Progression of ossification of the posterior longitudinal ligament following en bloc cervical laminoplasty

Degenerative Cervical Myelopathy: Epidemiology, Genetics, and Pathogenesis

STUDY DESIGN

Review.

OBJECTIVE

To formally introduce "degenerative cervical myelopathy" (DCM) as the overarching term to describe the various degenerative conditions of the cervical spine that cause myelopathy. Herein, the epidemiology, pathogenesis, and genetics of conditions falling under this hypernym are carefully described.

SUMMARY OF BACKGROUND DATA

Nontraumatic, degenerative forms of cervical myelopathy represent the commonest cause of spinal cord impairment in adults and include cervical spondylotic myelopathy, ossification of the posterior longitudinal ligament, ossification of the ligamentum flavum, and degenerative disc disease. Unfortunately, there is neither a specific term nor a specific diagnostic International Classification of Diseases, Tenth Revision code to describe this collection of clinical entities. This has resulted in the inconsistent use of diagnostic terms when referring to patients with myelopathy due to degenerative disease of the cervical spine.

METHODS

Narrative review.

RESULTS

The incidence and prevalence of myelopathy due to degeneration of the spine are estimated at a minimum of 41 and 605 per million in North America, respectively. Incidence of cervical spondylotic myelopathy-related hospitalizations has been estimated at 4.04/100,000 person-years, and surgical rates seem to be rising. Pathophysiologically, myelopathy results from static compression, spinal malalignment leading to altered cord tension and vascular supply, and dynamic injury mechanisms. Occupational hazards, including transportation of goods by weight bearing on top of the head, and other risk factors may accelerate DCM development. Potential genetic factors include those related to MMP-2 and collagen IX for degenerative disc disease, and collagen VI and XI for ossification of the posterior longitudinal ligament. In addition, congenital anomalies including spinal stenosis, Down syndrome, and Klippel-Feil syndrome may predispose to the development of DCM.

CONCLUSION

Although DCMs can present as separate diagnostic entities, they are highly interrelated, frequently manifest concomitantly, present similarly from a clinical standpoint, and seem to be in part a response to compensate and improve stability due to progressive age and wear of the cervical spine. The use of the term "degenerative cervical myelopathy" is advocated.

LEVEL OF EVIDENCE

5.

Magnetic Resonance Imaging Analysis of Deep Cervical Flexors in Patients with Ossification of the Posterior Longitudinal Ligament and Clinical Implication

OBJECTIVE

The purpose of this study was to analyze the cross-sectional area (CSA) of deep cervical flexors as measured by magnetic resonance imaging in ossification of the posterior longitudinal ligament (OPLL) patients with neck pain and, by implication, how this may relate to recruitment of the deep cervical flexors and sternocleidomastoid.

DESIGN

A retrospective case-control study was conducted. All 72 subjects were imaged using plain radiography, computed tomography, and magnetic resonance imaging.

RESULTS

There was a more limited cervical range of motion in the OPLL group than that in the control group. Cervical lordosis, T1 slope, and thoracic inlet angle values were significantly lower in the OPLL group than in the control group. Bilateral CSAs of the longus colli muscle and longus capitis muscle of the OPLL group were smaller than those of the control group. In addition, bilateral CSAs of the sternocleidomastoid of the OPLL subjects were greater than those of healthy subjects.

CONCLUSIONS

The authors found that the OPLL patients with chronic neck pain had lesser lordotic cervical alignment, smaller deep cervical flexor CSAs, and larger sternocleidomastoid CSAs than the control group did. The authors' theory is that the sternocleidomastoids in these OPLL patients have compensatorily hypertrophied in response to presumably atrophied deep cervical flexors.

Benefit of degenerative posterior longitudinal ligament removal during anterior decompression in cervical spondylotic myelopathy

It remains controversial whether degenerative posterior longitudinal ligaments should be removed during anterior decompression procedures for cervical spondylotic myelopathy. Few data are available from studies that have compared removing and retaining the degenerative posterior longitudinal ligament. The goal of this retrospective study was to evaluate the benefit of degenerative posterior longitudinal ligament removal during such operations. Clinical data on 130 patients with confirmed degenerative posterior longitudinal ligament who underwent anterior cervical decompression surgery were retrospectively reviewed. All procedures were performed by the same senior orthopedic surgeon at the authors' spinal surgery center. The degenerative posterior longitudinal ligament was removed in 62 patients (group A) and retained in 68 patients (group B). The 130 patients were followed for 36 months. The Japanese Orthopedic Association score improved from 9.0±2.7 to 14.7±1.5 in group A and from 9.4±2.6 to 14.1±1.7 in group B (P=.028). The recovery rate for spinal cord neurologic function was 66.7% in group A and 61.3% in group B (P=.031). Operating time was longer (P=.002) and the sagittal median diameter of the vertebral canal was enhanced in group A (P<.001). Narrowing of previously enlarged canals occurred at a significantly higher rate in group B (P=.044). No significant difference was found in the rates of common complications between groups. Removal of the degenerative posterior longitudinal ligament in anterior decompression procedures for cervical spondylotic myelopathy appeared to be beneficial and provided more complete decompression and better postoperative outcomes than surgery without removal of the ligament. Although this procedure was generally safe, it required longer operating times, was more technically challenging, and required more experienced surgeons than surgery without removal of the ligament.

Progression of ossification of the posterior longitudinal ligament of the thoracic spine following posterior decompression and stabilization

OBJECT

Despite its potential clinical impact, information regarding progression of thoracic ossification of the posterior longitudinal ligament (OPLL) is scarce. Posterior decompression with stabilization is currently the primary surgical treatment for symptomatic thoracic OPLL; however, it remains unclear whether thoracic OPLL increases in size following spinal stabilization. It is also unknown whether patients' clinical symptoms worsen as OPLL size increases. In this retrospective case series study, the authors examined the postoperative progression of thoracic OPLL.

METHODS

Nine consecutive patients with thoracic OPLL who underwent posterior decompression and fixation with a minimum follow-up of 3 years were included in this study. Thin-slice CT scans of the thoracic spine obtained at the time of surgery and the most recent follow-up were analyzed. The level of the most obvious protrusion of ossification was determined using the sagittal reconstructions, and the ossified area was measured on the axial reconstructed scan at the level of the most obvious protrusion of ossification using the DICOM (digital imaging and communications in medicine) software program. Myelopathy severity was assessed according to the Japanese Orthopaedic Association (JOA) scale score for lower-limb motor function on admission, at postoperative discharge, and at the last follow-up visit.

RESULTS

The OPLL area was increased in all patients. The mean area of ossification increased from 83.6 ± 25.3 mm(2) at the time of surgery to 114.8 ± 32.4 mm(2) at the last follow-up visit. No patients exhibited any neurological deterioration due to OPLL progression.

CONCLUSIONS

The present study demonstrated that the size of the thoracic OPLL increased after spinal stabilization. Despite diminished local spinal motion, OPLL progression did not decrease or stop. Physicians should pay attention to ossification progression in patients with thoracic OPLL.

Anterior decompressive surgery after cervical laminoplasty in patients with ossification of the posterior longitudinal ligament

BACKGROUND CONTEXT

Two surgical procedures, posterior decompressive surgery (PDS) and anterior decompressive surgery (ADS), are the treatment options for cervical ossification of the posterior longitudinal ligament (OPLL). Each procedure has advantages and disadvantages. Cervical laminoplasty, a type of PDS, is relatively easy to perform and can be used for patients with multilevel cord compression. ADS can often be more technically demanding.

OBJECTIVE

The purpose of this study was to clarify the clinical characteristics and surgical results of the patients for whom ADS was necessary after PDS.

STUDY DESIGN

Retrospective study.

METHODS

A total of 144 patients, followed for more than 3 years after cervical laminoplasty, were included. The neurologic status was graded using the Japanese Orthopedic Association (JOA score). Eleven patients underwent ADS after PDS. The clinical background and surgical outcomes were evaluated. Radiological findings of the 11 patients requiring ADS after PDS (PA group) and the 133 PDS patients not requiring ADS (P group) were compared.

RESULTS

In the PA group, the JOA score was slightly deteriorated during follow-up after cervical laminoplasty. Severe pain in the unilateral upper extremity and deterioration of cervical myelopathy were the most typical symptoms necessitating ADS. The incidence of the mixed type of OPLL was significantly higher in this group. The JOA score improved in all patients after ADS as a second surgery.

CONCLUSIONS

In our strategy for the surgical treatment of cervical OPLL, PDS with laminoplasty remains as the initial treatment, and in patients with neurological deterioration and newly developed clinical symptoms during follow-up, ADS is considered as a salvage procedure.

Three-dimensional evaluation of volume change in ossification of the posterior longitudinal ligament of the cervical spine using computed tomography

BACKGROUND

Two-dimensional imaging is not adequate for evaluating ossification of the posterior longitudinal ligament (OPLL). This study was designed to evaluate the accuracy of a novel computed tomography (CT)-based three-dimensional (3D) analysis method that we had devised to measure volume changes in OPLL.

SUBJECTS AND METHODS

Twenty OPLL patients (12 male and 8 female; mean age 63.6 years) who were being followed conservatively were examined twice with an interval of at least 1 year between the two scans. The mean interval was 22 (range 12-45) months. A 3D model was created with DICOM data from CT images, using the MIMICS(®) software to calculate the volume. The mean ossification volume was determined from two measurements. Since ossification size varies widely, evaluation of change in volume is generally affected by the original size. Therefore, the change in ossification volume between the first and second CT examinations was calculated as the annual rate of progression.

RESULTS

The type of OPLL was classified as continuous in 3 patients, segmented in 3, and mixed in 14. The mean ossification volume was 1,831.68 mm(3) at the first examination and 1,928.31 mm(3) at the second, showing a significant mean increase in ossification volume. The mean annual rate of lesion increase was 3.33% (range 0.08-7.79%).

CONCLUSION

The 3D method used allowed detailed OPLL classification and quantification of change in the ossified volume. Thus, this method appears to be very useful for quantitative evaluation of OPLL with only minimal measurement error.

Is cervical lordosis relevant in laminoplasty?

BACKGROUND CONTEXT

Laminoplasty aims to decompress the spinal cord and stabilize the cervical spine in patients with multilevel cervical lesions. Not every patient with cervical compressive myelopathy is a good candidate for laminoplasty. Most studies recommend that neutral or kyphotic alignments are contraindications for laminoplasty. However, cervical sagittal alignment does not have a strong and consistent effect on the clinical outcomes of laminoplasty. Moreover, many reports on the effect of cervical sagittal alignment did not designate the ideal definition of alignment and used different definitions of lordosis.

PURPOSE

To identify the effect of preoperative cervical alignment according to two different definitions after midline splitting double-door laminoplasty.

STUDY DESIGN

Retrospective cohort study.

PATIENT SAMPLE

From August 2008 to September 2010, 58 patients were diagnosed with cervical myelopathy and treated with midline splitting double-door laminoplasty.

OUTCOME MEASURES

The clinical results were assessed with the modified Japanese Orthopedic Association (JOA) score, neck disability index (NDI), and visual analog scale (VAS) and were compared to analyze the rate of change between preoperative and postoperative values. Postoperative radiological results at the final follow-up examinations were compared between groups to obtain the change in range of motion and sagittal alignment.

METHOD

The effect of cervical alignment on JOA, NDI, and VAS scales and also on change of alignment and change of range of motion (ROM) at the final follow-up examinations was analyzed statistically between two groups according to two different definitions such as Toyama classification and Cobb angle.

RESULTS

No difference was found between the two groups according to Toyama classification in terms of the postoperative improvement rate of the modified JOA score (p=.086), decreasing rate of the VAS (p=.940) or NDI (p=.211), postoperatively. Additionally, no difference was found for the decreasing rate of ROM (p=.427) or sagittal alignment (p=.864) based on the radiological evaluation results. Also, there was no difference between two groups according to Cobb angle in terms of the modified JOA score (p=.743), VAS (p=.548), or NDI (p=.32), postoperatively. Additionally, no difference was found for the ROM (p=1.000) or sagittal alignment (p=.440) based on the radiological evaluation results.

CONCLUSIONS

Despite nonlordosis cervical sagittal alignment, double-door laminoplasty would be effective for patients with cervical myelopathy because of cervical spondylotic myelopathy or ossification of the posterior longitudinal ligament. Furthermore, sagittal alignment is not the absolute and sole factor that surgeons should consider when determining the optimal treatment strategy.

Factors associated with intramedullary MRI abnormalities in patients with ossification of the posterior longitudinal ligament

STUDY DESIGN

A retrospective clinical study of 113 patients with ossification of the posterior longitudinal ligament (OPLL), who underwent either anterior or posterior surgery between 2006 and 2009.

OBJECTIVE

To evaluate the risk factors affecting the intramedullary spinal cord changes in signal intensity on magnetic resonance imaging (MRI) for the patients with OPLL.

SUMMARY OF BACKGROUND DATA

The relationship between the intramedullary spinal cord changes in signal intensity on MRI and neurological deficits, as well as the surgical outcomes, has been described. To obtain better prognosis, early surgery should be conducted in patients with OPLL who have potential abilities to develop intramedullary spinal cord changes in signal intensity on MRI. Various factors may be affecting the development of intramedullary spinal cord changes in signal intensity on MRI.

MATERIALS AND METHODS

The clinical and radiographic data of 113 patients with OPLL who underwent either anterior or posterior surgery between 2006 and 2009 were reviewed. Age, sex, complication, mean occupying ratio of OPLL (the greatest thickness of OPLL divided by the anteroposterior diameter of the bony spinal canal), duration of symptoms, type of OPLL, preoperative Japanese Orthopedic Association (JOA) score, and range of motion of the cervical spine were collected. Logistic regression analysis was used.

RESULTS

Changes in the intramedullary signal intensity on MRI were observed in 33 of the 113 patients. Statistical results show that duration of symptoms, occupying ratio of OPLL, preoperative JOA score, kyphosis, and instability of the cervical spine are the relevant risk factors for intramedullary spinal cord changes in signal intensity on MRI, with regression coefficients of 2.437, 0.953, -1.952, 2.093, and 1.516, respectively. For patients with OPLL, the longer the duration of the symptoms, or the higher occupying ratio of OPLL, or the lower preoperative JOA score, the greater the likelihood of intramedullary spinal cord changes in signal intensity on MRI.

CONCLUSIONS

As intramedullary spinal cord changes in signal intensity on MRI indicated severe damage to spinal cord and poor prognosis as we described before, early surgery is suggested for patients with OPLL who manifest one of the following factors: prolonged symptoms, high occupying ratio, low preoperative JOA score, kyphosis, or instability of the cervical spine. These factors are closely related to the intramedullary spinal cord changes in signal intensity on MRI.

Significance of segmental instability in cervical ossification of the posterior longitudinal ligament and treated by a posterior hybrid technique

STUDY DESIGN

Retrospective cohort case study.

OBJECTIVE

To evaluate significance of segmental instability (SI) in cervical ossification of the posterior longitudinal ligament (OPLL) myelopathy and effectiveness of a posterior hybrid technique in the treatment of OPLL associated with SI. Some studies suggested both static and dynamic compression factors accounted for the pathogenesis of myelopathy in the OPLL patients.

METHOD

Between May 2005 and August 2007, 15 patients with multilevel cervical OPLL, diagnosed to be associated with SI, were treated by a posterior hybrid technique including laminoplasty and fusion at instable levels with lateral mass screw fixation. Another 15 cohort patients without SI treated by laminoplasty in the same period were included in the control group. Radiological and clinical data were compared between two groups.

RESULTS

There were no significant differences in Preop. lordotic angle, extent of OPLL, type of OPLL and occupying rate, but more patients tended to present high-intensity zone (HIZ) on MRI in the group with SI. In 15 patients with SI, 17 intervertebral levels had SI, which were distributed at the noncontinuous levels of mixed-type OPLL or the adjacent levels of continuous-type OPLL. They were also consistent with the presence of HIZ levels in the major of patients. After operation, the lordotic angle was maintained well by the posterior hybrid technique in the OPLL with SI group, and was significantly greater than that in the OPLL without SI at the 3- and 4-year follow-up point. Postoperative kyphotic change of the cervical spine and postoperative progression of the ossified lesion were not observed in the OPLL with SI group, but they were respectively observed in four cases (26.7 %) and two cases (13.3 %) in the OPLL without SI group at the 4-year follow-up point. The preoperative C-JOA score in the OPLL with SI group was lower than that in the OPLL without SI group. The average C-JOA score and improvement rate were comparable in the first 2 years after operation between two groups, but there was a decrease in C-JOA score and improvement rate in the following 2 years in the OPLL without SI group. At the 3- and 4-year follow-up points, both postoperative C-JOA score improvement rate in the OPLL with SI group were superior to those in the OPLL without SI group. Each group had one case developing C5 palsy, but three cases in the OPLL without SI group developed late neurological deterioration due to postoperative kyphotic change or progression of the ossified lesion.

CONCLUSIONS

Segmental instability, a degenerative dynamic factor, is important to the OPLL myelopathy. The posterior hybrid technique seemed to be effective and safe in the treatment of selective OPLL patients associated with SI. The benefits may include providing stabilization environment for spinal cord recovery, and preventing progressive kyphotic change and progression of OPLL.

Interobserver and intraobserver reliability of the classification and diagnosis for ossification of the posterior longitudinal ligament of the cervical spine

PURPOSE

Ossification of the posterior longitudinal ligament (OPLL) of the cervical spine has been classified into four types by lateral plain radiographs, but the reliability of the classification and of the diagnosis of either cervical OPLL or cervical spondylotic myelopathy (CSM) was unknown. We investigated the interobserver and intraobserver reliability of the classification and diagnosis for OPLL by radiographs and computed tomography (CT) images.

METHODS

A total of 16 observers classified each patient's images into five groups; OPLL continuous, segmental, mixed, circumscribed type, or CSM. To evaluate interobserver reliability, the observers first classified only radiograph images, and next both radiographs and CT images. On another day they followed the same procedure to evaluate intraobserver reliability. We also evaluated interobserver and intraobserver reliability of the diagnosis of either cervical OPLL or CSM.

RESULTS

Interobserver reliability of the classification with radiographs only showed moderate agreement, but interobserver reliability with both radiographs and CT images showed substantial agreement. Intraobserver of reliability the classification was also improved by additional CT images. Interobserver reliability of the diagnosis with both radiographs and CT images was almost similar to with radiographs only. Intraobserver reliability of the diagnosis was improved by additional CT images.

CONCLUSIONS

This study suggested that the reliability of the classification and diagnosis for cervical OPLL was improved by additional CT images. We propose that diagnostic criteria for OPLL include both radiographs and CT images.

Does ossification of the posterior longitudinal ligament progress after laminoplasty? Radiographic and clinical evidence of ossification of the posterior longitudinal ligament lesion growth and the risk factors for late neurologic deterioration

Ossification of the posterior longitudinal ligament (OPLL) is a disease process characterized by progressive growth and calcification resulting in spinal canal compromise and serious neurological sequelae in advanced cases. Historically, OPLL has most commonly been treated with posterior surgical decompression. Although this procedure indirectly decompresses the spinal cord, it does not address the offending pathological entity, and further growth of the lesion may result in delayed neurological deterioration. This fact is particularly relevant because a number of long-term studies have revealed both longitudinal and transverse disease progression in individuals treated both surgically and conservatively. Despite these high rates of radiographically documented progression, however, the rate of neurological decline in patients undergoing posterior surgery with laminoplasty is low. In this article, the authors review the pathophysiology of OPLL, evidence of disease progression, and outcome data addressing conservative and surgical treatments.

Laminoplasty for cervical myelopathy

This article reviews cervical laminoplasty. The origin of cervical laminoplasty dates back to cervical laminectomy performed in Japan ~50 years ago. To overcome poor surgical outcomes of cervical laminectomy, many Japanese orthopedic spine surgeons devoted their lives to developing better posterior decompression procedures for the cervical spine. Thanks to the development of a high-speed surgical burr, posterior decompression procedures for the cervical spine showed vast improvement from the 1970s to the 1980s, and the original form of cervical laminoplasty was determined. Since around 2000, surgeons performing cervical laminoplasty have been adopting less invasive procedures for the posterior cervical muscle structures so as to minimize postoperative axial neck pain and obtain better functional outcomes of the cervical spine. This article covers the history of cervical laminoplasty, surgical procedures, the benefits and limitation of this procedure, and surgery-related complications.

Surgical management of cervical cord injury with ossification of the cervical posterior longitudinal ligament

OBJECTIVE

To identify an appropriate surgical approach for the management of cervical cord injury with ossification of the posterior longitudinal ligament.

METHODS

A retrospective study of 25 cases of cervical cord injury with ossification of the posterior longitudinal ligament was performed. Two cases were classified as Frankel grade A, three as grade B, fourteen as grade C, and six as grade D. Treatment procedures consisted of anterior decompression with instrumentation (twelve patients), posterior decompression (eight patients), and combined anterior and posterior decompression (five patients).

RESULTS

There were no iatrogenic injuries of great vessels, trachea, esophagus or spinal cord. All patients were followed up for 15-86 months (average, 38.3 months). All segment with anterior fixation attained solid fusion, without implants loosening or breakage. No reclosed open-door was found after posterior laminoplasty. Twenty-one patients improved by one to two Frankel grades. The patients with complete spinal cord injury achieved no neurologic recovery, but did experience relief of upper limb pain or numbness.

CONCLUSION

The surgical outcomes of cervical cord injury with ossification of the posterior longitudinal ligament were satisfactory. It is important to select a suitable surgical approach according to the findings on radiological imaging and the clinical characteristics and general condition of the patients.

Three-dimensional measurement of growth of ossification of the posterior longitudinal ligament

Object

Ossification of the posterior longitudinal ligament (OPLL) is a progressive disease that causes cervical myelopathy. Because 2D evaluation of ossification growth with plain lateral radiographs has limitations, the authors developed a unique technique to measure ossification progression and volume increase by using multidetector CT scanning.

Methods

The authors used serial thin-slice volume data obtained by multidetector CT scanning in 5 patients. The mean patient age was 63 years, and the mean follow-up duration was 3.1 years. First, a 3D model of OPLL was semiautomatically segmented at a specific threshold. Then, a preoperative model of OPLL was superimposed on a postoperative model using voxel-based registration of the vertebral bodies. Progression and volume increase were measured using a digital viewer that was developed by the authors. Progression was visualized using a color-coded contour on the surface of the OPLL model.

Results

All patients had progression of 0.5 mm or greater. The mean values concerning OPLL growth were as follows: maximum progression length, 4.7 mm; progression rate, 1.5 mm/year; volume increase, 1622 mm3; volume expansion rate, 37%; and volume increase rate, 484 mm3/year. The accuracy of superimposition by voxel-based registration, defined as closeness to the true value, was less than 0.31 mm. For intraobserver reproducibility of the volume measurement, the mean intraclass correlation coefficient, root mean square error, and coefficient of variation were 0.987, 16.0 mm3, and 1.7%, respectively.

Conclusions

Ossification of the posterior longitudinal ligament progresses even after surgery. Three-dimensional evaluation with the aid of CT scans is a useful and reliable method for assessing that growth.

Extensive laminectomy for the treatment of ossification of the posterior longitudinal ligament in the cervical spine

OBJECTIVE

To introduce the surgical strategy of extensive laminectomy (with inner 1/4 facet joint resection to expose the origin of the nerve root) and to discuss its benefit for the treatment of cervical ossification of the posterior longitudinal ligament (OPLL) with myelopathy.

METHODS

From January 1998 to December 2005, 82 patients with cervical OPLL underwent extensive laminectomy. We assessed neurological function using the Japanese Orthopedic Association (JOA) scoring system, neck/shoulder pain using a visual analogue scale (VAS), and cervical curvature index (CCI) by the Ishihara method; the expansion degree and the drift-back distance of the spinal cord was calculated using the MRI image.

RESULTS

The mean duration of follow-up was 41.6 months. The postoperative JOA score suggested that neurological function improved significantly with a recovery rate of 64%. The incidence rate of transient palsy of the C5 nerve root, which occurred in only 2 patients who recovered to useful function over 2 weeks, was 2.4%. The postoperative VAS score suggested that the pain in the neck/shoulder was mild. Although the postoperative CCI was small, there was no correlation with the length of follow-up period. The increased cross-sectional area of the dural sac at the level of maximum compression together with the significant drift-back distance of the spinal cord suggested that decompression was complete.

CONCLUSION

Extensive laminectomy is effective in treating cervical OPLL, with mild cervical/shoulder pain, low rate of C5 nerve root palsy, and no recurrence of spinal cord compression symptoms.

Analysis of demographics, risk factors, clinical presentation, and surgical treatment modalities for the ossified posterior longitudinal ligament

OBJECT

Ossification of the posterior longitudinal ligament (OPLL) is a rare disease that results in progressive myeloradiculopathy related to pathological ossification of the ligament from unknown causes. Although it has long been considered a disease of Asian origin, this disorder is increasingly being recognized in European and North American populations. Herein the authors present demographic, radiographic, and comorbidity data from white patients with diagnosed OPLL as well as the outcomes of surgically treated patients.

METHODS

Between 1999 and 2010, OPLL was diagnosed in 36 white patients at Barrow Neurological Institute. Patients were divided into 2 groups: a group of 33 patients with cervical OPLL and a group of 3 patients with thoracic or lumbar OPLL. Fifteen of these patients who had received operative treatment were analyzed separately. Imaging analysis focused on signal changes in the spinal cord, mass occupying ratio, signs of dural penetration, spinal levels involved, and subtype of OPLL. Surgical techniques included anterior cervical decompression and fusion with corpectomy, posterior laminectomy with fusion, posterior open-door laminoplasty, and anterior corpectomy combined with posterior laminectomy and fusion. Comorbidities, cigarette smoking, and previous spine surgeries were considered. Neurological function was assessed using a modified Japanese Orthopaedic Association Scale (mJOAS).

RESULTS

A high-intensity signal on T2-weighted MR imaging and a history of cervical spine surgery correlated with worse mJOAS scores. Furthermore, mJOAS scores decreased as the occupying rate of the OPLL mass in the spinal canal increased. On radiographic analysis, the proportion of signs of dural penetration correlated with the OPLL subtype. A high mass occupying ratio of the OPLL was directly associated with the presence of dural penetration and high-intensity signal. In the surgical group, the rate of neurological improvement associated with an anterior approach was 58% compared with 31% for a posterior laminectomy. No complications were associated with any of the 4 types of surgical procedures. In 3 cases, symptoms had worsened at the last follow-up, with only a single case of disease progression. Laminoplasty was the only technique associated with a worse clinical outcome. There were no statistical differences (p > 0.05) between the type of surgical procedure or radiographic presentation and postoperative outcome. There was also no difference between the choice of surgical procedure performed and the number of spinal levels involved with OPLL.

CONCLUSIONS

Ossification of the posterior longitudinal ligament can no longer be viewed as a disease of the Asian population exclusively. Since OPLL among white populations is being diagnosed more frequently, surgeons must be aware of the most appropriate surgical option. The outcomes of the various surgical treatments among the different populations with OPLL appear similar. Compared with other procedures, however, anterior decompression led to the best neurological outcomes.

A systematic review of complications in cervical spine surgery for ossification of the posterior longitudinal ligament

BACKGROUND CONTEXT

Surgical management of ossification of the posterior longitudinal ligament (OPLL) is associated with complications. However, surgical complications for OPLL have not been clearly documented.

PURPOSE

To review and summarize the incidence of surgical complications of OPLL in the cervical spine and evaluate the impact of surgical approach (anterior or posterior), year of study publication, follow-up duration, and the surgical outcome on complication incidence.

STUDY DESIGN

Systematic review.

METHODS

An English literature review was conducted especially on surgical complications of cervical OPLL. The incidence of complications was statistically summarized, with its correlation to surgical approaches, year of study publications, follow-up duration, and the surgical outcome was statistically evaluated.

RESULTS

Twenty-seven retrospective studies, including a total of 1,558 patients, were reviewed. The overall incidence of surgical complications of cervical OPLL was 21.8%. Neurologic deficit (8.3%, overall rate), cerebrospinal fluid leakage (CFL) (5.1%), axial pain (3.5%), and implant complications (3.5%) were relatively common. The incidence of complications for posterior approach was not statistically different from those for anterior procedures. However, with regard to individual complication, C5 palsy and axial pain occurred more frequently in patients approached posteriorly, whereas CFL, implant complications, hoarseness, dysphagia, and dyspnea appeared more common in anterior cases.

CONCLUSIONS

There is a relatively high incidence of surgical complications for cervical OPLL compared with other cervical degeneration diseases. It is, therefore, necessary for surgeons to take into consideration the risk of surgical complications when communicating with patients for decision making and to alert complications during or after surgical procedures.

Evaluation of ossification of the posterior longitudinal ligament by three-dimensional computed tomography and magnetic resonance imaging

BACKGROUND CONTEXT

Detection of ossification of the posterior longitudinal ligament (OPLL) of lesions by lateral radiography is sometimes difficult because the lesions are small. Three-dimensional computed tomography (3D CT) imaging has made it possible to detect lesions not been seen by lateral radiography.

PURPOSE

To evaluate the use of 3D CT in visualizing and classifying OPLL, and the added value of magnetic resonance imaging (MRI) in determining spinal cord compression.

STUDY DESIGN

Prospective case study in an academic department of orthopedic surgery.

PATIENT SAMPLE

Patients with OPLL diagnosed by lateral radiography of the cervical spine from April 2006 to March 2007 were identified.

METHODS

Ossification of the posterior longitudinal ligament visualized lateral radiography was classified according to the existing scheme as continuous, segmental, mixed, or other type. Ossification of the posterior longitudinal ligament visualized by 3D CT was organized into a classification system comprising flat, irregular, or localized types and were compared with the lateral radiographic images. Magnetic resonance imaging was done to determine the extent of spinal cord compression.

RESULTS

All 55 patients (35 men and 20 women; median age, 66 years) with OPLL were enrolled. Of these, 41 (75%) had a type of OPLL as visualized by 3D CT that corresponded with only one type of OPLL as visualized by lateral radiography. In 39 (71%) of 55, the areas of the ossified lesions visualized by 3D CT were the same as those visualized by lateral radiography. In the other 16, the lesions were either too small or too unclear to be visualized by lateral radiography. In all cases, 3D CT imaging showed that the transverse width of OPLL was within the bilateral Luschka joints, which was not noted by lateral radiography. In 13 of the 14 subjects who underwent MRI, spinal cord compression was noted at the superior or inferior edges of the ossified lesions that had been seen by 3D CT.

CONCLUSIONS

Three-dimensional computed tomography visualization of OPLL provided the basis of a classification system, superior to lateral radiography, and provided new information about OPLL. Combining 3D CT with MRI might be useful to provide details about spinal cord compression in OPLL.

Anterior cervical multilevel decompression and fusion using fibular strut as revision surgery for failed cervical laminoplasty

STUDY DESIGN

Retrospective analyses of six cases.

OBJECTIVE

To describe six patients with previous failed laminoplasty who were subsequently managed by anterior cervical decompression and fusion (ACDF) using fibular strut as revision surgeries.

SUMMARY OF BACKGROUND DATA

While several complications and unsatisfactory results of cervical laminoplasty have been reported, there is no general consensus on how to best surgically treat these pathological conditions.

METHODS

Six patients, who had been treated by laminoplasty for cervical spondylotic myelopathy (n = 2) or ossification of posterior longitudinal ligament (OPLL, n = 4) and had unfavorable outcomes, underwent ACDF using autogenous fibular strut grafts. The pathological factors associated with the poor outcomes were intraforaminal spur, slip, spondylotic change, disc herniation, and increase of OPLL in size. Clinical outcomes were assessed by evaluating the modified Japanese Orthopedic Association score (JOA score) of cervical myelopathy, severity of radicular pains, axial pains, and perioperative complications. In addition, C2-7 angle and the presence of bony union were analyzed.

RESULTS

The revision ACDF significantly increased the mean ± SD. JOA score, from 10.3 ± 3.9 to 13.5 ± 2.7 points (p = 0.028), with a recovery rate of 47.1 ± 26.7%. Radicular pain and axial pain also improved. C2-7 angle was not changed significantly. Solid fusion was achieved in all patients at 12.2 ± 4.2 months after revision surgery.

CONCLUSION

ACDF with fibular strut graft was effective as a revision procedure for failed laminoplasty.

Genetic differences in the osteogenic differentiation potency according to the classification of ossification of the posterior longitudinal ligament of the cervical spine

STUDY DESIGN

We categorized the four types of ossification of the posterior longitudinal ligament (OPLL) of the cervical spine into two groups. We biochemically investigated the genetic differences in the osteogenic differentiation potency between the two groups.

OBJECTIVE

To investigate the genetic differences in the osteogenic differentiation potency according to the OPLL classification.

SUMMARY OF BACKGROUND DATA

Clinical studies on OPLL have revealed that the risk of progression of the ossification area is greatest for continuous and mixed type OPLL. However, until now, these four types of OPLL have been studied as a single condition.

METHODS

We categorized the four types of OPLL into the OPLL continuous (continuous or mixed type) and OPLL segmental groups (segmental or circumscribed type). Paraspinal ligaments were aseptically obtained from OPLL patients during surgery. The fibroblast-like cells that migrated from the explants were used for experiments. The cells were placed in a 60-mm culture dishes for total ribonucleic acid preparation and 12 well microplates for alkaline phosphatase (ALP) activity staining. After cultures reached confluence, the cells were cultured in osteogenic medium. The messenger ribonucleic acid expression of bone morphogenetic protein-2 (BMP-2), osterix, tumor necrosis factor-α-stimulated gene-6, and ALP was analyzed by quantitative real time-polymerase chain reaction. Osteogenic differentiation of fibroblast-like cells was determined by histochemically detecting ALP production.

RESULTS

After osteogenic induction, BMP-2 expression increased in the OPLL continuous and segmental groups. Osterix expression increased in the OPLL continuous group only. Tumor necrosis factor-α-stimulated gene-6 expression was suppressed in the OPLL continuous and segmental groups. ALP expression as well as ALP activity staining was higher in the OPLL continuous group than in the OPLL segmental group. CONCLUSION.: The study revealed genetic differences in the osteogenic differentiation potency between the OPLL continuous and segmental groups. We propose to distinguish OPLL continuous group from segmental group in biochemical studies on OPLL.

Surgical management of cervical ossification of the posterior longitudinal ligament: natural history and the role of surgical decompression and stabilization

Object

Ossification of the posterior longitudinal ligament (OPLL) is a complex multifactorial disease process combining both metabolic and biomechanical factors. The role for surgical intervention and choice of anterior or posterior approach is controversial. The object of this study was to review the literature and present a single-institution experience with surgical intervention for OPLL.

Methods

The authors performed a retrospective review of their institutional experience with surgical intervention for cervical OPLL. They also reviewed the English-language literature regarding the epidemiology, pathophysiology, natural history, and surgical intervention for OPLL.

Results

Review of the literature suggests an improved benefit for anterior decompression and stabilization or posterior decompression and stabilization compared with posterior decompression via laminectomy or laminoplasty. Both anterior and posterior approaches are safe and effective means of decompression of cervical stenosis in the setting of OPLL.

Conclusions

Anterior cervical decompression and reconstruction is a safe and appropriate treatment for cervical spondylitic myelopathy in the setting of OPLL. For patients with maintained cervical lordosis, posterior cervical decompression and stabilization is advocated. The use of laminectomy or laminoplasty is indicated in patients with preserved cervical lordosis and less than 60% of the spinal canal occupied by calcified ligament in a “hill-shaped” contour.

Medium-term outcomes of C3-6 laminoplasty for cervical myelopathy: a prospective study with a minimum 5-year follow-up

C3-6 laminoplasty preserving muscle insertions into the C7 spinous process is reportedly associated with a significantly decreased frequency of postoperative axial neck pain. However, no prospective study has reported medium-term outcomes of C3-6 laminoplasty. The purpose of this study was to elucidate medium-term outcomes after C3-6 laminoplasty. Subjects comprised 31 patients with cervical myelopathy who underwent C3-6 laminoplasty preserving all bilateral muscles attached to the C2 and C7 spinous processes and were followed for ≥5 years. Clinical and radiological data were prospectively collected. Neurological status was assessed using Japanese Orthopaedic Association (JOA) score. Axial neck pain was graded as severe, moderate or mild. Sagittal alignment of the cervical spine and progression of ossification of the posterior longitudinal ligament (OPLL) were assessed by comparing serial lateral radiographs. Mean JOA score improved significantly from 10.6 before surgery to 14.7 at the time of maximum recovery, and slightly declined to 14.3 at final follow-up. In six patients who developed late deterioration, these conditions were unrelated to the cervical spine. As of final follow-up, only one patient (3.2%) had complained of axial neck pain persisting for 5 years. Although progression of OPLL was found in 63.6% of patients, none had experienced neurological deterioration due to this progression. At final follow-up, sagittal alignment of the cervical spine was more lordotic than before surgery. Medium-term outcomes of C3-6 laminoplasty were satisfactory. Frequencies of persistent axial neck pain and loss of cervical lordosis after surgery remained significantly decreased for ≥5 years postoperatively.

Single stage circumferential cervical surgery (selective anterior cervical corpectomy with fusion and laminoplasty) for multilevel ossification of the posterior longitudinal ligament with spinal cord ischemia on MRI

OBJECTIVE

Anterior cervical corpectomy with fusion (ACF) or laminoplasty may be associated with substantial number of complications for treating multilevel cervical ossification of the posterior longitudinal ligament (OPLL) with significant cord compression. For more safe decompression and stabilization in multilevel cervical OPLL with prominent cord compression, we propose circumferential cervical surgery (selective ACF and laminoplasty) based on our favorable experience.

METHODS

Twelve patients with cervical myelopathy underwent circumferential cervical surgery and all patients showed multilevel OPLL with signal change of the spinal cord on magnetic resonance imaging (MRI). A retrospective review of clinical, radiological, and surgical data was conducted.

RESULTS

There were 9 men and 3 women with mean age of 56.7 years and a mean follow up period of 15.6 months. The average corpectomy level was 1.16 and laminoplasty level was 4.58. The average Japanese Orthopedic Association score for recovery was 5.1 points and good clinical results were obtained in 11 patients (92%) (p < 0.05). The average space available for the cord improved from 58.2% to 87.9% and the average Cobb's angle changed from 7.63 to 12.27 at 6 months after operation without failure of fusion (p < 0.05). Average operation time was 8.36 hours, with an estimated blood loss of 760 mL and duration of bed rest of 2.0 days. There were no incidences of significant surgical complications, including wound infection.

CONCLUSION

Although the current study examined a small sample with relatively short-term follow-up periods, our study results demonstrate that circumferential cervical surgery is considered favorable for safety and effectiveness in multilevel OPLL with prominent cord compression.

Revision surgery following cervical laminoplasty: etiology and treatment strategies

STUDY DESIGN

Retrospective review of prospectively collected data.

OBJECTIVE

To identify the cause of failed open-door laminoplasty and to describe the surgical strategies for revision surgery.

SUMMARY OF BACKGROUND DATA

Although laminoplasty has become popular, few articles have addressed the cause of failed cervical laminoplasty requiring revision surgery.

METHODS

All patients who required revision surgery following open-door cervical laminoplasty were identified. Clinical data, method of surgical revision, time between surgeries, Nurick grade, radiologic parameters, and complications were analyzed. Laminoplasty failures were classified into 3 categories: "technique related," "inadequate symptomatic relief after treatment," or "recurrence of symptoms due to disease progression."

RESULTS

A total of 130 patients underwent cervical laminoplasty over a 10-year period (1996-2006), and 12 patients (9.2%) required revision surgery. The mean age was 50.7 years at the time of the index laminoplasty (range, 34-67 years) and 51.8 years (range, 35-70 years) at the time of the revision surgery. Mean duration of symptoms was 7.3 months before the index procedure (range, 2-17 months) and 5.6 months (range, 1-14 months) before revision surgery. The mean time interval between the index procedure and revision surgery was 16.6 months (range, 4-43 months). Of the 12 patients who required revision surgery, 5 had global lordosis of <10 degrees, 4 developed local kyphosis >13 degrees, and 5 had increased degenerative spondylolisthesis. Nonmyelopathic causes resulted in 50% of the revision surgery. Of 12 patients, 3 (25%) required revision surgery due to technique-related factors; 1 (8%) required surgery due to inadequate symptomatic relief after treatment; and 8 (67%) required revision surgery due to disease progression.

CONCLUSION

Of the 130 patients who underwent cervical laminoplasty over a 10-year period, 12 patients (9.2%) required revision surgery. Although laminoplasty is generally successful, failures due to disease progression, technique-related factors, and inadequate symptomatic relief after treatment can occur. Patients should, therefore, be counseled regarding the potential need for revision surgery when undergoing open-door laminoplasty.

A segmental partial laminectomy for cervical spondylotic myelopathy: anatomical basis and clinical outcome in comparison with expansive open-door laminoplasty

STUDY DESIGN

A comparative study regarding the clinical outcome of the 2-different surgical procedures for patients with cervical spondylotic myelopathy (CSM).

OBJECTIVES

To describe the anatomic basis of a segmental partial laminectomy (SPL) for the treatment of cervical spondylotic myelopathy and to compare the clinical outcome with traditional C3 to C7 expansive open-door laminoplasty (ELAP).

SUMMARY OF BACKGROUND DATA

Laminoplasty has been widely accepted for the treatment of CSM. However, some disadvantages have also been recognized. To resolve these problems, a SPL was performed. No previous studies have been reported regarding this surgical procedure.

METHODS

A total of 13 human cadavers were studied to analyze the spinal cord compression of cervical spondylosis. Twenty-six patients who underwent a SPL and 13 age- and gender-matched patients who underwent traditional C3-C7 ELAP were analyzed for their Japanese Orthopedic Association score, axial neck pain, and radiographic parameters (lordotic angle and ROM of cervical spine).

RESULTS

Based on cadaver studies, compression of the spinal cord was present in the articular segment, but not in the intraosseous segment. The removal of the ligamentum flavum and the superior edge of the lower lamina was sufficient for minimum posterior decompression of the cervical spinal cord.In comparison with the ELAP, the patients who underwent an SPL showed a similar recovery of the Japanese Orthopedic Association score, but the maintenance of the sagittal alignment and the range of motion were better after the SPL and postoperative neck and/or shoulder complaints also seemed to be reduced.

CONCLUSION

A SPL, may therefore, be a useful and effective surgical procedure for cervical spondylotic myelopathy.

A patient with two re-surgeries for delayed myelopathy due to progression of ossification of the posterior longitudinal ligaments after cervical laminoplasty

STUDY DESIGN

Case report.

OBJECTIVE

To discuss the development of delayed myelopathy due to the progression of ossification of the posterior longitudinal ligament (OPLL) after cervical laminoplasty.

SUMMARY OF BACKGROUND DATA

The progression of OPLL after cervical laminoplasty for the treatment of OPLL is often shown in long-term follow-up; however, few patients with reoperation due to OPLL progression have been reported.

METHODS

The patient was a 70-year-old male carpenter. At 57-years of age, he underwent open door laminoplasty between C3 and C7 with dome-like laminectomy of C2 for the treatment of myelopathy due to mixed-type OPLL (continuous type at C3-C4 and segmental type at C5). Five years after the initial surgery, the disorder of skilled motor activity in the bilateral hands and ambulatory difficulties recurred as a result of cranial progression of OPLL (between C2 and C4). He underwent laminectomy and posterior fusion between C2 and C5 and returned to work. Four years after resurgery, the same symptoms recurred.

RESULTS

CT revealed the progression of OPLL thickness at C5 level and longitudinal progression of OPLL to C6/7. Sagittal view of MRI demonstrated spinal cord compression between C5 and C6/7 because of OPLL at C5 and hypertrophic ligamentum flavum at C5-C6 and C6-C7. Posterior fusion extending up to C7 with laminectomy of C6 and C7 was performed. His symptoms were alleviated and he could walk again.

CONCLUSION

We reported a patient with OPLL who had undergone resurgery twice because of myelopathy due to the progression of ossification. It was important to establish a sufficiently longitudinal and transverse decompression, taking the risk of the unexpected progression of ossification into consideration.

A review of prognostic factors for surgical outcome of ossification of the posterior longitudinal ligament of cervical spine

For patients with ossification of the posterior longitudinal ligament (OPLL) who have neurological-symptoms, surgery is necessary but not always effective. Various clinical factors influence the surgical outcome. The studies identifying these factors have been inconclusive and conflicting. It is essential for surgeons to understand the significance of the factors and choose the optimal therapeutic strategy for OPLL. The objective of this review is to determine the clinical factors predictive of the surgical outcome of cervical OPLL. The authors conducted a review of literature published in the English language. They examined studies in which the correlation between clinical factors and outcome were statistically evaluated. The results showed that the traverse area of the spinal cord, the spinal cord-evoked potentials (SCEPs), the increase of the range of motion in the cervical spine (ROM), diabetes, history of trauma, the onset of ossification of the ligament flavum (OLF) in the thoracic spine, snake-eye appearance (SEA) and incomplete decompression may be predictive factors. Age at surgery seems to be closely related to the outcome of posterior surgical procedure. Whether the neurological score, OPLL type, pre-operative duration of symptoms, focal intra-medullar high signal intensity in T2-weighted (IMHSI) and progression of OPLL or kyphosis and expansion of the spinal canal predict the surgical outcome remains unclear. The use of uniform neurological score and proper statistic analysis should facilitate comparison of data from different studies. It is important to analyze the effect of each factor on groups with different surgical procedures as well as patients with different compressive pathology. Research on the etiology and pathology of cervical myelopathy due to OPLL should be helpful in precisely understanding these clinical factors and predicting surgical outcome.

Long-term outcome of laminectomy and instrumented fusion for cervical ossification of the posterior longitudinal ligament

Between January 2000 and December 2003, a total of 83 patients (64 men and 19 women, average age: 56.4 years, range: 42-78 years) who underwent posterior laminectomy and instrumented fusion for ossification of the posterior longitudinal ligament (OPLL) were included in this study to investigate the long-term outcome of this surgical option and clarify which factors affect the prognosis. After an average 4.8-year follow-up, the mean Japanese Orthopaedic Association (JOA) score significantly increased from 9.2 +/- 1.3 points before operation to 14.2 +/- 0.9 points at the latest follow-up (P < 0.01). The improvement rate (IR) of neurological function ranged from 11.1 to 87.5%, with a mean of 62.4 +/- 13.2%. Among 83 patients, 59 (71.1%) patients had a good prognosis (IR > or = 50%), and the other 24 (28.9%) patients had a poor prognosis (IR < 50%). Postoperative nerve root palsy was the main complication in this series. Radiographic study showed that whilst improving cervical lordosis could provide a better decompression effect and good prognosis, it could have simultaneously contributed to the high incidence of postoperative nerve root palsy.

Characteristics of ossified lesions in the upper cervical spine associated with ossification of the posterior longitudinal ligament in the lower cervical spine

BACKGROUND

Ossified lesions of the upper cervical spine behind the dens may cause cervical myelopathy. We investigated the prevalence of ossified lesions in patients with ossification of the posterior longitudinal ligament in order to clarify the characteristics of these patients.

METHODS

Fifty-six consecutive patients with ossification of the posterior longitudinal ligament in the cervical spine were included in the study. Multidetector computed tomography images of the whole spine were made. Ossified lesions of the upper cervical spine were defined as ossified lesions behind the dens as seen on axial computed tomography images. The prevalence of ossified lesions at the first cervical level was analyzed. The clinical and radiographic parameters were compared between the patients with ossified lesions at the first cervical level and the patients without such lesions.

RESULTS

Fourteen patients (25%) had ossified lesions of the upper cervical spine. The continuous type of ossification of the posterior longitudinal ligament in the lower cervical spine was common and the segmental type was rare in this group as compared with the types of ossification in the group without ossified lesions at the first cervical level. The patients with first cervical level ossification more frequently had ossification of the posterior longitudinal ligament in the thoracic and/or lumbar spine, compared with the patients without upper cervical ossification. One patient had cervical myelopathy as a result of the upper cervical ossified lesion.

CONCLUSIONS

Computed tomography imaging demonstrated the presence of ossified lesions behind the dens in 25% of patients with subaxial ossification of the posterior longitudinal ligament. These upper cervical ossified lesions were commonly seen in patients with multiple-level ossification of the posterior longitudinal ligament. When upper cervical ossified lesions cause severe narrowing of the spinal canal, they should be considered a potential cause of cervical myelopathy.

Multilevel cervical oblique corpectomy in the treatment of ossified posterior longitudinal ligament in the presence of ossified anterior longitudinal ligament

STUDY DESIGN

Clinical study.

OBJECTIVE

To highlight the value of the oblique corpectomy in managing patients with cervical myelopathy caused by extensive ossified posterior longitudinal ligament (OPLL) who also have a coexisting ossified anterior longitudinal ligament (OALL).

SUMMARY OF BACKGROUND DATA

OPLL, OALL, and diffuse idiopathic skeletal hyperostosis (DISH) may coexist, and the surgical treatment is varied. Patients with cervical myelopathy who are asymptomatic for the OALL may be managed by either anterior or posterior approaches, while those with dysphagia are best managed by an anterior approach that can deal with both pathologies simultaneously. The OALL resection is indicated only if symptomatic. The central corpectomy, while a good option for anterior decompression, requires complex reconstruction procedures. The oblique corpectomy preserves the ventral half of the vertebral body and does not require stabilization.

METHODS

In a series of 135 patients undergoing multilevel oblique corpectomy for cervical myelopathy, 3 had OPLL with massive OALL that was asymptomatic. The OPLL was removed using microdrills while preserving the OALL. Preoperative and postoperative MR imaging assessed cord compression and spinal alignment, whereas dynamic plain roentgenography assessed stability. Patients were assessed clinically for signs of dysphagia and dysphonia.

RESULTS

The cervical myelopathy improved in all 3 patients at a follow-up of 3 years, 1 year, and 6 months, respectively, with no development of dysphagia. One patient had a Horner's syndrome that improved by 6 months and another had a C5 radiculopathy that was improving by 6 months. Imaging showed good decompression of the spinal cord, with no kyphosis or instability.

CONCLUSION

The oblique corpectomy is a surgical option in patients with asymptomatic OALL in the setting of progressive myelopathy due to OPLL with intrinsic stability as a result of their OALL. This technique avoids a multilevel central corpectomy that is associated with significant instability often requiring reconstructive procedures.

How does the ossification area of the posterior longitudinal ligament thicken following cervical laminoplasty?

STUDY DESIGN

Retrospective case series.

OBJECTIVE

To investigate the progression of the thickness of the ossification area over time following cervical laminoplasty.

SUMMARY OF BACKGROUND DATA

Cervical laminoplasty has become the standard technique for the treatment of patients with myelopathy due to ossification of the posterior longitudinal ligament (OPLL). However, OPLL is a progressive disease, and an increase in the area of ossification following laminoplasty affects the surgical results. To date, complete analysis of the thickness of OPLL progression has not been undertaken because changes in the ossification thickness are minor compared with those of the longitudinal axis.

METHODS

Fifty-five patients who were available for serial radiographs more than 5 years after cervical laminoplasty were included. The extent of ossification thickness was assessed using lateral radiographs of the cervical spine and computer software. The neurologic evaluation was graded using the Japanese Orthopedic Association score (JOA score). The associations between the progression of OPLL and the clinical and radiologic data were analyzed. We also evaluated the progression of the thickness of the ossification area over time following surgery.

RESULTS

Twelve patients (21.8%) had progression in the OPLL thickness. Progression was marked in younger patients with the mixed or continuous types of OPLL. C3 involvement was also common in the patients with the OPLL progression. The progression of OPLL thickness was not directly related to the score-based recovery rate. The progression of OPLL was frequently observed at C2, C3, and C4 levels. Progression in OPLL thickness was detected in 42.1% of C2 ossifications, 13.3% of C3, 11.9% of C4, 4.1% of C5, 5.5% of C6, and 6.6% of C7.

CONCLUSION

Young patients with continuous or mixed-type OPLL and C3 involvement of ossification had a risk for progression in OPLL thickness following surgery. As the increased thickness of ossified lesions directly causes the narrowing of the spinal canal, it is important to pay attention to these risk factors and the increase in ossification before and after cervical laminoplasty in the surgical treatment of patients with OPLL.

Surgical strategy for cervical myelopathy due to ossification of the posterior longitudinal ligament: Part 2: Advantages of anterior decompression and fusion over laminoplasty

STUDY DESIGN

Retrospective study of 27 patients who underwent anterior decompression and fusion (ADF) for treatment of cervical myelopathy due to ossification of the posterior longitudinal ligament (OPLL).

OBJECTIVES

To compare surgical outcome of ADF with that of laminoplasty.

SUMMARY OF BACKGROUND DATA

During the period 1986 and 1996, laminoplasty was the only surgical treatment selected for cervical myelopathy at our institutions. According to surgical results of laminoplasty performed during this period, we have performed either laminoplasty or ADF for patients with OPLL since 1996.

METHODS

We reviewed clinical data obtained in 27 patients who underwent ADF between 1996 and 2003. Mean duration of follow-up was 6.0 years (range, 2-10 years). Surgical outcomes were assessed using the Japanese Orthopedic Association (JOA) scoring system for cervical myelopathy. Surgical results of ADF were compared with those of laminoplasty, which was performed in 66 patients during the period 1986 and 1996.

RESULTS

ADF yielded a better neurologic outcome at final follow-up than laminoplasty in patients with occupying ratio > or =60%, although graft complications occurred in 15% and additional surgical intervention was required in 26%. Neither occupying ratio of OPLL, sagittal shape of ossification, nor cervical alignment was found to be related to surgical outcome of ADF.

CONCLUSIONS

Although ADF is technically demanding and has a higher incidence of surgery-related complications, it is preferable to laminoplasty for patients with occupying ratio of OPLL > or =60%.

How does the ossification area of the posterior longitudinal ligament progress after cervical laminoplasty?

STUDY DESIGN

Retrospective case series.

OBJECTIVE

To investigate the progression pattern of ossification of the posterior longitudinal ligament (OPLL) after cervical laminoplasty.

SUMMARY OF BACKGROUND DATA

OPLL is a progressive disease, and an increased area of ossification affects the surgical results after laminoplasty. However, it is uncertain how the ossification area progresses with time after surgery.

METHODS

Fifty-five patients who were available for serial radiographs of more than 5 years were included. The extent of ossification in the longitudinal axis was assessed using computer software. The associations between the progression of OPLL and the clinical and radiologic data were analyzed.

RESULTS

Forty-one patients had OPLL progression. The patients were divided into three groups according to the pattern of progression. Group 1 consisted of patients 40 to 49 years of age with continuous or mixed type, showing slow progression at the beginning, then fast. Group 2 consisted of patients older than 50 years with continuous or mixed type, showing rapid progression at the beginning and then slow. The patients in Group 3 had segmental type with no or slight progression.

CONCLUSIONS

We speculated that the progression of OPLL decreases as the patient ages. These findings will be important for the management of patients with OPLL after surgery.

Repetitive tensile stress to rat caudal vertebrae inducing cartilage formation in the spinal ligaments: a possible role of mechanical stress in the development of ossification of the spinal ligaments

Object

Mechanical stress has been considered one of the important factors in ossification of the spinal ligaments. According to previous clinical and in vitro studies, the accumulation of tensile stress to these ligaments may be responsible for ligament ossification. To elucidate the relationship between such mechanical stress and the development of ossification of the spinal ligaments, the authors established an animal experimental model in which the in vivo response of the spinal ligaments to direct repetitive tensile loading could be observed.

Methods

The caudal vertebrae of adult Wistar rats were studied. After creating a novel stimulating apparatus, cyclic tensile force was loaded to rat caudal spinal ligaments at 10 N in 600 to 1800 cycles per day for up to 2 weeks. The morphological responses were then evaluated histologically and immunohistochemically.

After the loadings, ectopic cartilaginous formations surrounded by proliferating round cells were observed near the insertion of the spinal ligaments. Several areas of the cartilaginous tissue were accompanied by woven bone. Bone morphogenetic protein–2 expression was clearly observed in the cytoplasm of the proliferating round cells. The histological features of the rat spinal ligaments induced by the tensile loadings resembled those of spinal ligament ossification observed in humans.

Conclusions

The findings obtained in the present study strongly suggest that repetitive tensile stress to the spinal ligaments is one of the important causes of ligament ossification in the spine.

Postoperative Changes at the Lower End of Cervical Laminoplasty

INTRODUCTION

C3-C7 laminoplasty has been the standard treatment for cervical myelopathy, although several recent reports described C3-C6 laminoplasty for preserving the muscles inserting in C7 and reducing postoperative axial symptoms. However, postoperative changes at C6/C7 of the lower end of C3-C6 laminoplasty, especially regarding a possibility of postoperative spinal canal narrowing have not been measured. The purpose of this study was to clarify postoperative changes at the lower end of laminoplasty.

METHODS

Pre and postoperative spinal dura diameter at the lower end of conventional C3-C7 laminoplasty using MRI, and the related factors for spinal dura diameter and the causes of postoperative dura narrowing were investigated.

RESULTS

At the last follow-up after C3-C7 laminoplasty, dura diameter at C7/T1 was significantly wider after operation than before operation, and postoperative narrowing of dura diameter, which was found in 20% of patients, was a maximum amount of one millimeter. No pre and postoperative factor significantly correlated with dura diameter at C7/T1. The causes of postoperative narrowing at the lower end of laminoplasty were disc protrusion and/or posterior scar, or segmental angulation of the spinal cord.

CONCLUSION

In conclusion, the presence of preoperative subarachnoid space over one millimeter at C6/C7 may be able to be one of the radiological indications for C3-C6 laminoplasty.

Long-term results over 10 years of anterior corpectomy and fusion for multilevel cervical myelopathy

STUDY DESIGN

Retrospective long-term outcome analysis over more than 10 years.

OBJECTIVES

To assess the long-term results of anterior corpectomy and fibular strut grafting over > or =4 disc levels for cervical myelopathy, and identify factors affecting the late deterioration in clinical outcome.

SUMMARY OF BACKGROUND DATA

Few studies have shown long-term results after anterior corpectomy and strut grafting. There is little detailed information about the long-term effects of multilevel anterior corpectomy and fusion for cervical myelopathy.

METHODS

A total of 31 cases were available for the 10-year follow-up after surgery (86% follow-up rate). Clinical results and radiographic measurements were obtained before surgery, 3 months after surgery, and at follow-up.

RESULTS

There were 3 patients who had deterioration of the Japanese Orthopedic Association score of 1 point because of increasing hand numbness; 1 patient had adjacent disc degeneration, and 1 had pseudarthrosis without additional stenosis on magnetic resonance imaging. Adjacent disc degeneration did not affect the clinical results (P = 0.76).

CONCLUSIONS

The long-term follow-up showed stable clinical results for more than 10 years, which depended on the thorough removal of the possible causes of the myelopathy, such as ossification of the posterior longitudinal ligament or a degenerated disc. Adjacent disc degeneration has minimal effects on the long-term clinical results after anterior long fusion.

Ossification of the Posterior Longitudinal Ligament: An Update on Its Biology, Epidemiology, and Natural History

SIGNIFICANT PROGRESS HAS been achieved in basic research during the past decade on the pathogenesis of ossification of the posterior longitudinal ligament (OPLL), a multifactorial disease in which complex genetic and environmental factors interact. A review of the literature was conducted to update recent findings on the biology, epidemiology, natural history, and related diseases of OPLL. Gene analysis studies found specific polymorphisms that may be associated with OPLL in several collagen genes, which encode for extracellular matrix proteins. Polymorphisms in the nucleotide pyrophosphate gene, which is involved in regulation of calcification in chondrocytes, may also be associated with OPLL. However, the results of the gene analysis studies have not always been consistent. Involvement of many growth factors and cytokines, including bone morphogenic proteins and transforming growth factor-β, has been demonstrated in various histochemical and cytochemical analyses. Several transcription factors involved in cellular differentiation may also have a role. Recent epidemiological studies reaffirmed an earlier finding that diabetes mellitus is a distinct risk factor for OPLL. The long-term follow-up studies of OPLL patients are disclosing the natural history, as well as the frequency and rate of progression, of OPLL after surgical intervention. Further knowledge on the factors responsible for progression of OPLL may predict its behavior in each patient, and treatment may be tailored accordingly. The coexistence of OPLL with other diseases of ectopic ossification of the spine, such as ossification of the ligamentum flavum and diffuse idiopathic skeletal hyperostosis, is not uncommon. Scientific breakthrough in those diseases may, in turn, give insights into the pathogenesis of OPLL.

Clinical and prognostic analysis of ossified ligamentum flavum in a Chinese population

OBJECT

The authors performed a retrospective study of clinical and radiological data obtained in 27 Chinese patients with myelopathy induced by ossification of the ligamentum flavum (OLF) who underwent surgery between March 1990 and March 2002. The factors related to surgical outcome of thoracic OLF-induced myelopathy were also assessed.

METHODS

The preoperative clinical features and radiological findings were reviewed retrospectively. Preoperative and postoperative neurological status was assessed using the Japanese Orthopaedic Association (JOA) scoring system and the Nurick Scale. The ossified lesions were classified into five types (lateral, extended, enlarged, fused, and tuberous). Multiple linear regression and logistic regression analyses were performed to establish the factors affecting surgical outcome. The patients' chief complaints were lower-limb weakness and gait disturbance (93%), numbness and sensory deficit (89%), and low-back pain (48%). The coexisting pathological entities were disc herniation, canal stenosis, and ossification of posterior longitudinal ligament. The ossified ligamentum flavum was mainly located at the T10-12 (67%) and T1-3 (15%) levels. Symptoms in 26 patients improved but resolved completely in only 14 after surgery. The mean overall JOA score was 5.3 +/- 1.9 preoperatively and 7.9 +/- 2.3 postoperatively. There is a significant difference between the pre- and postoperative neurological status (p < 0.05) determined by the Student t-test. The recovery rate was 46.3 +/- 9.4%. Multiple regression analysis revealed negative correlation between the duration of preoperative symptoms and surgical outcome as well as a positive correlation between the preoperative JOA score and surgical outcome. Logistic regression analysis demonstrated that fecal and/or urinary incontinence, positive patellar and/or ankle clonus, and intramedullary high T2-weighted magnetic resonance (MR) imaging signal change had negative effects on the surgical outcome.

CONCLUSIONS

The clinical and radiological features of OLF in the Chinese population are similar to those observed in the Japanese population. The duration of preoperative symptoms and JOA score are the most important predictors of the postoperative JOA score and recovery rate. The patients with fecal and/or urinary incontinence, positive patellar and/or ankle clonus, and intramedullary high T2-weighted MR imaging signal change were at higher risk of poor outcome after surgery.

Spinal stenosis due to ossified lumbar lesions

OBJECT

Spinal stenosis due to lumbar ossified lesions is a rare pathological entity. The authors retrospectively evaluated the clinical features and surgical results associated with cases involving lumbar ossified lesion-induced stenosis.

METHODS

Data obtained in 20 surgically treated patients with lumbar hyperostotic spinal stenosis were included. To evaluate the background of the disease, body mass index and general complications were assessed. Whole-spine radiological examination was conducted. The presence of ossification of the posterior longitudinal ligament or ossification of the ligamentum flavum was evaluated. Surgical results were classified according to the Japanese Orthopaedic Association (JOA) scale. In the patients in whom neurological deterioration was observed during follow up, the causes of deterioration were reviewed. Seven patients (35%) were obese and six patients (30%) suffered diabetes mellitus. Twelve patients harbored coexisting cervical and/or thoracic ossified lesions. The overall mean JOA score improved from 10.2 to a peak of 22.5; at last follow-up examination the mean JOA score was 20.9. In female and older patients with a long history of preoperative symptoms, a low preoperative JOA score, and other spinal lesions, recovery tended to be poorer. Recovery was poor in one patient, and neurological deterioration due to coexisting ossified spinal lesions occurred in another patient during the follow-up period.

CONCLUSIONS

Because coexisting ossified lesions were frequently seen, whole-spine analysis is recommended. Early diagnosis and appropriate treatment are important to achieve a better surgical outcome.

Multicenter study investigating the postoperative progression of ossification of the posterior longitudinal ligament in the cervical spine: a new computer-assisted measurement

OBJECT

Ossification of the posterior longitudinal ligament (OPLL) often progresses after surgery, and this may cause late-onset neurological deterioration. There have been few studies, however, to clarify any correlation between progression and clinical outcome, partly because of the lack of studies involving reliable and reproducible methods by which detection of progression is made possible. The authors conducted a multicenter study to investigate the occurrence of postoperative progression and to elucidate the possible risk factors in a large-scale patient population, and a novel computer-assisted measurement method was used to provide the basis for future clinical studies.

METHODS

The authors analyzed lateral plain radiographs obtained immediately and at 1 and 2 years after surgery in 131 patients who underwent posterior decompression at 13 institutions. The x-ray films were transformed via scanner into digital images; the length and thickness of ossifications were measured using a new computer-assisted measurement system, and the incidence of progression was determined. Odds ratios for progression according to age group and types of OPLL were determined and compared to elucidate significant risk factors of progression.

CONCLUSIONS

This is the first multicenter study to investigate the incidence of OPLL progression after posterior decompression by using a standardized measurement method. The rate of postoperative progression at 2 years was 56.5%, which was comparable with results reported in other studies. Progression occurred more frequently in younger-age rather than in older-age patient populations at both 1 and 2 years postoperatively. Mixed-type and continuous-type OPLL progressed more frequently than the segmental-type lesion at 2 years. The results of the present study could serve as basis for future studies to assess the efficacy of drug therapy to prevent OPLL progression.

Computer-assisted measurement of the size of ossification in patients with ossification of the posterior longitudinal ligament in the cervical spine

BACKGROUND

Progression of ossification of the posterior longitudinal ligament in patients may lead to serious neurological deterioration. A government-funded study group established a manual method of measurement on plain radiographs to detect progression of the ossified lesion. However, this method did not gain wide acceptance because it was time-consuming and complicated, for which drawings of many lines and points are required. We have applied a computer-assisted measurement system to this task and have evaluated inter- and intraexaminer reliability, showing that it is quicker to use and more accurate than the manual method.

METHODS

Eight board-certified spine surgeons, acting as the examiners, measured the sizes of the ossified lesions on nine lateral cervical spine radiographs using the computer-assisted measurement system. Following insertion of digitized radiographic image data into a computer, the corners of the vertebral bodies on the displayed images are marked by the examiners, and the software automatically sets reference lines and points. The examiners identify upper, lower, and posterior margins of the ossified lesions, and the software calculates the dimensions of the ossified lesions. Data obtained from eight examiners for length and thickness underwent rigorous statistical analysis by calculating the intraclass correlation coefficients with 95% confidence intervals (CIs) to determine interexaminer reliability and Pearson's correlation coefficients between the two measurements by the same examiner to determine intraexaminer reliability.

RESULTS

The intraclass correlation coefficients were 0.927 and 0.968 with 95% CIs of 0.883-0.955 and 0.956-0.978 for measurements of length and thickness, respectively, of the ossified lesions. The Pearson's correlation coefficients for the two measurements by the same examiners were 0.943-0.985 for length and 0.957-0.991 for thickness.

CONCLUSIONS

The inter- and intraexaminer reliability using this measurement system was excellent. The method can detect progression of ossification of the posterior longitudinal ligament (OPLL) on plain radiographs with high precision and could become a standard method for measuring the size of OPLL.

Anterior corpectomy and fusion with fibular strut grafts for multilevel cervical myelopathy

OBJECT

The authors conducted a study to investigate the long-term results and postoperative complications of a new surgical technique, fibular strut graft-assisted anterior corpectomy and fusion for multilevel (> four) cervical myelopathy. Multilevel anterior corpectomy and subsequent strut graft placement is considered a challenging procedure because of complications relating to graft dislodgment, pseudarthrosis, greater operative duration, and increased blood loss.

METHODS

The study comprised 100 patients with cervical myelopathy who underwent anterior corpectomy and fusion and fibular strut graft placement at more than four disc space levels between 1989 and 1998. Single-screw fixation was used in conjunction with the autologous strut graft. Preoperative and postoperative plain radiographs, computerized tomography myelograms, and magnetic resonance images were obtained for assessment of fusion status. All complications and outcomes were analyzed based on clinical records to evaluate the results of the technique. There were no cases of graft dislodgment. The graft union rate was 85%. Analysis of clinical data showed that pseudarthrosis had no adverse effect on the clinical results. Adjacent-level disc degeneration occurred in 12% of patients, but in all cases the patients were asymptomatic. In 9% of cases C-5 palsy was observed but it recovered spontaneously. There were no infections and no case of neurological deterioration.

CONCLUSIONS

With this new graft technique, graft dislodgment, the major complication associated with strut graft surgery, was resolved completely. This simple technique involving single-screw fixation provided good results when used in conjunction with anterior decompression and strut graft fixation with a very low incidence of complications.

Factors related to long-term outcome after decompressive surgery for ossification of the ligamentum flavum of the thoracic spine

OBJECT

Factors related to long-term surgical outcome of thoracic myelopathy caused by ossification of the ligamentum flavum (OLF) have not been fully investigated. To evaluate these factors, the authors reviewed medical records obtained in patients who had undergone decompressive surgery for thoracic OLF.

METHODS

Thirty-four patients in whom decompressive surgery was performed for thoracic OLF (mean follow-up period 8 years) were recruited. Fourteen patients underwent simultaneous decompressive surgery for cervical or lumbar lesions. Patient age, duration of symptoms, OLF type, dural adhesion, neurological status classified by the Japanese Orthopaedic Association (JOA) scale before and after surgery (1 month postoperatively and at final follow up), and recovery rate were reviewed. The ossified ligamentum flavum was classified into five types according to Sato's classification by assessing preoperative computerized tomography scans. The mean preoperative JOA score (5) was significantly improved at 1 month after surgery (7.1) and at final follow up (7.9) (p < 0.05). Recovery rates at 1 month and at final follow up were 34.6 and 44.2%, respectively. No significant correlations were found between age, OLF type, and neurological status before and after surgery. In patients with dural adhesion, which was observed in cases of larger-type OLF (p < 0.02), lower JOA scores were observed compared with those in patients without dural adhesion both preoperatively and at 1 month after surgery (p < 0.05) but not at the final follow-up examination. Higher JOA scores and recovery rates were demonstrated in patients who had undergone simultaneous surgery than in those who had not undergone simultaneous surgery at 1 month (p < 0.05) but not at the final follow up. Using multiple regression analysis, the authors identified the duration of preoperative symptoms as the most important predictor of a high JOA score and recovery rate at the final follow up.

CONCLUSIONS

Duration of preoperative symptoms represents the most important predictor of long-term surgery-related outcome in patients treated for thoracic OLF. The type of ossified ligamentum flavum, dural adhesion, and simultaneous surgery for coexistent cervical or lumbar lesions do not appear to influence the long-term postoperative prognosis.

Minimum 10-year followup after en bloc cervical laminoplasty

The long-term outcome (> 10 years) after cervical laminoplasty was assessed and the postoperative problems were clarified. One hundred thirty-three patients had laminoplasty between 1981 and 1989 for treatment of cervical myelopathy and 126 patients were available for the current study. The clinical results were evaluated using the Japanese Orthopaedic Association score. The radiologic findings were analyzed by postural anomalies and range of motion. The average preoperative score was 9.1 points, and the postoperative score improved to 13.7 points within a year. The Japanese Orthopaedic Association score and recovery rate were maintained at 13.4 points and 55.1% at the last followup. In 20 patients, the Japanese Orthopaedic Association score worsened during the followup. The causes of deterioration were axial spread of ossification of the posterior longitudinal ligament, other spinal lesions, cerebral infarction, and peripheral neuropathy. Postoperative cervical radiculopathy occurred in nine patients. Postoperative radiculopathy resolved in five patients, but remained in four patients. Kyphotic changes were observed in eight patients. The recovery rate in patients with kyphosis was poor. The postoperative range of motion decreased to 25.1% of preoperative range of motion. Sixty one percent of patients had a reduction of range of motion. Satisfactory results of cervical laminoplasty were maintained for more than 10 years after surgery; however, there were several postoperative problems, such as neurologic deterioration, postoperative radiculopathy, progression of kyphosis, and range of motion limitation.

Cervical laminoplasty: a critical review

OBJECT

The technique of cervical laminoplasty was developed to decompress the spinal canal in patients with multi-level anterior compression caused by ossification of the posterior longitudinal ligament or cervical spondylosis. There is a paucity of data confirming its superiority to laminectomy with regard to neurological outcome, preserving spinal stability, preventing postlaminectomy kyphosis, and the development of the "postlaminectomy membrane."

METHODS

The authors conducted a metaanalysis of the English-language laminoplasty literature, assessing neurological outcome, change in range of motion (ROM), development of spinal deformity, and complications. Seventy-one series were reviewed, comprising more than 2000 patients. All studies were retrospective, uncontrolled, nonrandomized case series. Forty-one series provided postoperative recovery rate data in which the Japanese Orthopaedic Association Scale was used for assessing myelopathy. The mean recovery rate was 55% (range 20-80%). The authors of 23 papers provided data on the percentage of patients improving (mean approximately 80%). There was no difference in neurological outcome based on the different laminoplasty techniques or when laminoplasty was compared with laminectomy. There was postlaminoplasty worsening of cervical alignment in approximately 35% and with development of postoperative kyphosis in approximately 10% of patients who underwent long-term follow-up review. Cervical ROM decreased substantially after laminoplasty (mean decrease 50%, range 17-80%). The authors of studies with long-term follow up found that there was progressive loss of cervical ROM, and final ROM similar to that seen in patients who had undergone laminectomy and fusion. In their review of the laminectomy literature the authors could not confirm the occurrence of postlaminectomy membrane causing clinically significant deterioration of neurological function. Postoperative complications differed substantially among series. In only seven articles did the writers quantify the rates of postoperative axial neck pain, noting an incidence between 6 and 60%. In approximately 8% of patients, C-5 nerve root dysfunction developed based on the 12 articles in which this complication was reported.

CONCLUSIONS

The literature has yet to support the purported benefits of laminoplasty. Neurological outcome and change in spinal alignment are similar after laminectomy and laminoplasty. Patients treated with laminoplasty develop progressive limitation of cervical ROM similar to that seen after laminectomy and fusion.