Bilateral extensor medii digiti: a rare anatomical variation

A supernumerary extensor muscle to the middle finger was found to be present bilaterally in a male cadaver. It originated from the distal end of the ulna and its tendon inserted into the proximal phalanx of the middle finger. The bilateral presence and manner of insertion appear to be unique from a review of the literature. Morphological variability and clinical significance are reviewed. Such variations may be clinically significant during hand surgery, especially tendon transfer procedures.