Elbow Joint

Introduction

Introduction to the Elbow Joint

The elbow is a compound synovial hinge joint that connects the arm to the forearm. It consists of three separate articulations enclosed within a single joint capsule: the humeroulnar (trochlea of humerus with trochlear notch of ulna), the humeroradial (capitulum of humerus with head of radius), and the proximal radioulnar joint (head of radius with radial notch of ulna). Together, these permit flexion and extension of the forearm, as well as the rotational movements of pronation and supination that are essential for hand positioning.

The elbow's stability is provided by its congruent bony architecture and strong collateral ligaments, while its superficial position makes it vulnerable to fractures, dislocations, and overuse injuries. Understanding the intricate anatomy of the elbow is critical for diagnosing nerve entrapments, managing traumatic injuries, and performing safe surgical approaches.

Study

1. Articular Surfaces and Joint Classification

The elbow is a compound synovial joint comprising three articulations. The humeroulnar joint is a hinge (ginglymus) joint between the spool-shaped trochlea of the humerus and the deep trochlear notch of the ulna, responsible for flexion and extension. The humeroradial joint is a modified ball-and-socket joint between the rounded capitulum of the humerus and the concave proximal surface of the radial head. The proximal radioulnar joint is a pivot (trochoid) joint between the cylindrical radial head and the radial notch of the ulna, enclosed by the annular ligament. All three share a common synovial cavity.

2. Joint Capsule and Ligaments

The fibrous capsule encloses all three articulations. It is weak anteriorly and posteriorly to allow flexion and extension, but reinforced medially and laterally by strong collateral ligaments.

The ulnar (medial) collateral ligament is triangular and consists of three bands: the anterior band (the strongest, from the medial epicondyle to the coronoid process), the posterior band (to the olecranon), and the oblique band (deepening the socket). The anterior band is the primary restraint to valgus stress.

The radial (lateral) collateral ligament complex includes the radial collateral ligament (from lateral epicondyle to annular ligament and radial notch), the lateral ulnar collateral ligament (from lateral epicondyle to supinator crest of ulna, important for posterolateral rotatory stability), and the annular ligament (encircling the radial head, holding it against the ulna).

3. Synovial Membrane and Bursae

The synovial membrane lines the capsule and extends inferiorly into the proximal radioulnar joint. Three clinically important bursae surround the elbow: the subcutaneous olecranon bursa (over the point of the elbow), the intratendinous olecranon bursa (within the triceps tendon), and the bicipitoradial bursa (between the biceps tendon and radial tuberosity).

4. Relations

Anterior to the capsule lie the brachialis muscle, the biceps tendon, the median nerve, and the brachial artery. Posteriorly, the triceps tendon inserts onto the olecranon. Medially, the ulnar nerve passes behind the medial epicondyle in the cubital tunnel. Laterally, the common extensor origin and the radial nerve pass near the joint.

5. Movements

Flexion (0–150°) and extension (150–0°) occur at the humeroulnar and humeroradial joints, with the axis passing through the trochlea and capitulum. The normal carrying angle (cubitus valgus) is 10–15° in males and 15–20° in females. Pronation and supination occur primarily at the proximal and distal radioulnar joints, with the radius rotating around the ulna.

6. Blood Supply

The elbow joint is supplied by an extensive periarticular anastomosis (cubital anastomosis) formed by branches of the brachial, profunda brachii, radial, and ulnar arteries. Key contributors include the superior and inferior ulnar collateral arteries, the radial collateral and middle collateral arteries, and the radial and ulnar recurrent arteries.

7. Nerve Supply

In accordance with Hilton's law, the elbow receives innervation from the musculocutaneous nerve (C5, C6), the median nerve (C6, C7), the radial nerve (C5, C6, C7), and the ulnar nerve (C7, C8, T1). The anterior capsule is innervated predominantly by the musculocutaneous and median nerves, and the posterior capsule by the radial and ulnar nerves.

8. Clinical Considerations

Supracondylar fractures: Common in children, these can injure the brachial artery and the median or radial nerves. Volkmann's ischaemic contracture is a feared complication.

Posterior elbow dislocation: The most common type of elbow dislocation, often associated with fractures of the coronoid process, radial head, or olecranon. The ulnar nerve may be injured.

Pulled elbow (nursemaid's elbow): Subluxation of the radial head from under the annular ligament in young children, caused by sudden traction on the pronated and extended arm.

Lateral epicondylitis (tennis elbow): Overuse tendinopathy of the common extensor origin, particularly the extensor carpi radialis brevis tendon.

Medial epicondylitis (golfer's elbow): Overuse tendinopathy of the common flexor origin, particularly the pronator teres and flexor carpi radialis tendons.

Olecranon bursitis: Inflammation of the subcutaneous olecranon bursa, often due to repetitive pressure or trauma.

Summary

Summary of the Elbow Joint

The elbow is a compound synovial hinge joint uniting the humerus, radius, and ulna. Flexion and extension occur at the humeroulnar and humeroradial articulations; pronation and supination involve the radioulnar joints. The ulnar and radial collateral ligaments provide stability, while an extensive anastomotic network supplies the joint. The elbow is innervated by the musculocutaneous, median, radial, and ulnar nerves. Common clinical conditions include supracondylar fractures, dislocation, pulled elbow in children, epicondylitis, and olecranon bursitis.