Prevalence and symptom of ossification of posterior longitudinal ligaments in the Japanese general population

Background

Ossification of the posterior longitudinal ligaments (OPLL) causes myelopathy with progression or trauma. Most OPLL patients visit the hospital after severe symptoms occur, and surgery did not supply complete relief in severe symptoms related to OPLL. While it is necessary to diagnose OPLL early and observe carefully, the nature of symptoms and asymptomatic OPLL have been unclear. The purposes of this study were to investigate the prevalence and symptoms of ossification of the posterior longitudinal ligaments (OPLL) of the cervical spine in the general population.

Methods

The subjects were 1291 Japanese general residents. Radiographic OPLL was detected by lateral view of the cervical spine, and subjects were classified into OPLL and non-OPLL groups. Visual analog scales of neck stiffness, neck pain, arm pain, and the Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire were examined. Neck and arm symptoms were compared among the presence of OPLL, and among subtypes (continuous, segmental, and mixed types) statistically.

Results

Prevalence of OPLL was 3.7 % in overall participants, 3.9 % in symptomatic participants, and 2.2 % in asymptomatic participants. While 86.7 % of participants with OPLL had symptoms, the consultation rate was only 6.7 %. The female OPLL group had higher neck pain than the non-OPLL group, and neck function of JOACMEQ in the continuous type of OPLL was significantly restricted compared to those without OPLL and with the mixed type of OPLL.

Conclusions

Prevalence of OPLL was 3.7 %, and most of them had neck and arm symptoms; however, they did not visit hospitals. Asymptomatic OPLL had the potential risk for spinal cord injury and myelopathy. Early detection and careful observation would prevent the severe symptoms induced by OPLL.     

Impact of preoperative cervical sagittal alignment for cervical myelopathy caused by ossification of the posterior longitudinal ligament on surgical treatment

BackgroundSurgical procedures for cervical myelopathy caused by ossification of the posterior longitudinal ligament (OPLL) are often chosen based on OPLL size and cervical spine alignment. Recently, cervical sagittal alignment based on sagittal vertical axis (SVA) has received increased attention as an important determinant of radiological and clinical outcomes after surgery. This study aimed to investigate the impact of SVA-based cervical sagittal alignment on surgical treatment for cervical OPLL by reviewing a previous retrospective cohort in which its concept was not taken into account in the surgical procedure choices.MethodsWe reviewed a total of 96 consecutive patients who underwent surgery for cervical myelopathy caused by OPLL from 2008 to 2014. We performed anterior decompression with fusion (ADF) or posterior decompression with fusion (PDF) on patients with massive OPLL or kyphotic alignment, and we performed laminoplasty (LAMP) on patients without massive OPLL or kyphotic alignment. CSVA (center of gravity of the head - C7 SVA), CL (C2-7 lordotic angle) and C7 slope were measured in cervical X-ray at standing position. Clinical results were evaluated using C-JOA score. We divided patients into two subgroups based on the preoperative CSVA: the Low-CSVA (CSVA <40 mm) and High-CSVA (CSVA ≥40 mm) subgroups.ResultsIn the Low-CSVA subgroup, none of the three operations had an effect on the CL. In contrast, in the High-CSVA subgroup, while ADF and PDF had no effect on the CL, LAMP worsened the CL postoperatively. The recovery rates of the C-JOA scores in the Low-CSVA subgroup showed no significant differences among the three operations; however in the High-CSVA subgroup, LAMP resulted in worse recovery rate of the C-JOA score than ADF or PDF.ConclusionsLAMP is not suitable for patients with cervical myelopathy caused by OPLL who have high CSVA alignment, even in cases without massive OPLL or kyphotic alignment.     

Spinal cord cross-sectional area during flexion and extension in the patients with cervical ossification of posterior longitudinal ligament

Purpose

The pathomechanism of cervical myelopathy due to cervical ossification of posterior longitudinal ligament (C-OPLL) remains unclear. No previous literature has quantified the influence of dynamic factors on cervical myelopathy due to C-OPLL. The purpose was to investigate the influence of dynamic factors on the spinal column in the patients with C-OPLL using CT scan after myelography (MCT).

Methods

The study included 41 patients with cervical myelopathy due to C-OPLL. An MCT was done during neck flexion and extension, and spinal cord cross-sectional areas (SCCSA) were measured at each disc level between C2/3 and C7/T1. Ossification morphology at each segment was divided into three groups, connection department, coating part, and non-connection department of OPLL group. Dynamic changes of SCCSA in each group of ossification morphology were calculated. The relationship between clinical results and SCCSA at the narrowest level was investigated.

Results

MCT showed SCCSA changes during neck extension; 7.4 ± 5.1 mm² in the connection department, 5.8 ± 6.0 mm² in the coating part, and 6.7 ± 6.4 mm² in the non-connection department of OPLL group. There difference was not statistically significant. There was a weak correlation between the JOA score and SCCSA at the narrowest level (R = 0.49). There was no significant correlation between the recovery rate of JOA score and SCCSA at the narrowest level (R = 0.37).

Conclusion

Dynamic factors are seen both in cervical myelopathy patients with the continuous type of OPLL and others. Deterioration of myelopathy could be induced by motion effects even in the connection department of OPLL.     

Anterior corpectomy versus posterior laminoplasty for multilevel cervical myelopathy: a systematic review and meta-analysis

Background

Surgical strategy for multilevel cervical myelopathy resulting from cervical spondylotic myelopathy (CSM) or ossification of posterior longitudinal ligament (OPLL) still remains controversial. There are still questions about the relative benefit and safety of direct decompression by anterior corpectomy (CORP) versus indirect decompression by posterior laminoplasty (LAMP).

Objective

To perform a systematic review and meta-analysis evaluating the results of anterior CORP compared with posterior LAMP for patients with multilevel cervical myelopathy.

Methods

Systematic review and meta-analysis of cohort studies comparing anterior CORP with posterior LAMP for the treatment of multilevel cervical myelopathy due to CSM or OPLL from 1990 to December 2012. An extensive search of literature was performed in Pubmed, Embase, and the Cochrane library. The quality of the studies was assessed according to GRADE. The following outcome measures were extracted: pre- and postoperative Japanese orthopedic association (JOA) score, neurological recovery rate (RR), surgical complications, reoperation rate, operation time and blood loss. Two reviewers independently assessed each study for quality and extracted data. Subgroup analysis was conducted according to the mean number of surgical segments.

Results

A total of 12 studies were included in this review, all of which were prospective or retrospective cohort studies with relatively low quality. The results indicated that the mean JOA score system for cervical myelopathy and the neurological RR in the CORP group were superior to those in the LAMP group when the mean surgical segments were <3, but were similar between the two groups in the case of the mean surgical segments equal to 3 or more. There was no statistical difference in the surgical complication rate between the two groups when the mean surgical segments <3, but were significantly higher incidences of surgical complications and complication-related reoperation in the CORP group compared with the LAMP group in the case of the mean surgical segments equal to 3 or more. Besides, the operation time in the CORP group was longer than that in the LAMP group, and the average blood loss was significantly more in the CORP group compared with the LAMP group.

Conclusion

Based on the results above, anterior CORP and fusion is recommended for the treatment of multilevel cervical myelopathy when the involved surgical segments were <3. Given the higher rates of surgical complications and complication-related reoperation and the higher surgical trauma associated with multilevel CORP, however, it is suggested that posterior LAMP may be the preferred method of treatment for multilevel cervical myelopathy when the involved surgical segments were equal to 3 or more. In addition, taking the limitations of this study into consideration, it was still not appropriate to draw a strong conclusion claiming superiority for CORP or LAMP. A well-designed, prospective, randomized controlled trial is necessary to provide objective data on the clinical results of both procedures.     

A novel anterior decompression technique (vertebral body sliding osteotomy) for ossification of posterior longitudinal ligament of the cervical spine

Background Context

Conventional anterior decompression surgery for cervical myelopathy, including anterior corpectomy and fusion, is technically demanding and is known to be associated with a higher incidence of surgery-related complications, including cerebrospinal fluid (CSF) leakage, neurologic deterioration, and graft failure compared with posterior surgery.

Isolated posterior instrumentation for selected cases of thoraco-lumbar spinal tuberculosis without anterior instrumentation and without anterior or posterior bone grafting

Purpose

The aim of this prospective study is the analysis of the clinical and radiological outcomes of active thoraco-lumbar spinal tuberculosis treated with isolated posterior instrumentation without any posterior bone grafting or anterior inter-body bone grafting or anterior instrumentation.

Methods

The study was a prospective follow-up of 25 patients with active thoraco-lumbar spinal tuberculosis who underwent posterior spinal instrumentation with pedicle screws and rods. These patients had posterior stabilization of the involved segment of the spine without anterior or posterior bone grafting. The mean duration of follow-up was 3.3 years and the minimum duration of follow-up was 2 years.

Results

The mean kyphotic angle improved from 32.4° pre-operatively to 7.2° in the early follow-up period. Following a minor loss of correction during follow-up, the mean kyphotic angle settled at 11.5° at the time of final follow-up. Inter-body bony fusion was noticed at the final follow-up in all patients despite the absence of anterior bone grafting or cages.

Conclusion

Posterior instrumented stabilization followed by chemotherapy seems to be adequate for obtaining satisfactory healing of the lesions. Anterior inter-body bony arthrodesis occurs despite the absence of anterior bone grafts or cages. Careful patient selection is critical for successful outcome with this technique.     

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.     

Association of VKORC1-1639G>A polymorphism with susceptibility to ossification of the posterior longitudinal ligament of the spine: a Korean study

Background

Abnormalities of bone metabolism may be involved in the pathogenesis of ossification of the posterior longitudinal ligament (OPLL) of the spine. Besides its hemostatic effect, vitamin K epoxide reductase complex subunit 1 (VKORC1) plays a pivotal role in bone mineralization. The aim of this study is to investigate whether single nucleotide polymorphisms (SNPs) of the VKORC1 gene are associated with the occurrence of OPLL in a Korean population.

Method

A total of 98 patients with OPLL and 200 controls were genotyped for the VKORC1-1639G>A SNP (rs9923231) by polymerase chain reaction and restriction fragment length polymorphism analysis. All the patients (n?=?98) in this study underwent surgery (60, posterior-only approach; 36, anterior-only approach; 2, combined anterior and posterior approach) during their admission. We analyzed this association separately according to the gender and OPLL subgroup: OPLL continuous group (continuous type plus mixed type) and OPLL segmental group (segmental and localized type).

Results

We found that the genotype VKORC1-1639G>A frequency was significantly associated with the occurrence of the OPLL in the female group (adjusted odds ratio?=?5.22, 95 % confidence interval: 1.675 to 16.269, p?=?0.004). However, there was no overall association between the OPLL susceptibility and VKORC1-1639G>A polymorphism. A subgroup analysis did not show any significant correlation between VKORC1-1639G>A polymorphism and subgroup of OPLL either.

Conclusion

Our results suggest that the VKORC1-1639G>A SNP may increase susceptibility to OPLL in women. However, there was only a statistical association in the female group despite a number of stratified analyses. Therefore, the findings should be interpreted with caution, and further genetic study is needed to improve our understanding of the role of VKORC1 polymorphisms in determining the risk of OPLL occurrence.     

Osteoporotic thoracolumbar junctional fracture accompanied by spinous process fracture without posterior ligament injury: its clinical and radiologic significances

Purpose

To assess the clinical and radiologic outcome of osteoporotic thoracolumbar junctional fracture accompanied by spinous process fracture (SPF) without posterior ligament injury.

Methods

A total of 391 patients with single-level osteoporotic thoracolumbar junctional (T10-L2) fracture were selectively enrolled. The patients were divided into two groups by absence (group I) or presence (group II) of SPF. Clinical and radiologic parameters were compared between the two groups.

Results

Group I comprised of 332 patients with only vertebral body fracture, and group II comprised of 59 patients with both vertebral body and SPFs. In all cases of group II, SPFs were located just one level above the fractured vertebral body, and the injury of the posterior ligament was not found. At the time of injury, group II patients showed worse outcomes in anterior vertebral body compression percentage, kyphotic Cobb angle, cranial disk status, and the rate of the initial neurologic injury. Kyphotic alignment changes during 1-year follow-up were compared between the conservative subgroups of groups I and II. At the time of injury, there were no statistical differences in anterior vertebral body compression percentage and Cobb angle between the two conservative subgroups. However, the difference was significant after 1-year follow-up. Comparison of kyphotic alignment change at 12 months after diagnosis within group II was done according to the treatment method. Vertebroplasty subgroup in group II did not show benefit even in preventing such kyphotic alignment change, whereas instrumentation subgroup in group II showed lordotic alignment restoration despite more severe kyphotic alignment at the time of injury.

Conclusions

Osteoporotic thoracolumbar junctional fracture accompanied by spinous process fracture without posterior ligament injury represented more severe injury with flexion forces on the anterior column and tensile forces on the posterior column, and was related with more severe posttraumatic kyphotic changes during the 12-month follow-up.

     

Radiological risk factors for progression of ossification of posterior longitudinal ligament following laminoplasty

Background Context

Research shows the progression of ossification of the posterior longitudinal ligament (OPLL) following decompressive surgery for cervical myelopathy, particularly in cases presenting with continuous or mixed radiographic types. To date, no study has investigated OPLL progression within each motion segment.

Cervical curvature, spinal cord MRIT2 signal, and occupying ratio impact surgical approach selection in patients with ossification of the posterior longitudinal ligament

Objective

Factors impacting surgical options and outcomes in patients with cervical ossification of the posterior longitudinal ligament (OPLL) were explored.

Methods

A retrospective analysis was conducted of 127 eligible cervical OPLL patients (61 males, 66 females) aged 41–70 years (mean 55.2 years) selected from 152 total OPLL patients treated from 2002 to 2006, with 5–10-year (mean 6.8 years) follow-up. Patients underwent anterior subtotal corpectomy with ossification ligament resection (anterior surgery, n = 68) or posterior cervical double-door laminoplasty (posterior surgery, n = 59). Radiographic assessments of cervical curvature, T2-weighted MRI (MRIT2) signal, and OPLL occupying ratio were correlated with surgical strategy before surgery and at 1, 5 weeks, and 5 years.

Results

Lordosis increased following anterior surgery, though kyphosis improved by 10.3 %. The canal stenosis occupying ratio was >50 %, and short-term improvement following anterior surgery was significantly higher than posterior surgery (P > 0.0001). Superior neurological function was observed in patients with unchanged versus high spinal MRIT2 signals (P = 0.0434). No significant differences were observed in short-term outcomes between anterior and posterior surgeries in high spinal MRIT2 signal patients, but anterior surgery produced significantly better long-term outcomes at 1 week (P = 0.7564) and 1 year (P = 0.0071). Complications occurred in five anterior and three posterior surgeries.

Conclusion

Preoperative assessment of cervical curvature, MRIT2 signal, and occupying ratio can be used to guide clinical surgical approach selection to potentially produce better long-term outcomes in patients with OPLL.     

New classification system for ossification of the posterior longitudinal ligament using CT images

Background

Ossification of the posterior longitudinal ligament (OPLL) is most frequently seen in the cervical spine. The types of cervical OPLL are classified into continuous, mixed, segmental, and other based on plain lateral X-ray. Computed tomography (CT) imaging is often used in clinical practice for evaluating ossified lesions as it can detect their precise location, size, and shape. However, to date, no CT classification of OPLL lesions has been proposed.

Methods

One hundred and forty-four patients diagnosed with cervical OPLL by plain radiograph were included in this study. Sagittal and axial CT images of the cervical spine were obtained. We propose three classification systems: A, B, and axial. Classification A comprises two lesion types: bridge and nonbridge. Classification B requires examiners to describe all vertebral and intervertebral levels where OPLL exits in the cervical spine. Axial classification comprises central and lateral lesions identified on axial CT images. Seven observers evaluated CT images using this classification system, and intra- and interrater reliability were examined.

Results

Averaged Fleiss’ kappa coefficient of interrater agreement was 0.43 ± 0.26 among the seven observers, averaged intrarater reliability for the existence of OPLL was 72.4 ± 8.8 % [95 % confidence interval (CI) 67.5–76.8]. Fifty-four patients (37.5 %) had the bridge type and 90 the nonbridge type according to Classification A; 102 (70.8 %) had central and 42 (29.2 %) lateral OPLL in the axial classification. Four representative cases defined according to the three classification types are reported here.

Conclusion

Subcommittee members of the Investigation Committee on the Ossification of the Spinal Ligaments of the Japanese Ministry of Public Health and Welfare propose three new classification systems of cervical OPLL based on CT imaging: A, B, and axial.     

Prevalence and progression of radiographic ossification of the posterior longitudinal ligament and associated factors in the Japanese population: a 3-year follow-up of the ROAD study

Summary

The prevalence of radiographic cervical ossification of the posterior longitudinal ligament (OPLL) in 1,562 Japanese from a population-based cohort was 1.9 %. The presence of OPLL showed a significant association with the femoral neck bone mineral density (BMD), presence of diffuse idiopathic skeletal hyperostosis (DISH) and plasma pentosidine levels. Only one new case of radiographic OPLL was detected, but OPLL progressed in all affected subjects.

Introduction

The purpose of this study was to clarify the prevalence and progression of radiographic OPLL and the associated factors, using the population-based cohort Research on Osteoarthritis/osteoporosis Against Disability (ROAD).

Methods

In the ROAD study, 1,690 participants underwent X-ray examination of the entire spine and both knees. Radiographic OPLL, lumbar spondylosis, knee osteoarthritis and DISH were diagnosed by a single, well-experienced orthopaedic surgeon. An interviewer-administered questionnaire and tests for anthropometric measurements were administered, and the BMDs of the lumbar spine and proximal femur were determined. A new OPLL case was considered if heterotopic ossification in the posterior longitudinal ligament was absent at baseline but present during follow-up. Progression was defined as an increase in the maximum length or width of the ossification at follow-up over that at baseline.

Results

Radiographic OPLL was detected in 30 (17 men, 13 women) of 1,562 individuals who underwent X-ray examination of the cervical spine (prevalence?=?1.9 %). Its prevalence was significantly higher in men than in women (p?=?0.007), but no association with age was observed. In a logistic regression analysis, OPLL showed a significant association with the femoral neck BMD, presence of DISH and plasma pentosidine levels. Only one new case of radiographic OPLL was detected, but OPLL progressed in all affected subjects.

Conclusion

This population-based study clarified the prevalence of radiographic OPLL in the Japanese population as well as its progression. OPLL showed significant association with plasma pentosidine levels, BMD and DISH.     

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 mm³ at the first examination and 1,928.31 mm³ 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.     

Neurological manifestations of thoracic myelopathy

Introduction

Investigation of preoperative manifestations of thoracic myelopathy in a large population has not been reported. The aim of this study was to identify symptoms specific to anatomical pathology or compressed segments in thoracic myelopathy through investigation of preoperative manifestations.

Materials and methods

Subjects were 205 patients [143 men, 62 women; mean age, 62.2 (range 21–87 years)] with thoracic myelopathy who underwent surgery at our affiliate institutions from 2000 to 2011. The disease distribution included ossification of the ligamentum flavum (OLF) in 106 patients, ossification of the posterior longitudinal ligament (OPLL) in 17, OLF with OPLL in 17, intervertebral disc herniation (IDH) in 23, OLF with IDH in 3, and spondylosis in 39. We assessed (1) initial and preoperative complaints, (2) neurological findings, (3) Japanese Orthopaedic Association scores (JOA, full score, 11 points), (4) the compressed segments, and (5) preoperative duration. Multivariate analyses were performed to examine potential relationships between preoperative manifestations and anatomical pathology or compressed segments.

Results

The multivariate analyses revealed relationships between lower limb muscle weakness and T10/11 anterior compression; lower limb pain and T11/12 anterior compression; low back pain and T11/12 compression; and hyporeflexia in the patellar tendon reflex/foot drop and T12/L1 anterior compression.

Conclusion

This study elucidated symptoms specific to anatomical pathology or compressed segments in thoracic myelopathy. These relationships can be helpful in the initial investigation of thoracic diseases, although additional measures such as MRI or CT are necessary for definitive diagnosis.     

Anterior versus posterior approach in surgical treatment of tuberculous spondylodiscitis of thoracic and lumbar spine

Purpose

The aim of this study is to compare the clinical, radiological and functional outcome of anterior versus posterior surgical debridement and fixation in patients with thoracic and lumbar tuberculous spondylodiscitis.

Patients and methods

A total number of 42 patients with tuberculous spondylodiscitis of the thoracic and lumbar spine treated surgically were included in this study. Twenty patients (group A) underwent anterior debridement, decompression and instrumentation by anterior approach. Twenty-two patients (group B) were operated by posterolateral (extracavitary) decompression and posterior instrumentation. Operative parameters, clinical, radiographic and functional results for the two groups were analyzed and compared.

Results

The average follow-up period was 15 months (range 12–24) in both groups. The average operative time, blood loss and blood transfusion of anterior group were significantly less than the posterior one. There was significant better back pain relief, kyphotic angle correction and less angle loss in the posterior group than anterior. There was no significant difference between the two groups regarding neurological recovery, functional outcome and fusion rate.

Conclusion

Both anterolateral and posterolateral approaches are sufficient for achieving the goals of surgical treatment of thoracic and lumbar Pott’s disease but posterolateral approach allows significant better kyphotic angle correction, less angle loss, better improvement in back pain but unfortunately more operative time and blood loss.

     

Biomechanical study of the spinal cord in thoracic ossification of the posterior longitudinal ligament

Background

Ossification of the posterior longitudinal ligament (OPLL) in the thoracic spine produces myelopathy. This is often progressive and is not affected by conservative treatment. Therefore, decompressive surgery is usually chosen.

Objective

To conduct a stress analysis of the thoracic OPLL.

Methods

The three-dimensional finite element spinal cord model was established. We used local ossification angle (LOA) for the degree of compression of spinal cord. LOA was the medial angle at the intersection between a line from the superior posterior margin at the cranial vertebral body of maximum OPLL to the top of OPLL with beak type, and a line from the lower posterior margin at the caudal vertebral body of the maximum OPLL to the top of OPLL with beak type. LOA 20°, LOA 25°, and LOA 30° compression was applied to the spinal cord in a preoperative model, the posterior decompressive model, and a model for the development of kyphosis.

Results

In a preoperative model, at more than LOA 20° compression, high stress distributions in the spinal cord were observed. In a posterior decompressive model, the stresses were lower than in the preoperative model. In the model for development of kyphosis, high-stress distributions were observed in the spinal cord at more than LOA 20° compression.

Conclusions

Posterior decompression was an effective operative method. However, when the preoperative LOA is more than 20°, it is very likely that symptoms will worsen. If operation is performed at greater than LOA 20°, then correction of kyphosis by fixation of instruments or by forward decompression should be considered.