Three articulations share one capsule: a hinge between humerus and ulna, a contact with the radius, and a pivot between the two forearm bones
Elbow joint — a compound joint.
Anatomy · Joints & cartilage
Elbow joint
A hinge with a pivot built in
Upper limb · arm and forearm
The elbow is a compound synovial joint where the humerus meets both bones of the forearm inside a single capsule. The humeroulnar and humeroradial joints form a hinge for bending and straightening, while the proximal radioulnar joint is a pivot that lets the radius rotate in pronation and supination.
How to spot them
- ▸The bony point at the back is the olecranon of the ulna, with the medial and lateral epicondyles of the humerus to either side
- ▸The trochlea of the humerus fits the trochlear notch of the ulna like a pulley in a wrench
- ▸The radial head is held against the ulna by the annular ligament
- ▸The ulnar nerve runs in a groove behind the medial epicondyle
What to know
The bony point at its back is the olecranon, and a bursa over that point swells in students and miners
Elbow joint — olecranon bursitis.
Blame the ulnar nerve for the tingle when a spot behind the medial epicondyle is struck; the name puns on humerus
Elbow joint — the 'funny bone'.
A young child pulled by the hand can slip the head of the radius out from under the annular ligament
Elbow joint — nursemaid's elbow (radial head subluxation).
Overuse of the forearm extensor tendons at the lateral epicondyle causes a painful condition named after a racquet sport
Elbow joint — tennis elbow (lateral epicondylitis).
Key ideas
- Two kinds of movement in one place: hinge (flexion and extension at the humeroulnar and humeroradial joints) and pivot (pronation and supination at the radioulnar joint).
Quick-fire facts
- •OpenStax describes the elbow as a uniaxial hinge formed by the humeroulnar joint, with the humeroradial joint beside it; the proximal radioulnar joint is a pivot.
- •The olecranon is the proximal end of the ulna and forms the point of the elbow.
- •The ulnar collateral ligament on the medial side is the one damaged in many throwing injuries and is the basis of 'Tommy John' surgery.
- •The 'funny bone' is not a bone: it is the ulnar nerve passing behind the medial epicondyle, and the joke puns on humerus.
- •The annular ligament wraps the radial head and lets it spin against the ulna.
- •Nursemaid's elbow is a subluxation of the radial head in young children, typically from a sudden pull on the hand.
- •Tennis elbow is lateral epicondylitis; golfer's elbow is its medial counterpart.
- •With the arm straight and the palm forward the forearm angles slightly outward from the arm: the carrying angle.
Drill it — 7 cards
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Sources
- OpenStax — Anatomy of selected synovial joints (Anatomy and Physiology 2e)
- TeachMeAnatomy — Elbow joint
- NHS — Tennis elbow