Shunji Matsunaga

Strain on intervertebral discs after anterior cervical decompression and fusion.

STUDY DESIGN An analysis of the change in strain distribution of intervertebral discs present after anterior cervical decompression and fusion by an original method. The analytical results were compared to occurrence of herniation of the intervertebral disc on magnetic resonance imaging. OBJECTIVES To elucidate the influence of anterior cervical decompression and fusion on the unfused segments of the spine. SUMMARY OF BACKGROUND DATA There is no consensus regarding the exact significance of the biomechanical change in the unfused segment present after surgery. METHODS Ninety-six patients subjected to anterior cervical decompression and fusion for herniation of intervertebral discs were examined. Shear strain and longitudinal strain of intervertebral discs were analyzed on pre- and postoperative lateral dynamic routine radiography of the cervical spine. Thirty of the 96 patients were examined by magnetic resonance imaging before and after surgery, and the relation between alteration in strains and postsurgical occurrence of disc herniation was examined. RESULTS In the cases of double- or triple-level fusion, shear strain of adjacent segments had increased 20% on average 1 year after surgery. Thirteen intervertebral discs that had an abnormally high degree of strain showed an increase in longitudinal strain after surgery. Eleven (85%) of the 13 discs that showed an abnormal increase in longitudinal strain had herniation in the same intervertebral discs with compression of the spinal cord during the follow-up period. Relief of symptoms was significantly poor in the patients with recent herniation. CONCLUSIONS Close attention should be paid to long-term biomechanical changes in the unfused segment.

Natural History of Degenerative Spondylolisthesis: Pathogenesis and Natural Course of the Slippage

To clarify the natural course of degenerative spondylolisthesis, the mechanism and progression of disk slippage were studied clinically and radiographically in 40 patients. Progressive slippage was observed in 12 patients (30%). No progression of slippage was noted in patients who showed narrowing of the interyertebral disk, spur formation, subcartilaginous sclerosis, or ossification of ligaments. These suggest that the mechanisms of spinal restabilization prevent progression of the disease. General joint laxity was observed in many patients (65%), and this was believed to be involved in the pathogenic mechanism of this disease. There was no correlation between the clinical symptoms and progression of slippage. These findings suggest that careful consideration of the natural mechanisms of spinal restabilization as well as the natural course of the disease is important.

Genetic mapping of ossification of the posterior longitudinal ligament of the spine.

Ossification of the posterior longitudinal ligament of the spine (OPLL) is recognized as a common disorder among Japanese and throughout Asia. Estimates of its prevalence are in the range of 1. 9%-4.3%. Although its etiology is thought to involve a multiplicity of factors, epidemiological and family studies strongly implicate genetic susceptibility in the pathogenesis of OPLL. In this study we report an identification of a predisposing locus for OPLL, on chromosome 6p, close to the HLA complex. The evidence for this localization is provided by a genetic-linkage study of 91 affected sib pairs from 53 Japanese families. In this sib-pair study, D6S276, a marker lying close to the HLA complex, gives evidence for strongly significant linkage (P = .000006) to the OPLL locus. A candidate gene in the region, that for collagen 11A2, was analyzed for the presence of molecular variants in affected probands. Of 19 distinct variants identified, 4 showed strong statistical associations with OPLL (highest P = .0004). These observations of linkage and association, taken together, show that a genetic locus for OPLL lies close to the HLA region, on chromosome 6p.

Genetic study of ossification of the posterior longitudinal ligament in the cervical spine with human leukocyte antigen haplotype.

To evaluate the genetic background of ossification of the posterior longitudinal ligament, the relationship between the presence or absence of ossification and human leukocyte antigen haplotypes was studied in 33 families of patients with ossification of the posterior longitudinal ligament. The study revealed that human leukocyte antigen haplotypes formed certain types of clusters, and that some human leukocyte antigen haplotypes were very rare in the Japanese population, suggesting the involvement of human leukocyte antigen-linked factors in the pathogenesis of ossification of the posterior longitudinal ligament of the cervical spine. In the families of these patients, ossification of the posterior longitudinal ligament was demonstrated by radiography in 56% (10/18) of the siblings. Each of these siblings shared both human leukocyte antigen haplotypes with the patient. None of those who shared only one human leukocyte antigen haplotype with the patient had developed ossification of the posterior longitudinal ligament. From these findings, the presence of both pathogenic human leukocyte antigen haplotypes is considered to be necessary for the development of ossification of the posterior longitudinal ligament, and this genetic predisposition may be activated by multiple factors, including regressive degeneration due to aging and the environment.

Analysis of the cervical spine alignment following laminoplasty and laminectomy

Very little detailed biomechanical examination of the alignment of the cervical spine following laminoplasty has been reported. We performed a comparative study regarding the buckling-type alignment that follows laminoplasty and laminectomy to know the mechanical changes in the alignment of the cervical spine. Lateral images of plain roentgenograms of the cervical spine were put into a computer and examined using a program we developed for analysis of the buckling-type alignment. Sixty-four patients who underwent laminoplasty and 37 patients who underwent laminectomy were reviewed retrospectively. The subjects comprised patients with cervical spondylotic myelopathy (CSM) and those with ossification of the posterior longitudinal ligament (OPLL). The postoperative observation period was 6 years and 7 months on average after laminectomy, and 5 years and 6 months on average following laminoplasty. Development of the buckling-type alignment was found in 33% of patients following laminectomy and only 6% after laminoplasty. Development of buckling-type alignment following laminoplasty appeared markedly less than following laminectomy in both CSM and OPLL patients. These results favor laminoplasty over laminectomy from the aspect of mechanics.

Ossification of the posterior longitudinal ligament of the cervical spine: etiology and natural history.

Study Design. Review article. Objective. To review the etiology, natural history, measurement tools, and image diagnosis of ossification of the posterior longitudinal ligament (OPLL) of the cervical spine. Summary of Background Data. OPLL is a well-known disease that causes myelopathy. Genetic factors are very important for development of OPLL. However, the pathogenetic gene and natural history of OPLL have not been clarified. Methods. The authors reviewed studies about the etiology, natural history, measurement tools, and diagnosis of OPLL, which had been performed by the members of the Investigation Committee on the Ossification of the Spinal Ligaments of the Japanese Ministry of Health, Labour, and Welfare. Results. The prevalence of OPLL in the general Japanese population was reported to be 1.9% to 4.3% among people older than 30 years. Genetic factors are important for development of OPLL, and some candidate genes have been reported. Clinical course of OPLL has been clarified by a prospective long-term follow-up study. Some radiographic predictors for development of myelopathy were introduced. Image diagnosis of OPLL is easy by plain radiographs, but magnetic resonance imaging and computed tomography are useful to determine cord compression by OPLL. Conclusion. OPLL should be managed on the basis of the consideration of its natural history. Elucidation of pathogenetic genes of OPLL will introduce a new approach for management of OPLL.

Clinical course of conservatively managed rheumatoid arthritis patients with myelopathy.

Study Design. The clinical course of rheumatoid arthritis patients with myelopathy who do not undergo surgery was studied. Objectives. To establish a more accurate prognosis for rheumatoid arthritis patients who do not undergo surgery. Summary of Background Data. Cervical myelopathy has been reported in two thirds of rheumatoid arthritis patients with atlantoaxial dislocation. Atlantoaxial fusion, or occipitocervical fusion, is widely performed on these patients. However, several researchers reported serious complications from the surgery, including nonunion, worsening myelopathy, and high mortality. The natural course of disease in rheumatoid arthritis patients with myelopathy should be known before definitive treatments can be outlined. Materials and Methods. Twenty‐one rheumatoid arthritis patients with myelopathy resulting from atlantoaxial dislocation were studied. Fourteen of the 21 cases were associated with upward migration of the odontoid process. All of these patients were recommended for surgery, but they refused. Patients were reviewed by direct examination yearly. Radiographic changes and clinical course, including the survival rate, were observed. Results. Atlantodental interval and Redlund‐Johnell measurements deteriorated. The patients showed no neural improvement, and deterioration was found in 16 (76%) cases during follow‐up. All patients became bedridden within 3 years of the onset of myelopathy. Seven of the 21 patients died suddenly for unknown reasons, 3 died of pneumonia, and 1 died of multiple organ failure. The three sudden‐death cases showed progressive upward migration of the odontoid process. The cumulative probability of survival was 0% in the first 7 years after the onset of myelopathy. Conclusions. The clinical results for rheumatoid arthritis patients with myelopathy treated without surgery are extremely poor. Surgical treatment is recommended for rheumatoid arthritis patients with myelopathy.

Significance of occipitoaxial angle in subaxial lesion after occipitocervical fusion.

Study Design. The significance of occipitoaxial angle in the development of subaxial subluxation after occipitocervical fusion was determined in a minimum 5-year follow-up study performed retrospectively. Objective. To clarify the association between the position of the fixed occipital bone and axis and the development of subaxial subluxation. Summary of Background Data. There have been few reports describing the association between the position of fixation of the occipital bone and axis and subaxial lesion in occipitocervical fusion. Materials and Methods. Thirty-eight patients with rheumatoid arthritis who underwent occipitocervical fusion for irreducible atlantoaxial dislocation were reviewed. The angle between the McGregor line and the inferior surface of the axis (O–C2) was measured in healthy volunteers and patients who had undergone occipitocervical fusion. The association between any changes in the alignment of the cervical vertebrae and the development of subaxial subluxation during follow-up periods was studied. Results. The number of the patients in whom postoperative kyphosis and swan neck deformity developed was only five, but in four (80%) of them, retroversion of the occipital bone was used to increase the O–C2 angle. In 14 patients, in whom anteversion of the occipital bone against the axis was excessive, 12 (86%) patients experienced subaxial subluxation after surgery. In the patients in whom fixed O–C2 angles were in normal range, only one patient developed such abnormal changes in the middle and lower cervical vertebrae. Conclusion. It is necessary to give attention to the position of the fixed occipital bone and axis during procedures of occipitoaxial fusion for patients with rheumatoid arthritis.

The natural course of myelopathy caused by ossification of the posterior longitudinal ligament in the cervical spine.

The natural course of ossification of the posterior longitudinal ligament, particularly the relationship between the onset of myelopathy and factors associated with its aggravation, was studied in 207 patients during an average period of 10 years 3 months. Myelopathic signs were already present in 37 (18%) patients at the time of the initial examination. Fourteen of these 37 patients showed aggravation of symptoms during the observation period. Myelopathy appeared during the observation period in 33 (16%) of the 207 patients. One hundred thirty-seven (66%) patients were free of myelopathy. Some patients had no myelopathic signs, despite severe spinal stenosis, because of the ossification. In these patients, the range of motion of the cervical spine was severely limited, indicating that dynamic factors are important in the development of myelopathy. In treating this disease, it is necessary to take into consideration the natural course of the disease and to identify the involvement not only of static factors, such as compression caused by ossification, but also of dynamic factors.

Genetic analysis of ossification of the posterior longitudinal ligament.

STUDY DESIGN The human leukocyte antigen (HLA) haplotypes in families of patients with known ossification of the posterior longitudinal ligament (OPLL) were reviewed. OBJECTIVE To clarify how genetic factors relate to the development of OPLL. SUMMARY OF BACKGROUND DATA The association between genetic factors and the development of OPLL is still unknown. MATERIALS AND METHODS The association between HLA haplotypes and OPLL was studied in families of 24 patients with OPLL. RESULTS The prevalence of OPLL was higher in the siblings showing a higher share of identical HLA haplotypes: 10 (53%) of 19 with concurrence of two strands, and 5 (24%) of 21 with concurrence of one strand. Of 21 subjects who had no HLA haplotype identical with that in OPLL patients, only one showed evidence of OPLL. CONCLUSION Genetic factors predispose toward the development of OPLL.