Muscles associated with the wrist include those of the forearm and hand that act to move the wrist and digits. Movements of the wrist include abduction and adduction, moving the hand from side to side, or extension and flexion of the hand, moving the palm backwards or forwards relative to the forearm.
Muscles of the forearm that act on the wrist and hand are referred to as extrinsic muscles, or external to the hand. The muscle bodies form the proximal fleshy roundness, and are located in the forearm. The tendons of these muscles pass under the flexor retinaculum and the extensor retinaculum, limiting stiffness during contraction.
The wrist joint can be acted upon in several ways to produce several movements that include marginal movements including radial deviation (abduction, or movement towards the thumb) and ulnar deviation (adduction, or movement towards the pinky finger), radial abduction, ulnar abduction, and movements in the plane of the hand including palmar flexion and extension. Extension of the wrist can also occur, as well as intermediate or combined movements, in addition to movements that occur in concert with the rotation caused by supination or pronation of the distal radioulnar joint.
The extensor carpi radialis longus is one of the five main muscles that control movements of the wrist. A long muscle, it acts to extend the wrist, but also abduct the hand, specifically moving the hand towards the thumb. The abductor pollicis longus (APL) abducts the thumb, but can also abduct the wrist and flex the hand.
The extensor pollicis longus, larger than the extensor pollicis brevis, is a muscle of the dorsal forearm. It acts to extend the terminal phalanx of the thumb, and in combination with the extensor pollicis brevis, extends and abducts the wrist.
The extensor carpi ulnaris acts to extend the wrist, but when acting alone moves the hand toward the ulnar side. The flexor carpi ulnaris acts opposite of the extensor carpi ulnaris, flexing and adducting the hand.
The extensor digitorum muscle extends the medial four digits of the hand. A muscle of the forearm, it arises from the lateral epicondyle of the humerus and inserts into the middle and distal phalanges to the fingers.
The extensor digitorum communis acts to extend the phalanges, wrist, and elbow. The primary action of the muscle is on the phalanges, with contraction also resulting in spreading and separating the fingers by extension.
The extensor indicis is a narrow, long muscle deep in the forearm parallel to the extensor pollicis longus. It extends the index finger, but prolonged action also assists in extending the wrist and mid-carpal joints. Like the extensor digiti minimi, it lacks oblique bands (also referred to as connexus intertendinei) that link the tendons on the dorsal sides of the hand.
The flexor digitorum superficialis is a muscle of the deep anterior forearm flexes the fingers at the proximal interphalangeal joints. The flexor digitorum profundus is a muscle of the deep forearm that flexes the fingers.