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Extensor pollicis longus extends the terminal phalanx of the thumb. While abductor pollicis brevis and adductor pollicis, both attached to the extensor pollicis longus tendon, can extend the thumb's interphalangeal joint to the neutral position, only extensor pollicis longus can achieve full hyperextension at the interphalangeal joint.
The extensor pollicis brevis originates on the ulna distal to the abductor pollicis longus, from the interosseus membrane, and from the dorsal side of the radius. Passing through the first tendon compartment together with the abductor pollicis longus, it is attached to the base of the proximal phalanx of the thumb.
The extensor carpi radialis longus (ECRL) has the most proximal origin of the extrinsic hand extensors. It originates just distal to the brachioradialis at the lateral supracondylar ridge of the humerus, the lateral intermuscular septum, and by a few fibers at the lateral epicondyle of the humerus. [1]
The intrinsic muscle groups are the thenar and hypothenar (little finger) muscles; the interossei muscles (four dorsally and three volarly) originating between the metacarpal bones; and the lumbrical muscles arising from the deep flexor (and which are special because they have no bony origin) to insert on the dorsal extensor hood mechanism.
The second compartment is occupied by the two radial wrist extensors, the extensor carpi radialis longus and the extensor carpi radialis brevis. The third compartment exclusively accommodates the extensor pollicis longus, which hooks around Lister's tubercle of radius and inserts to the thumb. The fourth compartment is the largest of all.
Extensor digitorum; Extensor digiti minimi (little finger only) Extensor indicis (index finger only) of phalanges, at interphalangeal joints [4] Lumbricals of the hand; Dorsal interossei of the hand; Palmar interossei; of thumb [5] Extensor pollicis brevis (proximal phalange) Extensor pollicis longus (distal phalange)
The posterior interosseous nerve supplies all the muscles of the posterior compartment of the forearm, except anconeus muscle, brachioradialis muscle, and extensor carpi radialis longus muscle. In other words, it supplies the following muscles: Extensor carpi radialis brevis muscle — deep branch of radial nerve; Extensor digitorum muscle
Hyperextension of the wrist can lead to fracture of Lister's tubercle, as pressure is increased from the extensor pollicis longus tendon. [7] An "island-shaped" fracture can also expose the tendon to a rough edge and lead to tendon rupture (usually long after the initial fracture).