Bitendinous insertion of abductor pollicis longus coexistent with a rare accessory antebrachial muscle: Clinico-anatomical considerations

Reports of the anomalous orientation of the musculature of the first osseofibrous extensor compartment of the wrist are not uncommon; especially that of Abductor Pollicis Longus (APL) muscle. Such variations can be explained phylogenetically; owing to a synonymous occurrence in primates. In this report, we highlight a unique variation in the APL muscle of the left side in an adult male cadaver. The present anomaly consisted of a bitendinous insertion of APL on the base of the first metacarpal, complemented by an additional muscle belly arising from the fascia covering Extensor Carpi Radialis Longus (ECRL). Such an accessory muscle is speculated to greatly alter kinematics at the wrist and thumb, thus affecting the daily activities of the hand. Such multiple tendons of APL are beneficial clinically in providing additive support to the first carpo-metacarpal joint and act as effective aids in tendon transfers and reconstructive procedures of the hand. In contrast, they can pose as surgical hazards in post-operative cases of De Quervain's disease. Thus, it is imperative for surgeons and clinicians to acquire a prior substantial knowledge of such anatomical variants of APL before attempting any treatment of this region.