Identification of a third belly of the opponens pollicis muscle

Résumé fourni par la source

We have recently reported that fatty infiltration (FI) of the opponens pollicis (OPP) muscle is a common finding in patients with thumb carpometacarpal joint (CMC) osteoarthritis (OA). This FI is found in a reproducibly focal area of the deep proximal OPP, which we have provisionally called the “the third belly”, to distinguish it from the previously described superficial and deep bellies of the OPP. The purpose of this study was to describe the anatomic features of the OPP third belly in our dissections of 14 human cadaver hands, and in the histology of an adult hand and a fetal hand. The OPP third belly was found in all 14 dissected hands. It is the deepest and most proximal part of the OPP and completely covers the palmar surface of the trapezium and the palmar CMC capsule, with independent innervation directly from the motor branch of the median nerve. The OPP third belly location and structure suggest a possible function to stabilize the CMC joint, which can be affected by underlying OA. It can be identified with accuracy on clinical imaging. Further studies should elucidate its specific biomechanical role in CMC pathology.

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