An anomalous muscle in the hand that can cause carpal tunnel syndrome: A case report

Introduction Intrinsic and extrinsic muscles of the hand show frequent variations. Knowledge of these muscle variations is important during diagnosis and treatment of carpal tunnel syndrome, hand surgery and some plastic surgery procedures. We report here the presence of an anomalous muscle in the hand between the first and second lumbricals. Case report The flexor digitorum superficialis had five tendons and the two lateral-most tendons among them gave origin to this abnormal muscle of the hand. The fleshy belly of the muscle was supplied by a branch of the median nerve. Distally the tendon of the anomalous muscle and most of the lateral tendon of the flexor digitorum superficialis muscle merged with the second tendon of the flexor digitorum superficialis muscle. The common tendon was inserted to the base of the middle phalanx of the index finger. Further, the first lumbrical had two heads: a lateral head and a medial head. The lateral head took its origin from the lateral-most tendon of the flexor digitorum profundus muscle and the medial head took origin from the lateral part of the fleshy belly of the abnormal muscle. Its insertion and nerve supply were normal. Conclusion The abnormal muscle can produce a bulge in the palm and it might compress the median nerve in the carpal tunnel, resulting in carpal tunnel syndrome.