Published papers

Reversible spinal cord injury (SCI) at C6 level in rats, produced by the weight-placed method, resulted in a severe motor functional deficit initially, followed by a gradual recovery. During the recovery, choline acetyltransferase (CAT) distribution in the cervical spinal cord was investigated at 2, 4, 7, 14 and 28 days after the injury by quantitative immunohistochemistry with a fluorescence microphotometry system. At C6 level, the flourescence intensity of the ventrolateral anterior horn (VLAH), which reflected the concentration of CAT, decreased to approximately 50% of that of the sham-operated group at 2 days. It then recovered to 60% at 4 days after the injury, and remained unchanged thereafter. Fluorescence intensities in VLAH at C4-5 and C7-8 levels decreased to approximately 60-70% at 2 days after the injury, but it recovered and increased to 110-130% thereafter.

Study Design: An experimental study was conducted to evaluate MRI signal changes within the spinal cord after the injury in rats. Objectives: To clarify the significance of MRI signal changes in the injured cervical cord. Setting: Tokyo, Japan. Methods: Cervical spinal cord injury was produced in rats by placing a 20-g, or 35-g weight on exposed dura at the C6 level for 5 min (20 g- or 35 g-compression group). Motor function was evaluated by the inclined-plane method at 2, 7 and 28 days after the injury. T1- and T2-weighted images were produced by the spin-echo method with a static magnetic field strength of 2.0 tesla, at 2 and 28 days after the injury, and then the histopathological examinations were performed. Results: In the 20-g compression group which recovered from the paralysis at 28 days. MR images were T1 iso signal/T2 high signal 2 days after the injury and T1 iso signal/T2 high signal after 28 days. The changes in MRI signal 2 and 28 days represented edema and gliosis, respectively. In the 35-g compression group, which incompletely recovered from paralysis at 28 days. MR images were T1 iso-signal/T2 low signal surrounded by high signal 2 days after the injury and T1 low/T2 high signal at 28 days. The MRI signal changes 2 and 28 days reflected hemorrhage with edema and cavities, respectively. Conclusion: T2 low signal of the spinal cord observed early after injury reflects hemorrhage and may serve as an indicator of a poor prognosis. T1 low/T2 high signals from the subacute to chronic period indicated persistence of paralysis and limited recovery of function.

This study was designed to evaluate the relationship between minor trauma and surgical results of cervical ossification of the posterior longitudinal ligament (OPLL), focusing on static compressive and dynamic factors contributing to cord compression plus the type of attendant OPLL. Of the 91 patients treated surgically, 26 had sustained minor trauma (injury group), and the other 65 had no trauma (noninjury group). The pre- /postoperative JOA scores and recovery ratio for the injury group were significantly lower than those for the noninjury group. In the segmental, localized, and mixed types, which had good ranges of motion of the cervical spine, the recovery ratios of the injury group were significantly lower than those of the noninjury group. In the continuous type, which had a poor range of motion and severe spinal cord compression, there was no significant difference in the recovery ratio between the injury and noninjury groups. Thus, dynamic factors may play an important role in neurologic deterioration after minor trauma in patients with segmental, mixed, and localized cervical OPLL.

We conducted a multiple regression analysis on the surgical results (minimum follow-up of 5 years) of 55 patients who underwent expansive open-door laminoplasty (open-door ELAP) for cervical myelopathy due to ossification of the posterior longitudinal ligament (OPLL) in order to determine statistically the impact of factors influencing the results. Duration of myelopathy was found to be a significant factor indicating poor results, while progression of ossification and age at the time of surgery were significant factors indicating deterioration. Three other factors (preoperative severity of myelopathy, degree of spinal canal expansion and changes of the curve indices before and after surgery did not have a significant influence on the results. To improve the surgical results, it is thus essential to operate on patients as soon as they develop symptoms of myelopathy. There exists a certain limitation in posterior decompression for OPLL including open-door ELAP until prevention of the progression of ossification becomes possible.

We studied degenerative changes in the cervical intervertebral discs of 497 asymptomatic subjects by MRI and evaluated disc degeneration by loss of signal intensity, posterior and anterior disc protrusion, narrowing of the disc space and foraminal stenosis. In each subject, five disc levels from C2-C3 to C6-C7 were evaluated. The frequency of all degenerative findings increased linearly with age. Disc degeneration was the most common observation, being present in 17% of discs of men and 12% of those of women in their twenties, and 86% and 89% of discs of both men and women over 60 years of age. We found significant differences in frequency between genders for posterior disc protrusion and foraminal stenosis. The former, with demonstrable compression of the spinal cord, was observed in 7.6% of subjects, mostly over 50 years of age. Our results should be taken into account when interpreting the MRI findings in patients with symptomatic disorders of the cervical spine.

Study Design. Magnetic resonance imaging findings of an increased signal in the cervical cord in patients undergoing surgery for ossification of the posterior longitudinal ligament were analyzed to determined whether an increased signal on T2-weighted images correlated with a poorer outcome. Objectives. To clarify whether preoperative magnetic resonance imaging findings of a high signal in the cord constitute a poor prognostic factor. Summary of Background Data. The importance of a high, T2-weighted, intramedullary signal on preoperative magnetic resonance studies in patients undergoing surgery for ossification of the posterior longitudinal ligament requires further clarification. Methods. Of 91 patients having cervical surgery for ossification of the posterior longitudinal ligament, 26 had a history of minor trauma. High, T2-weighted signals in the cord were note din 23 patients who had sustained trauma and in 39 patients who had no history of trauma. Patients were divided into four groups according to the presence or absence of a high cord signal and/or a trauma history. Pre- and postoperative Japanese Orthopaedic Association scores and recovery ratios then were evaluated. Results. The pre-and postoperative Japanese Orthopaedic Association scores and recovery ratios of the patients with a high signal and a trauma history were significantly less than those with no high signal but with a trauma history. Among the patients with no history of trauma, however, there were no significant differences in the pre- and postoperative JOA scores and recovery ratios between the patients with a high signal and those with no high signal. Conclusion. A high preoperative cord signal on T2- weighted magnetic resonance images for patients undergoing surgery for ossification of the posterior longitudinal ligament constitutes a poor prognostic factor, when trauma has placed a role.

We investigated dorsal shift and anteroposterior spinal cord diameter after expansive open-door laminoplasty, comparing pre- and postoperative computed tomographic myelographic images to clarify the relationships between surgical outcome and these changes. Dorsal shift occurred at the midcervical spine in cervical spondylotic myelopathy (CSM) but was less extensive in ossification of the posterior longitudinal ligament (OPLL). Spinal cord anteroposterior diameter expanded for OPLL but did not for CSM. Correlation of outcome and dorsal shift was not significant for OPLL or CSM. Correlation of outcome and expansion was significant for OPLL, but not for CSM.

We examined the utility of anterior decompression and bony fusion via the extrapleural approach in the treatment of thoracic myelopathy secondary to ossification of the posterior longitudinal ligament (OPLL). Patient outcome and complications were analyzed in 48 patients treated with this procedure, with a follow-up of at least 2 years. The Japanese Orthopaedic Association score was used to evaluate the severity of the thoracic myelopathy, and the recovery rate was used to evaluate the surgical outcome. The outcome, postoperative complications, radiographic evaluations of bony union, and progression of OPLL within the area of anterior decompression were examined. The T3 vertebral body was the highest level to which anterior decompression was applied. The average follow-up period was 57 months with a recovery rate of 56.7% which stabilized 1 year after operation. However, the surgical outcome was less favorable in patients with long-standing myelopathy, extensive OPLL, or thoracic OPLL with coexisting intraspinal ligament ossification. Four patients experienced deterioration of their myelopathy, and seven patients had the postoperative complication of extraspinal leakage of cerebrospinal fluid. The myelopathy was transient in all but one patient. Radiographic studies showed that bony union was achieved and restenosis of the spinal canal due to progression of OPLL within the area of decompression did not occur. We conclude that anterior decompression and bony fusion using the extrapleural approach provides a good outcome and is useful in treating mid- and lower thoracic OPLL when performed carefully at an early stage of disease.