The brachialis is the primary elbow flexor, acting regardless of forearm rotation position. Unlike the biceps (which is supination-dependent), brachialis is equally effective in all positions. It inserts onto bone (ulna) not tendon, so it cannot sublux.
| Origin | Anterior surface of the humerus — distal half, around the deltoid tuberosity |
|---|---|
| Insertion | Ulnar tuberosity and coronoid process of the ulna |
| Nerve Supply | Musculocutaneous nerve (C5, C6) — main supply; Radial nerve (C7) — lateral third additional supply |
| Blood Supply | Brachial artery |
| Actions | Flexes the elbow — the pure elbow flexor, active in all forearm positions; The most powerful elbow flexor when the forearm is supinated |
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Brachialis has dual innervation from both the musculocutaneous and radial nerves, making it uniquely preserved in either nerve palsy. In anterior elbow approaches, the brachialis is split longitudinally to access the distal humerus while preserving both nerve supplies. Myositis ossificans of the brachialis (post-traumatic) follows elbow dislocation or fracture, producing a painful flexion block.
Palpated in the anterior arm between the two biceps heads during resisted elbow flexion with the forearm in pronation (removes biceps contribution).
Post-traumatic heterotopic ossification within the brachialis after elbow dislocation producing a progressive flexion block, managed conservatively for 12-18 months then surgically if persistent.
