Targeted Muscle Reinnervation in the Hand: A Technical Roadmap

Abstract

Targeted muscle reinnervation (TMR) transfers cut the nerve endings to the motor nerves of the nearby muscles to reduce neuroma pain and/or enhance prosthetic function. To guide surgeons, anatomic "roadmaps" describe nerve transfer options for TMR at various locations. This study aimed to landmark and measure motor entry points (MEPs) to the hand interossei muscles in the context of TMR for digital nerve neuroma management. Ten fresh-frozen cadaveric hands were dissected to describe the innervation arising from the deep branch of the ulnar nerve to the dorsal interossei (DIs) and palmar interossei (PIs) muscles. The location of MEPs relative to the bone and soft tissue landmarks and the size of the target nerves were measured. The MEPs for the DIs and PIs were found in the central third of the metacarpal. The MEPs to the PIs averaged 23.3-24.7 mm from the median nerve. The length of nerve proximal to the MEP was limited, ranging between 6.5 ± 2.6 mm for the first PI and 10.5 ± 2.7 mm for the second PI. Similarly, minimal nerve proximal to the MEP of the DI was available for mobilization. Access to the first PI innervation required substantial release of the thenar musculature. Motor nerve diameter averaged 0.85-0.97 mm. In considering TMR for the management or prevention of digital nerve neuromas, the motor branches to the second and third PIs are the most accessible and best approached volarly, whereas motor branches to the DIs take more direct routes into the muscle, making volar exposure difficult. Nerve length proximal to the MEP is short, requiring that most of the nerve length for neurorrhaphy comes from the digital nerve. Size mismatch at the neurorrhaphy site is favorable compared to more proximal TMR. Targeted muscle reinnervation in the hand is technically feasible for a patient with a symptomatic neuroma after digital amputation.