Evaluation of Intrinsic Hand Musculature Reinnervation following Supercharge End-to-Side Anterior Interosseous–to–Ulnar Motor Nerve Transfer

Supercharge end-to-side (SETS) anterior interosseous (AIN) to ulnar motor nerve transfer is commonly performed in our institution to augment intrinsic hand function. Following observations of recovery patterns, we hypothesized that despite its more distal innervation the first dorsal interosseous (FDI) recovers to a greater extent than the abductor digiti minimi (ADM). The objective of this work was to evaluate the clinical and electrodiagnostic pattern of reinnervation of intrinsic hand musculature following SETS AIN to ulnar motor nerve transfer. A retrospective cohort of prospectively collected data included all patients who underwent a SETS AIN to ulnar motor nerve transfer. Two independent reviewers performed data collection. Reinnervation was assessed with two primary outcome measures(i) clinically with serial Medical Research Council strength assessments and (ii) electrodiagnostically with serial motor amplitude measurements. Statistical analysis was performed using non-parametric statistics. Seventeen patients (65% male, mean age 56.9±13.3 years) were included with a mean follow-up of 16.7±8.5 months. Preoperatively, all patients demonstrated clinically significant weakness and electrodiagnostic evidence of denervation. Postoperatively, strength and motor amplitude increased significantly for both the FDI (p=0.002, p=0.016) and the ADM (p=0.044, p=0.015). Despite comparable preoperative strength (p=0.098), postoperatively FDI achieved significantly greater strength when compared to the ADM (p=0.023). Following SETS AIN to ulnar motor nerve transfer recovery of intrinsic muscle function differs between ADM and FDI, with better recovery observed in the more distally innervated FDI. Further work to elucidate the underlying physiologic and anatomic basis for this discrepancy is indicated.