The Spine Journal 11 (2011) 832–838

Clinical Study

‘‘Spring-back’’ closure associated with open-door cervical laminoplasty

Hai-Qiang Wang, MDa, Kin-Cheung Mak, MBBS, FRCSEd, FHKCOS, FHKAM(Ortho)b,Dino Samartzis, DScb, Tarek El-Fiky, MDc,

Yat W. Wong, MBBS, FRCSEd, FHKCOS, FHKAM(Ortho)b, Zhuo-Jing Luo, MDa,Xin Kang, MDb, Wai Y. Cheung, MBBS, FRCSEd, FHKCOS, FHKAM(Ortho)b,

Keith D.K. Luk, MBBS, MCh(Ortho), FRACS, FRCSEd, FRCS, FHKCOS, FHKAM(Ortho)b,Kenneth M.C. Cheung, MBBS, MD, FRCS, FHKCOS, FHKAM(Ortho)b,*

aDepartment of Orthopaedics, Xijing Hospital, Fourth Military Medical University, 15 Changle Western Rd, Xi’an, Shaanxi Province, China 710032bDepartment of Orthopaedics & Traumatology, Queen Mary Hospital, University of Hong Kong,

102 Pokfulam Rd, Professorial Block, 5th Floor, Hong Kong, SAR, ChinacDepartment of Orthopaedic Surgery, Alexandria University, Alexandria, Egypt

Received 2 August 2010; revised 23 May 2011; accepted 29 July 2011

Abstract BACKGROUND CONTEXT: Spring-back c

FDA device/drug

Author disclosure

close. DS: Nothing to

to disclose. ZJL:Noth

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1529-9430/$ - see fro

doi:10.1016/j.spinee.2

omplication after open-door laminoplasty as de-scribed by Hirabayashi is a well-known risk, but its definition, incidence, and associated neurologicoutcome remain unclear.OBJECTIVE: To investigate the incidence and the neurologic consequence of spring-back closureafter open-door laminoplasty.STUDY DESIGN: A retrospective radiographic and clinical review.OUTCOME MEASURES: Lateral cervical spine X-rays were evaluated. Anteroposterior diame-ters (APD) of the vertebral canal of C3–C7 were measured. Spring-back was defined as loss ofAPD on follow-up in comparison to immediate postoperative canal expansion. The loss of the end-on lamina silhouette with consequent reappearance of the lateral profile of the spinous processeswas also assessed to verify the presence of spring-back. Spring-back closure was classified basedon whether the collapse was total or partial, and whether all the operated levels or only a subsethad collapsed (ie, complete vs. partial closure, segmental closure vs. total-construct closure). Neuro-logic status was documented using the Japanese Orthopaedic Association (JOA) score.METHODS: Thirty consecutive patients who underwent open-door laminoplasty from 1995 to 2005at a single institution with a minimum follow-up of 2 years were assessed. They were all operated onusing the classic Hirabayashi technique. Radiographic outcomes were assessed independently by twoindividuals.RESULTS: Sixteen men and 14 women with an average follow-up of 5 years (range, 2–12 years)were included. Of these patients, 24 had cervical spondylotic myelopathy and six had ossificationof the posterior longitudinal ligament. Spring-back closure was found in three patients (10%) and7 of 117 laminae (6%) within 6 months of the operation, which was further confirmed by computedtomography and magnetic resonance imaging. All spring-back closures were partial segmental clo-sures. Gender and agewere not significant factors related to spring back (pO.05). Themean JOA scoreon follow-up was 12.5, with a recovery rate of 40%. All patients with spring back and available JOAdata exhibited postoperative neurologic deterioration. Of the three patients with spring back, twopatients underwent revision surgery, whereas one declined.CONCLUSIONS: Spring-back closure occurred in 10% of our patients at or before 6 months aftersurgery. The incidence of spring-back by level (ie, 117 laminae) was 6%, mainly occurring at thelower cervical spine. All spring-back closures were partial segmental closures, most commonly

status: Not applicable.

s: HQW: Nothing to disclose. KCM: Nothing to dis-

disclose. TEF: Nothing to disclose. YWW: Nothing

ing to disclose.XK:Nothing to disclose.WYC:Noth-

: Nothing to disclose. KMCC: Nothing to disclose.

* Corresponding author. Department of Orthopaedics & Traumatology,

Queen Mary Hospital, University of Hong Kong, 102 Pokfulam Rd, Pro-

fessorial Block, 5th Floor, Hong Kong, SAR, China. Tel.: þ(852) 2855-

4254; fax: þ(852) 2817-4392.

E-mail address: ken-cheung@hku.hk (K.M.C. Cheung)

nt matter � 2011 Elsevier Inc. All rights reserved.

011.07.026

833H.-Q. Wang et al. / The Spine Journal 11 (2011) 832–838

involving C5 and C6. Postoperative neurologic deficit was associated with spring-back closure; there-fore, surgeons should adopt preemptive surgical measures to prevent the occurrence of such a compli-cation. � 2011 Elsevier Inc. All rights reserved.

Keywords: Laminoplasty; Spring-back; Closure; Complication; Outcome

Introduction

Cervical laminoplasty is an established procedure fortreatment of cervical myelopathy [1–5]. Throughout theyears, various laminoplasty techniques have been described.However, open-door laminoplasty, first described byHirabayashi [6] in the 1970s, is commonly performed. Theprocedure allows widening of the spinal canal without per-manently removing the dorsal cervical elements, thereby ad-dressing the disadvantages of laminectomy (ie, spinal cordvulnerability, cervical kyphosis, etc). Although successfuloutcomes have been associated with this procedure, variouspostoperative complications may occur, such as axial neckpain, neck stiffness, nerve root palsy, loss of lordosis, and‘‘spring-back’’ closure of the elevated lamina [3,7–11].

Collapse or spring-back of the open door, whereby thelamina closes back on the spinal cord, has been a salientconcern. Such a complication would negate the benefit ofthe procedure, leading to immediate restenosis of the canal.Since the initial description of open-door laminoplasty, re-ports of spring-back closure emerged as the procedure wasmore widely adopted. Although there have been numerousreports on the long-term results of open-door laminoplasty[9,10,12–18], little is known of the actual definition, the de-tailed incidence, and the attendant neurologic outcomesassociated with spring-back closure. As such, the followingstudy proposes a definition of spring-back closure as wellas addresses the incidence and clinical outcomes associatedwith spring-back complication based on a review of pa-tients who underwent open-door laminoplasty at a singleinstitution.

Materials and methods

Between January 1995 and December 2005, 30 consec-utive patients who underwent open-door laminoplasty at theDuchess of Kent Children’s Hospital, Hong Kong, were re-viewed retrospectively. The diagnosis of cervical myelopa-thy was made based on clinical signs and symptoms, withcorresponding levels of stenosis confirmed by magnetic res-onance imaging of the cervical spine.

Surgical technique

The operative levels were dependent on the neurologicstatus and the radiological findings. The open-door lamino-plasty technique described by Hirabayashi and Satomi [11]was used. Because the C3–C5 spinous processes were typi-cally very short, they did not necessitate shortening or

cutting, thereby preserving the supraspinous and interspi-nous ligaments. Normally, the tips of the C6 and/or C7 spi-nous processes were shortened because they were too longin comparison to the other spinous processes, and if notshortened, the posterior elements may be pushed back afterwound closure. Both the hinge- and open-side gutters werecreated with a high-speed burr. The open-side gutter wascompleted with a Kerrison rongeur and the laminae elevatedby gently pushing the spinous processes toward the hingeside. Stay sutures were inserted between the base of the spi-nous process and the facet joint capsule at each level. Theneck was immobilized with a rigid collar for 3 weeks.

Radiographic assessment

Pre and postoperative lateral cervical spine X-rays wereobtained for all patients. Standardization was achieved byensuring 150-cm film-to-tube distance and centering on theC4 body. Radiographs were digitized and entered intoa Digital Imaging and Communications in Medicine picturearchiving and communication system. Visualization andmeasurements were taken using a Radworks 5.1 (ApplicareMedical Imaging BV, Zeist, The Netherlands) system. Post-operative X-rays were taken on the day after the operation,and subsequently during outpatient follow-up. Follow-upwas usually scheduled at 2 to 4weeks after hospital dischargeand at 3- to 6-month intervals thereafter in the first 2 years.

The anteroposterior diameter (APD) of the vertebral canalfor each level was measured independently by two orthope-dic spine surgeons. Preoperative APD was measured usingWolf’s method (Fig. 1A) [19]. Postoperative APD was mea-sured from the middle of the posterior border of the vertebralbody to the anterior cortex of the elevated lamina (Fig. 1B),which is fully compatible with the preoperative APDmeasurement.

Spring-back complication was defined as loss of initialelevation of the lamina as determined on the postoperativefollow-up radiographs. A classification scheme was pro-posed and illustrated in Table 1. In the lateral cervicalX-ray, a closed lamina would also appear as substitution ofthe oval or teardrop silhouette of the elevated lamina by theshape of the remaining spinous process profile. SignificantAPD decrease was corroborated by the loss of the oval orteardrop silhouette on the lateral X-ray. Thus, for any patientwith spring-back, there could be partial or complete closure(for any one level), whereas the involvement maybe segmen-tal (only a subset of levels operated is/are affected) or totalconstruct (all levels involved). Although there may be othercombinations of spring-back, some levels are less likely

ContextLaminoplasty is a commonly used technique for the

treatment of cervical myelopathy due to ossification of

posterior latitudinal ligament or multilevel degenerative

stenosis. One risk of the open-door technique is subse-

quent reclosure or so-called spring-back of the lamina.

ContributionIn this small study from one center, 10% of cases were

found to have spring-back, and each of these cases was

found to be associated with neurologic deterioration.

ImplicationWhile the study is small and derives from just one cen-

ter, the findings suggest that radiographic follow-up to

rule out spring-back, especially if neurologic deteriora-

tion is detected, is worthwhile. Of note, the frequency

might be more or less at other centers where subtle

changes in technique might impact complications.—The Editors

834 H.-Q. Wang et al. / The Spine Journal 11 (2011) 832–838

involved, and the intact spinous processes with their liga-mentum flavum and their supraspinous and interspinous lig-aments may not allow them as such.

Neurologic outcome assessment

Neurologic status was appraised using the JapaneseOrthopaedic Association (JOA) score for assessing cervicalmyelopathy [20]. A trained occupational therapist per-formed all the JOA score assessments for each patient.The JOA score recovery rate was used to reflect the degreeof postoperative recovery of normal function [1–3,9–11,21].

Statistical analysis

All data were collected and coded on a spreadsheet. SPSSvr. 14 (Chicago, IL, USA) statistical software was used toperform the statistical analyses. Descriptive and frequencystatistics were performed of various data parameters. Inter-class coefficient was used to assess inter-rater reliability. Re-liability scores of less than 0.79, 0.80 to 0.89, and greaterthan 0.90 were regarded as poor, good, and excellent, re-spectively [22]. Descriptive and frequency statistics wereperformed as well as Mann-Whitney U, chi-square, andFisher exact tests were appropriate. A p value less than .05was considered statistically significant.

Results

There were 16 men (53.3%) and 14 women (47.7%), witha mean age of 63.6 years (6standard deviation [SD], 12.7years; range, 24–83 years). Of these patients, 24 had cervical

spondylotic myelopathy and six patients had ossification ofposterior longitudinal ligament. The mean follow-up periodwas 4.9 years (6SD, 2.8 years; range, 2–12 years). Twocases had concomitant noniatrogenic interbody fusion ofthe cervical spine (ie, congenital or spontaneous). In total,117 laminae were elevated. The mean number of elevatedlaminae were 3.9 (6SD, 0.9) for each patient. Levels of lam-inoplasty were as follows: C3–C6 in 17 patients (56.7%),C3–C7 in six patients (20%), C3–C5 in three patients(10%), C3–C4 in two patients (6.7%), C4–C6 in one patient(3.3%), and C4–C5 in one patient (3.3%). The reason for thereduced length of laminoplasties in some patients were be-cause they were involved in a pilot trial comparing anteriorwith posterior surgery, and care was taken to ensure the de-compression was equivalent in the anterior versus posteriorgroup.

Radiographic assessment

A good to high inter-rater reliability was noted in the as-sessment of spring-back (O0.89). Spring-back was noted inthree of 30 patients (10%), affecting seven of 117 elevatedlaminae (6%) (Fig. 1C–G). The order of involvement wasas follows: C3 (0 of 28; 0%), C4 (1 of 30; 3.3%), C5 (3 of28; 10.7%), C6 (3 of 24; 12.5%), and C7 (0 of 6; 0%) (Fig. 2).

In all three patients, spring-back was noted as partialclosure and occurred within 6 months of surgery. All werepartial segmental closures. Furthermore, closure was at con-tiguous levels among those multilevel collapses. Spring-back did not occur in any of the two patients with anteriorcolumn fusion. Gender and age were not significant factorsrelated to spring-back closure (pO.05).

Neurologic outcomes

The average preoperative JOA score was 9.5 (6SD, 3.4).By 6 months, the JOA score was 12.1 (6SD, 3.1) with a re-covery rate of 35% using the method of calculation proposedby Hirabayashi et al. [1]. At final follow-up, the postopera-tive JOA score was 12.5 (6SD, 3.2), producing a recoveryrate of 40%. All patients with spring-back and availableJOA data exhibited neurologic deficit (Table 2).

In the three patients who exhibited radiological spring-back, two had a decreased JOA score and thus requireda laminectomy to decompress the spinal cord. Among thesetwo patients, one patient’s radiological spring-back preda-ted the clinical manifestation more than 8 years. For thethird patient, the JOA score was 12 preoperatively andthe subsequent change in neurologic status did not affectthe JOA score significantly; thus, decided against furthersurgical intervention.

Discussion

In our study, 10% (3 of 30) of patients had spring-back,whereby 6% (7 of 117) of all elevated laminae had such

Fig. 1. Radiographs of a patient who experienced spring-back with anteroposterior diameter (APD) measurements (mm). (A) Preoperative X-ray showing

APD measured using Wolf’s method, from the middle of the posterior border of the vertebral body to the anterior border of the lamina. (B) Postoperative X-

ray illustrating the oval or teardrop silhouette of the elevated lamina and the increased APD measurements. (C) Spring-back closure occurred at C5 and C6,

whereby the end-on cortical silhouette of the elevated lamina was replaced by the lateral profile of the spinous process. Note the corresponding decrease in

APD of more than 4 mm at these two levels. (D, E) Computed tomography and (F, G) magnetic resonance imaging scans demonstrated and confirmed spring-

back closure of C5 and C6.

835H.-Q. Wang et al. / The Spine Journal 11 (2011) 832–838

closure. This was despite the use of stay sutures in everypatient. The complication rate per patient was significantlyhigher than that reported by Satomi et al. [18] (1.5%) orChiba et al. [10] (3.7%), although their definition of

spring-back remains unclear and Chiba only measured theanteroposterior canal diameter at C4. The variation betweenour incidence rate in comparison to previously reported ac-counts of spring-back may be attributed to our detailed

Fig. 2. The incidence of spring-back with respect to level in cervical spine.

Table 1

Classification of ‘‘spring-back’’ closure

Partial closure� incomplete closure of an

individual lamina

Segmental closure� a subset of the elevated laminas

had spring-back closure

Complete closure� complete closure of an

individual lamina, ie, APD

same as preoperative or less

Total construct closure� all elevated laminas had

spring-back closure

APD, anteroposterior diameter.

Although further combinations are possible, it is limited by the liga-

mentum flavum and the supra- and interspinous ligaments of the intact spi-

nous processes.

836 H.-Q. Wang et al. / The Spine Journal 11 (2011) 832–838

classification of how spring-back was defined. On the otherhand, our series represented the initial phase after adoptionof the Hirabayashi procedure and experience probablyplayed a role in the spring-back rate.

Our study further defined spring-back based on two pa-rameters (Table 1): whether at a particular level the laminacollapsed to its preoperative position (ie, complete vs. par-tial closure of a specific level) and whether all the operatedlevels suffered lamina collapse (ie, total construct closure).Not a single patient from our series had total construct clo-sure. Furthermore, of the involved laminae, all were partialclosures. In other words, not all levels are affected equally.Specifically, C5 and C6 had closure rates of 10.7% and12.5%, respectively, whereas C4 had 3.3%.

In their very first 15 patients, Hirabayashi and Satomi [11]reported ‘‘several cases’’ that experienced spring-back. Sub-sequent to using stay sutures, these patients ‘‘almost alwaysmaintained the canal open successfully.’’ As such, the au-thors attributed spring-back to the absence of stay sutures.In a subsequent report, Satomi et al. [17] noted three of 80patients (1.5%) with laminar closure. Chiba et al. [10] notedthat 1 of 27 patients (3.7%) undergoing cervical lamino-plasty developed postoperative myelopathy because of clo-sure of the elevated lamina. However, these reports did notprovide detailed definition or temporal relationship betweenspring-back closure and neurologic deterioration, and themethod of identifying spring-back closure may have beenlimited. A recent prospective randomized study evaluatingthe clinical outcome of single open-door versus doubleopen-door laminoplasties noted one patient of 17 who hadspring-back at 3 months and required an anterior surgery.Matsumoto et al. [23] provided a very precise method ofevaluating spring-back, the canal-to-body ratio. By dividingthe APD of the spinal canal by that of the width of the corre-sponding vertebral body, magnification error was reduced.However, there is some controversy in the value of usingcanal-to-body ratios, given the intrinsic variability of thetwo parameters.

The authors suggest a much simpler method of screeningfor restenosis after cervical laminoplasty. According toHirabayashi et al. [3], using stay sutures for cervical single-door expansion laminoplasty, a mean of 3- to 5-mm APDwidening was noted and that 4 mm was the optimal APD

for neurologic recovery. By using 4mm inAPD as our cutoff,wewere able to identify individuals whowere likely to sufferfrom the clinical consequence of spring-back. Only three pa-tients suffered clinical deterioration, and all had spring-backby our definition. Indeed, preoperative planning by way ofcomputed tomography and magnetic resonance imaging fortwo of the patientswho agreed for revision surgery confirmedrestenosis, primarily at those levels that demonstrated APDloss of 4 mm or more. The third patient declined further sur-gery and because of resource limitations did not have theseinvestigations. Arguments against thismethodwould includevariations in APD related to gender and height. In 2004, LimandWong [24] showed that this variation in sagittal diameterwas less among ethnicChinese and further argued that the lat-eral radiographic sagittal diameter of the canal was a bettermethod for diagnosing cervical canal stenosis than theTorg-Pavlov ratio, which is essentially a canal-to-body ratio.Further larger scale prospective studies are needed to definethe predictive value in terms of likelihood of clinical deteri-oration, but our method proved to be a very practical toolfor identifying patients who need closer scrutiny, if not fur-ther investigation and treatment.

Cervical motion has been studied in normal and abnor-mal subjects, as well as postoperative patients. In the normalcervical spine, most motion of the subaxial spine occurs atthe lower regions [25–28]. Most studies examining the post-laminoplasty movement of the cervical spine showed a de-creased range of motion from 17% to 50% [29]. Miyazakiet al. [30] reviewed the relative contribution of each levelat various stages of degeneration, and his numbers indicatedthat until end-stage degeneration, C5 and C6 still contributesignificantly to the flexion-extension arc of the cervicalspine. Also, a study of the axial rotation of the postlamino-plasty cervical spine showed that angular movement wassimilar to that before the operation [31]. Taking these twostudies into account, a plausible explanation for the in-creased risk of spring-back at C5 and C6 may be that evenin the setting of a laminoplasty, motion is still relatively con-centrated in these areas.

The JOA recovery rate of 40% found in our study was rel-atively low when compared with other studies, which

Table 2

Neurologic outcome in patients with spring-back complication

Case Age (y) Sex

Spring-back

assessment (mo)

Preoperative

JOA score

Postoperative best

JOA score

Postoperative JOA

score after spring-back

Final follow-up

JOA score

1 48 M 6 6 10 6 7.5

2 77 F 6 12 13 12.5 13

3 69 F 6 3 11 8.5 9

M, male; F, female; JOA, Japanese Orthopaedic Association.

837H.-Q. Wang et al. / The Spine Journal 11 (2011) 832–838

showed upward of 50% [1,10,18]. This may be explained bythe finding by Satomi et al. [18] that the recovery rate wasadversely affected once the patient was 60 years or older.The average age of our patients was 64 years, whereas thatof Satomi et al. [18] and Chiba et al. [10] were 57 and 55years, respectively.

Numerous studies have reported spring-back complica-tion after laminoplasty, but the degree of closure and thetemporal relationship between collapse of the lamina andneurologic deterioration was not elucidated. Althougha slight amount of collapse (ie, 1 mm or less) is a commonoccurrence, in our patients, this was not usually associatedwith neurologic deterioration. However, using our radio-graphic definition and correlation with APD measurements,we noted that 4-mm collapse was eventually associated witha decreased JOA score.

Various methods have been proposed to prevent laminaclosure. Apart from modification of original technique byHirabayashi et al., others have proposed the use of interposi-tion bone graft, miniplates, and suture anchors [29,32–35].From our study, we noted that spring-back was mostcommon at C5 and C6, with low occurrence at C3 and C7.We have also shown that significant spring-back (ie, loss ofthe teardrop silhouette or APD decrease of 4 mm or more)will cause neurologic compromise. Although the techniqueby Hirabayashi et al. of suturing the elevated laminae tothe facet capsules is an improvement over having no attach-ment at all (based on their first publication), our study sug-gests further augmentation may be necessary. Therefore, ifresources are limited, miniplates or suture anchors such asMitek (DePuy Mitek, Inc., Raynham, MA, USA), may beconsidered at C5 and C6, in addition to nonabsorbable staysutures, as a more secure and stable means to affix the ele-vated laminae.

Although our study noted interesting observations regard-ing spring-back closure after open-door cervical lamino-plasty, various limitations were present. For one, our studyconsisted of a relatively small sample size andwas retrospec-tive in nature. However, because the concept and occurrenceof spring-back was largely neglected in previous reports, wefeel that our study can provide some added information re-garding such a potential complication. Furthermore, anotherpotential limitation of the study is the lack of advanced imag-ing for every patient to correlate with the plain radiographicassessments. However, advanced imaging was performed inthe spring-back cases, which confirmed the complication.

Nevertheless, additional larger prospective studies areneeded to further verify our findings and expand on our def-inition of spring-back.

Conclusions

Spring-back is not an infrequent complication, and isoftentimes associated with neurologic compromise. In ourstudy population, the overall incidence of spring-back wasnoted as 10% of our patients, mainly occurring at C5 andC6. Moreover, spring-back may occur within the first 6months after surgery and may potentially be associated withneurologic compromise. Furthermore, spring-back closurewas noted to be partial and usually not involving the entirelaminoplasty construct. Given that significant spring-backis associated with neurologic compromise, we suggest aug-menting only at the high-risk levels, that is, C5 and C6. Inaddition, to our knowledge, our article is the first to proposea detailed description of spring-back closure after open-doorlaminoplasty and, in doing so, hopefully enabled a simple yetreliable method for defining, screening, and communicatingthis phenomenon.

Acknowledgment

We thank Daniel YT Fong and Florence Mok for theirhelp in the statistical analyses, and Karlen Law for herwork on the JOA score assessment.

References

[1] Hirabayashi K, Miyakawa J, Satomi K, et al. Operative results and

postoperative progression of ossification among patients with ossifi-

cation of cervical posterior longitudinal ligament. Spine 1981;6:

354–64.

[2] Hirabayashi K, Toyama Y, Chiba K. Expansive laminoplasty for my-

elopathy in ossification of the longitudinal ligament. Clin Orthop

Relat Res 1999;359:35–48.

[3] Hirabayashi K, Watanabe K, Wakano K, et al. Expansive open-door

laminoplasty for cervical spinal stenotic myelopathy. Spine 1983;8:

693–9.

[4] Iwasaki M, Okuda S, Miyauchi A, et al. Surgical strategy for cervical

myelopathy due to ossification of the posterior longitudinal ligament:

part 2: advantages of anterior decompression and fusion over lamino-

plasty. Spine 2007;32:654–60.

[5] Kawahara N, Tomita K, Shinya Y, et al. Recapping T-saw lamino-

plasty for spinal cord tumors. Spine 1999;24:1363–70.

838 H.-Q. Wang et al. / The Spine Journal 11 (2011) 832–838

[6] Hirabayashi K. [Expansive open-door laminoplasty for cervical spon-

dylotic myelopathy]. [in Japanese]. Jpn J Surg 1978;32:1159–63.

[7] Hosono N, Sakaura H, Mukai Y, et al. The source of axial pain after

cervical laminoplasty-C7 is more crucial than deep extensor muscles.

Spine 2007;32:2985–8.

[8] Baba H, Maezawa Y, Furusawa N, et al. Flexibility and alignment of

the cervical spine after laminoplasty for spondylotic myelopathy.

A radiographic study. Int Orthop 1995;19:116–21.

[9] Seichi A, Takeshita K, Ohishi I, et al. Long-term results of double-

door laminoplasty for cervical stenotic myelopathy. Spine 2001;26:

479–87.

[10] Chiba K, Ogawa Y, Ishii K, et al. Long-term results of expansive

open-door laminoplasty for cervical myelopathy–average 14-year

follow-up study. Spine 2006;31:2998–3005.

[11] Hirabayashi K, Satomi K. Operative procedure and results of expan-

sive open-door laminoplasty. Spine 1988;13:870–6.

[12] Azuma S, Seichi A, Ohnishi I, et al. Long-term results of operative

treatment for cervical spondylotic myelopathy in patients with athe-

toid cerebral palsy: an over 10-year follow-up study. Spine 2002;27:

943–8; discussion 948.

[13] Hale JJ, Gruson KI, Spivak JM. Laminoplasty: a review of its role in

compressive cervical myelopathy. Spine J 2006;6:289S–98S.

[14] Iwasaki M, Kawaguchi Y, Kimura T, et al. Long-term results of

expansive laminoplasty for ossification of the posterior longitudinal

ligament of the cervical spine: more than 10 years follow up. J Neu-

rosurg 2002;96:180–9.

[15] Kimura I, Shingu H, Nasu Y. Long-term follow-up of cervical spon-

dylotic myelopathy treated by canal-expansive laminoplasty. J Bone

Joint Surg Br 1995;77:956–61.

[16] Ogawa Y, Toyama Y, Chiba K, et al. Long-term results of expansive

open-door laminoplasty for ossification of the posterior longitudinal

ligament of the cervical spine. J Neurosurg Spine 2004;1:168–74.

[17] Satomi K, Nishu Y, Kohno T, et al. Long-term follow-up studies of

open-door expansive laminoplasty for cervical stenotic myelopathy.

Spine 1994;19:507–10.

[18] Satomi K, Ogawa J, Ishii Y, et al. Short-term complications and long-

term results of expansive open-door laminoplasty for cervical stenotic

myelopathy. Spine J 2001;1:26–30.

[19] Wolf BS, Khilnani M, Malis L. The sagittal diameter of the bony cer-

vical spinal canal and its significance in cervical spondylosis. J Mt

Sinai Hosp N Y 1956;23:283–92.

[20] Yonenobu K, Abumi K, Nagata K, et al. Interobserver and intraob-

server reliability of the japanese orthopaedic association scoring

system for evaluation of cervical compression myelopathy. Spine

2001;26:1890–4; discussion 1895.

[21] Kawai S, Sunago K, Doi K, et al. Cervical laminoplasty (Hattori’s

method). Procedure and follow-up results. Spine 1988;13:1245–50.

[22] Liu A, Schisterman EF, Wu C. Multistage evaluation of measurement

error in a reliability study. Biometrics 2006;62:1190–6.

[23] Matsumoto M, Watanabe K, Tsuji T, et al. Risk factors for closure of

lamina after open-door laminoplasty. J Neurosurg Spine 2008;9:

530–7.

[24] Lim JK, Wong HK. Variation of the cervical spinal Torg ratio with

gender and ethnicity. Spine J 2004;4:396–401.

[25] Fielding JW. Cineroentgenography of the normal cervical spine.

J Bone Joint Surg Am 1957;39:1280–8.

[26] Fielding JW. Normal and selected abnormal motion of the cervical

spine from the second cervical vertebra to the seventh cervical verte-

bra based on cineroentgenography. J Bone Joint Surg Am 1964;46:

1779–81.

[27] Ordway NR, Seymour RJ, Donelson RG, et al. Cervical flexion, ex-

tension, protrusion, and retraction. A radiographic segmental analy-

sis. Spine 1999;24:240–7.

[28] Panjabi M, Dvorak J, Duranceau J, et al. Three-dimensional move-

ments of the upper cervical spine. Spine 1988;13:726–30.

[29] Steinmetz MP, Resnick DK. Cervical laminoplasty. Spine J 2006;6:

274S–81S.

[30] Miyazaki M, Hong SW, Yoon SH, et al. Kinematic analysis of the re-

lationship between the grade of disc degeneration and motion unit of

the cervical spine. Spine 2008;33:187–93.

[31] Sugimoto Y, Tanaka M, Nakanishi K, et al. Assessing range of cervi-

cal rotation after laminoplasty using axial CT. J Spinal Disord Tech

2007;20:187–9.

[32] Chen HC, Chang MC, Yu WK, et al. Lateral mass anchoring screws

for cervical laminoplasty: preliminary report of a novel technique.

J Spinal Disord Tech 2008;21:387–92.

[33] Lee JY, Hanks SE, Oxner W, et al. Use of small suture anchors in cer-

vical laminoplasty to maintain canal expansion: a technical note.

J Spinal Disord Tech 2007;20:33–5.

[34] O’Brien MF, Peterson D, Casey AT, et al. A novel technique for lam-

inoplasty augmentation of spinal canal area using titanium miniplate

stabilization. A computerized morphometric analysis. Spine 1996;21:

474–83; discussion 484.

[35] Yang SC, Yu SW, Tu YK, et al. Open-door laminoplasty with suture

anchor fixation for cervical myelopathy in ossification of the poste-

rior longitudinal ligament. J Spinal Disord Tech 2007;20:492–8.