Chapter 32

### Big Picture

The forearm (antebrachium) consists of the radius and ulna. Proximally, the forearm articulates with the humerus through the elbow complex (humeroulnar and humeroradial joints). Distally, the forearm articulates with the carpal bones through the wrist complex, enabling a wide array of actions. The muscles of the forearm that act upon the elbow, wrist complex, and the digital joints are organized into two fascial compartments, similar to those of the arm muscles. The anterior compartment contains flexor muscles and the posterior compartment contains extensor muscles.

### Actions of the Wrist

The configuration of the wrist complex allows for motion in two planes (Figure 32-1A):

• Flexion
• Extension

###### Figure 32-1

A. Actions of the wrist joint. Superficial (B) intermediate (C) and deep (D) muscles of the anterior forearm.

### Forearm Muscles of the Anterior Compartment

The actions produced by the muscles in the anterior compartment of the forearm depend upon which joints the muscles cross. Some muscles cross the elbow, wrist, digits, and perhaps a combination of each. The muscles in the anterior compartment of the forearm have the following similar features:

• Common attachment. Medial epicondyle of the humerus.
• Common innervation. Median nerve with minimal contribution from the ulnar nerve.
• Common action. Flexion.

The vascular supply to the anterior forearm muscles is from branches of the ulnar and radial arteries.

The muscles in the anterior compartment of the forearm are divided into three groups: superficial, intermediate, and deep.

• Superficial group (Figure 32-1B)
• Pronator teres muscle. Possesses two heads and crosses the elbow complex. The humeral head of the pronator teres muscle attaches to the medial epicondyle and the supraepicondylar ridge of the humerus, and the ulnar head attaches to the coronoid process. Distally, the pronator teres muscle attaches to the midshaft of the radius. The pronator teres muscle primarily produces pronation at the forearm. The median nerve provides innervation (C6–C7) to the pronator teres muscle.
• Flexor carpi radialis muscle. Attaches to the medial epicondyle and the base of metacarpals 2 and 3. The primary action of the flexor carpi radialis muscle is wrist flexion and radial deviation. The median nerve (C6–C7) supplies innervation to this muscle.
• Palmaris longus muscle. Attaches to the medial epicondyle of the humerus and courses superficially over the flexor retinaculum to the palmar aponeurosis in the hand. The primary action of the palmaris longus muscle is to resist shearing forces of the palmar aponeurosis; it is also considered a wrist flexor. Innervation is provided by the median nerve (C7–C8). It is important to note that the palmaris longus muscle may be absent on one or both sides in some individuals....

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