腰椎椎間板ヘルニアにおける transitional vertebra の意義

Abstract

Lumbosacral transitional vertebra is a common variation in the lumbosacral spine. It is not known whether the function of the nerve roots is altered when this variation is present. We retrospectively reviewed the charts of 46 patients who underwent microdiscectomy for lumbar herniated discs in our institution, and examined the preoperative neurological and radiological findings. We compared the distribution of muscle weakness and sensory disturbance of patients with lumbosacral transitional vertebra with those with normal configuration. Lumbarized S1 vertebra was found in 8 (17%) of the 46 patients. The level of the herniated disc was L5/S1 in all 8 cases. The distribution of motor weakness caused by S1 nerve root compression was significantly different in patients with lumbarized S1 from those with normal lumbosacral configuration. The pattern of muscle weakness caused by S1 root compression in patients with lumbarized S1 closely resembled that of L5 root compression in patients with normal configuration. A similar finding was obtained in the analysis of sensory disturbance. Our results suggest that the function of lumbosacral nerve roots is altered in patients with lumbarized S1 in such a way that the S1 nerve root serves the usual function of an L5 nerve root.