The elbow is a hinge joint composed of three articulations: humeroulnar, radiohumeral, and radioulnar. These articulations provide a high degree of inherent stability to the elbow and are supported by several ligamentous structures—the radial collateral, ulnar collateral, annular ligaments, and the anterior capsule (Fig. 14–1). The biceps, triceps, brachialis, brachioradialis, and anconeus provide muscular dynamic stability.
Elbow injuries are caused by a direct blow, valgus stress from throwing, or axial compression. Acute traumatic injuries may result in fractures to the radius and ulna or the distal humerus. With repetitive valgus stress, patients may develop chondromalacia, loose bodies in the posterior or lateral compartments, injury to the ulnar collateral ligament, injury of the flexor pronator muscle group, osteochondritis dissecans, or ulnar neuritis.1
The important ligamentous structures of the elbow. The annular ligament holds the radial head in position. The radial collateral ligament is broader and blends with the annular ligament. A. Medial view. B. Lateral view.
The distal humerus is divided into two condyles (Fig. 14–2). The coronoid fossa is the area of very thin bone that serves as the surface of contact with the coronoid process of the olecranon when the elbow goes into full flexion. The articular surface of the medial condyle is called the trochlea. It serves as the articulating surface of the ulnar olecranon. The lateral articular surface of the distal humerus is the capitellum, which articulates with the radial head.
The important landmarks of the distal humerus. The bone between the condyles is very thin.
The nonarticular portions of the condyles are called epicondyles, and serve as points of attachment for the muscles of the forearm—pronator-flexors attach to the medial epicondyle, while supinator-extensors attach to the lateral epicondyle. Just proximal to either epicondyle are the supracondylar ridges that also serve as points of attachment for the forearm muscles. The muscles surrounding the elbow impact fracture alignment (Figs. 14–3 and 14–4). With a fracture, continual traction by these muscles results in displacement of the fragments, and on occasion, nullification of an adequate reduction.
The muscles surrounding the elbow. These muscles act to displace fractures occurring at their attachments. BR, brachioradialis; ECRL, extensor carpi radialis longus; CE, common extensor tendon; PT, pronator teres; CFT, common flexor tendon; BB, biceps brachia; T, triceps.
The triceps and the biceps act to pull the radius and the ulna proximally and thus cause displacement of elbow fractures.