Muscles of forearm

The muscles of forearm are organized into two primary compartments: the anterior (flexor-pronator) compartment and the posterior (extensor-supinator) compartment.

Anterior Compartment

The anterior compartment muscles are arranged into three layers:

• Superficial Layer: This layer includes the pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. All of these muscles typically originate from the medial epicondyle of the humerus via the common flexor tendon.

• Intermediate Layer: This layer consists solely of the flexor digitorum superficialis.

• Deep Layer: The deepest layer comprises the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.

The main functions of these muscles are to flex the wrist and fingers and pronate the forearm (turn the palm downwards). Most muscles in this compartment are innervated by the median nerve, with the exceptions of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus, which receive innervation from the ulnar nerve.

Posterior Compartment

The posterior compartment is divided into two layers:

• Superficial Layer: This group includes the brachioradialis, extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi, and extensor carpal ulnaris. These muscles primarily originate from the lateral epicondyle of the humerus via the common extensor tendon.

• Deep Layer: The deep group consists of the supinator, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis.

The primary actions of these muscles are extension of the wrist and fingers and supination of the forearm (turning the palm upwards). Innervation is predominantly by the radial nerve and its branches, with the posterior interosseous nerve (a continuation of the deep branch of the radial nerve) supplying most of the deep extensors.