Ultrasound-Guided Near-Nerve Needle Assessment of the End-to-Side Anterior Interosseous to Ulnar Motor Nerve Transfer Contribution to Hand Intrinsic Reinnervation in Compressive Ulnar Neuropathy.

INTRODUCTION/AIMS: In severe ulnar neuropathy at the elbow (UNE), occasionally surgeons will employ an end-to-side (ETS) nerve transfer of the anterior interosseous nerve (AIN) motor branch of pronator quadratus (PQ) to the ulnar motor component distally (AIN ETS). We used an ultrasound (US)-guided near-nerve monopolar needle stimulation of the AIN to determine the specific contribution of the transferred PQ motor branch to the ulnar-innervated hand intrinsic muscles following AIN ETS in patients with UNE.

METHODS: After inserting the monopolar needle under US guidance, direct stimulation of the AIN was performed while recording from the abductor digiti minimi (ADM), first dorsal interosseous (FDI), and flexor pollicis longus (FPL). The presence or absence of a compound muscle action potential (CMAP) was noted from each muscle.

RESULTS: The technique was used in two patients with chronic UNE, one with a cubital tunnel decompression and AIN ETS and the other with a decompression alone. In the patient with decompression and AIN ETS, direct stimulation of the AIN revealed a low amplitude CMAP recorded from the FDI and FPL, suggesting AIN axonal contribution to FDI in the setting of prior AIN ETS. In the patient with decompression alone, near-nerve stimulation generated an expected CMAP in the FPL but no response in the hand intrinsics.

DISCUSSION: This study may demonstrate the utility of US-guided near-nerve monopolar needle AIN stimulation and suggests that it is a reliable technique to isolate the AIN contribution to hand intrinsic reinnervation following AIN ETS.