CHAPTER 31: Arm

ARM

BIG PICTURE

The arm, or brachial region, contains the humerus and is located between the shoulder and elbow. The humerus articulates with the forearm (antebrachium) at the elbow complex, which consists of three bones: humerus, ulna, and radius. The articulations of these bones result in three separate joints that share a common synovial cavity, enabling the forearm to flex, extend, pronate, and supinate on the humerus.

ACTIONS OF THE ELBOW COMPLEX

The elbow complex consists of the joints and actions (Figure 31-1A–C):

• Humeroulnar joint. Articulation between the humerus (trochlea) and ulna (trochlear notch).

• Humeroradial joint. Articulation between the humerus (capitulum) and radius (head).

  • Flexion. Bending of the elbow (i.e., biceps brachii and brachialis muscles; musculocutaneous nerve).

  • Extension. Straightening of the elbow (i.e., triceps brachii muscle; radial nerve).

• Proximal radioulnar joint. Articulation between the radius (head) and ulna (radial notch).

  • Pronation. Pivoting the elbow (forearm) into the prone position (palms down) (i.e., pronator teres muscle; median nerve).

  • Supination. Pivoting the elbow (forearm) into the supine position (palms up) (biceps brachii muscle; musculocutaneous nerve).

MUSCLES OF THE ARM

BIG PICTURE

The muscles of the arm are divided by their fascial compartments (anterior and posterior), and primarily act on the elbow. Identifying the joints that the muscles cross provides useful insight into the actions of these muscles (Table 31-1).

MUSCLES OF THE ANTERIOR COMPARTMENT OF THE ARM

The muscles in the anterior compartment of the arm have the following in common:

• Common action. Flexion of the elbow (due to their anterior orientation to the humeroulnar hinge joint).

• Common innervation. Musculocutaneous nerve (C5–C7).

The following muscles are within the anterior compartment of the arm (Figure ...