Measurement of the local pressure of the intervertebral foramen and the electrophysiologic values of the spinal nerve roots in the vertebral foramen.

STUDY DESIGN The intraoperative findings of the local pressure of the intervertebral foramen and the electrophysiologic values of the spinal nerve roots were evaluated. OBJECTIVE To investigate the neurophysiologic changes of the spinal nerve roots in the vertebral foramen. SUMMARY OF BACKGROUND DATA As far as we know, few reports have so far described the neurophysiologic changes of the spinal nerve roots in the vertebral foramen. METHODS The local pressure of the intervertebral foramen was continuously measured while the lumbar spine posture was changed in 66 vertebral foramens. In addition, 20 L5 nerve roots were electrophysiologically evaluated using the compound muscle action potentials (CMAPs) from tibialis anterior (TA) muscle after L5 nerve root stimulation. RESULTS The local pressure of the intervertebral foramen was significantly increased during lumbar spine extension (P < 0.001); moreover, the latency and amplitude of the CMAPs both significantly deteriorated in line with the increasing local pressure. CONCLUSIONS Our findings suggested that a double compression of the nerve root exists in lumbar spinal stenosis with lumbar spine extension, which includes the spinal canal and the vertebral foramen.