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Anatomy and Principles of Evaluation

Articulations of the distal humerus and proximal ulna and radius form the elbow joint (Figure 267-1).

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.

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. The ulnar nerve is palpable as a cord just posterior to the medial epicondyle, and is vulnerable to injury with trauma over this area.

The neuroanatomy is best understood by appreciating the neural control of basic wrist and finger movement (Figure 267-2). 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 branch travels around the proximal radius and controls the muscles of finger and thumb extension. The remainder of the radial nerve is purely sensory and innervates the dorsal aspect of the hand from the thumb to the radial half of the ring finger. Thus, the proximal portion of the radial nerve controls the more proximal function of wrist extension, the distal branch (posterior interosseus nerve) controls the more distal function of finger extension, and another branch is purely sensory. Therefore, an isolated injury to the posterior interosseous branch affects finger extension but spares wrist extension and sensation to the dorsum of the hand. The single best test of radial nerve motor function is to have the patient extend both the wrist and fingers against resistance (Table 267-1). Sensation is tested over the dorsum of the thumb index web space.

Figure 267-2.

Neural innervation of the forearm, wrist, hand, and digits. A. Radial nerve innervation. B. Median nerve innervation. C. Ulnar nerve ...

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