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Muscle Upper Arm

Brachialis Detail

musculus brachialis detail

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.

An expanded entry for Brachialis.

Anatomical Data

Origin, Insertion & Supply

OriginAnterior surface of the humerus, distal half, around the deltoid tuberosity
InsertionUlnar tuberosity and coronoid process of the ulna
Nerve SupplyMusculocutaneous nerve (C5, C6), main supply; Radial nerve (C7). Lateral third additional supply
Blood SupplyBrachial artery
Biomechanics

Function & Actions

Actions
  • Flexes the elbow, the pure elbow flexor, active in all forearm positions
  • The most powerful elbow flexor when the forearm is supinated

It is the main flexor of the elbow in every forearm position, doing most of the work when lifting or lowering a load with the elbow.

Clinical Relevance

Clinical Notes

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.

Palpation

Palpated in the anterior arm between the two biceps heads during resisted elbow flexion with the forearm in pronation (removes biceps contribution).

Pathology

Common Injuries & Conditions

Brachialis Myositis Ossificans

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.

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