Analysis of cauda equina action potentials recorded from the ligamentum flavum after peroneal nerve and tibial nerve stimulation during surgery for lumbosacral radiculopathies

Abstract We investigated the clinical utility of the cauda equina action potentials (CEAPs) recorded intraoperatively from the ligamentum flavum after peroneal nerve or tibial nerve stimulation at the knee. The CEAPs evoked by stimulation on the asymptomatic side in 33 patients with unilateral radiculopathies served as the control. The normal limits of the onset latencies of the CEAPs and their difference between two adjacent levels were defined as a mean plus two standard deviations of the control values. Using these criteria, we tested the patients with lumbar disc herniation (LDH) at L4-5 by stimulating the symptomatic side. In the 14 patients, the latency difference across the lesion site was beyond the normal limits in 11 patients (79%) for the peroneal-CEAPs and in 12 (86%) for the tibial-CEAPs. Conclusion The CEAP latency difference between two adjacent levels provides a more reliable measure than the absolute value in evaluating the conduction abnormalities for L4-5 LDH.