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Targeted Muscle Reinnervation In The Hand: An Anatomical Study For Identification Of Target Motor Entry Points
Timothy H.F. Daugherty, M.D., M.S., Brian A. Mailey, M.D., Reuben A. Bueno, Jr., M.D., Michael W. Neumeister, M.D..
Southern Illinois University, Springfield, IL, USA.

PURPOSE: Targeted muscle reinnervation has emerged as a treatment for and prevention of symptomatic neuromas and may be beneficial in the hand. Anatomic studies establishing feasibility in the hand or landmarks to identify the motor entry points to the intrinsic muscles have not been performed. The purpose of this study was to provide details regarding the motor entry points to the intrinsic muscles, determine which motor entry points are identifiable dorsally, and develop recommended sensory to motor entry point nerve coaptations for prophylactic TMR at the time of ray amputation or for management of symptomatic neuromas.
METHODS: Motor entry points to the intrinsic hand muscles were dissected in five fresh latex-injected cadavers. Number of motor entry points, diameter, surface of entry, and distance from dorsal (Listerís tubercle) and volar (hamate hook) landmarks was recorded for each target muscle. The digital sensory nerve diameters were measured for size comparison.
RESULTS: Motor entry points were identified to all nineteen intrinsic muscles through a volar approach and twelve muscles through dorsal approach. For all fingers there were at least two motor entry points consistently identified dorsally at the base of each amputation site innervating expendable muscles. Motor entry points to the thenar muscles were only reliably identified through a volar approach. Two recommended nerve coaptations for each digit amputation were identified. All had favorable sensory:MEP diameter ratio of less than 2:1. Recommended targets for index finger amputation include transfer of the radial digital nerve to the MEP to first dorsal interossei (1.46mm average diameter, 62.69% distance from Listerís tubercle to the metacarpophalangeal joint of amputated finger; sensory:MEP diameter ratio of 1.32) and ulnar digital nerve to first palmar interossei (0.98mm, 58.32%; 1.69). The long finger radial digital nerve is best coapted to the MEP for second dorsal interossei (1.26mm, 60.11%; 1.48) and ulnar digital nerve to third dorsal interossei (1.26mm, 57.41%; 1.24). Ring finger ideal targets include the radial digital nerve to the MEP for fourth dorsal interossei (1.22mm, 62.75%; 1.46) and ulnar digital nerve to third lumbrical (1.12mm, 81.62%; 1.5). Lastly, the ideal target for the small finger radial digital nerve is to the MEP for third palmar interossei (0.76mm, 64.11%; 1.95) and ulnar digital nerve to fourth lumbrical (0.9mm, 82.04%; 1.71).
CONCLUSION: Targeted muscle reinnervation is feasible to be performed in the hand. The intrinsic muscles have motor entry points found at consistent distances from bony landmarks both dorsally and volarly. These results can be applied clinically to assist surgeons in identifying the locations of motor entry points to the intrinsic muscles when performing targeted muscle reinnervation in the hand for both neuroma treatment and prevention.


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