Hideo Kataoka

Biomechanical study of cervical flexion myelopathy using a three-dimensional finite element method

OBJECT The goal of this study was to perform a biomechanical study of cervical flexion myelopathy (CFM) using a finite element method. METHODS A 3D finite element model of the spinal cord was established consisting of gray matter, white matter, and pia mater. After the application of semi-static compression, the model underwent anterior flexion to simulate CFM. The flexion angles used were 5 degrees and 10 degrees , and stress distributions inside the spinal cord were then evaluated. RESULTS Stresses on the spinal cord were very low under semi-static compression but increased after 5 degrees of flexion was applied. Stresses were concentrated in the gray matter, especially the anterior and posterior horns. The stresses became much higher after application of 10 degrees of flexion and were observed in the gray matter, posterior funiculus, and a portion of the lateral funiculus. CONCLUSIONS The 5 degrees model was considered to represent the mild type of CFM. This type corresponds to the cases described in the original report by Hirayama and colleagues. The main symptom of this type of CFM is muscle atrophy and weakness caused by the lesion of the anterior horn. The 10 degrees model was considered to represent a severe type of CFM and was associated with lesions in the posterior fand lateral funiculi. This type of CFM corresponds to the more recently reported clinical cases with combined long tract signs and sensory disturbance.

The limit of low speed peripheral nerve elongation; neurological and circulatory aspects

We studied peripheral nerve elongation of rabbit sciatic nerves. External fixators developed in our department were applied to 32 rabbit femurs in vivo. The rabbits underwent osteotomy of the femur and were divided into two groups subjected to different sciatic nerve elongation speeds: group I (0.45 mm/day) and group II (1.35 mm/day). The sciatic nerves were elongated 1.5, 3.0, 4.5, 6.0 and 7.0 cm by the external fixators, and the corresponding actual percentage of elongation of the nerves were 8, 16, 24, 30 and 40%. After elongation, nerve electrophysiology, nerve blood flow and pathology were studied. Forty percent elongation decreased nerve blood flow to 69 +/- 5.1% of contralateral controls in group I and to 20 +/- 4.8% in group II. Although no decrease in motor conduction velocity (MCV) was observed at any elongation distance, compound muscle action potential (CMAP) amplitude gradually decreased with increasing elongation. In group I, after 40% elongation, specimens showed the following pathologic changes: thinning of myelin sheath, atrophy and detachment of the axon from the myelin sheath. Furthermore, in group II, 40% elongation induced disorganization of the myelin sheath and Wallerian degeneration. Consequently 40% elongation was regarded as critical at speeds of both 0.45 and 1.35 mm/day.

Regulation of nitric oxide generation by up-regulated arginase I in rat spinal cord injury

Recently, arginase is suggested to regulate nitric oxide production by competing with nitric oxide synthase for the same substrate, L-arginine, in experimental asthma. We investigated the role of arginase and its relationship to nitric oxide production after spinal cord injury. Rats were subjected to laminectomy and complete transection of their spinal cords (injury group) or laminectomy only (sham group). In the injury group, arginase I was increased in the macrophages at the transection edge, and the peak was observed 48 h after spinal cord injury. However, nitric oxide production decreased significantly in the injury group despite increased nitric oxide synthase2 mRNA expression compared with the sham group. We also demonstrated the reduction in L-arginine concentrations, which was inversely associated with changes in arginase activity. Therefore, arginase appeared to regulate nitric oxide production by consuming L-arginine. The regulation of arginase activity and L-arginine levels may improve nitroxidative stress and reduce tissue damage in spinal cord injury.

F-18 FDG PET/CT findings in a case of spinal cord sarcoidosis.

We describe FDG PET/CT findings in a rare case of histologically proven cervical spinal cord sarcoidosis (SCS) which mimics spinal cord myelopathies or tumors on magnetic resonance imaging. FDG PET/CT showed coexistence of FDG-avid cervical cord focus and intrathoracic lymphadenopathies. Corticosteroid therapy showed rapid improvement of this patient’s SCS-related neurologic symptoms, and disappearance of the hypermetabolic cervical cord focus and lung lymphadenopathies on follow-up FDG PET/CT scan, regardless of still-remained cervical cord lesion on magnetic resonance imaging. FDG PET/CT appears helpful for establishing the diagnosis of SCS in cases with FDG-avid intrathoracic lymphadenopathies and for early evaluation of response to treatment.

Environmental factors involved in axonal regeneration following spinal cord transection in rats

A recent study of a rat model treated with grafted collagen filament (CF) after spinal cord transection showed dramatic recovery of motor function but did not report on the acute-stage phenomenon. In the present study, we describe molecular and histological aspects of the axonal regeneration process during the acute stage following spinal cord transection. The spinal cord of 8-week-old rats was completely transected, and a scaffold of almost the same size as the resected portion was implanted in the gap. Changes in the mRNA expression of four neurotrophic factors [nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), NT-3, and glial cell-derived neurotrophic factor (GDNF)] were analyzed after 72 h. The expression of BDNF and NT-3 mRNA increased significantly in the CF-grafted group compared to the nongrafted group. Immunostaining for BDNF and NT-3 revealed that cells positive for these neurotrophic factors extended along the collagen filaments in the CF-grafted group. Similarly, astrocytes extended into the collagen filament scaffold together with the neurotrophic factors and partly across a border line. These findings indicate that collagen filament helps to reduce scar tissue, supports the expression of neurotrophic factors, and serves as a scaffold for the outgrowth of regenerating axons.

Selective laminoplasty after the preoperative diagnosis of the responsible level using spinal cord evoked potentials in elderly patients with cervical spondylotic myelopathy: a preliminary report.

Study Design A preliminary report of a new operative method termed selective laminoplasty after the preoperative diagnosis of the responsible level using spinal cord evoked potentials (SCEPs) in elderly patients with cervical spondylotic myelopathy. Objective To introduce the method and clinical results for selective laminoplasty. Summary of Background Data Clinical results for conventional laminoplasty and anterior decompression and fusion guided by SCEPs have been reported. However, there have been no reports that consider SCEP results for selecting the optimal level in lamioplasty for cervical spondylotic myelopathy. Methods Seven elderly patients who underwent selective laminoplasty were followed for a minimum of 12 months. The T2-high–intensity area on magnetic resonance imaging, the responsible level detected by SCEPs, and the laminoplasty level were recorded. The operative time, intraoperative bleeding, clinical results including the Japanese Orthopaedic Association score, recovery rate, Nurick grading scale, and visual analog scale of axial pain were investigated preoperatively and postoperatively. Results The responsible intervertebral levels were at C3-C4 in 3 patients and at C4-C5 in 4 patients. These were identical for SCEP recorded after median nerve stimulation and transcranial electric stimulation. High-intensity area on T2-weighted magnetic resonance imaging was seen in 6 patients (3 at C3-C4 and 3 at C4-C5). The average operative time was 106 minutes and the average amount of bleeding was 20 mL. Neurologic recovery was achieved in all patients except 1 who had severe myelopathy. Visual analog scales of axial pain were 41.3±33.9 before surgery and 18.0±19.4 at final follow-up. The Japanese Orthopaedic Association score and the Nurick grade improved in 6 patients but did not change in 1 patient. Conclusions Preliminary clinical results for selective laminoplasty were satisfactory in all but 1 case. Although long-term results are not yet available, we consider this method to be less invasive and capable of giving satisfactory clinical results and benefits for elderly patients.

Dynamic electrophysiological examination of cervical flexion myelopathy.

Cervical flexion myelopathy is thought to arise following compression of the spinal cord by vertebrae or intervertebral discs and dura mater, or from overstretching of the spinal cord induced by cervical spinal flexion. However, the influence of spinal flexion on the spinal cord and the detailed origins of this disease are unknown. In this article the authors report a case of cervical flexion myelopathy in which dynamic electrophysiological examination was performed using an epidural electrode. This investigation showed the real-time influence of flexion of the cervical spine on spinal cord function. This technique was considered to be useful for diagnosis and in decision making for treatment. Anterior fusion was the optimal surgical method for treating this disease.

Transection method for shortening the rat spine and spinal cord

Previous studies have presented evidence which indicates that the regeneration of axons in the spinal cord occurs following spinal cord transection in young rats. However, in a transection-regeneration model, the completeness of the transection is often a matter of dispute. We established a method for shortening the rat spine and spinal cord to provide a spinal cord injury (SCI) model in which there was no doubt about whether the axonal transection was complete. In the future, this model may be applied to the chronic period of complete paralysis following SCI. Adult, female Wistar rats (220–250g) were used in the study. The spinal cord was exposed and a 4-mm-long segment of the spinal cord was removed at Th8. Subsequently, the Th7/8 and Th8/9 discs were cut between the stumps of the spinal cord to remove the Th8 vertebra. The stitches which had been passed through the 7th and 9th ribs bilaterally were tied gradually to bring together the stumps of the spinal cord. Almost all the rats survived until the end of the experiment. Uncoordinated movements of the hind limbs in locomotion were observed at 4 weeks after surgery. However coordinated movements of the hind limbs in locomotion were not observed until the end of the experiment. After 12 weeks, an intracardiac perfusion was performed to remove the thoracic spine and the spinal cord. There were no signs of infection. The bone fusion of the Th7 and Th9 vertebrae was observed to be complete in all specimens and the alignment of the thoracic spine was maintained. The spinal canal was also correctly reconstituted. The stumps of the spinal cord were connected. Light microscopy of the cord showed that scar tissue intervened at the connection site. Cavitation inhibiting the axonal regeneration was also observed. This model was also made on the assumption that glial scar tissue inhibits axonal regeneration in chronic SCI. Axonal regeneration was not observed across the transected spinal cord in this model. Attempts should be made to minimize the damage to the spinal cord and the surgery time for successful axonal regeneration to occur. The model developed in this study may be useful in the study of axonal regeneration in SCI.

Cervical hemilaminoplasty: technical note.

Ten patients with cervical spinal schwannomas were operated using a new posterior approach, termed cervical hemilaminoplasty. A thread wire saw (T-saw) was used to cut the lamina at the center of the spinous process and at the unilateral pars interarticularis on the affected side. The unilateral lamina, the inferior articular process, and half of the spinous process were resected as a single mass. After tumor excision, the resected lamina was restored to the original site and fixed. Fusion technique was not required. The mean number of resected and restored lamina was 1.5. No instability of the cervical spine was detected using flexion/extension x-ray photography. Although worsening of radicular motor function was observed in 2 cases, the weakness was not permanent and both cases showed full recovery. Postoperative magnetic resonance imaging was performed in 7 of the 10 cases and showed no recurrences. Cervical hemilaminoplasty is a useful posterior approach method for spinal tumors and especially dumbbell-type tumors. This method provides wide exposure of the foramen and of the inside of the canal. Furthermore, it allows reconstruction of the posterior element of the spinal canal and results in good stability.