Elbow Joint Anatomy
The elbow is a synovial hinge joint between the distal end of the humerus and the proximal ends of the radius and ulna (Fig. 3.88). Laterally, the capitulum of the humerus articulates with the slightly concave upper surface of the head of the radius. Medially, the trochlea of the humerus articulates with the deep trochlear notch of the ulna. In the anatomical position (in which the elbow is extended and the forearm is supinated) the orientation of the joint surfaces produces a carrying angle, which displaces the hand somewhat laterally. This angle between the long axes of the arm and the forearm disappears when the forearm is pronated. The joint capsule (Figs 3.89 & 3.90) attaches proximally to the shaft of the humerus above the radial and coronoid fossae anteriorly and to the margins of the olecranon fossa posteriorly. Distally, it attaches to the anular ligament of the proximal radioulnar joint and to the margins of the trochlear notch of the ulna. Synovial membrane lines the capsule and clothes the underlying pads of fat that project into the radial, coronoid and olecranon fossae of the humerus. The cavity of the elbow joint is continuous with that of the proximal radioulnar joint.
There are two collateral ligaments (Figs 3.89 & 3.90). The radial (lateral) collateral ligament passes between the lateral epicondyle and the anular ligament. The ulnar (medial) collateral ligament attaches proximally to the medial epicondyle, while distally its fibres diverge and attach to the medial aspects of the coronoid and olecranon processes of the ulna. Stability of the joint depends on the integrity of these collateral ligaments, which hold the trochlea of the humerus firmly in the trochlear notch.
Rotation of the ulna is prevented by the shape of the articular surfaces of the trochlea. Dislocation of the joint is usually associated with ligamentous or bony injury.
Only flexion and extension occur at the elbow joint. Flexion (about 150°) is produced mainly by biceps and brachialis with a contribution from brachioradialis when the elbow is partially flexed. Flexion is limited by contact between the anterior surfaces of the arm and the forearm. Extension is often assisted by gravity. Active extension is produced by triceps assisted by anconeus. In full extension the olecranon engages in the olecranon fossa of the humerus, limiting the movement and increasing joint stability.
The flexors and extensors of the wrist and hand arising from the humerus close to the joint do not contribute significantly to elbow movements.
Behind the elbow joint lies the tendon of triceps (Fig. 3.91). Immediately anterior to the capsule are brachialis and the tendon of biceps in the cubital fossa (Fig. 3.29). The brachial artery and median nerve are separated from the capsule by brachialis. The ulnar nerve lies behind the medial epicondyle in contact with the ulnar collateral ligament. The vessels and nerves are vulnerable to injury in traumatic dislocation of the joint.
The elbow receives blood from the anastomosis around the joint formed by branches of the brachial, radial and ulnar arteries. The vessels supplying the joint are accompanied by articular nerves derived from branches of the musculocutaneous, radial, ulnar (and sometimes the median) nerves.