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Anatomy
The elbow articulation is composed of three distinct joints. (Figures 1 and 2). The humeroulna, considered the principal elbow joint, is formed by the trochlear of the humerus articulating with the trochlear notch of the ulna. It is a hinge joint, between the arm and the forearm, allowing flexion and extension. The humeroradial, formed by the capetellum articulating with the head of the radius; and the superior radioulna, allow pronation and supination.
All three are contained within a single synovial cavity. This joint capsule is attached to the humerus at the proximal margin of the coronoid fossa, anteriorly, and the olecranon fossa, posteriorly.1 It extends distally to encompass the entire articulation,2 attaching distally to the trochlear notch and the annular ligament. The capsule comprises of an inner synovium and an outer fibrous layer separated by a layer of fat. Normally, only the anterior distal humeral fat is visible as the posterior fat is depressed within the olecranon fossa.1 When the forearm is supinated and the elbow is extended, a valgus angle of approximately 15 deg is formed between the humerus and forearm, referred to as the carrying angle.2
The most prominent bony landmark of the elbow is the olecranon. Localised swelling may be present directly over the olecranon as an olecranon bursitis, occurring secondary to repetitive irritation or direct trauma to the region.3
The shaft of the humerus flares to form the medial and lateral epicondyles,2 the medial being easily palpable and more prominent than the lateral.4 The flexor and pronator muscles of the forearm arise from the medial epicondyle and the extensor muscles of the forearm arise from the lateral epicondyle. The distal articular surface of the humerus is a continuation of the epicondyles and forms two distinct articulations. The grooved medial surface is the trochlea; articulating with the ulna and the rounded lateral surface, the capitulum or capitellum, which articulates with the radial head. Above the trochlea there are apposing depressions in the anterior and posterior surfaces - the coronoid fossa and the olecranon fossa, respectively.2
The elbow ligaments (Figure 3) consist of the ulna collateral (medial), radial collateral (lateral), and annular ligaments. The annular ligament is attached to the ulna and clasps the head and neck of the radius in...