Forearm - Anterior Muscles

Here we'll learn the deep and superficial muscles of the anterior forearm, which flex the wrist and digits. Most of the muscles we'll learn are innervated by the median and ulnar nerves of the brachial plexus. Muscles: Flexor carpi ulnaris, Palmaris longus, Flexor carpi radialis, Pronator teres, and Brachioradialis. Be aware that, despite its anterior location and complimentary actions, brachioradialis is often considered a posterior-compartment muscle because of its origins and radial nerve innervation. Many of these muscles arise from the common flexor tendon on the medial epicondyle of the humerus. Medial epicondylitis (aka, Golfer's elbow) results from inflammation of the common flexor tendon on the medial epicondyle of the humerus. Two origins and insertions:

• The humeral head arises from the common flexor tendon on the humerus, and the ulnar head arises from the posterior ulna and olecranon process.
• The two heads merge, and flexor carpi ulnaris inserts on the wrist: one tendon inserts on the base of metacarpal V and the other inserts on the pisiform and hook of the hamate.
• Because it crosses the wrist and inserts medially, flexor carpi ulnaris flexes and adducts the wrist.

• Arises from the common flexor tendon and inserts into the palmar aponeurosis.
• This muscle flexes the wrist.

Be aware that palmaris longus is absent in approximately 10% of people (this may vary by population). The palmar aponeurosis is a fan-like sheet of connective tissue that inserts into the skin; it improves hand grip and protects the structures of the hand.

• Arises from the common flexor tendon and inserts into the second and third metacarpals.
• Because it crosses the wrist and inserts laterally, flexor carpi radialis flexes and abducts the wrist.

The next two muscles act on the forearm:

• Two heads:

The humeral head arises from the common flexor tendon and inserts on the mid-shaft of the lateral radius; The ulnar head arises from the coronoid process of the ulna and merges with the humeral head.

• Pronator teres flexes the forearm and pronates it.

• Arises on the lateral side of the humerus (on the supracondylar ridge) and inserts on the styloid process of the radius. It is a powerful flexor of the forearm.

Muscles: Pronator quadratus, Flexor digitorum profundus, Flexor pollicis longus, and Flexor digitorum superficialis.

• This is a quadrilateral-shaped muscle that arises from the distal ulna and inserts on the radius.
• As its name suggests, it pronates the forearm (turns the palms down).

• Arises from the ulna and interosseous membrane (the connective tissue between the radius and ulna) and gives rise to four long tendons that insert on the distal phalanges of digits 2-5.
• Because it crosses the wrist and the joints of the fingers, flexor digitorum profundus flexes the wrist and digits two through 5.

• Arises from the radius and interosseus membrane and gives rise to a long tendon that inserts on the distal phalanx of digit 1. "Pollicis" refers to the thumb.
• Flexor pollicis longus flexes the digit 1.

• Multiple points of origin: it arises from the medial epicondyle of the humerus, the coronoid process of the ulna, and from the oblique line of the radius.
• Like the deeper version, flexor digitorum superficialis gives rise to four tendons that split to insert on the sides of the middle phalanges of digits two through five.
• Notice that the split in the tendons for flexor digitorum superficialis provides space for the tendons of flexor digitorum profundus to pass through to the distal phalanges of the digits.
• Flexor digitorum superficialis flexes the wrist and digits two through five.

• A strap-like band of connective tissue called the flexor retinaculum crosses laterally over the tendons of the anterior forearm muscles at the wrist, forming the "carpal tunnel".

• The median nerve also travels through the carpal tunnel; compression of the median nerve causes carpal tunnel syndrome.