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.
