Overview

TypeHinge synovial (with pivot component)

Range of flexion≈0–145°

Carrying angle≈5–15° (greater in females)

The humero-ulnar joint (trochlea in the trochlear notch) is a true hinge and provides most of the bony stability; the humeroradial joint (capitulum with the concave radial head) allows both flexion–extension and rotation of the radius. Both lie in one capsule with the proximal radioulnar (pivot) joint. Range: ≈0–145° of flexion.

The capsule is thin anteriorly and posteriorly and strengthened at the sides by collateral ligaments. The triangular ulnar (medial) collateral ligament has anterior, posterior and oblique bands; its anterior band is the principal restraint to valgus stress (critical in throwing athletes). The fan-shaped radial (lateral) collateral ligament blends with the annular ligament, which encircles the radial head and holds it against the radial notch of the ulna. Fat pads lie in the coronoid, radial and olecranon fossae between the capsule and synovium.

With the elbow extended and the forearm supinated, the forearm deviates laterally from the arm by the carrying angle (≈5–15°, greater in women), allowing the forearm to clear the hips when carrying objects. In full extension the medial and lateral epicondyles and the tip of the olecranon lie in a straight line; in 90° flexion they form an isosceles triangle — this relationship is disturbed in dislocation but preserved in supracondylar fracture.

Location: Between the arm and the forearm.

Parts & subdivisions

Humero-ulnar joint
Trochlea ↔ trochlear notch; hinge.
Humeroradial joint
Capitulum ↔ radial head.
Proximal radioulnar joint
Shares the capsule; pivot for pronation/supination.
Ulnar (medial) collateral ligament
Anterior, posterior and oblique bands; resists valgus.
Radial (lateral) collateral ligament
Lateral epicondyle to annular ligament; resists varus.
Annular ligament
Ring around the radial head.

Anatomy

Innervation: Musculocutaneous, radial, median and ulnar nerves (Hilton’s law).
Arterial supply: Cubital anastomosis — superior and inferior ulnar collateral, middle and radial collateral, radial and ulnar recurrent and interosseous recurrent arteries.
Articulations: Humerus ↔ ulna (humero-ulnar), humerus ↔ radius (humeroradial); proximal radioulnar joint in the same capsule.
Ligaments: Ulnar collateral, radial collateral and annular ligaments; quadrate ligament (radial neck to ulna).

Function

Flexion and extension of the forearm (brachialis, biceps, brachioradialis / triceps, anconeus)
Positions the hand toward or away from the body
Transmits forces between hand and shoulder

Clinical significance

Elbow dislocation

The second most commonly dislocated major joint in adults; usually posterior (FOOSH with the elbow extended). The "terrible triad" — posterior dislocation + radial head fracture + coronoid process fracture — is highly unstable. Check the brachial artery and median and ulnar nerves.

Pulled elbow (nursemaid’s elbow)

In children aged 1–4 a sudden pull on the extended pronated arm slips the radial head partly out of the annular ligament; the child holds the arm pronated and refuses to use it. Reduced by supination–flexion or hyperpronation.

Epicondylitis

Lateral epicondylitis ("tennis elbow") — tendinopathy of the common extensor origin (extensor carpi radialis brevis); medial epicondylitis ("golfer’s elbow") — common flexor origin.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.