Elbow joint

Question 1

Outline the elbow joint.

Answer 1

• Synovial joint of the hinge variety between the lower end of the humerus and the upper ends of radius and ulna. It communicates with the proximal radioulnar joint.
• The lower end of the humerus has the prominent conjunction of capitulum and trochlea.
• The capitulum is a portion of a sphere which articulates with the upper surface of the head of the radius. It projects forwards and downwards, and is not visible on the posterior aspect of the humerus.
• In contrast the trochlea, which lies medial, is a grooved surface that extends around the lower end of the humerus to the posterior surface of the bone and articulates with the trochlear notch of the ulna.
• The groove of the trochlea is limited medially by a sharp ridge that extends further distally. Laterally a blunter ridge blends with the articular surface of the capitulum more proximally. Thus a tilt is produced at the lower end of the humerus that accounts in part for the carrying angle of the elbow. * Fossae immediately above the capitulum and trochlea receive the head of the radius and coronoid process of the ulna, respectively, in full flexion; posteriorly a deep fossa receives the olecranon in full extension.
• The upper surface of the cylindrical head of the radius is spherically concave to fit the capitulum.
• The upper end of the ulna shows the deep trochlear notch. A curved ridge crosses the notch connecting the prominences of coronoid process and olecranon; the ridge fits the groove in the trochlea of the humerus. The obliquity of the shaft of the ulna to this ridge accounts for most of the carrying angle at the elbow.

Question 2

Describe the capsule of the elbow joint.

Answer 2

• The capsule is attached to the humerus at the medial and lateral margins of the trochlea and capitulum, respectively, but in front it is attached above the coronoid and radial fossae, and at the back above the olecranon fossa.
• Distally, the capsule is attached to the margins of the trochlear notch of the ulna, and to the annular ligament of the proximal radioulnar joint.
• It is not attached to the radius.
• The capsule and lower part of the annular ligament are lined with synovial membrane, which is attached to the articular margins of all three bones. * The synovial membrane thus lines the fossae on the lower end of the humerus. * The quadrate ligament, which is attached to the lower margin of the radial notch of the ulna and the neck of the radius, prevents downward herniation of the synovial membrane between the anterior and posterior free edges of the annular ligament.

Question 3

Outline the ligaments of the elbow joint.

Answer 3

• The ulnar collateral (medial) ligament of the elbow joint is triangular and consists of three bands.
• The anterior band is the strongest. It passes from the medial epicondyle of the humerus to a small tubercle (previously called the sublime tubercle) on the medial border of the coronoid process.
• The posterior band joins the sublime tubercle and the medial border of the olecranon.
• A thin middle band connects these two and its grooved surface lodges the ulnar nerve on its way from the arm to the forearm.
• The radial collateral (lateral) ligament is a triangular band. Its apex is attached to the lateral epicondyle and its base fuses with the annular ligament of the head of the radius.
• The anterior and posterior ligaments are merely thickened parts of the capsule.
• The annular ligament is attached to the anterior and posterior margins of the radial notch of the ulna, and clasps the head and neck of the radius in the proximal radioulnar joint. It has no attachment to the radius, which remains free to rotate in the annular ligament.