Hello there once again! It’s Matt from Kenhub, and in this tutorial, we will be discussing the abductor pollicis longus. The deep extensors of the forearm consist of five muscles located at the posterior side of the forearm. One of them, the abductor pollicis longus, an extrinsic muscle of the hand, is going to be the focus of this tutorial. The muscle bellies and tendons of this group of muscles form the surface of the distal forearm and the wrist where they can be easily palpated.
The abductor pollicis longus muscle originates at the dorsal surfaces of both the radius and ulna and the interosseus membrane. This muscle also lies just below the supinator muscle. The abductor pollicis longus has its insertion at the base of the first metacarpal bone, the metacarpal bone of the thumb. Often, the insertion tendons splits into two and, additionally, attaches to the trapezium.
Like all extensors of the forearm, these five muscles are innervated by the radial nerve. The radial nerve divides into a superficial branch and deep branch at the height of the radial head. The deep branch becomes the posterior interosseus nerve which is responsible for the innervation of almost all deep extensors.
The main function of the deep extensors is to move the joints of the hand and fingers. The abductor pollicis longus pulls the thumb forward at the saddle joint resulting in abduction which leads to a lateral movement of the radius at the wrist joint at the same time known as radial deviation. This muscle also functions to carry out dorsiflexion of the metacarpal joint of the thumb.
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