American Society for Peripheral Nerve

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Evaluation of Intrinsic Hand Musculature Reinnervation Following Supercharged End-to-Side Anterior Interosseous to Ulnar Motor Nerve Transfer
Zach Zhang, MD1; Linden Kyle Head, MD, HBA, BSc, BPHE2; Katie Hicks, BSc2; Gerald Wolff, BSc, MD, FRCSC2; Kirsty Usher Boyd, BHSc, MD, FRCSC2
1University of British Columbia, Vancouver, BC, Canada, 2University of Ottawa, Ottawa, ON, Canada

Introduction: 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 patients do show improved ulnar-innervated intrinsic hand strength but that the first dorsal interosseous (FDI) recovers to a greater extent than the abductor digiti minimi (ADM). An institutional review of SETS AIN to ulnar motor nerve transfers was performed to evaluate the clinical and electrodiagnostic patterns of reinnervation.

METHODS: A retrospective cohort study was performed on all patients who underwent a SETS AIN to ulnar motor nerve transfer from 2011 to 2017. Inclusion criteria were: isolated ulnar nerve pathology, SETS AIN to ulnar motor nerve transfer, and minimum of 6-months follow-up. Preoperative, intraoperative, and postoperative data were collected and reviewed. Reinnervation was assessed clinically with serial British Medical Research Council strength assessments and electrodiagnostically with serial motor amplitude measurements. Statistical analysis was performed using parametric (student's t-test) and non-parametric statistics (Wilcoxon signed rank test, Kruskal-Wallis test, Spearman's rho).

RESULTS: Seventeen patients (65% male, mean age 56.9 13.3 years) were included with a mean follow-up of 16.7 8.5 months. Etiology and chronicity were variable but all patients preoperatively demonstrated clinically significant weakness and electrodiagnostic evidence of denervation of their intrinsic hand musculature. All patients underwent a SETS AIN to ulnar motor nerve transfer and Guyon's canal release. Postoperatively, strength and motor amplitude increased significantly for both the FDI (p=0.002, p=0.046) and the ADM (p=0.044, p=0.020). Despite comparable preoperative strength (p=0.098), postoperatively the FDI achieved significantly greater strength when compared to the ADM (p=0.023).

CONCLUSIONS: In our practice, SETS AIN to ulnar motor nerve transfer is a beneficial procedure for patients presenting with proximal ulnar nerve pathology to restore intrinsic hand function. Recovery of intrinsic muscle function differs between the more proximally innervated ADM and the more distal FDI, with better recovery observed in the FDI. Patients and hand therapists should be counseled about this when discussing prognosis. Further work to elucidate the underlying physiologic and anatomic basis for this discrepancy is indicated.

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