Abductor pollicis longus

The abductor pollicis longus is a key muscle in the posterior (extensor) compartment of the forearm, crucial for thumb movement.

Origin

The muscle originates from the posterior surfaces of the ulna and radius, as well as the intervening interosseous membrane, typically in the middle third of the forearm.

Course and Insertion

The muscle forms a thick tendon which passes distally under the extensor retinaculum, traversing the first dorsal (lateral) compartment of the wrist. The tendon then inserts mainly into the lateral aspect of the base of the first metacarpal bone of the thumb. It may also send slips to the trapezium bone or the abductor pollicis brevis muscle.

Innervation

The abductor pollicis longus is innervated by the posterior interosseous nerve, a branch of the deep branch of the radial nerve (C7 and C8).

Action

The primary action of abductor pollicis longus is to abduct the thumb at the carpometacarpal joint, moving the thumb away from the palm perpendicularly. It also assists in extending the thumb (moving the thumb in the plane of the palm).

Anatomical snuffbox

The tendon of the abductor pollicis longus helps to form the lateral (radial) border of the anatomical snuffbox at the wrist, along with the tendon of extensor pollicis brevis.