level stabilized.

The typical diseased lumbar segment which is considered for artificial lumbar disc treatment is of-ten collapsed in vertical height and has loss of normal lordosis, Modic endplate changes in the bodies adja-cent to the effected disc space, and little motion on flexion/extension. Because of the mechanical changes in the degenerative condition in the disc space, this natural disease process is already placing more forces on the adjacent levels. The application of an artificial lumbar disc will restore normal motion, height, and lordosis, and the forces on the adjacent level will be decreased. Thus, an artificial lumbar disc may have beneficial effects compared to the natural history of the unoperated degenerative state.

3. Artificial Lumbar Disc DesignThe design of a lumbar artificial disc has multiple very strict requirements. These devices must have superb mechanical strength and endurance. They are designed to last several decades, as many of these devices will be implanted in young individuals. Me-chanical testing of 100,000,000 motion cycles over a 40-year life span would be a typical design criteria. The base materials need to be biocompatible with no significant surrounding inflammatory reaction ei-ther due to the base material reaction or secondary to any debris. The devices need to induce no organ-otoxic or carcinogenic reaction from the base mate-rial or potential debris. The biomechanical functional movement requirements of an artificial lumbar disc are quite strict, as they need to replicate the full bio-mechanics of a normal disc. This normal motion in-cludes translation and rotation in all three planes of motion – x, y, and z axes. The implant geometry and materials would determine the static configuration, dynamic motion, schematics, and any constrained na-ture of the motion. The exact placement of the lumbar artificial disc in the disc space is determined by its biomechanical design. Different designs will require different placement accuracy - the “sweet spot” for

the implant. Fixed pivot devices may need a higher placement precision than devices utilizing a sliding core or an elastopolymer.

History of the lumbar artificial disc goes back to Fernstrom 35 years ago, who first placed spher-ical metal balls in the disc space. It was noted that a majority of these patients had ball migration into the vertebral body with subsequent collapse of the disc space. Relatively recently, a nucleus pulposus re-placement with a hygroscopic gel or fluid filled cy-lindric sacs has been developed for use after a stan-dard discectomy in which the annulus is still holding the disc space to a normal height. These are currently under development and have not started a US FDA trial at the current time. Replacements of the entire disc after severe degenerative changes have several designs. These classes of designs have included me-chanical bearing devices and a rubber/silicone/poly-mer nucleus between metal endplates made out of ei-ther chromium cobalt or titanium, with the potential of bony ingrowth surfaces at the endplates.

Although many different spinal dynamic stabi-lization systems go under the category of “artificial disc”, these need to be separated as they have dif-ferent indications and potentially different applica-ble disease states. The first group of devices for the lumbar disc are intended to prevent the collapse of a lumbar disc space following a standard free frag-ment disc herniation surgery (8,17,18). These devices are designed to be placed in the center of the disc to halt the secondary changes that would happen over the subsequent years and would hopefully provide sta-bility over many decades, eliminating the need for fusion or rebuilding of the disc space at a later date. The second class of devices is for patients with se-vere degenerative disc disease with loss of the disc height but normal lordosis, instability of the disc, and little to no significant bony pathology posteri-orly. This set of devices requires good facets, poste-rior ligaments, and muscular structures, as the aim to replace only the degenerative disc component of the entire lumbar joint. These are currently what will be termed “artificial lumbar discs” and will be the focus of the rest of this chapter.

Four different designs are currently in US FDA IDE trial currently. It is notable that these devices do not replace the posterior column degenerative changes, nor do they augment them. In fact, a contraindica-tion to any of these devices would be a spondyloly-


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sis or significant spondylosis with facet hypertrophy and potential or ongoing nerve root compression. The third category of devices increases the posterior col-umn stiffness (6,14,15), with one currently in a US FDA IDE trial and others reported in European surgical series. The fourth class of devices is the total lumbar joint replacement, which would replace both anterior and posterior components. Currently, no devices are available in any US FDA trial, nor are any being im-planted elsewhere in the world. In the lumbar spine, in addition to the hard implants, which have metal ends which attach onto the bony endplates, there are also some soft implants made either of all elastic with potential laminations or of a sac of fiber filled with some fluid or matrix (9-11,16). Currently, none of the soft implants is in US FDA trials.

There are potential base material problems with all current technology solutions to the bearing sur-face for the hard lumbar artificial disc replacement designs. Broadly, these fall into three separate clas-sifications: a metal-metal design, metal-ceramic de-sign, or metal-plastic design. The metal-metal de-signs have the potential problem of metal and/or metal ionic debris; the metal-ceramic designs that the ceramic component may shatter, and that the metal on plastic design that of plastic wear. At first thought, the wear associated with a metal-plastic bearing surface would seem to exclude it from use in the lumbar spine because of excessive long-term wear. This initial opinion is an extrapolation from the well-known fact that the plastic components in the current artificial hips and knees have a 10-year life-time and then require revision. As the lumbar artifi-cial disc is made of these same base materials, chro-mium cobalt and high-density polyethylene, it thus might be inferred the lumbar artificial disc would also require the plastic cores to be replaced every ten years. There are three facts, however, which refute the seemingly common sense idea. First of all, with each step, the hip and the knee move approximately 50 degrees, whereas the lumbar spine will only tilt a few degrees. This greatly decreases the “sandpaper effect” by over an order of magnitude. Next, in the lumbar design, the high-density polyethylene is not constrained but is open on the sides. This is a marked contrast to the hips, where the plastic is constrained in a ball/socket-type joint. In the hip joints, the high-pressure points which arise at the constrained met-al-plastic interface greatly accelerate the plastic wear. Because of the nonconstrained nature of the plastic

in the lumbar application, there are no wear-accel-erated pressure points. Furthermore, there is good experience from Europe that there is no plastic wear in 10 years of implantation, verifying the estimation of the expected lifetime to be far greater than that of the hips and knees.

A separate class of dynamic stabilization devices is currently being studied and tested in the cervical spine. These devices, although also called “artificial disc”, vary greatly from the artificial lumbar disc. First of all, the cervical discs are experiencing much lower loads than the lumbar discs, and they have different biomechanical characteristics. But more im-portantly, in the cervical spine, bony pathology and osteophytes causing radiculopathy and/or myelopa-thy dominate as causes for intervention, rather than pure axial disc pain, as is the case in the lumbar in-dication for an artificial disc. The potential patient groups to be studied and outcome variables would be quite different between the cervical and the lum-bar artificial disc studies. Furthermore, the results in the lumbar area are not necessarily directly transfer-able to the cervical spine.

In summary, all artificial discs are not the same. There will be major biomechanical differences be-tween cervical and lumbar implants in the design, the disease treated, and outcome expected. One needs to be concerned about the pathology one is treating, whether the disc is normal disc height, and the pres-ence of degenerative disc disease, osteophytes, and facet disease.

3.a. Prodisc Artificial Lumbar DiscProdisc, from Spine Solutions, Inc., was recently ac-quired by Synthes-Stratec Spine. In a recent press re-lease out of Oberdorf, Switzerland dated February 6, 2003 on their website, Synthese-Stratec listed the pur-chase price at $350,000,000 and stated their belief that the global market potential for total disc replacement (Spine Arthroplasty) will grow to 3 billion by 2008. The initial Prodisc product design was designed in the late 1980s and used by Thierry Marmay, a French orthopedic spine surgeon. From 3/1990 to 2/1993, Dr. Marmay implanted this artificial disc in 64 patients. In 1999, he went back to examine these patients. He was able to locate 58 of the surviving 61 patients for a 95% follow-up at 7 to 10 years status post procedure. At that time, he found that all of the implants were intact and mechanically functioning. There had been


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ry no implant removals, revisions, or failures. Further-more, there was no evidence of subsidence into the bony endplate on follow-up radiographs compared with the peri-operative films. There was a highly sig-nificant reduction in patient reported back pain and leg pain, and 92.7% of these patients were either sat-isfied or extremely satisfied with the results of this procedure. In this study, 2/3 of the patients had a sin-gle level implant and 1/3 had two levels. No differ-ences were noted between one and two level diseases. Most importantly, at this long-term follow-up there were no device-related safety issues, no untoward ef-fects, no complications, and no adverse events. This Prodisc was based on spherical articulation and had metal endplates made of chromium cobalt alloy. The current Prodisc (Figure 1), which is now in US FDA

IDE trials, is two chromium cobalt endplates and a high-density polyethylene core, and is applied with an inserter no wider than the implant. It has a fin in the midline to help in the stabilization and position-ing. Because the high-density polyethylene is fixed to the inferior plate, it functions as a fixed pivot de-sign and the instantaneous axis of rotation is within the lower body rather than in the disc space.

3.b. Flexicore Artificial Lumbar DiscAnother design, which has just started US FDA IDE trials, is Flexicore (Figure 2). This is a metal-on-metal bearing surface of chromium cobalt. It is a 13mm ball-and-socket joint, which places the stationary center of rotation centrally between the endplates.

Figure 1: Prodisc Artificial Lumbar Disc.

A. Expanded view showing the two metal endplates and polyethylene core which attach to the lower metal endplate.

B. Assembled Prodisc Artificial Lumbar Disc construct.C. Inserter applying Prodisc Artificial Disc to inner space.D. Prodisc in a disc space after detachment of the inserter.E/F. A one-level L5-S1 Prodisc stabilization.G/H. An L4-5 and L5-S1 two level Prodisc stabilization.


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3.c. SB Charité Lumbar Artificial DiscThe SB Charité was designed to restore disc space height and motion segment flexibility, and was spe-cifically design to duplicate the kinematics and dy-namics of a normal motion segment (12,13). It was de-

signed to restore anatomic lordosis, which will result in normal facet joint motion loading and unloading (Figure3). The SB Charité uses two metal alloy end-plates of chromium cobalt and a high-density poly-ethylene free-floating core. The free-floating core of-

Figure 2: Flexicore Artificial Lumbar Disc AP & Lateral View: This device is a metal-on-metal device with some

contour to the endplate attachment to match the normal anatomy and cleat attachment.

Figure 3: SB Charité Artificial Lumbar Disc

A. Construct and disassembled parts showing the two metal endplates and ultra high-density polyeth-ylene core.

B. Shows the various size footprints which are available. The metal endplates are also available in dif-ferent angulations.


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fers the theoretical advantage of allowing the spacer to shift dynamically within the disc space during regular spinal motion, moving posteriorly in flex-ion and anteriorly in lumbar extension. This pro-vides not only unloading of the posterior facet struc-tures during this normal replication of motion, but also allows forgiveness for slight off-center position-ing of the implant.

Several clinical studies have been published docu-menting the European experience with this disc since 1987. Worldwide experience with this unconstrained anatomic disc replacement is now greater than 10,000 cases. Several studies are historically notable. Cino-tti reported on 46 Italian patients in 1996 with 2 to 5 year follow-up. He noted no implant failures, but did report a re-operation rate of 19% for continued pain. Overall satisfaction was 63%. Lemaire reported his French series in 1997 following 105 patients with a mean follow up of 51 months with 79% good out-comes and no device failures. Zeegers reported 50 patients in 1999 in a Dutch series, which showed 70% good results with 2-year follow-up. The US FDA IDE study was launched in March 2000 with the Texas Back Institute as the principal institution. Since that time, all patients have been enrolled in the FDA multi-center study with complete 2 year follow up to be completed in December of 2003. Entry was finished at the end of 2001, and all patients will be past their

two-year follow-up at 2003 with prompt submission to the FDA plan. Currently, the centers that entered patients into the randomized FDA IDE study have access to the Charité disc on a limited basis as part of a continuing access study.

The SB Charité dynamic stabilizer comes in a va-riety of base metal sizes as far as the footplate to fit different sized disc spaces (12). In addition, there are various endplate angles to match the distracted disc space anatomy. The plastic core is inserted between the two metal endplates and also comes in a variety of heights. The sizing of the endplates, angles, and heights are done intraoperatively. The SB Charité is implanted with metal endplates of chromium co-balt on the superior and inferior bony endplates of the disc space and a UHMW polyethylene core in-between the highly polished insert interfaces. There is a slight difference in the curvature between the polyethylene cores and the metal endplates, which allows the core to slide. Spinal forces are transmitted down through the anterior column in a normal man-ner after the disc is inserted. The core translation al-lows duplication of anatomic translation (Figures 4, 5 and 6). In the normal physiological circumstances, there is a slight translation during the flexion/exten-sion motion and lateral bending motion. A normal disc is able to handle this translation. In sagittal rota-tion (flexion-extension) in the normal circumstance,

Figure 4:A. SB Charité Implanted in a model of a spine showing the position of the device and how it trans-

mits forces down the anterior column in A. B. Showing the translation of a normal lumbar disc in flextion/extension motion.C. The translation, which is available in the sliding core of the SB Charité to simulate this translation

motion.


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Figure 5:A. Flexion/extension views showing the instantaneous axis of rotation in A and how it changes in a

Greek alpha-type pattern during this motion.B. Shows in pure y-axis rotation about a fixed point how the posterior elements would swing, caus-

ing more force on one facet than the other.

Figure 6: Comparing a fixed inferior component with a sliding intermediary component. In the fixed inferior

component during flexion has more force near the front part of the Artificial Disc and potentially jam-ming of the facets posteriorly. This is in contrast to B where the sliding intermediary component allows

translation release force both on the plastic core and the facets posteriorly.


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the instantaneous axis of rotation, although gener-ally in the center of the disc, moves in a pattern that duplicates the Greek letter alpha. The Charité dupli-cates this motion. Coronal motion, likewise, has this slight translation in order to reproduce the normal biomechanics of the intact disc space. Axial rotation also requires a slight coupled rotation-translation to reduce the forces on the posterior facets. Pure axial rotation on a pivot point in the disc space will re-sult in direct compression of one facet joint while re-leasing the pressure on the other. If one compares a fixed pivot design to a sliding core design, the facet pressure would be more in a fixed pivot design than a sliding core design. The exact clinical benefit for those patients who are most helped by the sliding core design will be determined by the outcome of the clinical studies currently underway. It is evident from measurements of centers of intervertebral ro-tation in cadavers that the SB Charité not only pre-serves normal motion (Figure 7) at the repaired disc space, but also at adjacent levels (3). Fusion has been

reported to greatly distort the instantaneous axis of rotation at adjacent levels (3).

This mobile sliding core in the Charité artificial disc works in a similar fashion to the mobile knee bearing in many of the contemporary knee designs. In essence, this could be considered a second gen-eration device or an advanced type design over a fixed pivot, much like the mobile core in the knee is considered an advanced design over fixed bear-ings. In biomechanical studies, this mobile sliding core results in true physiological restoration of the lumbar segment.

The SB Charité US FDA study studied one level disease only - L4-5 and L5-S1 (Figure 8). The patients had no radiculopathy, although they could have re-ferred buttock or upper leg pain. Those patients with predominant pain below the knee were excluded from the study. Patients had a positive discogram with concordant pain, and most had MRI’s show-ing collapsed disc space, black disc on T2 weighting

Figure 7: Shows a couple of flexion/extension translations for both the normal disc and the SB Charité both hav-ing an average translation of about 2mm. Note how the SB Charité simulates the motion of a normal

segment, including the translation3.


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indicating decreased water content of the disc, and Modic endplate changes. There were no major social issues. This pivotal study enrolled 360 patients and was randomized between the SB dynamic stabilizer and a BAK stand alone ALIF with autologous iliac crest bone arthrodesis.

A typical patient x-ray is in figure 8A at L5-S1. The corresponding MRI shows the Modic endplate changes in the collapse of L5-S1, as well as some wa-ter loss in L4-5 in this particular patient (Figure 8B). The discogram would have excluded L4-5 as the sig-nificant pain generator. Another patient is shown in Figure 8C in which L4-5 is the major pain generator with a minor loss of water at L5-S1. In this patient, the L5-S1 disc space would have been excluded as a major pain generator by discography.

The surgical approach to the L4/5 and L5/S1 area is performed using standard general surgery tech-

niques to gain access to the retroperitoneal space and dissect the great vessels from the lumbar disc spaces (13). In the surgical procedure, the anterior lon-gitudinal ligament is opened for the width of the disc implant; a generous discectomy is performed, with care taken not to disturb the bony endplates, although all of the cartilaginous endplates are re-moved. The discectomy is enlarged to expose the cortical bone circumferential rim. Deviations from perfectly flat endplates are encountered usually pos-teriorly with a posterior lipping or slightfish mouth-ing noted. These are removed with a .25-inch chisel or a Kerrison punch. This disc space preparation is performed in anticipation of accepting the flat metal endplates of the Charité implant. Care needs to be taken during this stage not to damage the bony endplates, as these support the metal plates of the artificial disc. Additionally, especially at L5-S1, the anterior longitudinal ligament in the degenerative

Figure 8: Typical pre-operative films in patients who underwent an SB Charité in the clinical trial.

A. Radiograph demonstration collapse of the L5-S1 disc space.

B. Severe degenerative disc disease at L5-S1 with secondary Modic endplate changes on this T2 weighted MRI.

C. Severe changes at L4-5 with Modic endplate changes adjacent.

D. Discogram with abnormal L5-S1 disc. This is also a pain generator site for this patient. In the pre-operative discograms in the patient that corresponded to Figure B (L4-5), and in the figure that cor-responded to Figure C (L5-S1) would have been excluded as major pain generators.


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disease stage can be exceptionally thick (sometimes getting over 1cm). This needs to be removed to clearly define the anterior bony margin, such that when the implant is placed, it can be verified both with fluoroscopy as well as visually that the ante-rior cleats of the implant are below the anterior cor-tical margin. Once this is accomplished, a sizer is used to assess the disc space to choose the matching metal endplate footprint. A spreader is then placed into the disc space to perform parallel distraction. This parallel disc space distraction is accomplished by using a paint paddle-type instrument, which is placed within the spreader; the posterior liga-ment is actually stretched and/or ripped to some extent, increasing the posterior height of the disc space. Despite the heaviness of the distractor, clos-ing only on the handles will effectively fishmouth the disc space distraction, opening up mostly only the anterior disc with little or no posterior distrac-tion. The parallel distraction is accomplished by us-ing force to twist the paint paddle instrument be-tween the distractor blades and then just taking up the slack with the distractor handles. Once the disc space has been distracted, often additional disc ma-terial that was contained within the buckled liga-ment within the neural canal is delivered into the disc space. This is then removed with a Kerrison or biopsy punch. The distracted space may provide a better view of the posterior osteophytes and their removal is completed. Next, the metal endplates of the artificial disc are inserted and tapped into posi-tion. Care is taken to have the centerline marked as determined by fluoroscopy either with a burn mark or with a self-tapping 3.5mm screw placed within the bony body adjacent to the disc space. The screw is smooth on the top, allowing the great vessels to slide over if necessary and also providing an unam-biguous unique marker. The screw is also seen on a A-P and lateral fluoroscopy. The metal endplates of the implant are impacted into the disc space, po-sitioned posteriorly within the disc space, and then parallel distracted. At this expansion with the paint paddle instrument parallel distraction, it is essential that only the very lateral edges of the implant are touched, as one does not want to scratch the inside of the cups. Scratching the articulating metal cups of the implant would result in a very significant in-crease in the amount of plastic wear. Once the end-plates have been put in, trial cores size the distracted space and then the final core is placed. Verification

is made that the plastic core is in the correct posi-tion to articulate with the cups and then distraction is fully taken off. Then with a slight tapping on the core, the endplate sliders are removed. During the procedure of the disc space distraction, in approx-imately 2/3 of the cases some epidural bleeding or significant bone bleeding along the posterior edge is encountered. This is easily handled with strips of Avitene placed in the disc space and then com-pressed down against the remaining posterior lon-gitudinal ligament area with a standard 4x4 sponge. After allowing this to sit for approximately 2 to 3 minutes, the sponge can be removed, leaving the thin layer of Avitene in place. This is easier to do during the initial discectomy or after the metal end-plates have been inserted than after the core is in-serted. A-P and lateral fluoroscopy are used to aid in positioning the device and to provide final radio-logical verification. Visual verification is also used anteriorly to ascertain that the implant is recessed below the anterior cortical margin. A bone tamp is used on the sides of the metal endplates of the im-plant to do minor adjustments and also to impact the anterior cleats within the bony structure (Figu-res 9 through 14).

If the SB Charité were required to be revised, there would be two approaches. One approach would be to redo the anterior surgery. This would involve dissecting the retroperitoneal area and deal-ing with the postop scarring and hence increased risk of great vessel damage compared to an unop-erated case. This would allow removal of the SB Charité lumbar disc. The plastic core would be re-moved first, and then the metal endplates could be separated from the bony endplates by using a chisel between them and levering away from the bone into the disc space. This would allow the placement of another artificial disc in the disc space, as the bony endplates would not be significantly damaged. Al-ternately, a posterior operation with rod-screw sta-bilization and posterior lateral fusion could be used to fuse the lumbar segment, which would use the SB Charité as an anterior load share. More impor-tant than the exact surgical technique used would be clinically characterizing the pain generator if the patient had reoccurring or persistent pain. This would have to be done by a variety of radiologic and provocative studies. Discogram at adjacent lev-els would be helpful, as would epidural facet injec-tions, and potentially even an anesthetic discogram


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at adjacent levels to see if that would remove a ma-jority of the pain.

Although detailed outcome studies analysis will await the submission to the FDA, it is the author’s opinion that the artificial disc patients are doing quite well clinically. Initially, the outcome of the groups in the first months is considerably different. In the fusion patients, a bone graft is taken and the patients are within a brace for three months. With the SB Charité artificial lumbar disc, there is no bone graft taken, so there is no bone graft to heal no brace used. Walking and mobility happen quickly with both procedures. The abdominal incision usually heals and is only a

minor discomfort in 2 to 3 weeks. The LINK Charité artificial disc is a finished surgical technique, as it re-quires no bony healing or fusion to occur. When the patient gets to the recovery room, the surgical pro-cedure is like putting a hinge on a door - the door is ready to use once the hinge is put on. In the pa-tients with a stabilization and arthrodesis ALIF, how-ever, the bone has to heal to a mature fusion , which can take 6 to 12 months. There is also potential for bony non-union.

In follow-up x-ray studies, the patients have mobility in both flexion/extension and lateral bend-ing in the level that was dynamically stabilized

Figure 9: Lateral radiograph with some intraoperative photographs of an L5-S1 SB Charité placement.

A. Screw placed in the inferior portion of the L5 body to serve as a midline marker and was aligned with the Steinman pin, which was placed within the disc space.

B. Insertion of the distractor.C. Result of parallel distraction.D. Start of the implant going down with the mid-tooth at the midline marker of the visible screw.E. Metal endplates in place in a posterior position.F. Parallel distracted endplates.G. Endplates separated and the cups clearly visible within the disc space.H. Completed implant within the disc space.I/J. AP and lateral radiographic of the completed implant.


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Figure 10: Preparation of the disc space.

A. Removal of the discB. Video picture showing the removal of the discC. Demonstrates a chisel flattening out the endplates as necessary.

Figure 11: A/B. Shows sizer going into the disc space, which determines the size of the footplate of the

SB Charité to be used.


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Figure 12: This figure demonstrates the application of the distractor and the parallel distracting showing how a second unit is placed on in A&B to provide impact force for driving the metal endplates down to the desired posterior position. C&D show the paint-paddle-type instrument used for the parallel distrac-tion. E/F show how the parallel distraction is obtained by first obtaining some distraction in E, insert-ing of the parallel paint paddle-type device and turning it at right angles to provide force at the poste-

rior ligament to separate that and distract it out.

Figure 13: An intraoperative photograph of the self-retaining retractors in place and the distractor unit in the wound, demonstrating its angled handle.


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Figure 14: A series off of intraoperative video showing the trial core in A. B shows the disc space is distracted

with the metal cups clearly visible in the posterior longitudinal ligament. C shows the core being in-serted. D shows the core in place with good position and the core and the cups being verified visually.

E shows the final construct.

Figure 15: A patient in flexion/extension and lateral bending showing clear motion of the device in both angula-

tion and with translation of the core in both planes of motion.


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(Figure 15). X-ray evidence shows clear move-ment of the core translation with the flexion/ex-tension movement. The author’s initial impression is that the clinical outcome results are comparable or better than historical fusion results reported in the literature.

4. ConclusionEstimations as to when these devises will be avail-able on the US market vary greatly. At the time of this chapter’s writing, it is estimated that the SB Charité will be available by Spring/Summer 2004. The Pro-disc may be delayed 1 to 3 years beyond that. Flex-icore and Marerick are just starting their IDE trials and may be delayed 4 to 5 years. All other designs would be five years or more out.

In conclusion, lumbar dynamic stabilization with a SB Charité artificial lumbar disc dynamic stabilizer is a promising treatment modality for axial lumbar pain and preserving joint motion in selected patients. The two-year clinical outcome after a single level dis-cogenic degenerative disc disease appears superior to historical fusion results. Additional research will be done in the coming years to see whether topping off a lumbar fusion will help prevent adjacent level disease and whether this device can be used below a scoliosis when the degenerative changes occur, and whether multilevel disease will have the same good clinical response as the single level appears to be having in this clinical study.

5. References1. Arnold PM, Kirschman DL, Meredith C. Prosthetic

Vertebral Disc Replacement. In AR V, RR B, SM Z eds. Principles and Practice of Spine Surgery. Phil-adelphia: Mosby, 2003:379-84.

2. Bao QB, McCullen GM, Higham PA, et al. The ar-tificial disc: theory, design and materials. Biomate-rials 1996;17:1157-67.

3. Cunninghan BW, Godron JD, Dmitriev AE, et al. Biomecahnical Evaluation of Total Disc Replace-ment Arthroplasty: An In Vitro Human Cadaveric Model. Spine 2003;28:S110-S7.

4. Dooris AP, Goel VK, Grosland NM, et al. Load-shar-ing between anterior and posterior elements in a lumbar motion segment implanted with an artifi-cial disc. Spine 2001;26:E122-9.

5. Eijkelkamp MF, van Donkelaar CC, Veldhuizen AG, et al. Requirements for an artificial intervertebral disc. Int J Artif Organs 2001;24:311-21.

6. Freudiger S, Dubois G, Lorrain M. Dynamic neutral-isation of the lumbar spine confirmed on a new lum-bar spine simulator in vitro. Arch Orthop Trauma Surg 1999;119:127-32.

7. Hedman TP, Kostuik JP, Fernie GR, et al. Design of an in-tervertebral disc prosthesis. Spine 1991;16:S256-60.

8. Klara PM, Ray CD. Artificial nucleus replacement: clinical experience. Spine 2002;27:1374-7.

9. Korge A, Nydegger T, Polard JL, et al. A spiral im-plant as nucleus prosthesis in the lumbar spine. Eur Spine J 2002;11:S149-53.

10. Kotani Y, Abumi K, Shikinami Y, et al. Artificial in-tervertebral disc replacement using bioactive three- dimensional fabric: design, development, and prelim-inary animal study. Spine 2002;27:929-35; discus-sion 35-6.

11. Lee CK, Langrana NA, Parsons JR, et al. Devel-opment of a prosthetic intervertebral disc. Spine 1991;16:S253-5.

12. Link HD, Buttner-Janz K. Link SB Charité artificial disc: history, design, and biomechanics. In DL K, JR J eds. Spinal Restabilization Procedures. Amsterdam: Elsevier Science BV, 2002:293-316.

13. McAfee PC. Artificial disc prosthesis: the Link SB Charité III. In DL K, JR J eds. Spinal Restabiliza-tion Procedures. Amsterdam: Elsevier Science BV, 2002:299-310.

14. Senegas J. Mechanical supplementation by non-rigid fixation in degenerative intervertebral lumbar segments: the Wallis system. Eur Spine J 2002;11:S164-9.

15. Stoll TM, Dubois G, Schwarzenbach O. The dynamic neutralization system for the spine: a multi-center study of a novel non-fusion system. Eur Spine J 2002;11:S170-8.

16. Urbaniak JR, Bright DS, Hopkins JE. Replacement of intervertebral discs in chimpanzees by silicone-dacron implants: a preliminary report. J Biomed Mater Res 1973;7:165-86.

17. Wilke HJ, Kavanagh S, Neller S, et al. [Effect of ar-tificial disk nucleus implant on mobility and inter-vertebral disk high of an L4/5 segment after nucle-otomy]. Orthopade 2002;31:434-40.

18. Wilke HJ, Kavanagh S, Neller S, et al. Effect of a prosthetic disc nucleus on the mobility and disc height of the L4-5 intervertebral disc postnucleot-omy. J Neurosurg 2001;95:208-14.

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SPINAL STEREOTACTIC BODY

RADIOTHERAPYUgur Selek M.D.

1. IntroductionMetastasis to the spinal column is an emergent prob-lem in cancer patients which is not rare and occurs in almost 40%. (1) The aim in management of metas-tasis to the spinal column is to decrease the sequelae including pain, instability, and neurological deficit to avoid progressive myelopathy resulting in the loss of motor, sensory, and autonomic functions. Although the treatment is palliative, the durability of the pro-gression free period without any sequel is essential. As the treatment options increase in number, com-prehensible multidisciplinary approach needs to be in charge to effectively implement the proper treatment. Surgery is inevitable in case of cord compression, however if there is no vertebral instability in immedi-ate requirement of reconstruction and stabilization of the spinal column, radiotherapy has developed into a noninvasive and effective modality by Stereotac-tic body radiotherapy (SBRT) option. Conventional radiotherapy of 30 Gy in 10 fractions or 45 Gy in 25 fractions can be effective in acute palliation of pain and neurological symptoms of spinal metastases; how-ever the outcome might not be robust in many conse-quences without the conventional reirradiation possi-bility. Spinal SBRT has the advantage of minimizing dose to the spinal cord while delivering higher doses to the spinal tumor; and is a potential treatment op-tion for preferably low volume vertebral metastases as a primary choice, whereas it can also be offered in postoperative setting or in salvage setting subsequent to previous irradiation or recurrence after surgery.

Stereotactic body radiotherapy (SBRT) SBRT is a non invasive image-guided process of radio-therapy intervention which uses a three-dimensional

coordinate system to locate small targets inside the body in order to deliver high precision and an in-creased load of radiation for highest local control pos-sible. “Stereotactic” (or “stereotaxic”) means “solid ordering” in Greek. The American Society of Ther-apeutic Radiology and Oncology (ASTRO) defines SBRT as an external beam radiation therapy method used to very precisely deliver a high dose of radia-tion to an extracranial target within the body, us-ing either a single dose or a small number of frac-tions with high targeting accuracy and rapid dose falloff gradients encompassing tumors. (2,3) Theoreti-cally, any location inside the body can be subjected to SBRT with required reliable set up and imaging. Single-fraction SBRT with simulation, planning, and treatment on the same day is called as Stereotactic body radiosurgery (SBRS), while SBRT covers all frac-tionated treatment sessions using larger daily doses of radiation than conventional fractionated doses of 1.8-3 Gy/fraction/day.

Single fraction SBRT has been reported by many centers with various dose ranges, (4-6) as growing liter-ature for multiple fraction SBRT exist. (7-10) The reason-ing of single or multiple fractionations in spinal SBRT depends on clinical judgment; small volume tumors with enough safety margins from spinal cord might be preferred to be treated with single fraction SBRT, while tumors with paraspinal extension, or having multiple level or prevertebral involvement, or being close to bowel could be elected to be treated with 3 to 5 multiple fractions SBRT. General conservative con-sideration is the capability of more than one fraction to balance possible positional set up inaccuracies in comparison to single fraction SBRT. Therefore, the safety band of fractionated SBRT with adequate con-fidence could be the first option in conditions with

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high setup or normal tissue toxicity risk despite its disadvantage of inconvenience. Examples of Inten-sity modulated SBRT are given in Figures 1-5 as our current clinical approach of delivery in three frac-tions. Single fraction SBRT is mainly built on strict one-time immobilization for same day simulation, planning and delivery of treatment while increasing real time imaging capabilities such as cone beam CT mounted on the linear accelerators for exact setup provides flexibility in the timing of simulation and treatment on different days.

Experience on spinal stereotactic radiosurgery was set off with the early series of Hamilton et al at University of Arizona that used an invasive rigid fixation device for immobilization of the spine in nine patients with recurrent spinal tumors and pre-scribed median 8 Gy. (11) One of the initial important studies demonstrating targeting accuracy within 1.5 mm for actual patient treatment was reported by Ryu et al. (12) These were establishing clinical feasi-bility of the accuracy and precision of SBRT to treat tumors adjacent to the spinal cord. Chang et al de-tailed near-simultaneous computed tomographic im-age-guided SBRT at M. D. Anderson Cancer Center for 15 patients with metastatic spinal disease using a comparatively conservative regimen of 30 Gy in 5 fractions with a maximum dose constraint for spinal cord of 10 Gy with no neurologic toxicity in median 9 months. (13) Bilsky et al reported on their prelimi-nary Memorial Sloan Kettering Cancer Center clini-cal experience in treating 16 paraspinal tumors with stereotactic IMRT where used 20 Gy tumor dose in 4 or 5 fractions with a maximum dose constraint for spinal cord of 6 Gy. (14)

Succeeding clinical studies with spinal SBRT dem-onstrated the efficacy for rapid pain relief and im-provement of neurological function. (4,12,15-19) In general palliation of pain is the most invested and reported main cause of irradiation of spinal column metas-tases with complete pain relief after SBRT was re-ported in various series at 33% to 86%. (5,12,20,21) Other cancer related symptoms besides pain also need to be investigated. Quality of life is also improved sec-ondary to pain relief. (19) SBRT could help in reduc-tion of symptom burden in terms of other cancer related symptoms such as fatigue, pain, sleep dis-turbance, drowsiness, and distress with better local control and activity of daily living, ability to work, and mood. (13)

Ryu et al. at Henry Ford Hospital reported on 49 patients treated with single doses of 10–16 Gy with a complete pain relief of 46% at 8 weeks and both complete and partial pain relief of 85%, while pain relapsed in 7% and tumor progressed in 5%. (4) Gerszten et al published SBRT of 12.5–25 Gy with long-term pain improvement in 86%. (5) Yamada et al. noted that patients without local failure after sin-gle fraction SBRT doses of 18–24 Gy had long term symptom palliation. (6) Gibbs et al. used 16–25 Gy in one to five fractions and disclosed 84% improvement of initial symptoms. (7,8) Nelson et al reported 39% and 51% complete and partial pain relief at one month respectively with three fractions of SBRT (range, one to four fractions). (9) Gerszten et al at the University of Pittsburgh treated 500 cases of spinal metastases with 12.5 to 25 Gy Cyberknife based single-fraction SBRT. (5) Long-term pain improvement occurred in 86% while tumor control was achieved in 90% of treated lesions. Ryu and colleagues defined that me-dian duration of pain control with spine SBRT was 13.3 months. (4) The currently ongoing RTOG 0631 trial will assess pain relief as its primary endpoint where patients with spinal metastases are randomized to re-ceive either 8 Gy x1 fraction of conventional radiation therapy or 16 Gy x 1 fraction of SBRT. (22)

Conventional palliative radiotherapy has recog-nized role on pain control for bone metastases for an intermediate period of time, while robust tumor control on spinal metastases likely require higher doses. Spinal SBRT might be a promising solution to decrease pain and neurological complications in-cluding metastatic epidural spinal cord compression (MESCC) due to inadequately conventionally treated spinal metastases. (23-25) Higher doses than conventional fractionation of 30 Gy in 10 fractions might have a better chance of preventing bony destruction of the spinal column leading to spinal instability. The ma-jor limiting factor avoiding higher dose prescription to spinal column is the low threshold of spinal cord radiation tolerance.

SBRT is a competent technique with ability of im-age-guidance to precisely deliver higher doses to se-cure a safe dose gradient at the spinal cord and tumor interface. This noninvasive modality achieves more than 80% of objective radiological tumor control at the treated spine. (5,10,15) Thus, a new era of therapeu-tic window with low risk of spinal cord injury is in charge with SBRT. Spinal SBRT could become a smart

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alternative to surgery in selected cases with avoidance of possible operative risks, besides a proper way of reirradiation of spinal column metastases which are generally not irradiated by conventional means.

2. IndicationsRationale of the large dose per fraction in SBRT is to ablate tumor cells and/or overcome radioresistance resulting in greater log cell kill. There are four ma-jor indications:

spinal metastases without instability•

postoperative adjuvant approach for high risk •local recurrence postoperative salvage approach for clinical pro-•gressionsalvage approach for local disease progression •or recurrence after conventional radiotherapy to the spine

Conditions of Patient EligibilityLocalized• (solitary or not more than two contigu-ous spine levels) spinal column metastasis. Distance• to spinal cord is important for eligibility and SBRT is considered if ≥ 3 mm gap is present between the spinal cord and the edge of the epi-dural lesion. Surgery is preferable if closer than 3 mm to cord. SBRS might be opted if surgery is not an option despite underdosage of epidu-ral component.Paraspinal• mass component ≤ 5 cm in the greatest dimension contiguous with spine metastasisWell• -controlled systemic diseaseKarnofsky• Performance Status > 40Previous• irradiation not more than 45 Gy (1.8-2 Gy/fraction) or 30 Gy (3Gy/fraction) Radioresistant• tumors metastatic to spinal column such as renal cell carcinoma, melanoma, and sar-comas are considered to benefit more in compar-ison to other cancers.

3. ContraindicationsRadiosensitive metastases such as plasmacytoma, •lymphoma, and germ cell primary: Conventional fractionation radiation therapy with 1.8 - 3 Gy/fraction/day to a total dose of 45-30 Gy is the

standard first choice of treatment in these histol-ogy due to tumor control curve lying to the left of the normal tissue complication curve.Tumors enclosing the spinal cord, compress-•ing the cord or thecal sac, involving the epidu-ral space require surgical decompression which subsequently requires SBRT after resection of the proximal disease to the spinal cord. Cord or cauda equina compression with neu-•rologic deterioration: Emergent surgery is en-couragedUnstable spine (e.g. compression fracture; > 50% •loss of vertebral body height): Emergent surgery is encouragedNon-ambulatory patients•

Previous radiotherapy dose greater than 45 Gy •(1.8-2 Gy/fraction) or 30 Gy (3Gy/fraction)

4. ProceduresSpinal SBRT requires extensively improved immobi-lization, imaging and delivery precision to limit tar-get movement during planning and delivery. Deliv-ery can be via planar or non-coplanar multiple static beams or rotational fields of varying degrees with or without beam intensity modulation. Stereotactic lo-calization of the lesion is essential by appropriate im-aging modality, such as bony landmarks, fiducials, or computed tomography (CT) to ensure accurate beam placement. Quality assurance (QA) must be followed strictly for SBRT accuracy. The quality of a SBRT treatment depends on the coordinated team effort along an accurate treatment planning and de-livery process with reliable verification.

The responsible radiation oncologist (RO) care-fully evaluates the planned treatment impact through benefits and potential risks, educated design and conduct of treatment, and cautious follow-up af-ter SBRT. (2) RO needs to determine patient-specific and reproducible positioning, and stability of setup appropriately; and to supervise simulation process with spatial accuracy and precision of the imaging modality. After defining the target, RO prescribes dose, sets limits according to normal tissue dose con-straints, approves the final treatment plan prepared by the medical physicist, and closely directs the ac-tual treatment process.


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SBRT targeting and treatment ensures adequate dose coverage of the target with rapid falloff to nor-mal tissues by numerous coplanar or non-coplanar beams or large arcs of radiation with apertures, as well as by intensity-modulated radiation delivery. Intensity-modulated radiation therapy (IMRT) is a sophisticated form of three-dimensional conformal radiation therapy granting necessary and appropri-ate coverage of tumor with falling doses to the spi-nal cord in constraints. Computer-controlled mul-tileaf collimation of the modern linear accelerators provides precision and conformality to irradiate any shape of tumors such as surrounding the spi-nal cord. The use of a newly developed fusion and matching capacities of real time on board imaging as KV portal films and cone beam CT accurately iden-tifies planned target for treatment.

4.a. ImmobilizationAs SBRT is designed to deliver high ablative doses to the spinal column tumor in one to couple of frac-tions; limiting the volume and maximum dose of the spinal cord that is irradiated is crucial to avoid potentially catastrophic toxicities. Tumor motion in general is a very complicated challenge for SBRT in other body SBRT approaches due to respiratory movement of organs. Fortunately, spinal column is a comparatively less mobile axis with respiration. If a reproducible minimization of target motion via im-mobilization is ensured, physiologic tumor motion is not an issue to be accounted via tracking or gat-ing which is an obligation such as for lung or liver tumors. Precise imaging and positioning are man-datory to accompany and unify immobilization. Despite conventionally fractionated approach, irra-diating a large volume of normal tissue to account for setup uncertainty is unacceptable in SBRT dose range. Therefore, the basics of spine SBRT are pa-tient positioning, targeting, and delivery with mini-mal dosimetric margins.

A reproducible immobilization method is re-quired which facilitates the real-time imaging and positioning at the SBRT linear accelerator. The im-mobilization is to decrease the set-up uncertainty in multiple fractions while verification of isocenter is re-quired at each fraction by cone beam and/or KV im-age guidance. Immobilization should be in a stable supine and comfortable position to prevent patient movement. Stereotactic whole body cradle vacuum bag or alpha cradle with or without shrink-wrapping

is used in general for customized immobilization to surround the patient on three sides to conform pa-tient’s external contours with reference to the treat-ment delivery coordinate system. There is couple of commercial systems used to ease the reproducible immobilization such as Body Pro-LokTM or BodyFIX® Stereotactic Systems. A rigid head and neck immo-bilization device such as thermoplastic mask should be used for metastasis to cervical spine or cervico-thoracic junction.

4.b. Target and Critical Structures delineation

The gross tumor/target volume (GTV) is contoured with relevant imaging studies; GTV is expanded to the clinical target volume (CTV) due to the pattern of microscopic spread, and coordinate the proper planning target volume (PTV) beyond the CTV with information of the mechanical and setup un-certainty. (10,26,27)

Gross tumor volume (GTV): Contour gross le-•sion Clinic tumor volume (CTV): GTV=CTV•

Planning tumor volume (PTV): CTV + 1-2mm•

Lower-dose CTV (CTV lower-dose): Contour re-•maining entire vertebral body and posterior ele-ments and ensure more generous margin poste-rior to diseased vertebraeThe spinal cord volume is contoured 5-6 mm su-•perior to 5-6 mm inferior to the GTV. (28) Critical structures are contoured starting at 10 •cm above the target volume to 10 cm below the target. (29)

4.c. Physics and Dosimetry of SBRTSBRT is performed with high conformality of the prescribed potent dose to the tumor volume, with steep dose fall off to decrease normal tissue toxic-ity. This delivery requires multiple, non-opposing, non-coplanar beams or arcs. (30,31) While minimizing the entrance dose to prevent severe acute skin toxic-ities, beam angles, beam number and beam weight-ing to isocenter are arranged to reduce the volume of tissue at intersection of beams to maintain an ac-ceptable maximum dose in target and circumferen-tial dose falloff. SBRT physics seek to provide 95% planning target volume coverage with an appropri-ate prescription isodose line (Figures 1-5).

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Figure 1a

Figure 1a: Intensity modulated SBRT was delivered for thyroid carcinoma metastasis to T11 vertebral body to 27

Gy in 3 fractions at 9 Gy per fraction using 6 MV photons with multiple coplanar beams. Dose distribu-tion in axial, sagittal and coronal view. Prescription is to 95% of CTV.

Figure 1b

Figure 1b: 8 coplanar beams are assigned to this prescription: 180, 205, 225, 245, 095, 115, 135, 155.

Figure 2a

Figure 2a: Intensity modulated SBRT was delivered for breast carcinoma metastasis to T8 vertebral body to 27 Gy in 3 fractions at 9 Gy per fraction using 6 MV photons with multiple coplanar beams. Dose distribution

in axial, sagittal and coronal view. Prescription is to 92% of GTV.


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Figure 2b

Figure 2b: Dose volume histogram demonstrating the doses to regions of interest.

Figure 3

Figure 3: Intensity modulated SBRT was delivered for metastatic colorectal cancer to C6-C7 vertebral bodies,

neural foramina and posterior elements to a total dose of 27 Gy in 3 fractions at 9 Gy per fraction using 6 MV photons with semi-coplanar beams.

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The medical physicist is responsible for the tech-nical aspects of SBRT. This requires acceptance testing and commissioning of the SBRT system for its geo-metric and dosimetric precision and accuracy; moni-tor and assure proper functioning of the linear accel-erator and CT simulator of SBRT system, the image guidance system, the image-based 3D and/or intensi-ty-modulated treatment planning system, determine and check the appropriate beam-delivery parameters, and calculation of the radiation beam parameters con-sistent with the beam geometry according to the plan approved by the radiation oncologist. (2)

4.d. Quality Assurance (QA)QA is basically verification process of radiation isoce-nter, cone beam isocenter, CT-CT matching software.

SBRT QA secures the combined testing, proper func-tioning and communication of image-guidance and treatment delivery systems within acceptable toler-ances which guarantees the information from the imaging system matching the planned beams to the exact position within the patient. This is performed with designation of image guidance system to de-fine ≥1 test points of predefined coordinates and then testing treatment planning system to irradiate these same test points. Adequate image guidance is man-datory according to coordinate the stereotactic target-ing of tumor between imaging system and delivery system, and body frames based only on frame fidu-cials are not adequate without proper image guid-ance. The frame-based SBRT includes a stereotactic body frame with adequate imaging system, and the

Figure 4a

Figure 4: Intensity modulated SBRT was delivered for pancreas carcinoma metastasis to T8-9 vertebral body with paraspinal extension to 27 Gy in 3 fractions at 9 Gy per fraction using 6 MV photons with multiple co-

planar beams. Dose distribution in axial, sagittal and coronal view. Prescription is to 96.5% of CTV.

Figure 5.

Figure 5: Intensity modulated SBRT was delivered for renal cell carcinoma metastasis to L5-S1 vertebral body to 27 Gy in 3 fractions at 9 Gy per fraction using 6 MV photons with multiple coplanar beams. Dose dis-

tribution in axial, sagittal and coronal view. Prescription is to 96% of GTV.


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frameless SBRT includes one or more of the follow-ing, implanted metallic seeds within or close to the tu-mor; or landmark bone anatomy as a fiducial marker for matching with the planning digital reconstructed radiographs (DRR), or volumetric data obtained from on board CT to match the planning CT.

SBRT is basically an image-based and guided treatment with relevant image fusion, and/or local-izing of target volumes. The images are necessary to delineate the gross tumor volume and normal tissue margins besides defining target coordinates of treat-ment beams. CT is practical and spatially undistorted to be used for SBRT where a virtual patient model for treatment planning can be established for the treat-ment plan evaluation and dose calculation. MRI is also helpful for exact delineation and MRI with CT images fusion is used to minimize geometrical dis-tortions inherent in MR images. These images input are used in 3D planning process.

It is viable to mention that treatment planning software estimates doses to critical structures which is definitely restricted by the accuracy of irradiation beam data measurements by ion chambers under effect of size or volume of the system, and possible leakage of multileaf collimators besides leaf shape. (13) Therefore, one should be aware of the potential risk on treatment planning of over or under-estimating the actual doses delivered in order to be conserva-tive to limit doses to the spinal cord. It is essential to establish QA of the delivery system to increase the confidence of safety and setup data demonstrating consistent daily patient setups within 1mm of treat-ment isocenter.

4.e. SBRT Equipment Currently, many commercially available treatment units capable of refined image guidance can perform spine SBRT. (31) Decreasing the uncertainty with near real-time imaging for positioning and delivery is the major requirement, and patient positional imaging is obtained to align the patient in the treatment po-sition in order to perform shifts at each fraction set up. None of them has a clear superiority to others in spinal SBRT. However, the key is proper training and experience of the team in SBRT.

The treatment devices can be categorized ac-cording to their imaging capabilities for positioning and delivery. Integrated gantry mounted cone beam CT and KV & MV on board imaging systems (The

Trilogy™ Stereotactic System from Varian Medical Systems, The Elekta Synergy®), CT scanner linked to a linear accelerator via a shared tabletop (The Sie-mens Primaotom), orthogonal X-ray cameras (The CyberKnife, Accuray, Inc., Sunnyvale, CA, USA, the Novalis, Brainlab, Ammerthalstrabe, Germany) and megavoltage CT mounted in the system (The Tomo-therapy HI-ART, TomoTherapy, Inc., Madison, WI, USA). The SBRT could be delivered as three major ways of application:

(a) Irradiation with a circular approach with a moving source or table, named arc treatment

(b) Irradiation with stationary fields shaped by a multileaf collimator with gantry-based systems

(c) Irradiation with multiple microstationary fields by cylindric collimator with the CyberKnife concept

4.f. Radiotherapy set up and Patient positioning

Acceptable and appropriate image-guidance (IG) for localization includes the accuracy of less than 2 mm from simulation/planning to the end of treatment. There are mainly four ways of IG noted below for image guided radiotherapy (IGRT):

Cone-beam CT equipment mounted to the linear •accelerator performing with the treatment beam or an auxiliary kV x-ray head to acquire multiple images for volume reconstruction to fine tune pa-tient set ups with ultra-precise CT scans;Spiral dose delivery equipment using the treat-•ment beam to collect helical CT information for image guidance;Any equipment that can produce stereoscopic •planar views of the patient in the treatment posi-tion using either the treatment beam with a stan-dard electronic portal imaging device (EPID) or a kV x-ray source with opposed imaging panel in order to localize anatomic points in space or implanted fiducial markers to reposition patients quickly and accuratelyA standard CT scanners linked to a linear accel-•erator via a shared tabletop (e.g., on rails) in the same room with the treatment equipment.

4.g. FractionationThe prescription dose changes in SBRT with the frac-tion number from single to five. (10,26,27) CTV lower-

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dose includes entire vertebral body and posterior el-ements. Two thirds of prescription dose is planned to be prescribed to entire vertebral body and poste-rior elements.

16-24• Gy in single fraction 27• Gy in 3 fractions 30• Gy in 5 fractions Lower total doses with lower dose per fraction •(21 Gy in 3 fractions or 25 Gy in 5 fractions) is prescribed owing to the discretion of the respon-sible RO (e.g. lesion below L2 adjacent to psoas muscle to decrease plexopathy risk, etc)

5. Complications and AvoidanceSpinal cord is the major dose-limiting critical or-gan at risk in SBRT and radiation-induced myelop-athy (RIM) could be a debilitating complication to be avoided. The dose constraints for other organs at risk are detailed in the literature. (29)

5.a. Spinal Cord ToleranceAn extremely sharp fall-off of radiation dose beyond the tumor is required and this makes it possible to safely treat spinal column metastatic lesions with high total doses in single or fractionated SBRT.

Although radiation-induced myelopathy (RIM) is one of the most critical complications associated with radiation therapy, the factual spinal cord tol-erance to SBRT has not been clearly defined due to highly conservative constraints followed in general. The RIM is based on white matter injury with de-myelination and necrosis of the spinal cord, as well as on vasculopathies and glial reaction. (32) In spinal SBRT, therapeutic ratio is increased with greater sep-aration between the spinal cord normal tissue com-plication curve and the spinal tumor control prob-ability curve. The spinal cord is highly sensitive to fraction size as being a late responding tissue where the actual fraction size to the spinal cord needs to be relatively small in comparison to hypofractionated high stereotactic radiation doses. The reported inci-dence of spinal cord complications is too low in the radiotherapy literature to project threshold of a safe dose of the spinal cord.

Because of different fraction sizes in a mainly pal-liative setting, it is difficult to conclude spinal cord tolerance to hypofractionation. A cornerstone study

from Medical Research Council by Macbeth et al. used various regimens to palliate non-small cell lung cancer patients with 8.5 Gy X 2, 4.5 Gy X 6, 5 Gy X 6, 3 Gy X 10, 3 Gy X 12, and 3 Gy X 13 and estimated RIM as 0.6% (3 patients) with 8.5 Gy X 2 fractions at 8 to 42 months and 1.3% (2 patients) with 3 Gy X 13 fractions at 8 to 10 months. (33,34) It is also encour-aging to see that no RIM was reported after 3 Gy X 15 fractions (=45 Gy) in two studies. (35,36) Kramer et al compared palliative regimens of 30 Gy in 10 frac-tions and 16 Gy in 2 fractions in a Dutch trial of non-small cell lung cancer and reported no RIM. (37) On the other hand, there are other palliative studies stat-ing occurrence of RIM up to 13.3% with 40 Gy in 10 fractions to the spinal cord and up to 11.4% with 33.5 Gy in 6 fractions. (38-41)

As RIM is a very debilitating complication, it is logical to hold spinal cord constraint conservative and schemas limiting the maximum spinal cord dose to less than total 10 Gy in case of prescription dose of 27 Gy in 3 fractions, or 30 Gy in 5 fractions need to be preferred. (6,13,14,42) Single session SBRT series re-ported safety of limiting the surface dose of the spinal cord to 10 Gy, 12 Gy, and even 14 Gy appears safe, however it sounds rational to keep it to less than to-tal 10 Gy due to the fact that it is currently unclear with limited follow up. (4,5,11,12,15-18,20,43-45) Data support-ing the single dose constraint of 10 Gy stating no RIM was the report of the Medical Research Council of 114 patients by Macbeth et al that estimated the risk of RIM to be zero by two years, (34) and single dose constraint of 8 Gy stating no RIM were the reports of the Hamburg University Hospital of 199 patients by Rades et al and The Radiation Therapy and Oncol-ogy Group (RTOG) of 455 patients including spinal patients by Hartsell et al. (46-48) The most recent and solid data is by Ryu et al revealing Henry Ford Hos-pital experience on a partial volume tolerance of spi-nal cord after single dose of SBRT in 230 procedures of 177 patients, where the spinal cord volume was defined as 6 mm above and below the SBRT target. They have concluded that partial volume tolerance of the human spinal cord is at least 10 Gy to 10% of the cord volume. (28)

As the data on reirradiation is also very limited, Rades et al. reported their reirradiation of the spine experience of 62 patients after initial course of 8 Gy in one fraction or 20 Gy in 5 fractions with no in-cidence of RIM after second course of 8 Gy in one


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fraction, 15 Gy in 5 fractions, or 20 Gy in 5 fractions with a median follow-up of 8 months after reirradi-ation (range 2-42 months). (49) Although retrospec-tive, Rades et al noted that the cumulative BED2 ≤120 Gy of spinal reirradiation appeared to be ef-fective and safe. (50)

ConclusionSBRT has becoming to gain a significant and prom-ising role as a non-invasive modality to be used in conjunction with other complementary modalities in the management of spinal metastasis along with the important collaboration of spine surgeons, and radiation oncologists.

6. References1. Klimo P, Jr., Schmidt MH. Surgical management of

spinal metastases. Oncologist 2004;9:188-196.2. Potters L, Kavanagh B, Galvin JM, et al. American

Society for Therapeutic Radiology and Oncology (ASTRO) and American College of Radiology (ACR) practice guideline for the performance of stereotactic body radiation therapy. Int J Radiat Oncol Biol Phys 2010;76:326-332.

3. Potters L, Steinberg M, Rose C, et al. American So-ciety for Therapeutic Radiology and Oncology and American College of Radiology practice guideline for the performance of stereotactic body radiation therapy. Int J Radiat Oncol Biol Phys 2004;60:1026-1032.

4. Ryu S, Jin R, Jin JY, et al. Pain control by image-guided radiosurgery for solitary spinal metastasis. J Pain Symptom Manage 2008;35:292-298.

5. Gerszten PC, Burton SA, Ozhasoglu C, et al. Radio-surgery for spinal metastases: clinical experience in 500 cases from a single institution. Spine 2007;32:193-199.

6. Yamada Y, Bilsky MH, Lovelock DM, et al. High-dose, single-fraction image-guided intensity-mod-ulated radiotherapy for metastatic spinal lesions. Int J Radiat Oncol Biol Phys 2008;71:484-490.

7. Gibbs IC. Spinal and paraspinal lesions: the role of stereotactic body radiotherapy. Front Radiat Ther On-col 2007;40:407-414.

8. Gibbs IC, Kamnerdsupaphon P, Ryu MR, et al. Im-age-guided robotic radiosurgery for spinal metas-tases. Radiother Oncol 2007;82:185-190.

9. Nelson JW, Yoo DS, Sampson JH, et al. Stereotactic body radiotherapy for lesions of the spine and paraspi-

nal regions. Int J Radiat Oncol Biol Phys 2009;73:1369-1375.

10. Chang EL, Shiu AS, Mendel E, et al. Phase I/II study of stereotactic body radiotherapy for spinal metas-tasis and its pattern of failure. J Neurosurg Spine 2007;7:151-160.

11. Hamilton AJ, Lulu BA, Fosmire H, et al. LINAC-based spinal stereotactic radiosurgery. Stereotact Funct Neurosurg 1996;66:1-9.

12. Ryu S, Fang Yin F, Rock J, et al. Image-guided and intensity-modulated radiosurgery for patients with spinal metastasis. Cancer 2003;97:2013-2018.

13. Chang EL, Shiu AS, Lii MF, et al. Phase I clinical evaluation of near-simultaneous computed tomo-graphic image-guided stereotactic body radiother-apy for spinal metastases. Int J Radiat Oncol Biol Phys 2004;59:1288-1294.

14. Bilsky MH, Yamada Y, Yenice KM, et al. Intensity-modulated stereotactic radiotherapy of paraspinal tu-mors: a preliminary report. Neurosurgery 2004;54:823-830; discussion 830-821.

15. Ryu S, Rock J, Rosenblum M, et al. Patterns of fail-ure after single-dose radiosurgery for spinal metas-tasis. J Neurosurg 2004;101 Suppl 3:402-405.

16. Gerszten PC, Burton SA, Ozhasoglu C, et al. Stereot-actic radiosurgery for spinal metastases from renal cell carcinoma. J Neurosurg Spine 2005;3:288-295.

17. Gerszten PC, Burton SA, Quinn AE, et al. Radiosur-gery for the treatment of spinal melanoma metasta-ses. Stereotact Funct Neurosurg 2005;83:213-221.

18. Gerszten PC, Burton SA, Welch WC, et al. Single-fraction radiosurgery for the treatment of spinal breast metastases. Cancer 2005;104:2244-2254.

19. Degen JW, Gagnon GJ, Voyadzis JM, et al. CyberKnife stereotactic radiosurgical treatment of spinal tumors for pain control and quality of life. J Neurosurg Spine 2005;2:540-549.

20. Rock JP, Ryu S, Shukairy MS, et al. Postoperative radiosurgery for malignant spinal tumors. Neuro-surgery 2006;58:891-898; discussion 891-898.

21. Mahan SL, Ramsey CR, Scaperoth DD, et al. Evalu-ation of image-guided helical tomotherapy for the retreatment of spinal metastasis. Int J Radiat Oncol Biol Phys 2005;63:1576-1583.

22. RTOG 0631. Phase II/III Study Of Image-Guided Radiosurgery/SBRT For Localized Spine Metasta-sis. Radiation Therapy Oncology Group. Activation Date: August 7, 2009. http://www.rtog.org/members/protocols/0631/0631.pdf.

23. Yokogushi K, Ishii S, Ono N, et al. [Indication and method for surgical treatment of metastatic spinal tumors]. Gan To Kagaku Ryoho 1988;15:1509-1514.

Ugur Selek M.D.

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Minim


24. Klimo P, Jr., Kestle JR, Schmidt MH. Clinical trials and evidence-based medicine for metastatic spine disease. Neurosurg Clin N Am 2004;15:549-564.

25. Wise JJ, Fischgrund JS, Herkowitz HN, et al. Compli-cation, survival rates, and risk factors of surgery for metastatic disease of the spine. Spine 1999;24:1943-1951.

26. Sahgal A, Larson DA, Chang EL. Stereotactic body radiosurgery for spinal metastases: a critical review. Int J Radiat Oncol Biol Phys 2008;71:652-665.

27. Nguyen QN, Shiu AS, Rhines LD, et al. Management of spinal metastases from renal cell carcinoma us-ing stereotactic body radiotherapy. Int J Radiat On-col Biol Phys 2010;76:1185-1192.

28. Ryu S, Jin JY, Jin R, et al. Partial volume tolerance of the spinal cord and complications of single-dose radiosurgery. Cancer 2007;109:628-636.

29. Timmerman RD. An overview of hypofractionation and introduction to this issue of seminars in radia-tion oncology. Semin Radiat Oncol 2008;18:215-222.

30. Kavanagh BD, Timmerman RD. Stereotactic ra-diosurgery and stereotactic body radiation ther-apy: an overview of technical considerations and clinical applications. Hematol Oncol Clin North Am 2006;20:87-95.

31. Chang BK, Timmerman RD. Stereotactic body radi-ation therapy: a comprehensive review. Am J Clin Oncol 2007;30:637-644.

32. Schultheiss TE, Kun LE, Ang KK, et al. Radiation response of the central nervous system. Int J Radiat Oncol Biol Phys 1995;31:1093-1112.

33. Macbeth F. Comments on A case of radiation my-elopathy after 2 x 8.5 Gy for inoperable non-small cell lung cancer, Dardoufas et al., European Journal of Cancer, 31A, Nos 13/14, pp. 2418-2419, 1995. Eur J Cancer 1996;32A:1616-1617.

34. Macbeth FR, Wheldon TE, Girling DJ, et al. Radia-tion myelopathy: estimates of risk in 1048 patients in three randomized trials of palliative radiotherapy for non-small cell lung cancer. The Medical Research Council Lung Cancer Working Party. Clin Oncol (R Coll Radiol) 1996;8:176-181.

35. Choi NC, Grillo HC, Gardiello M, et al. Basis for new strategies in postoperative radiotherapy of bronchogenic carcinoma. Int J Radiat Oncol Biol Phys 1980;6:31-35.

36. Hazra TA, Chandrasekaran MS, Colman M, et al. Survival in carcinoma of the lung after a split course of radiotherapy. Br J Radiol 1974;47:464-466.

37. Kramer GW, Wanders SL, Noordijk EM, et al. Re-sults of the Dutch National study of the palliative

effect of irradiation using two different treatment schemes for non-small-cell lung cancer. J Clin On-col 2005;23:2962-2970.

38. Fitzgerald RH, Jr., Marks RD, Jr., Wallace KM. Chronic radiation myelitis. Radiology 1982;144:609-612.

39. Abramson N, Cavanaugh PJ. Short-course radiation therapy in carcinoma of the lung. A second look. Ra-diology 1973;108:685-687.

40. Guthrie RT, Ptacek JJ, Hass AC. Comparative analy-sis of two regimens of split course radiation in carci-noma of the lung. Am J Roentgenol Radium Ther Nucl Med 1973;117:605-608.

41. Dische S, Warburton MF, Saunders MI. Radiation myelitis and survival in the radiotherapy of lung cancer. Int J Radiat Oncol Biol Phys 1988;15:75-81.

42. Dodd RL, Ryu MR, Kamnerdsupaphon P, et al. Cy-berKnife radiosurgery for benign intradural extramed-ullary spinal tumors. Neurosurgery 2006;58:674-685; discussion 674-685.

43. Gerszten PC, Ozhasoglu C, Burton SA, et al. Eval-uation of CyberKnife frameless real-time image-guided stereotactic radiosurgery for spinal lesions. Stereotact Funct Neurosurg 2003;81:84-89.

44. Gerszten PC, Ozhasoglu C, Burton SA, et al. Cy-berKnife frameless single-fraction stereotactic ra-diosurgery for benign tumors of the spine. Neuro-surg Focus 2003;14:e16.

45. Gerszten PC, Ozhasoglu C, Burton SA, et al. Cy-berKnife frameless stereotactic radiosurgery for spi-nal lesions: clinical experience in 125 cases. Neuro-surgery 2004;55:89-98; discussion 98-89.

46. Rades D, Stalpers LJ, Hulshof MC, et al. Effectiveness and toxicity of single-fraction radiotherapy with 1 x 8 Gy for metastatic spinal cord compression. Ra-diother Oncol 2005;75:70-73.

47. Rades D, Stalpers LJ, Veninga T, et al. Evaluation of five radiation schedules and prognostic factors for metastatic spinal cord compression. J Clin On-col 2005;23:3366-3375.

48. Hartsell WF, Scott CB, Bruner DW, et al. Random-ized trial of short- versus long-course radiotherapy for palliation of painful bone metastases. J Natl Can-cer Inst 2005;97:798-804.

49. Rades D, Stalpers LJ, Veninga T, et al. Spinal reir-radiation after short-course RT for metastatic spi-nal cord compression. Int J Radiat Oncol Biol Phys 2005;63:872-875.

50. Rades D, Rudat V, Veninga T, et al. Prognostic fac-tors for functional outcome and survival after reir-radiation for in-field recurrences of metastatic spi-nal cord compression. Cancer 2008;113:1090-1096.

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NEUROSTIMULATION FOR PAIN SECONDARY

TO SPINE PROBLEMSGiancarlo Barolat M.D.

1. IntroductionElectrical stimulation through implanted neurostim-ulation devices is playing an increasingly important role in the management of patients with lumbar spine/nerve roots problems. The role of neurostim-ulation is purely in the control of severe refractory pain. Neurostimulation has no role in the manage-ment of weakness or numbness secondary to me-chanical compression of the neural structures. The increasing role of neurostimulation is due to the fol-lowing considerations: 1- in many instances, even a well planned and technically correct spine surgical procedure fails to produce satisfactory pain relief. 2- A neurostimulation procedure can be performed on a reversible, temporary trial basis, and its efficacy can therefore be assessed without committing to the full procedure. 3- The reduction in pain, when pres-ent, can be obtained without affecting the structure of the spine (unlike a fusion procedure).

In order to obtain good results, the lead(s) must be positioned strategically on the neural structures and must generate a tingling sensation (paresthesiae) that covers the area of pain. (1,2,3)

It is becoming clear that neurostimulation plays a very important role in the management of patients with a variety of lumbar spine-related problems, and that its role is not limited only to patients who have failed innumerable surgical procedures.

2. IndicationsThere are two main indications for neurostimula-tion in lumbar spine problems: a- neuropathic pain b- situations where the pain is mostly axial and the

results of a lumbar fusion are questionable (such as with multi-level disk degeneration)

2.a. Neuropathic PainThere are two main types of neuropathic pain in pa-tients with lumbar spine problems.

2.a.1. RadiculitisThe pain occurs exactly along the distribution of a specific nerve root, and may mimic a compressive radiculopathy. Radiculitis is due to intrinsic dam-age to the nerve fibers in the nerve root, and does not respond to surgical decompression of the nerve root. Radiculitis can be caused by stretch injury, se-vere compressive damage to the nerve root (such as in the case of a large disk herniation) or due to intra-operative iatrogenic damage. Radiculitis and mechanical radiculopathy can coexist. Radiculitis pain is characterized by the fact that it is constant (in fact ,most commonly worse at night) and that there is a substantial component of burning pain sensation.

2.a.2. Arachnoiditis.Arachnoiditis is caused by intradural scarring around the nerve roots. This takes the appearance, on im-aging studies, of “clumped nerve roots”. The main symptom is diffuse burning pain, without a clear radicular distribution, accompanied by progressive bladder dysfunction and episodes where the leg(s) “give out” for a few seconds. Unfortunately, the cor-relation between intradural nerve root scarring and the clinical syndrome is not well defined. Many pa-tients who clearly have “arachnoiditis” on imaging studies do not suffer from the clinical syndrome. On the other hand, the majority of the patents who suf-

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fer from the clinical presentation of “arachnoiditis” do not exhibit signs of intradural scarring on imag-ing studies.

2.b. Alternative to Spine SurgeryNeurostimulation should also be considered as an al-ternative to a major surgical procedure on the lumbar spine when a) the yield of the surgery is predictably low, such as in patients with low back pain and sev-eral degenerated non-contiguous disks b) when the symptomatology is mostly lumbar axial pain.

Many of the studies in the literature refer to a syn-drome called “failed back syndrome” (FBS). This syn-drome remains vaguely defined. This syndrome may encompass many different types of pain; including pain localized to the center of the lower lumbar area, pain in the buttocks, or diffuse lower extremity(s) pain. The etiology of this syndrome has included arachnoiditis, epidural fibrosis, radiculitis, microin-stability, and recurrent disk herniations. Many pub-lished series distinguish between back and leg pain, but the details of the pain syndromes are seldom de-fined. Spinal Cord Stimulation (SCS ) is accepted in the treatment of leg pain, but its widespread use for relief of pain in the lower lumbar area still remains to be defined.

Four prospective series aimed at studying the ef-fects of SCS on FBS. Barolat et al. prospectively en-rolled patients with low back pain or low back pain greater than or equal in severity to the leg pain. (4)

These patients underwent implantation with a multi-lead paddle electrode and were followed for one year. The study demonstrated a 69% successful re-duction in back pain and 88% successful reduction in leg pain at one year follow-up. In 1996, Burchiel et al. demonstrated similar results. (5) They reported on 70 patients with a one-year follow-up and showed successful management of pain in 55% of patients. Medication usage and work status were not im-proved. North et al. conducted the first prospective, randomized comparison of Spinal Cord Stimula-tion (SCS) with other treatment modalities with a 6 month cross-over arm in the study. (6) In that study, 51 patients with FBS consented to randomization. The study demonstrated significant difference between the patients who opted for crossover from SCS to re-operation versus the opposite. The study concluded that SCS is a viable alternative to re-operation for FBS. Kumar recently published a large (100 FBS pa-

tients) prospective randomized controlled multi-cen-ter study. (7) Patients were treated with conventional medical management (CMM) with or without SCS. At 12 months follow-up 48% of SCS patients and 18% of only CMM patients experienced >50% leg pain re-lief. SCS patients had significantly greater health-re-lated quality of life and functional capacity.

The longitudinal studies by North showed that in patients with post-surgical lumbar arachnoid or epi-dural fibrosis without surgically remediable lesions, SCS is superior to repeated surgical interventions on the lumbar spine (for back and leg pain) and to dorsal ganglionectomy (for leg pain.)[8) A few studies have reported on the cost-effectiveness of SCS in FBSS.[9) Bell et al. compared the costs of SCS with surgeries and alternative treatments. (10) They calculated the estimated cost of therapy for each group over a five-year period without quantifying the improvements offered by successful SCS. The authors reported that, in patients who responded favorably to SCS, the ther-apy would pay for itself within 2.1 years.

3. EquipmentAll contemporary neurostimulation systems con-sists at least of two components, a lead (otherwise known as electrode) and a pulse generator (which contains a lithium battery). The lead(s) is implanted on the targeted neural structure and the pulse gen-erator is implanted in a subcutaneous pocket in a convenient location.

3.a. Leads (Figure 1)Today’s technology allows the implanting physician to deliver effective stimulation to the spinal cord /nerve roots and peripheral nerves via two types of leads, the ones that can be inserted percutaneously and the ones which require an open technique and direct vi-sualization for insertion. . At least two contacts of op-posite polarities are necessary to produce an electri-cal current (unless the case of the pulse generator is programmed to functions as an active pole.)

3.a.1. Percutaneous leadsMost contemporary percutaneous leads are either quadripolar or octopolar (referring to the number of contacts present on the lead.). The chief differ-ence between systems includes the number of con-tacts, the length of the contacts, and the spacing be-


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tween them. In addition, insertion of multiple parallel electrodes permits construction of different config-uration matrices, which can create variably focused electrical fields. Inherently, percutaneous electrodes are more flexible, thus allowing them to be inserted through a Touhy needle, although some require the presence of a stylet for insertion. Percutaneous elec-trodes have several advantages. First and foremost they can be inserted through a needle, therefore avoiding surgical dissection of the paraspinal mus-cles and bony removal. Additionally, they can be eas-ily advanced over several segments in the epidural space, allowing testing of several spinal cord levels and optimizing electrode position. Further, there is the added benefit of performing a trial stimulation to assess candidacy for a permanent implant and a temporary percutaneous electrodes can easily be re-moved in the implanting physician’s office. Perma-nent percutaneous implantation technique is similar except that a surgical incision is required to anchor

the electrode in place, extension wires must be tun-neled a few inches away from the insertion site and a return trip to the operating room is necessary for removal or internalization of the electrode. There are disadvantages to percutaneous leads as well. These leads have a tendency to migrate and the stimula-tion may be more susceptible to postural changes. The electrical field generated by percutaneous leads is fairly narrow (as compared to plate electrodes) and power requirements are higher. Also, these electrodes must be placed under fluoroscopic guidance and this requires wearing heavy shielded garments and may expose the patient, as well as the implanting physi-cian, to non-negligible levels of radiation.

3.a.2. Paddle leads (or plate leads)Plate-type electrodes may sometime be referred to as ribbon electrodes, paddle electrodes, or laminotomy electrodes. The most commonly utilized plate leads contain 8 or 16 electrical contact arranged in vari-

Figure 1: Various types of Paddle and Percutaneous Leads

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ous configurations.. Similar to percutaneous leads, differences between the varying plate leads also in-clude the number of contacts, the length of the con-tacts, and the spacing between the contacts. Plate-type electrodes must be implantated under direct vision. Most implants can be done through a skin incision between 2.5 - 4cm long, and the amount of bony removal is usually minimal. The implant-ing physician can usually explore about four to five levels in the thoracic spine and five to six levels in the cervical spine by advancing the electrode in ei-ther a cephalad or a caudal direction. Multiple dif-ferent electrode configurations can also be obtained with plate electrodes. The greatest advantage of the plate electrodes resides is their lesser propensity to migrate and better long term effectiveness. Some preliminary data by North as well as the author’s experience, also suggest a broader stimulation pat-tern and lower stimulation requirements with plate electrodes. Finally, plate electrodes might be the only

option in the case of previous spine surgery at the implant levels.

3.b. Pulse generators (IPG) (Figure 2)All current pulse generators contain two main parts a) the electronic circuitry and b) a lithium battery. The pulse generator is implanted in a subcutaneous pocket. The most common locations for the pocket are the buttock, the abdomen and the infra-clavic-ular area. All the functions of the pulse generator (polarity, voltage, rate, pulse width, complex pro-grams) can be modified non-invasively through a programmer. The battery can be externally (trans-cutaneously) rechargeable or non-rechargeable. Re-chargeable batteries last on average 4-5 years longer than a correspondent non- rechargeable. Recharge-ability has allowed the manufacturers to reduce the size of the pulse generator. The patient has a control-ling unit, which can modify many of the functions of the pulse generator.

Figure 2: Various types of Implantable Pulse Generators


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4. Surgical Procedure

4.a. Targets Four different target areas are available for neuro-stimulation in lumbar spine problems. They are not mutually exclusive and, in fact, often times they can be combined in the same procedure (11) :- The dorsal columns. To stimulate the dorsal col-

umns the leads must be placed in the dorsal epi-dural space in the thoracic spine. The most com-mon lead placement levels are at the T8-T10 spine levels. From those levels one can reasonably ex-pect to achieve stimulation in the lower extrem-ities, in the buttocks area and in the lumbar area below the belt line. (Figure 3)

- Dorsal roots. The dorsal roots can be stimulated by placing the leads in the dorsal epidural space between the L1 and the L5 spine levels. Dorsal root stimulation is more appropriate when the pain to be addressed is located in the foot or in the knee. (Figure 4)

- Peripheral nerves. Stimulation of the sciatic nerve in the posterior thigh can be performed when the pain is l in the distribution of the L5-S1 nerve roots distribution and it is localized mostly below the knee. (Figure 4-5)

- Subcutaneous nerve fibers. In this instance the leads are placed in the subcutaneous tissue di-rectly in the painful area. This is indicated mostly for pain localized in the lumbar area, either as an adjunct or instead of dorsal column stimula-tion. (12-14) (Figure 6-7)

Figure 3:

A- Two paddle leads, one in the low thoracic spine and one in the upper lumbar spine to achieve, re-spectively, dorsal column and lumbar nerve root stimulation

B- Paddle lead on the S1-2-3 nerve roots

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4.b. StrategiesDepending on the location of the pain, there are 3 different approaches. The approaches are not mutu-ally exclusive and can be combined even within an individual patient.- If the pain affects a large portion of a lower ex-

tremity, the modality of choice is Dorsal Col-umn Stimulation with the electrode(s) strategi-cally placed to direct paresthesiae to the painful area.

- If the pain is mostly in the foot or in the knee, a more effective strategy consists in placing the electrodes on the L5-S1 or the L3-4 nerve roots re-spectively. Alternatively, one can place the leads on the appropriate peripheral nerves (sciatic, fem-oral)

- Low back pain constitutes a most challenging problem. It is not clear yet which is the best electrode configuration to selectively and ex-clusively stimulate the low back fibers from the

intraspinal space. Some studies have suggested an array of two parallel narrowly spaced octa-polar electrodes. Others have obtained satisfac-tory stimulation with a tripolar array. A prom-ising alternative is the stimulation of the small subcutaneous fibers through subcutaneously im-planted electrodes. (12-14) This allows to gener-ate paresthesia directly and specifically in the axial pain area.

4.c. Screening trialMost implanting physicians encourage a temporary screening trial. The necessity of this has been debated and different approaches have been advocated.

The three options available are:• No trial. The entire system is implanted at the

time of surgery.• Surgical implantation of the lead(s) and exter-

nalization (Staged trial): The leads are implanted and externalized via a temporary disposable ex-tension cable. The patient is then assessed, for a

Figure 4: Sciatic Nerve Stimulator in patient with intractable S1 radiculopathy following multiple lumbar spine surgeries.

A- Positioning on the operating room table for lead insertion B- X-ray of the implanted system. One lead, two connectors and the IPG in the front of the thigh.


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few days and then is taken back to the operating room. If pain relief and paresthesiae coverage is adequate, the extension is cut-off, the pulse gen-erator is connected to the lead(s) and implanted. If the stimulation did not help, the electrodes are removed. (Figure 5)

• Temporary electrode implantation: The patient is implanted with a temporary percutaneous lead(s) which is externalized. During the ensuing few days the patients tries the stimulation and as-sesses its efficacy. The patient is then re-evalu-ated, usually a week later, and the electrode is removed. In the case of a successful trial, the pa-tient undergoes implantation of the system at a later date. (Figure 6)

The efficacy of any one approach is debatable and more likely should be tailored to each individual pa-tient. First, the degree of pain relief warranting perma-nent implantation has been debated. However, most authors agree on at least a 50% relief in pain symp-toms. With this criterion, it is estimated that approx-imately 15% to 20% of patients fail the trial and are not subjected to permanent implantation. Further, an outpatient percutaneous electrode trial is a reversible intervention. It allows the patient to become famil-iar with and understand the paresthesiae that may aid in their pain relief. A percutaneous stimulation trial also allows evaluation of stimulation at multi-ple spinal levels, by gradually withdrawing the elec-trode, to locate the optimal location.

Figure 5: Femoral Nerve Stimulator in a patient with intractable anterior thigh pain following intra-operative L4

nerve root damage.

A- Patient finished one week trial with the lead externalized. IPG to be implanted in the left abdomen. B- Lead placed on the femoral nerve C- X-ray of the lead in place

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In our experience, a trial screening is very helpful and accomplishes a number of purposes. It exposes and educates the patients to the stimulation-induced paresthesiae and gives them some initial exposure to the potential pain relief without commitment to a permanent implantation. It further allows screen-ing of a small group of patients who may not benefit from stimulation at all. Trial screening has not been shown to increase the morbidity of this modality in any significant manner.

In our practice successful stimulation can be dem-onstrated given the following factors:• Careful psychological screening to demonstrate

absence of major psycho-pathology.• Patient must demonstrate a stable social and fam-

ily structure as well as remain highly motivated.

• Realistic expectations that chronic pain cannot be eliminated with adherence to the indication and results alluded to previously.

• Trial stimulation followed by intra-operative test-ing showing good coverage of the painful area with paresthesiae perceived as a pleasant smooth tingling sensation.

5. Complications

5.a. Neurological damageThe most dreaded complication related to the in-sertion of an epidural spinal cord stimulator which may occur which is not foreign to any type of spine surgery is neurological injury from the procedure.

Figure 6: Trial implantation of subcutaneous leads for intractable low back pain. Patient was not deemed candi-

date for spine surgery.

A- Pain area markedB- Leads being inserted through a percutaneous needleC- leads secured and taped to the skin. Small antibiotic-impregnated discs at the sites of lead exit.


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Fortunately, the number of cases of neurological in-jury has been extremely low and has been much less than 1%. Intraoperative injury may occur dur-ing percutaneous implantation or during plate elec-trode placement.

Percutaneous needle placement could result in direct penetration of the spinal cord with the Touhy needle or intradural placement of an electrode

An epidural hematoma may also be a cause of postoperative neurological deficit. In a consecutive series of 5,000 implanted plate electrodes, the author has experienced four instances of postoperative para-plegia due to epidural hematoma at the site of elec-trode implantation. In three of the four cases prompt surgical evacuation resulted in complete reversal of the neurological deficit.

5.b. Electrode migration and Implant Failures.

Electrode migration is not an uncom-mon problem and may require a reoper-ation to recapture adequate paresthesia. This concept is particularly important be-cause if the implanted electrode migrates, this is likely to result in failure of spinal cord stimulation. Electrode migration is more common with percutaneous than with plate electrodes and tends to occur most commonly in the first few days. Re-view of the literature suggests between 1-15% incidence of electrode migration. Over the years, hardware related com-plications have substantially decreased. Connectors may loosen if not tightened appropriately, and fluid might infiltrate the connectors. Other complications with the equipment may include a 1-4% inci-dence of unspecified hardware failure or <2% incidence of battery failure. There may additionally be a 1-8% incidence of lead breakage, more commonly in the cervical spine.

5.c. InfectionInfections of the implanted hardware have been reported with an incidence

varying between 0.5 and 15%. An acceptable infection rate should not exceed 3-5%. Infection usually affects the implanted pulse generator/radio-receiver and the cabling connecting to the electrode. Very seldom does the infection spreads to the epidural space. Infections can occur any time from a few days after implanta-tion to a few years. The author has seen cases of in-fections that occurred one year after an apparently uncomplicated SCS implantation. Infections present with persistent tenderness over the implanted hard-ware. Swelling, redness and other signs of inflamma-tion may be present. The ultimate treatment for an in-fection is complete removal of the hardware followed by a prolonged course of intravenous antibiotics. Su-perficial infections might be treated with antibiotics without the removal of the hardware.

Figure 7:A- X-ray of the case represented in Fig 6B- Another case of lumbar subcutaneous lead implant in pa-

tient with persistent intractable low back pain following interbody fusion

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ry 6. References1. Barolat G, Zeme S, Ketcik B. Mapping of sensory

responses to epidural stimulation of the intraspinal neural structures in man. J Neurosurg 1993; 78: 233-9.

2. Holsheimer J, Barolat G, Struijk JJ, et al. Significance of the spinal cord position in spinal cord stimula-tion. Acta Neurochir 1995; 64 (Suppl):119-24.

3. Holsheimer J, Strujik JJ. How do geometric factors influence epidural spinal cord stimulation? A quan-titative analysis by computer modeling. Stereotact Funct Neurosurg 1991; 56: 234-249.

4. Barolat G, Oakley JC, Law JD, et al. Epidural spi-nal cord stimulation with multiple electrode pad-dle lead is effective in treating intractable low back pain. Neuromodulation 2001; 4(2): 59-66.

5. Burchiel KJ, Anderson VC, Brown FD, et al. Pro-spective, multicenter study of spinal cord stimula-tion for relief of chronic back and extremity pain. Spine 1996; 21(23): 2786-2794

6. North RB, Kidd DH, Piantadosi S. Spinal cord stim-ulation versus reoperation for failed back surgery syndrome: a prospective, randomized study de-sign. Acta Neurochirurgica - Supplementum 1995; 64: 106-108. 272

7. Kumar K, Taylor RS, Jacques L, et al. Spinal cord stimulation versus conventional medical manage-ment for neuropathic pain: a multicentre random-ized controlled trial in patients with failed back sur-gery syndrome. Pain 2007;132(1-2):179-88.

8. North RB, Ewend MG, Lawton MT, et al. Failed back surgery syndrome: 5-year follow-up after spi-nal cord stimulator implantation. Neurosurgery 1991; 28(5): 692-699.

9. Turner JA, Loeser JD, Bell KG. Spinal cord stimula-tion for chronic low back pain: a systematic litera-ture synthesis. Neurosurgery 1995; 37(6):1088-1095

10. Bell GKK. Cost-effectiveness analysis of spinal cord stimulation in treatment of failed back surgery syn-drome. Journal of Pain & Symptom Management 1997; 13(5): 286-295.

11. Bernstein CA, Paicius RM, Barkow SH, Lempert-Co-hen C. Spinal cord stimulation in conjunction with peripheral nerve field stimulation for the treatment of low back and leg pain: a case series. Neuromod-ulation 2008; 11: 116–123.

12. Barolat G. Techniques for Subcutaneous Peripheral Nerve Field Stimulation for Intractable Pain. In Neuro-modulation, Editors: E. Krames, H. Peckham, A. Rezai. Elsevier Publisher, Chapter 88, pp 1017-1020, 2009

13. Paicius RM, Bernstein CA, Lempert-Cohen C. Pe-ripheral nerve field stimulation for the treatment of chronic low back pain: Preliminary results of long-term follow-up. A case series. Neuromodulation 2007;10: 279–290

14. McCeney M, Krutch J, Barolat G. A Case Report of Subcutaneous Peripheral Nerve Stimulation for the Treatment of Axial Back Pain Associated with Failed Back Surgery Syndrome. Neuromodulation, Volume 11, 2; 112-115, 2008.

Mark Sedrak M.D., Zachary A. Smith M.D., Ausaf Bari M.D., Michael Selch M.D., Antonio A.F. De Salles M.D. Ph.D.

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STEREOTACTICALLY-GUIDED SPINAL RADIOSURGERY


1. IntroductionHamilton et al. first described spinal SRS in 1995 us-ing a linear accelerator. (14)

Advances in radiosurgical technology and tech-niques have now allowed for safe and effective treat-ment of many conditions involving the spine. As expe-rience with this treatment has become more accepted and widely used, spinal radiosurgery has even be-come an important treatment alternative to surgery, primarily because of its appealing non-invasive na-ture, convenience, and efficacy. (4, 7, 8, 19)

Stereotactically-guided spinal radiosurgery has become a pivotal tool in the treatment of metastatic cancers, arteriovenous malformations, gliomas, ependymomas, and peripheral nerve sheath tumors. Metastatic cancer is the single most common use for this technology. Up to 70% of the 1 million individuals in the United States who are diagnosed with cancer will develop spinal metastases. Additionally, nearly 10% of cancer patients develop symptomatic spinal metastases (15). These spinal lesions, when symptom-atic, can cause pain, skeletal instability, and neural compression. Early diagnosis and treatment of these lesions can be critical. Appropriate treatment has the potential to improve patient quality of life and in many circumstances significantly delay or pre-vent the progression of disease. Although surgery plays a critical role in certain cases, radiation is con-sidered the primary treatment for spinal metastases especially when multiple lesions are present with-out neurological deficits (6).

In this chapter, we will review the basic princi-ples of radiation treatment, including the tolerance of the spinal cord to radiation, histological tumor types,

the physical properties of tissue response to radia-tion, and the current literature evidence in support-ing the safety and efficacy of this technique. Many forms of technology are available for spinal radio-surgery are based on the use of a linear accelerator (linac), which include Cyberknife and Novalis. Other technologies include Gamma Knife, which utilizes radioactive decay, and Proton Beam radiation. Our focus in this chapter will be on the linac based sys-tems, but many of the principles are similar. Early results and experience demonstrate that SRS is both a safe and effective modality for the treatment of spinal lesions.

2. Tumor versus Normal Surrounding tissue: Variable response to Radiation and the role of Stereotaxis

The most important limiting factor with radiation treatment for lesions in the spine is radiation to the spinal cord parenchyma. Occasionally, surrounding tissues such as the esophagus or retroperitoneal or-gans may also need to be considered. The spinal cord is a particularly sensitive part of the CNS to the ef-fects of radiation making precisely calculated treat-ment plans a requirement for safe and effective treat-ment without significant side effects.

Conventional external beam radiotherapy is the classic and established technique utilized for the ra-diation treatment of spinal lesions. With this form of radiation treatment a dose of 20-40 Gy can safely be delivered to the spine (including the spinal cord) in 5-20 fractions. Numerous studies have found that the risk of radiation myelits following fractionated

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radiation therapy is very small (1). With this form of treatment, the factor limiting the total dose delivered is the tolerance of the spinal cord to radiation (10). Early studies evaluating the effects of spinal cord irradia-tion demonstrated that the risk of myelitis from irra-diation of 45-50 Gy in 2 Gy fractions was 0.4 %. This dose subsequently was established as the benchmark for subsequent treatments (16).

Stereotactic spinal radiosurgery has a tremen-dous advantage over conventional radiation methods in that there is often minimal radiation exposure to normal anatomic structures (eg: spinal cord, bowel, kidney, esophagus). The physics behind SRS/SBRT allows for a geometrical advantage in delivering the radiation, which therefore allows for minimal expo-sure to the neighboring structures. Furthermore, a major advantage of stereotactic radiosurgery is that the tumor can receive a higher dose and the cord a lower dose than is possible with conventional radi-ation therapy (7).

The volume of the cord exposed to radiation plays a role in the development of radiation myelitis. Spi-nal cord constraint to 10 Gy to 10% of partial cord volume is often utilized (20). Also, 12 Gy is considered the maximum tolerant amount of spinal cord radia-tion. Furthermore, planning software allows for cal-culation of radiation dosing and in the circumstance of there being a more significant dose to important surrounding structures, modifications in the plan can be performed or the decision to stereotactically frac-tionate doses can also be entertained.

Mathematical modeling of likelihood of radiation myelitis is most often achieved using the linear-qua-dratic (LQ) model. The LQ model models biologic response to radiation. The surviving fraction of cells after a dose D is defined as:

SF = exp − (αD + βD2) .

The values of α and β depend on the tissue irra-diated. The surviving fraction is dependant on cell killing that is linearly related to dose (αD ) and qua-dratically related to dose (βD2) .

The LQ model is used to arrive at a biologically effective dose (BED). This is defined as:

BED = nd * (1 + d/(α/β)) where d is the dose per fraction and n is the number of fractions. The alpha beta ratio (α/β) is estimated to be 2 for late responding

normal tissues (including the spinal cord) and 10 for more rapidly dividing malignant cells (or early re-sponding tissues such as tumor).

BED can be used to compare various dose frac-tionation schemes and extrapolate from the well-stud-ied data in fractionated radiation of the spinal cord. While validated in conventionally fractionated radi-ation therapy, the LQ model and BED have not been validated for use in hypofractionated radiation or SRS. BED is however, often used as a basis for com-paring radiation dose fractionation schemes in hy-pofractionated treatments. Because of the question in using BED for application in radiosurgical cases, one must take clinical and case specific factors into consideration when making a final decision on frac-tionation in radiosurgery.

Another consideration in the treatment of tumors is the tumor type and the necessary radiobiological dose to treat. Tumors with a low α/β ratio (eg, sarco-mas) may respond to larger fraction sizes (12). Mecha-nisms for these radiobiological differences is unclear. Some evidence suggests that single-fraction therapy of more than 15 Gy results in tumor death by apop-tosis, perhaps through a sphingomyelinase pathway

(9). However, microvascular damage may also occur in high-dose fractions. Because of this microvascu-lar effect, radiosurgery expanded its applications not only to primary or secondary malignancies, but also in the treatment of vascular lesions such as ar-teriovenous malformations. Depending on the nidus and location of the spinal AVM, either stereotactic ra-diosurgery (single dose) or stereotactic radiotherapy (fractionated doses) can be utilized.

Benign tumors such as meningiomas, schwan-nomas and neurofibromas may also be success-fully treated with stereotactic radiosurgery. Much of this treatment strategy began with intracranial le-sions such as vestibular schwannomas and menin-giomas. Effective doses of radiation at 12-16Gy in a singe dose can often be safely delivered with good long-term control. (21)

Metastatic cancer to the spine is the most com-mon indication for spinal radiosurgery. Early diag-nosis and treatment of metastatic cancer with stereot-actic radiosurgery may prevent the need for open surgery on many of these complex cancer patients.

(18) Because this does not directly compromise other cancer treatments such as chemotherapy, these treat-ments can occur concomitantly.


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The most common symptom leading to spinal radiosurgery related to metastatic disease is pain. In fact, pain is often used as an indication for radiation. Pain relief after radiosurgery is a major objective of treatment and when this occurs there is thought to be good success with the treatment. (10,19). Several re-ports show that more than 80% of patients who pre-sented with pain improved after radiation (13). Local tumor control rate of 90% at 6 months was achieved for both metastatic lesions and benign tumors (5,6). Most radiosurgery failure may be secondary to significant epidural mass in the spinal canal or insufficient ra-diation dose due to previous radiation.

Twenty-one spinal AVM were treated from 1997-2006 at a single institution (22). AVM obliteration was partial in 4 and complete in 2 of the 6 patients on follow-up angiography. Significant obliteration was observed in nearly every case observed on MRI at 1 year.

Another applications have been used including radiosurgery for the prevention of fibrosis after nerve root exploration (11) or to target ganglia and nerve struc-tures in the spine to treat dermatomal pain (12).

3. Other techniques in Spinal Radiosurgery:

Image guidance systems such as the Exac Trac re-lies on X-ray confirmation just before and during the radiation treatment to ascertain the position of the patient for added verification. Now, cone beam CT scan is also available as part of the radiosurgery de-livery device. Near real-time computer generated im-age fusion has allowed the development of these ste-reotactic techniques no longer dependent on a rigid fixation device. (17)

In many instances, lesions can be seen in spinal im-aging and be of unclear significance. These lesions can be benign or be signs of metastatic disease. Image fusion

in many instances, utilizing PET-CT fusion, can help de-termine if a lesion has hypermetabo-lism. These “hot” spots can then be targeted with ra-diosurgery. Many believe this is bene-ficial in early detec-tion and improved treatment. In addi-tion, diffusion ten-sor imaging has also allowed for in-teresting anatomic analysis of the spi-nal cord, guiding decision making for radiosurgical treatment.

Figures: IsoBED curves calculated using the LQ model solid lines, various colors are superimposed onto isoeffect data black color� digitized for early and late effects in various organs and tissues of laboratory animals. The values for / used in the present modeling are displayed in matching color to the left of each curve. The LQ-L model�dashed red line� with DT = 4.2 Gy and the tangent at DT appears to fit the isoeffect data for lung better than does the LQ model�solid red line�.(2)

Figure:IsoBED curves calculated using the LQ model solid lines, various colors are super-imposed onto isoeffect data black color digitized for early and late effects in vari-

ous organs and tissues of laboratory animals. The values for α/β used in the present modeling are displayed in matching color to the left of each curve. The LQ-L model dashed red line with DT = 4.2 Gy and the tangent at DT appears to fit the isoeffect

data for lung better than does the LQ model solid red line.


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Figure: 53 year old female with metastatic breast cancer who developed neck pain. A mass was seen at C2. Stereotactic radiosurgery was administered with a dose of 12 Gy to 90%. Images show the initial lesion seen and a new MRI 1.5 years later.

Figure:53 year old female with metastatic breast cancer who developed neck pain. A mass was seen at C2.

Stereotactic radiosurgery was administered with a dose of 12 Gy to 90%. Images show the initial lesion seen and a new MRI 1.5 years later.

Figure: Example of large metastatic focus that can be safely treated with stereotactic radiosurgery and avoidance of dangerous dose to spinal cord.

Figure:Example of large metastatic focus that can be safely treated with stereotactic radiosurgery and avoid-

ance of dangerous dose to spinal cord.


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Figure: Imaging showed a lower thoracic metastatic lesion on the left just in front of the pedicle-body junction. A) CT scan demonstrates osteoblastic activity in this region. B) MRI demonstrates a non-enhancing mass that’s T1 hypointense. C) PET imaging shows this spot as being hypermetabolic D) Final treatment plan with very safe dose affecting lower spinal cord, but high dose given to metastatic lesion.

Figure:Imaging showed a lower thoracic metastatic lesion on the left just in front of the pedicle-body junction.

A) CT scan demonstrates osteoblastic activity in this region. B) MRI demonstrates a non-enhancing mass that’s T1 hypointense. C) PET imaging shows this spot as being hypermetabolic D) Final treat-ment plan with very safe dose affecting lower spinal cord, but high dose given to metastatic lesion.


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ry 4. References:1. Ang K, Price R, Stephens L, Jiang G, Feng Y, Schultheiss

T, Peters L: The tolerance of primate spinal cord to re-irradiation. International Journal of Radiation Oncology* Biology* Physics 25:459-464, 1993.

2. Astrahan M: Some implications of linear-quadrat-ic-linear radiation dose-response with regard to hy-pofractionation. Medical physics 35:4161, 2008.

3. Benedict S, Yenice K, Followill D, Galvin J, Hinson W, Kavanagh B, Keall P, Lovelock M, Meeks S, Pa-piez L: Stereotactic body radiation therapy: The re-port of AAPM Task Group 101. Medical physics 37:4078.

4. Benzil D, Saboori M, Mogilner A, Rocchio R, Moor-thy C: Safety and efficacy of stereotactic radiosur-gery for tumors of the spine. Special Supplements 101:413-418, 2004.

5. Chang S, Meisel J, Hancock S, Martin D, McManus M, Adler Jr J: Treatment of hemangioblastomas in von Hippel-Lindau disease with linear accelerator-based radiosurgery. Neurosurgery 43:28, 1998.

6. Chang U, Youn S, Park S, Rhee C: Clinical Results of CyberknifeÆ Radiosurgery for Spinal Metasta-ses. Journal of Korean Neurosurgical Society 46:538, 2009.

7. De Salles A, Pedroso A, Medin P, Agazaryan N, Sol-berg T, Cabatan-Awang C, Espinosa D, Ford J, Selch M: Spinal lesions treated with Novalis shaped beam intensity-modulated radiosurgery and stereotactic radiotherapy. Special Supplements 101:435-440, 2004.

8. Finn M, Vrionis F, Schmidt M: Spinal radiosurgery for metastatic disease of the spine. Cancer control 14:405, 2007.

9. Garcia-Barros M, Paris F, Cordon-Cardo C, Lyden D, Rafii S, Haimovitz-Friedman A, Fuks Z, Kolesnick R: Tumor response to radiotherapy regulated by en-dothelial cell apoptosis. Science 300:1155, 2003.

10. Gerszten P, Burton S, Ozhasoglu C, Welch W: Ra-diosurgery for spinal metastases: clinical experience in 500 cases from a single institution. Spine 32:193, 2007.

11. Gerszten P, Moossy J, Flickinger J, Welch W: Low-dose radiotherapy for the inhibition of peridural fi-brosis after reexploratory nerve root decompression

for postlaminectomy syndrome. Journal of Neuro-surgery: Pediatrics 99, 2003.

12. Gerszten P, Ryu S: Spine radiosurgery. Thieme Med-ical Pub, 2008.

13. Gibbs I: Spinal and paraspinal lesions: the role of ste-reotactic body radiotherapy. IMRT, IGRT, SBRT: advances in the treatment planning and delivery of radiotherapy:407, 2007.

14. Hamilton A, Lulu B, Fosmire H, Stea B, Cassady J: Preliminary clinical experience with linear acceler-ator-based spinal stereotactic radiosurgery. Neuro-surgery 36:311, 1995.

15. Jacobs W, Perrin R: Evaluation and treatment of spi-nal metastases: an overview. Neurosurgical Focus 11:1-11, 2001.

16. Marcus Jr R, Million R: The incidence of myelitis af-ter irradiation of the cervical spinal cord. Interna-tional Journal of Radiation Oncology* Biology* Physics 19:3-8, 1990.

17. Murphy M, Chang S, Gibbs I, Le Q, Hai J, Kim D, Martin D, Adler J: Patterns of patient movement during frameless image-guided radiosurgery. In-ternational Journal of Radiation Oncology* Biol-ogy* Physics 55:1400-1408, 2003.

18. Rao G, Ha C, Chakrabarti I, Feiz-Erfan I, Mendel E, Rhines L: Multiple myeloma of the cervical spine: treatment strategies for pain and spinal instability. Journal of Neurosurgery: Pediatrics 5, 2006.

19. Ryu S, Fang Yin F, Rock J, Zhu J, Chu A, Kagan E, Rogers L, Ajlouni M, Rosenblum M, Kim J: Im-age guided and intensity modulated radiosurgery for patients with spinal metastasis. Cancer 97:2013-2018, 2003.

20. Ryu S, Jin J, Jin R, Rock J, Ajlouni M, Movsas B, Rosenblum M, Kim J: Partial volume tolerance of the spinal cord and complications of single dose ra-diosurgery. Cancer 109:628-636, 2007.

21. Selch M, Lin K, Agazaryan N, Tenn S, Gorgulho A, DeMarco J, DeSalles A: Initial clinical experience with image-guided linear accelerator-based spinal radiosurgery for treatment of benign nerve sheath tumors. Surgical neurology 72:668-674, 2009.

22. Sinclair J, Chang S, Gibbs I, Adler Jr J: Multisession CyberKnife radiosurgery for intramedullary spinal cord arteriovenous malformations. Neurosurgery 58:1081, 2006.

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ADVANCED TECHNOLOGIES - turknorosirurji.org.trder the longus colli muscles after the dissection. The C2/3 disc space is identified after the blunt dissection and mar-ked with 2 mm