論文

This study on rats was designed to evaluate the change of biceps muscle fibers by enzyme histochemical examination and the change of distribution of motoneurons innervating biceps muscle fibers by retrograde tracer examination after incomplete spinal cord injury. Incomplete spinal cord injury was produced by placing a 20 g weight on exposed dura at the C6 level. The number of the labeled motoneurons of C6 segment significantly decreased compared with that in the control, but there were no significant changes in the other segments at 4 weeks after the injury. Moreover, there was type grouping of biceps muscle fibers at 4 weeks after the injury. These findings indicated that the incomplete cervical spinal cord injury at C6 level in rats caused the partial denervation and then reinnervation of biceps muscle fibers by the collateral sprouting of the remaining motoneurons which belonged to the same motoneuron pool of the injured motoneurons.

The tiptoe-walking Yoshimura (twy) mouse is a model of chronic spinal cord compression caused by ossification of intraspinal ligaments. Choline acetyltransferase (CAT), which is known to be a specific marker of cholinergic neurons, best reflects spinal motoneuron function. Changes in CAT immunoreactivity following chronic spinal cord compression in twy mice were investigated quantitatively in order to elucidate spinal motoneuron functional changes according to the degree and direction of compression. Thirty 24-week-old twy mice were used in this study. They were divided into three groups according to the direction of spinal cord compression (anterior, posterior, and lateral) and the CAT immunoreactivities in whole sections of their upper cervical spinal cords were investigated quantitatively using a fluorescence microphotometry system. The lateral compression group showed histological spinal motoneuron atrophy and loss on the compressed, but not the non-compressed, side. Spinal motoneuron atrophy and loss were observed when the severity of spinal canal stenosis due to the ossified lesion, expressed as the occupation rate, was 30% or more, but the spinal motoneurons appeared normal when it was below 30%. The CAT immunofluorescence intensity of the anterior horn showed a linear negative correlation with the degree of canal stenosis. When the occupation rate was below 20%, the CAT immunofluorescence intensities in the anterior horns of the compression and control groups did not differ significantly. The CAT immunofluorescence intensity of twy mice with occupation rates of 20% or more were significantly lower than that of those with occupation rates below 20%. Furthermore, the CAT immunofluorescence intensity was significantly lower on the compressed than the noncompressed side of the lateral compression group. Thus, our findings indicate that an occupation rate of about 20% may be the critical level for functional changes in the spinal motoneurons.

Anterior decompression and fusion via an extrapleural approach was performed for 33 patients with myelopathy arising from thoracic disc herniation and the clinical usefulness and problems related to this procedure were assessed on the basis of surgical results and complications. The severity of the myelopathy was evaluated by the Japanese Orthopaedic Association score, and the surgical results were based on the recovery rate. The upper-level limit of decompression and fusion via the extrapleural approach was T4-5. The recovery rate for the mean postoperative follow-up period of 41 months was 66.7%. An age of 60 years or more, long duration of illness and severe preoperative myelopathy were indicators of a poor prognosis. Two patients suffered from a postoperative transient pulmonary complication due to hemothorax. X-ray examinations revealed good bone union in all the patients. The present study indicates that anterior decompression and fusion via the extrapleural approach is a useful technique which can be used to achieve a high success rate in the surgical treatment of thoracic disc herniation, if intervention is early.