Elbow joint

Location: Between the arm and the forearm, a little below the medial and lateral epicondyles of the humerus, which can be felt on either side.

Bones taking part

• Humerus (distal end: trochlea and capitulum)
• Ulna (trochlear notch)
• Radius (head)

Articulating surfaces

• Humero-ulnar: the spool-shaped trochlea of the humerus with the trochlear notch of the ulna
• Humeroradial: the rounded capitulum of the humerus with the slightly concave upper surface of the head of the radius
• The coronoid fossa (in flexion, for the coronoid process), radial fossa (for the radial head) and olecranon fossa (in extension, for the olecranon) receive the ulna and radius at the ends of movement.

Structural

Synovial joint (hinge type), made up of the humero-ulnar and humeroradial articulations in one capsule.

Functional

Diarthrosis (freely movable).

Synovial subtype

Hinge (ginglymus).

Axes

Uniaxial: flexion and extension about one transverse axis through the trochlea and capitulum.

Capsule & cavity

One fibrous capsule encloses the humero-ulnar, humeroradial and proximal radioulnar joints. It is thin in front and behind, where flexion and extension need slack, and thickened on each side into the collateral ligaments. Anteriorly and posteriorly it attaches to the humerus above the coronoid and radial fossae and the olecranon fossa, and to the ulna around the margins of the trochlear notch and coronoid process; below it blends with the annular ligament rather than attaching to the radius, so the radial head can rotate.

• Shortens and lengthens the limb so the hand can be brought to the face or moved away from the body.
• Positions the hand at different distances from the trunk.
• Transmits forces from the forearm to the arm, for example when pushing or lifting.

Stability vs mobility: A stable joint. The trochlea fits deeply into the trochlear notch of the ulna, and strong collateral ligaments support each side. In full extension the olecranon fits into the olecranon fossa, adding bony support. The trade-off is that movement is limited to one plane.

• Dislocation of the elbow is usually posterior, typically from a fall on the outstretched hand with the elbow flexed; the ulnar nerve can be stretched or injured.
• Subluxation of the radial head ('pulled elbow' or 'nursemaid's elbow') happens in young children when the forearm is suddenly pulled; the radial head slips out of the annular ligament. This is a problem of the proximal radioulnar joint within the elbow capsule.
• Olecranon bursitis ('student's elbow') follows repeated pressure on the back of the elbow.
• Injury to the ulnar collateral ligament is seen in throwing athletes from repeated medial stress.
• Supracondylar fractures of the humerus in children lie close to the joint and can injure the brachial artery and median nerve.

• Classify it as a synovial hinge joint, uniaxial, with flexion and extension only.
• Name the two articulations: humero-ulnar (trochlea–trochlear notch) and humeroradial (capitulum–radial head).
• State clearly that the proximal radioulnar joint shares the capsule but is a separate pivot joint; pronation and supination are not elbow movements.
• Describe the ulnar collateral ligament's three bands and its attachments.
• Explain why the radial collateral ligament attaches to the annular ligament and not the radius.
• Name the flexors (brachialis, biceps, brachioradialis) and extensors (triceps, anconeus).

• Listing pronation and supination as elbow movements.
• Writing that the radius articulates with the trochlea; the radius meets the capitulum.
• Calling the elbow a multiaxial joint because the forearm can rotate; the elbow joint proper is uniaxial.
• Saying the annular ligament attaches to the radius; it attaches to the ulna and only encircles the radial head.
• Forgetting that the elbow, humeroradial and proximal radioulnar joints share one capsule.