Congenital hypoplastic thumb with absent thenar muscles: anomalous digital neurovascular bundle.

Congenital hypoplastic thumb with absent thenar muscles and an associated single midline digital neurovascular bundle is reported in four patients. Several other anomalies localized to the hand were encountered in all patients, including instability of the metacarpophalangeal joint of the thumb and anomalous extrinsic tendons of the involved thumb. Multiple congenital abnormalities were also found in all patients, especially in relation to the spine.