The elbow joint is very stable because of the wrench shape of th trochlear notch of the ulna, which fits around the pulley-shaped trochlea of the humerus. The joint is also strengthened by strong medial and lateral collateral ligaments.
The surface of the elbow joint is covered by hyaline cartilage that protects and cushions the joints. The large muscle in the back of the arm, the triceps, attaches to the point of the ulna (called the olecranon). When this muscle contracts, it straightens out the elbow. The biceps muscle in the front of the arm, when contracted, bends the elbow.
Capsule of the elbow jointAnteriorly, the capsule is attached to the humerus along the upper margins of the coronoid and radial fossae and to the front of the medial and lateral epicondyles. Below, it is attached to the margin of the coronoid process of the ulna and to the anular ligament, which surrounds the head of the radius.
Posteriorly, the capsule is attached above to the margins of the olecranon fossa of the humerus. Below, it is attached to the upper margin and sides of the olecranon process of the ulna and to the anular ligament.
Ligaments of the elbow jointThe lateral ligament is triangular in shape and is attached by its apex to the lateral epicondyle of the humerus, and by its base to the upper margin of the anular ligament.
The medial ligament is also triangular in shape and consists principally of three strong bands: (1) The anterior band, which passes from the medial epicondyle of the humerus to the medial margin of the coronoid process. (2) The posterior band, which passes from the medial epicondyle of the humerus to the medial side of the olecranon. (3) The transverse band, which passes between the ulnar attachments of the two preceding bands.
Synovial membraneThe synovial membrane of the elbow joint lines the capsule and covers the floors of the coronoid, radial, and olecranon fossae; it is continuous below with the synovial membrane of the superior radioulnar joint.
Movements of the elbow jointThe elbow joint is capable of flexion and extension. Flexion is limited by the anterior surfaces of the forearm and arm coming into contact. Extension is checked by the tension of the anterior ligament and the brachialis muscle. Flexion is performed by the brachialis, biceps brachii, brachioradialis, and pronator teres muscles. Extension is performed by the triceps and anconeus muscles.
The long axis of the extended forearm lies at an angle to the long axis of the arm. This angle, which opens laterally, is called the carrying angle and is about 170° in the male and 167° in the female. The angle disappears when the elbow is fully flexed.
Important anatomical relationsAnteriorly: The brachialis, the tendon of the biceps, the median nerve, and the brachial artery.
Posteriorly: The triceps muscle, a small bursa intervening.
Medially: The ulnar nerve passes behind the medial epicondyle and crosses the medial ligament of the joint.
Laterally: The common extensor tendon and the supinator.
Related category• ANATOMY AND PHYSIOLOGY
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