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.
Three bursae around the elbow are of clinical significance: one between the olecranon and the triceps, another between the radius and the insertion of the biceps tendon, and finally the olecranon bursa, which lies between the skin and the olecranon process. Bursitis about the elbow most commonly involves the olecranon bursa (Fig. 14–5).
The olecranon bursa may become inflamed secondary to infectious or noninfectious causes.
Examination of the elbow reveals several palpable bony landmarks. Laterally, three bony prominences make up a triangle and correspond to the olecranon, radial head, and lateral epicondyle. An effusion of the elbow is indicated by swelling and tenderness between the lateral epicondyle and olecranon.
The neurovascular structures of the elbow include the brachial artery and the radial, ulnar, and median nerves (Fig. 14–6). The ulnar nerve is palpated on the medial surface of the elbow as it runs through the cubital tunnel. Assessment of the neurovascular structures is of critical importance when evaluating and treating elbow fractures. Further discussion will be included under the management of specific fractures.
The neurovascular structures at the elbow.
An anteroposterior (AP) and lateral radiograph should be obtained (Fig. 14–7). Oblique views will aid in the diagnosis of some elbow fractures.
The normal radiographic appearance of bony articulations of the elbow. A. AP view. B. Lateral view.
A diagnostic aid in evaluating radiographs of suspected supracondylar fractures in children is the carrying angle. The intersection of a line drawn through the midshaft of the humerus and a line through the midshaft of the ulna on an AP extension view determines the carrying angle (Fig. 14–8). Normally, the carrying angle is between 0 and 12 degrees. Traumatic or asymmetric carrying angles of >12 degrees are often associated with fractures.
The carrying angle demonstrated by a line drawn through the midshaft of the ulna and another line through the midshaft of the humerus. The normal carrying angle is between 0 and 12 degrees. A carrying angle of >12 degrees is often associated with fractures of the distal humerus.
The lateral view at 90-degree flexion is the most important view as it allows the physician to note the radiocapitellar and anterior humeral line as well as evaluate the fat pads.