Reinnervation assessment using a modified nerve conduction study protocol following end-to-side anterior interosseous nerve transfer in advanced cubital tunnel syndrome: A case series and proof of concept study.

INTRODUCTION

Supercharge end-to-side (SETS) anterior interosseous nerve (AIN) transfer augments motor recovery in advanced cubital tunnel syndrome (CuTS). However, standard electrodiagnostic studies cannot differentiate between native ulnar nerve regeneration and reinnervation via AIN transfer. We aimed to establish a proof-of-concept for a modified nerve conduction study (NCS) protocol by employing median nerve stimulation to electrophysiologically isolate and evaluate AIN-mediated motor recovery.

METHODS

We retrospectively analyzed 13 patients with advanced CuTS who underwent AIN SETS transfer (mean follow-up duration: 1.6 years). Postoperative NCS was performed by stimulating the median nerve at the elbow and recording compound muscle action potentials (CMAPs) from the first dorsal interosseous (FDI) and abductor digiti minimi (ADM). Contralateral measurements were obtained at the follow-up for comparative reference.

RESULTS

All 13 patients demonstrated FDI CMAPs upon median nerve stimulation. Among the 8 patients with longitudinal data, 6 showed a progressive increase in the median nerve-stimulated CMAP amplitudes over time. The mean median nerve-stimulated FDI CMAP was 3.1 mV on the operative side versus 2.3 mV on the contralateral side; however, the difference was not statistically significant. Notably, no median nerve-stimulated CMAP responses were recorded from the ADM in any patient.

DISCUSSION: This modified NCS protocol demonstrated median nerve-stimulated CMAP at the FDI, confirming reinnervation after AIN SETS transfer. The selective CMAP recovery in the FDI, but not in the ADM, reflects a site-specific reinnervation pattern resulting from AIN coaptation to FDI-specific ulnar fibers. Therefore, future prospective studies in larger cohorts are warranted to refine this protocol as a standard clinical assessment.