The carpal tunnel consists of nine tendons and the median nerve. Pronation is defined as the radius pulling medially along its longitudinal axis over the ulna, causing the palm to face posteriorly. The pronator trees and pronator quadratus assist in pronation of the forearm. The deep compartment of the contains the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. The intermediate compartment contains the flexor digitorum superficialis. All these muscles originate as part of the common flexor origin at the medial epicondyle. The palmaris longus is also present in the superficial compartment but is often absent in many people. The superficial compartment contains the pronator teres, the flexor carpi radialis, and the flexor carpi ulnaris. The anterior compartment is known as the flexor compartment since the muscles primarily function to flex the wrist and digits. The anterior compartment consists of a deep and superficial layer. Of note, the mobile wad is occasionally included as part of the posterior compartment. The extensor carpi radialis longus and extensor carpi radialis brevis insert on the second and third metacarpal base respectively. The brachioradialis which is the strongest flexor of the forearm. The brachioradialis inserts just proximal the radial styloid. The brachioradialis originates over the proximal two-thirds of the lateral supracondylar ridge of the humerus, while both extensor carpi radialis longus and extensor carpi radialis brevis originate over the distal lateral supracondylar ridge. Similarly, the tendon of the extensor digiti minimi of the superficial posterior compartment travels ulnar to the extensor digitorium tendon the small finger, and assists in small finger extension. The deep compartment also contains the extensor indices whose tendon lays radial to the extensor digitorium tendon to the index finger, and it assists in index finger extension. The remaining deep muscles function to extend and abduct the thumb. Supination is defined as the radius rotating laterally around its longitudinal axis over the ulna, causing the palm to face anteriorly. The supinator functions to supinates the forearm. The deep group contains the supinator, abductor pollicis longus, extensor pollicis brevis, and the extensor pollicis longus. The primary function of these muscles is digit and wrist extension, with the extensor carpi ulnaris assisting in ulnar deviation of the wrist during wrist extension. These muscles are relatively subcutaneous as there is usually not much subcutaneous fat on the dorsal aspect of the forearm. The superficial group includes the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, and anconeus. The posterior compartment of the forearm is also known as the extensor compartment since the muscles primarily function to extend the wrist and digits of the hand. The posterior compartment of the forearm contains a superficial and deep muscle group. The intermediate compartment contains the flexor digitorum superficially. The deep compartment of the contains the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. The muscles are separated into deep, intermediate, and superficial groups. The superficial compartment contains the pronator teres, the flexor carpi radialis, and the flexor carpi ulnaris. The anterior compartment contains muscles that act to flex the wrist and digits. The mobile wad consists of three muscles: the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis. The deep group includes the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicia. The muscles are further broken down into deep and superficial groups. The superficial group includes the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, and anconeus. The muscles found in the posterior compartment primarily function to extend the wrists and digits. The compartments of the forearm are separated by an interosseous membrane found between the radius and ulna in addition to a lateral intermuscular septum. These include the anterior compartment, posterior compartment, and the mobile wad. It consists of several muscles and an extensive neurovascular network encased in three compartments. The forearm is the region of the body spanning from the elbow to the wrist.
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