Which motor branch to use? Targeted muscle reinnervation for digital neuromas: An anatomical study

Symptomatic neuromas following digital nerve injury frequently cause persistent pain and impair hand function. Targeted muscle reinnervation (TMR) is a promising approach that redirects regenerating axons into motor branches; however, its success in the hand relies on precise anatomical knowledge and identification of expendable motor targets. We aimed to identify and characterize motor branches in the hand to guide optimal TMR target selection.

Twenty-six arms were dissected to map the motor branches from the median and ulnar nerves to the thenar, hypothenar and lumbrical muscles. The anatomical course, length and diameter of each branch were documented, and anatomical variations were classified. Each branch was evaluated for consistency and expendability to determine its suitability as a TMR target.

Thenar innervation demonstrated three main distribution patterns. The opponens pollicis (OP) and flexor pollicis brevis (FPB) motor branches were consistently present and deemed expandable, whereas the abductor pollicis brevis branch was preserved owing to its essential role in thumb opposition. Although lumbrical innervation patterns showed variability, branches to the lumbricals of digits 2-3 were reliably identified and suitable for TMR. Hypothenar innervation showed two main patterns, with the flexor digiti minimi (FDM) and abductor digiti minimi (ADM) branches being consistently identified as targets.

This study provides digit-specific anatomical information on motor branches in the hand that could be used in TMR. For digits 1-3, the OP, FPB and lumbrical branches to digits 2-3 appeared to be promising options; for digits 4-5, the FDM and ADM branches represent useful targets.