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 epicondyles are nonarticulating surfaces that serve as sites of origin for forearm, wrist, and digit flexors and pronators (medial), and extensors and supinators (lateral). Medially, the trochlea articulates with the olecranon to form a uniaxial hinge joint. Laterally, the capitellum abuts the radial head to form a pivot joint. Between the condyles, the coronoid fossa is anterior, and the olecranon fossa is posterior. These allow for full flexion and extension of the ulna. The radial fossa lies proximal to the capitellum anteriorly and permits full flexion of the radius.
The radius and ulna are joined together along their entire length by a fibrous interosseous membrane, and articulate only at their ends to form the complex proximal and distal radioulnar joints. The ulna is a comparatively straight bone, whereas the radius has an important outward bowing. During the motions of supination and pronation, the radius rotates around the relatively fixed ulna. Because these bones have such a close relationship to one another, injury to one will have a direct impact on the other. A displaced or angulated fracture of one bone typically disrupts the other or causes a dislocation at the proximal or distal radioulnar joint.
Several important neurovascular structures lie in close proximity to the distal humerus, and evaluation of their function is essential. These include the brachial artery, palpable just medial to the distal biceps tendon in the antecubital fossa, 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
|Test for sensory function
|Dorsum of the thumb index web space
|Two-point discrimination over the tip of the index finger
|Two-point discrimination over the little finger
|Test for motor function
|Extend both wrist and fingers against resistance
|"OK" sign with thumb and index finger; abduction of the thumb (recurrent branch)
|Abduct index finger against resistance
The neuroanatomy is best understood by appreciating the neural control of basic wrist and finger movement (Figure 270-2). The radial nerve travels over the lateral epicondyle and supplies the muscles of wrist extension before it branches off into the posterior interosseous nerve. This deep branch travels around the proximal radius and through the supinator muscle and controls the muscles of finger and thumb extension. The remainder of the radial nerve lies adjacent to the radial artery. This superficial ...