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The arm (brachium) consists of the humerus, which articulates distally with the forearm (antebrachium) through the elbow complex. The elbow complex 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.
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Actions of the Elbow Complex
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The articulations of the humerus, radius, and ulna in the elbow result in the following actions:
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- Flexion and extension (Figure 31-1A)
- Humeroulnar joint. Articulation between the trochlear notch of the ulna and the trochlea of the humerus.
- Humeroradial joint. Articulation between the head of the radius and the capitulum of the humerus.
- Pronation and supination (Figure 31-1B and C)
- Proximal radioulnar joint. Articulation between the head of the radius and the radial notch of the ulna.
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The muscles of the arm are divided by their fascial compartments (anterior and posterior), and may cross one or more joints. Identifying the joints that the muscles cross and the side on which they cross can provide useful insight into the actions of these muscles (Table 31-1).
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Muscles of the Anterior Compartment of the Arm
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The muscles in the anterior compartment of the arm are primarily flexors (of the shoulder or elbow or both) because of their anterior orientation (Figure 31-1D). The musculocutaneous nerve (C5–C7) innervates the muscles in the anterior compartment of the arm. However, each muscle does not necessarily receive each spinal nerve level between C5 and C7. The following muscles are located in the anterior compartment of the arm:
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- Coracobrachialis muscle. Attaches ...