Targeted Muscle Reinnervation in the Hand: An Anatomic Feasibility Study for Neuroma Treatment and Prevention
Timothy H. F. Daugherty, MD1, Brian A Mailey, MD2, Michael W Neumeister, MD1 and Reuben A. Bueno Jr, MD1, (1)Institute for Plastic Surgery, Southern Illinois University School of Medicine, Springfield, IL, (2)Southern Illinois University School of Medicine, Springfield, IL
Introduction: 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 locate the motor entry points to the intrinsic muscles have not been performed. The purpose of this study was to provide details for and measurements of the motor entry points to the intrinsic muscles, determine which motor entry points are identifiable through a dorsal approach as would be performed during ray amputation, and develop recommended sensory to motor entry point nerve coaptations for prophylactic TMR at the time of ray amputation.
Materials & 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 (Lister's tubercle) and volar (hamate hook) landmarks was recorded for each intrinsic hand muscle. The digital sensory nerve diameters were measured for size comparison of the nerve coaptations.
Results: Motor entry points were identified to all nineteen intrinsic muscles through a volar approach and to twelve muscles through a dorsal approach. At least two motor entry points for expendable muscles are available for TMR through the dorsal amputation site of each finger (index-small). 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 recommended coaptations had favorable sensory:MEP diameter ratio of less than 2:1.
Conclusions: The intrinsic muscles have motor entry points located at consistent distances from bony landmarks both dorsally and volarly. Targeted muscle reinnervation is feasible to be performed in the hand due to the consistency of these locations and favorable nerve coaptation ratios. Results from this study can be applied clinically to assist surgeons in identifying the location 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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