A case report of an accessory flexor digitorum profundus indicis contributing the first lumbrical.

Variations of the musculature within the upper extremity have been widely documented, with clinical implications ranging from motor dysfunction to compressive neuropathies. Herein, we described an aberrant muscle that originated from the anterior proximal forearm, formed a tendon that coursed through the carpal tunnel, and converged with the flexor digitorum profundus muscle to contribute to the first lumbrical. Additionally, the second lumbrical consisted of two heads, originating from the index and middle finger tendons of flexor digitorum profundus. Documentation and recognition of such anatomic variants is important, as this anatomic pattern may contribute to anterior interosseous or median nerve compression, incoordination, complications during surgery, and other clinical manifestations.