• Muneharu Ando, Tetsuya Tamaki, Mamoru Kawakami, Akihito Minamide, Yukihiro Nakagawa, Kazuhiro Maio, Yoshio Enyo, and Munehito Yoshida.
• Department of Orthopedic Surgery, Wakayama Rosai Hospital, 93-1 Kinomoto, Wakayama city, 640-8505 Wakayama, Japan. mando@gaia.eonet.ne.jp
• Eur Spine J. 2013 Apr 1;22(4):833-9.

BackgroundThe diagnosis of lumbar intraforaminal and extraforaminal stenosis (lumbar foraminal stenosis) is sometimes difficult. However, sensory nerve action potential (SNAP) decreases in amplitude when the lesion is at or distal to the dorsal root ganglion. Therefore, the amplitude of SNAP with lumbar foraminal stenosis should be decreased. In this cohort study, the usefulness of SNAP for the preoperative diagnosis of L5/S foraminal stenosis was assessed.MethodsIn 63 patients undergoing unilateral L5 radiculopathy, bilateral SNAPs were recorded for the superficial peroneal nerve (L5 origin). The patients were divided into two groups according to the results of imaging examinations. Group A (37 patients) included patients whose lesion was located only at the intraspinal canal. In group B (26 patients), the lesion was located only at the intra- or extraforaminal area. All patients received surgery and the symptoms were diminished. The ratios of the amplitudes of SNAPs on the affected side to that on the unaffected side were compared between groups A and B.ResultsSNAPs could not be elicited bilaterally in four patients. The amplitude ratio for group B (median 0.42, max 1.17, min 0) was significantly lower than that in group A (median 0.85, max 1.43, min 0) (p < 0.001 by Mann-Whitney U test). Using a cut-off value of 0.5 for the amplitude ratio, the sensitivity for the diagnosis of lumbar foraminal stenosis was 91.3 % with a specificity of 85.7 %.ConclusionsMeasurement of SNAP could be useful to diagnose a unilateral L5/S foraminal stenosis.

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