Comparison of Ulnar Intrinsic Function following Supercharge End-to-Side Anterior Interosseous-to-Ulnar Motor Nerve Transfer: A Matched Cohort Study of Proximal Ulnar Nerve Injury Patients

Background: There are few studies supporting supercharge end-to-side nerve transfer for high ulnar nerve injury. The current study hypothesized that patients with a supercharge end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer would demonstrate superior return of intrinsic function compared with conventional treatment only. Methods: A retrospective matched-cohort study matched supercharge end-to-side transfer patients based on age, level of injury, and mechanism to ulnar nerve injury patients who did not have the transfer. The primary outcome was return of ulnar intrinsic function, based on clinical examination and/or electromyography. Dichotomous and continuous variables were compared with Fisher's exact and t tests, respectively. Results: Thirteen supercharge end-to-side patients were identified (>1 year follow-up). The average age of both cohorts was 35 years. Ulnar nerve transection above the proximal third of the forearm represented 54 percent of patients; compressive injuries represented 46 percent. Eleven supercharge end-to-side transfer patients (84 percent) demonstrated intrinsic function recovery compared with five (38 percent) non-supercharge end-to-side patients (p < 0.05). Average time to initial motor recovery was similar between the two groups (supercharge end-to-side, 2.9 months; non-supercharge end-to-side, 3.8 months; p > 0.2). Intrinsic function return was more likely following nerve transection with the supercharge end-to-side procedure (85 percent versus 14 percent; p = 0.03), whereas compression injuries had comparable intrinsic function return regardless of the supercharge end-to-side transfer (67 percent versus 67 percent; p = 1.0). Conclusions: This matched cohort study demonstrates that the supercharge end-to-side transfer results in increased ulnar intrinsic reinnervation following ulnar nerve injury. This finding may be most relevant following transection injuries. Improved outcomes associated with supercharge end-to-side and ulnar nerve repair warrant further investigation.