Takanori Kojima

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.

Investigation of motor dominant C5 paralysis after laminoplasty from the results of evoked spinal cord responses.

Background Postoperative motor dominant C5 paralysis was known as one of several complications after laminoplasty. Several theories have been proposed for postoperative segmental paralysis after laminoplasty, but its etiology remains unclear. Objective To investigate the possible mechanism for postoperative motor dominant C5 paralysis from intraoperative electrophysiological studies using evoked spinal cord potentials (ESCPs). Methods A total of 66 patients who had undergone laminoplasty due to compressive cervical myelopathy were studied retrospectively. In all patients, the symptomatic intervertebral levels of cervical myelopathy were identified by several types of the ESCPs. Motor dominant C5 paralysis was determined as at least 1 level down compared with pre-operative shoulder abduction according to the manual muscle testing. Results Five patients (7.6%) showed postoperative motor dominant C5 paralysis. C5 paralysis occurred from 1 to 3 days after surgery and compromised unilaterally in all 5 patients. The causes of cervical myelopathy were cervical spondylosis in 3 patients and ossification of the posterior longitudinal ligament in 2 patients. One patient with severe impairment (2 in manual muscle-testing [MMT] scale) did not show clinical recovery. The other 4 patients recovered to 4 or 5 on the MMT score from 3 to 6 months after the onset. Based on the findings of ESCPs, the C4-5 level was affected by cervical myelopathy in all 5 patients with postoperative motor dominant C5 paralysis (C4-5 level in 3 patients, both C4-5 and C5-6 levels in 2 patients). A high signal intensity area on T2-weighted magnetic resonance imaging (MRI) was observed in all patients who showed apparent motor dominant C5 paralysis in this study. Conclusions Cervical myelopathy at the C4-5 level is a potential risk for motor dominant C5 paralysis. Although it is merely a speculation, when C5 radiculopathy occurs after laminoplasty, C5 paralysis becomes clinically apparent because the deltoid muscle gets predominantly innervated by C5 root due to intramedullary spinal cord damage on the C6 segment in C4-5 myelopathy before surgery. It may represent the high signal intensity area on T2-weighted MRI at the C4-5 level.

Intraoperative electrophysiologic studies on the functions of nerve roots involved in cervical dumbbell-shaped schwannoma and their clinical utility.

Background It is difficult to expect the degree of neurologic deficits after resection of involved nerve roots before and during the surgery for cervical dumbbell-shaped schwannoma. We present the results of studies for cervical nerve root functions in patients with cervical schwannoma using intraoperative electrophysiologic assessment and the potential of their clinical relevance is also discussed. Objective To present the utility of intraoperative electrophysiologic studies to detect the functions of the nerve roots involved in cervical schwannoma and adjacent nerve roots. Methods Five patients with dumbbell-shaped cervical schwannoma arising from the cervical nerve roots composing the brachial plexus were studied. Compound muscle action potentials (CMAPs) after stimulation of nerve roots involved in the schwannoma were recorded from upper limb muscles anatomically correspond to their myotome. Adjacent nerve roots were also stimulated. Motor-evoked potentials (MEPs) after transcranial electric stimulation were also recorded during surgery. In 3 patients, sensory nerve action potentials (SNAPs) after digital nerve stimulation were also recorded from cervical nerve roots. Results In 4 patients, CMAPs after stimulation of cervical nerve roots involved with the schwannoma were not obtained or were very small compared with those obtained after stimulation of adjacent nerve roots. In 2 of 4 patients, SNAPs after digital nerve stimulation were recorded with small amplitude from the nerve roots involved in schwannoma. Minimal (n=2, within 80% attenuation of amplitude) or no changes (n=2) were observed after total resection of the schwannoma and no apparent motor weakness occurred in these 4 patients. In a patient with cervical schwannoma involved in C8 nerve root, CMAPs with large amplitude were recorded after stimulation of the C8 nerve root. SNAPs after stimulation of digit V were recorded with larger amplitude from the T1 root compared with those recorded from the C8 nerve root. Intradural parts of the tumor arising from C8 posterior rootlets were completely removed after transaction of posterior rootlets. During removal of intraforaminal parts of the tumor, motor evoked potentials were decreased over 50% of controls. Incomplete removal was chosen to avoid deterioration of motor function. Transient dysesthesia of digit V and slight weakness occurred after surgery. Conclusions The residual function of motor and sensory nerve roots involved with cervical schwannoma differed between individuals and could be detected using intraoperative electrophysiologic assessment.

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.

Epidurally recorded spinal cord evoked potentials in patients with cervical myelopathy and normal central motor conduction time measured by transcranial magnetic stimulation

OBJECTIVE Use epidural recording of evoked spinal cord potentials (ESCPs) to investigate the pathology of cervical spondylotic myelopathy (CSM) in patients with normal central motor conduction time (CMCT) in upper and lower limbs. METHODS A total of 75 patients with CSM were studied. All patients were examined before surgery for motor evoked potentials (MEPs) following transcranial magnetic stimulation (TMS). They were also evaluated during surgery by epidurally recorded ESCPs following stimulation of the median nerve, brain and spine. RESULTS Seven patients (9%) showed normal CMCT in upper and lower limbs upon TMS examination. Only the ESCPs following median nerve stimulation (MN-ESCPs) were abnormal in these patients. In 5 of the 7 patients, a marked block in conduction of MN-ESCPs was observed at the C3-4 intervertebral level. The remaining two patients showed attenuation in the amplitude of MN-ESCPs at mid-cervical levels. CONCLUSIONS We present 7 cases of CSM with negative CMCT findings. From the MN-ESCP results, we surmise that the pathology of CSM with normal CMCT is due predominantly to dysfunction of sensory systems involved in the upper limbs. SIGNIFICANCE Examination by TMS is useful in the diagnosis of CSM but the possibility of negative CMCT findings upon TMS must be borne in mind. Multi-functional evoked spinal cord responses demonstrate that lesions in the sensory system are the major underlying pathology.

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.