Electrophysiologic evaluation of denervated muscles in incomplete paraplegia using macro electromyography

Objective: To evaluate denervated muscles in persons with incomplete paraplegia due to thoracolumbar spinal injury (TLSI) using macro electromyography in determining indications for functional electrical stimulation (FES). Design: A randomized clinical trial and a criterion standard. Setting: A department of orthopedic surgery in a university hospital. Patients and Other Participants: Eighteen patients with incomplete paraplegia, including 11 with TSLI, and 50 healthy adults. Intervention: Area and amplitude of macro motor unit potential (macro MUP) were measured at the tibialis anterior, the vastus lateralis, and the vastus medialis. The normal limits of macro MUP parameters were defined based on values from healthy subjects. Abnormal denervated muscles were detected by macro EMG and conventional EMG in paralytic patients. The correlation between macro MUP parameter values and muscle forces of the tibialis anterior and quadriceps femoris induced by electrical stimulation was analyzed. Main Outcome Measures: The number of abnormal muscles, parameter values, and muscle force induced by electrical stimulation. Results: Abnormal muscles were found only in the TLSI patients and 13 abnormal muscles were detected by macro EMG only. The abnormal muscles defined by macro EMG showed insufficient contraction induced by electrical stimulation. The increase of parameter value negatively correlated with the muscle force (tibialis anterior area r = -.797, amplitude r = -.866; quadriceps area r = -.866, amplitude r = -.893; p < .001). Conclusions: These results suggest that macro EMG is useful in detecting denervated muscles, in determining indications for FES, and in predicting FES effects before implantation of electrodes.