Quantitative Ultrasound Analysis of Muscle Reinnervation Following Anterior Interosseous Nerve-To-Ulnar Motor Branch Supercharged End-To-Side Transfer Surgery: A Preliminary Study.

INTRODUCTION/AIMS: Routine assessment of muscle reinnervation primarily relies on clinical and electromyographic evaluation. The aim of this preliminary study was to evaluate sensitivity of quantitative ultrasound analysis for monitoring intrinsic hand muscle recovery following anterior interosseous nerve (AIN)-to-ulnar motor branch supercharged end-to-side (SETS) transfer.

METHODS

Eight patients (five male, three female; mean age 54.5 years, range 10-80) underwent anterior ulnar nerve transposition with AIN-to-ulnar motor branch SETS transfer. High-resolution ultrasound assessed the first dorsal interosseous (FDI) and hypothenar muscles pre- and postoperatively using quantitative grayscale and cross-sectional thickness (CST) analysis. Functional outcomes included key pinch and grip strength.

RESULTS

Preoperatively, affected FDI and hypothenar muscles exhibited significantly higher grayscale and lower CST values compared with the contralateral side. Following surgery, this difference decreased significantly in both muscle groups (FDI: mean difference [MD] -19.9, 95% CI -33.5 to -6.3; p = 0.013; hypothenar: MD -21.2, 95% CI -32.1 to -10.3; p = 0.006). CST measurements improved in the FDI muscle (MD -7.1 mm, 95% CI -11.3 to -2.9; p = 0.009), while there was no significant CST change in the hypothenar muscle (MD -2.3 mm, 95% CI -4.9 to 0.4; p = 0.081). There was a significant correlation between FDI muscle grayscale values and key pinch strength (R2 = 0.31), whereas hypothenar echogenicity showed no correlation with grip strength (R2 = 0.0001).

DISCUSSION: This preliminary study suggests that quantitative ultrasound of intrinsic hand muscles appears sensitive and can detect structural changes during reinnervation following AIN-to-ulnar motor branch SETS transfer.