Articulations of the distal humerus and proximal ulna and radius form the elbow joint (Figure 270-1).
Elbow anatomy. A. Anterior view. B. Lateral view. C. Medial view.
The distal humerus is comprised of the medial and lateral condyles. The articulating surfaces of the medial and lateral condyles are the trochlea and the capitellum, respectively. Medially, the trochlea articulates with the olecranon of the ulna to form a uniaxial hinge joint. Laterally, the capitellum abuts the radial head to form a pivot joint. The medial and lateral epicondyles are nonarticulating surfaces where the forearm, wrist, and digit flexors and pronators (medial), and extensor and supinator (lateral) muscles originate.
The radius and ulna articulate at their ends to form the proximal and distal radioulnar joints and are joined along their entire length by a fibrous interosseous membrane. The ulna is a fairly straight bone, whereas the radius has an important outward bowing. During supination and pronation, the radius rotates around the relatively fixed ulna. Because these bones have such a close relationship, injury to one will frequently impact the other.
Several neurovascular structures lie in proximity to the distal humerus, and evaluation of their function is essential. These include the brachial artery and the radial, median, and ulnar nerves (Table 270-1).
TABLE 270-1Sensory and Motor Function Testing of the Radial, Median, and Ulnar Nerves ||Download (.pdf) TABLE 270-1 Sensory and Motor Function Testing of the Radial, Median, and Ulnar Nerves
| ||Radial ||Median ||Ulnar |
|Sensory function (test with 2-point discrimination) ||Dorsum of the thumb and index web space ||Tip of the index finger ||Tip of the little finger |
|Motor function (test against resistance) ||Extend wrist and fingers (“Rock” and “Paper” motions) ||“OK” sign with thumb and index finger; abduct thumb (“thumbs up” motion) ||Abduct index finger (“Scissors” motion) |
The neuroanatomy is best understood by appreciating the neural control of wrist and finger movements (Figure 270-2). The radial nerve travels over the lateral epicondyle into the forearm before splitting into a deep branch that pierces through the supinator muscle and a superficial branch that lies adjacent to the radial artery. The proximal portion of the radial nerve controls the more proximal function of wrist extension, the deep branch (posterior interosseous nerve) controls the more distal function of finger and thumb extension, and the superficial branch is purely sensory, providing sensation over the dorsal aspect of the hand from the thumb to the radial half of the ring finger. Thus, an isolated injury to the posterior interosseous branch affects finger extension but spares wrist extension and sensation to the dorsum of the hand. This can be seen in a compression ...