Efficacy of intraoperative direct electrical stimulation of the spinal root and measurement of distal motor latency in lumbar spinal stenosis

Purpose The measurement of distal motor latency (DML) is an established method for diagnosing entrapment peripheral neuropathy. DML can also serve as an index for disease severity and prognosis. We considered that measuring DML could be useful in estimating the severity of spinal root impairment and predicting prognosis in patients with lumbar spinal stenosis (LSS). The purpose of this study was to investigate the efficacy of intraoperative direct electrical stimulation of the spinal root and the measurement of DML in LSS. Methods In 39 patients with LSS, a total of 93 spinal roots were stimulated, and evoked electromyography was recorded at the leg muscles after decompression. DML was measured and its correlation with clinical severity, as evaluated by Zurich claudication questionnaire (ZCQ) and Short Form 36 (SF-36), was investigated. Results For the stimulation of the L3, L4, and L5 spinal root, the mean DML (ms) were 6.8 (±1.4), 7.4 (±1.3), and 6.0 (±1.3) in gluteus medius, 9.3 (±1.5), 9.2 (±1.5), and 9.0 (±1.6) in biceps femoris, 9.7 (±1.0), 9.8 (±1.8), and 9.4 (±1.2) in vastus medialis, 16.1 (±1.0), 14.7 (±1.3), and 14.1 (±1.5) in tibialis anterior, and 16.4 (±1.4), 14.3 (±1.8), and 13.9 (±1.9) in gastrocnemius muscles. Statistically significant positive correlations were observed between DML and height. Preoperative symptom and function scores of ZCQ and postoperative bodily pain scores of SF-36 were significantly worse in the patients with prolonged DML. Conclusions DML is thought to be useful for estimating the severity of spinal root impairment and for predicting the prognosis.