Background The aim of the current study is to investigate the first and second lumbrical nerves as potential fibers donors to the deep motor branch of the ulnar nerve to avoid intrinsic atrophy in high ulnar nerve injuries. Methods Sixteen fresh frozen cadaveric hands were dissected, the radial lumbrical nerves accessed, and a coaptation, either in reverse end‐to‐side or in double end‐to‐side through a bridge nerve graft, was created to the deep motor branch of ulnar nerve. Semithin sections were taken from samples of donor and recipient nerves for qualitative (nerve architecture) and quantitative studies (fiber count and donor/recipient ratio). Results The first lumbrical showed a robust trunk and a superior axon density (9,126.50 ± 2,923.41 axons/mm2) to the ulnar motor branch (7,506.50 ± 1,137.50 axons/mm2 distal to the opponens tunnel and 7,947.75 ± 1,741.24 axons/mm2 before its terminal branching); the ulnar motor branch showed a higher axon number (2,633.51 ± 410.00 distal to the opponens tunnel and 2,345.75 ± 2,101.56 before its terminal branching) than the first lumbrical (1,410.56 ± 823.89); section areas occupied by axons were higher in proximal (0.20 ± 0.16) and distal (0.26 ± 0.20) ulnar samples than the first lumbrical (0.17 ± 0.16). Donor/recipient ratio first lumbrical/deep motor branch of the ulnar nerve were 1:1.86 (distal to the opponens tunnel) and 1:1.67 (at its terminal branching); data about the second lumbrical were ruled out because of bias. Conclusions A transfer from the first lumbrical nerve to the deep motor branch of the ulnar nerve in palm is suitable to avoid intrinsic atrophy.

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