1 Abstracts in German, French, Italian, Spanish, Japanese,and Russian are printed at the end of this supplement.

Technical noteSimple endoscope tested for atraumatic screwremoval technique in trauma surgery

Romano Matthys

AO Development Institute, Clavadelerstrasse, 7270 Davos, Switzerland

KEyWORDS:simple endoscope,internal fixation,screw removal

Summary1 A simple endoscopic device was designed and tested for atraumaticremoval of bone screws. It consists of a transparent rod modified to allow illumi-nation of the surgical field. A special retractor helps to display the implant buriedin a thick layer of tissue. In vitro and simulated in vivo tests were successful.

Problem and objective

In the course of surgical intervention, the traumaof the approach can often be greater than thatcaused by the required treatment. For instance,the approach to a fractured acetabulum is far moretraumatic than the subsequent osteosynthesis. Com-puter-aided navigation with endoscopy can makean important contribution to reducing the trauma.Although the removal of osteosynthesis screws fromlong bones is a relatively straightforward procedurethat hardly requires the complexity of navigation,the implant may be beneath a thick soft-tissue layermaking it difficult to see or resulting in the processof gaining access being unnecessarily traumatic.Removing the screws without surgically exposing theimplant and still providing a safe coupling requiresidentification of the screw size and the type of driverecess. While the size of the screw can be identifiedradiologically, the type of screw drive cannot bedetermined in this way. There are currently severaldifferent types of screw drive in widespread use

(cruciate-, cross- or hexagonal-recess, Phillips™,Pozidrive™, Torx™, and Stardrive™). It is an essentialprerequisite for implant removal to identify thetype of screw drive in advance in order to have theappropriate screwdriver to hand. This requirementbecomes even more important if emergency treat-ment after an accident takes place away from thepatient’s home resulting in the patient being oper-ated on later by different surgeons who may nothave access to the relevant information. It is alsoa prerequisite to have a reliable drive coupling tofree the screw drive from ingrown soft tissue. Themethod for identification and cleaning should onlyrequire a minimally invasive approach.

Sincewearenotawareofany technique that fulfilsthe above-mentioned requirements, we developed asimple endoscopic procedure that consists basicallyof a slim, pen-shaped, optical waveguide.

Material

The pen, the “LiLouPen”, is made from a transparentmaterial, preferably glass or a synthetic material(Fig. 1), that is both stress free and homogeneous.Glass has the advantage that an optical reference

1 Abstracts in German, French, Spanish, Japanese, andRussian are printed at the end of this supplement.

Injury, Int. J. Care Injured (2007) 38S1, S108—S111

www.elsevier.com/locate/injury

0020–1383/$ — see front matter # 2007 Published by Elsevier Ltd.doi:10.1016/j.injury.2007.02.016

Technical note – Simple endoscope tested for atraumatic screw removal in trauma surgery S109

Figure 2: View of the optional miniature light source(polyamide body with pre-mounted battery and LED).The body is removably attached to the rear end of thepen. The light is switched on by pushing the premountedbattery into the body.

Figure 1: View of the LiLouPen (Plexiglas or glass with or without Fresnel lens geometry). The Fresnel lens is designedto feed light from the environment into the optical waveguide.

(hologram) can be included. A synthetic materialpermits simple surface shaping in the manner ofa Fresnel lens for light input. In a bright operativeenvironment the image needs to be illuminated anddisplayed with minimal dissipation, which requirestotal internal reflection. The light for the illumina-tion comes from sources in the environment (theaterlights) or from an additional light source attachedto the pen (Fig. 2).

A cylindrical retractor is used to expose the fieldof view, which enables the soft tissues betweenthe end of the pen and the implant to be displacedradially, exposing only the tip of the pen. The re-tractor is an expandable cylindrical sleeve witha longitudinal slotted conical tip that fits snuglyaround the pen. This conical tip serves as a trocar,enabling atraumatic insertion and careful expansionof the required field of view on final advancementof the pen.

Method

Typical application: the retractor sleeve with thepartially inserted pen is first advanced through asmall skin incision. The pen is then pushed in tocontact with the implant, which displaces the softtissue radially, thus opening the field of view.

S110 R Mathys

Figure 3: Testing in vitro by application on a foam model.The image obtained is shown in Figure 4.

Light is fed into the pen either passively, by makinguse of the Fresnel lens and the light in the environ-ment, or actively, with the aid of a miniature LEDlight source attachment (Fig. 2). The implant can belocated by moving sideways and/or tilting the tip ofthe pen. If an additional instrument is required, eg,to remove tissue from the screw head, a small hookcan be inserted along the pen, passing between thetip of the pen and the screw head (Fig. 3). In a similarway, the tip of the screwdriver can be connectedsecurely to the screw head under vision.

Tests were carried out to investigate the applica-tion of the device under surgical conditions. Theother issues investigated included whether the tis-sue could be adequately manipulated and whetherirrigation of the operative field was sufficient to ob-tain a perfect image in the presence of bleeding.

Handling test in vitro

Implant removal after plate osteosynthesis was firstsimulated on an artificial bone (Synbone #0060) witha foam cover. Special attention was paid to evaluat-ing the conditions of visibility (Figs. 3 and 4) and lightand the application of the retractor sleeve.

Handling test in vivo

The tests performed on a fresh sheep leg aimed toclarify whether a satisfactory image could be ob-tained despite the thick soft tissue covering and thepresence of blood (Figs. 5 and 6).To this end, a plate-screw osteosynthesis was performed on the sheepfemur. The screw heads were located and identifiedwith the LiLouPen. The screw was then removed withthe screwdriver that had been inserted with the aidof the LiLouPen. The quality of the image, the dis-placement of tissue, and the screw-to-screwdriverconnection were investigated.

Figure 4: Visual field obtained with the model shownin Figure 3. The implant and, in particular, the type ofscrew drive is clearly visible.

Technical note – Simple endoscope tested for atraumatic screw removal in trauma surgery S111

Figure 6: Visual field obtained in the presence of ahematoma. The implant and, in particular, the type ofscrew drive connection is visible.

Figure 5: Simulation of an in vivo situation on the sheepfemur. The fracture hematoma was simulated by localinjection of approximately 20 ml blood. The issue wasto clarify whether an adequate visual field could beobtained under difficult conditions.

Results

In the experimental set-up, obtaining the imagewas straightforward even without the retractor.The size and type of screw mechanism was easilyand accurately determined. The instruments, eg,the screwdriver, was seen clearly and applied undervision.

The tests on the sheep femur with simulated he-matoma showed that although the screw head wasclearly visible, the reduced field of vision meant thatthe view of the overall topography was not ideal.Theadditional application of the retractor was neces-sary and advantageous. The view was considerablyimproved by irrigation with Ringer solution. Theadditional light source proved valuable.

Discussion

Since the connective tissue between the skin andthe bone could only be partially displaced by thepen alone, it was necessary to construct and use aretractor. The retractor had to be expandable andcapable of also being used as a trocar. This retractorsimplified the insertion of the LiLouPen.

The illumination of the field of vision was sufficientunder laboratory conditions. However, under surgi-cal conditions (bright illumination of surrounding,bleeding, irrigation) either the Fresnel technique orthe attachable light source was required. With theseadjuncts the LiLouPen proved to be functionally ad-equate, simple and atraumatic in its application.

Correspondence Address

Romano MatthysAO Development ServicesAO FoundationClavadelstrasse 87270 Davos PlatzTel: +41 (0)81 414 2598Fax: +41 (0)81 414 2285e-mail: romano.matthys@aofoundation.org

This paper has been written entirely by the author. Theprototype discussed was developed at the AO Develop-ment Institute, Davos