Anatomical variations of the abductor pollicis longus: a pilot study

BACKGROUND: The abductor pollicis longus (APL) originates from the lateral part of the dorsal surface of the body of the ulna below the insertion of the anconeus muscle, from the interosseous membrane, and from the middle third of the dorsal surface of the body of the radius. However, the number of its accessory bands and their insertion vary considerably. MATERIALS AND METHODS: Fifty upper limbs (2 paired, 31 male, 19 female) were obtained from adult Caucasian cadavers, and fixed in 10% formalin solution before examination. RESULTS: The APL muscle was present in all specimens. The muscles were divided into three main categories, with type II and III being dived into subtypes. Type I was characterised by a single distal attachment, with the tendon inserting to the base of the I metacarpal bone. Type II was characterised by a bifurcated distal attachment, with the main tendon inserting to the base of the first metacarpal bone; this type was divided into three subtypes (a-c). Type III was characterised by the main tendons inserting to the base of the first metacarpal bone, while the accessory band was characterised by mergers (fusion) with other tendons. This type was divided into two subtypes (a, b). CONCLUSIONS: The abductor pollicis longus is characterised by high morphological variability.