Electrophysiological Study for Nerve Root Entrapment in Patients With Isthmic Spondylolisthesis.

STUDY DESIGN: A case series study.

OBJECTIVE: To investigate the electrophysiological location of nerve root entrapment in patients with isthmic spondylolisthesis.

SUMMARY OF BACKGROUND DATA: Although the lesion of the nerve root in patients with isthmic spondylolisthesis has been thought to be located at the pars interarticularis due to proliferation of fibrous cartilage, there is no electrophysiological study in relation to this accomplished fact.

METHODS: We performed an electrophysiological study in 12 patients with isthmic spondylolisthesis during surgery. All patients presented with low-grade isthmic spondylolisthesis and unilateral radiculopathy, and underwent single-level posterior lumbar interbody fusion with instrumentation. After a total facetectomy, nerve root action potentials were recorded by stimulating the ipsilateral peroneal nerve at the popliteal fossa. Four needle electrodes were inserted into the affected nerve root at the intraspinal canal, pars interarticularis, disk level, and extralateral to the disk. The waveforms that showed either a positive waveform pattern or polyphasic waveform pattern were regarded as abnormal potentials. We also confirmed surgical records and preoperative images to investigate the relationship to the electrophysiological findings.

RESULTS: An abnormal waveform pattern was demonstrated at the pars interarticularis in 6 patients, at the disk level in 5, and at the extralateral site in 1. On the basis of the electrophysiological findings of this study, the nerve root lesion was not always found on only the pars interarticularis in patients with isthmic spondylolisthesis. A relationship between the electrophysiological findings and surgical records or preoperative images was not found.

CONCLUSIONS: The electrophysiological investigation in this study shows that the nerve root entrapment in patients with isthmic spondylolisthesis occurs not only at the pars interarticularis but also distal to the isthmus. This study suggests the possibility of insufficiency of decompression only at the pars interarticularis for patients with isthmic spondylolisthesis.