Reducing the Distance Between Anode and Cathode to Make Handheld Nerve Stimulators More Selective in Nerve Fascicle Selection: Report of Two Cases

Precise nerve fascicle identification is important in certain peripheral nerve procedures. Although we believe bipolar nerve stimulation with intraoperative neuromonitoring is a superior method, many rely on clinical response evoked by handheld monopolar nerve stimulators. We present a modification in the use of the latter for a more precise fascicle stimulation. A 55-year-old man with a right high brachial plexus injury and a 47-year-old woman with a left median nerve schwannoma were scheduled for exploration and ulnar-to-musculocutaneous nerve transfer, and for surgical excision respectively. Intraoperatively, we used a disposable handheld monopolar nerve stimulator in an unorthodox way, placing the anode right next to the cathode (both touching the same nerve fascicle). In the first case, a fascicle that showed flexor carpi ulnaris (FCU) and intrinsic hand muscle contraction with standard stimulation (anode placed on patient's skin), showed only FCU activation with our modified method, and was chosen as donor. A BMC grade M4 elbow flexion was achieved 9 months after surgery. In the second case, safe schwannoma excision was performed after our modified stimulation technique caused thenar muscle activation in a single, unaffected fascicle, while standard monopolar stimulation showed activation in several fascicles. No unexpected motor/sensory deficits were noted during follow-up. This report shows an easy modification in the use of handheld nerve stimulators that improves selectiveness when looking for nerve fascicles.