REIDER PART 103

Ci iapter 3_Elbow and Forearm 93

tumors, and fractures. The presentation depends on which branch of the nerve is involved and at what level.

Radial Tunnel Syndrome. As previously noted, the most common entrapment neuropathy of the radial nerve occurs in the radial tunnel at the arcade of Frohse. In addition to the finding of tenderness at this site, the long finger extension test can also suggest the presence of a radial tunnel syndrome. To perform the long finger extension test, the examiner instructs the patient to fully extend the fingers with the wrist also extended about 30°. The patient is instructed to maintain extension of the fingers while the examiner presses down on the dorsum of the long finger, attempting to passivcly flex the metacarpophalangeal joint (Fig. 3-48). If this maneuver reproduces the patients familiar pain in the region of the radial tunnel, the diagnosis of radial tunnel syndrome is further strengthened. The long finger extension test can sometimes be painful in the presence of extensor origin tendinitis (lateral epicondylitis). The site of maximal tenderness can usually be used to distinguish these two conditions, howcver, because in exten$or origin tendinitis the point of maximal tenderness is just distal to the lateral epicondyle whcrcas in radial tunnel syndrome, the point of maximal tenderness is about 4 finger-breadths distal to this same landmark.

Muscular weakness is unusual in radial tunnel syndrome. When weakness is encountered in the presence of an apparent radial neuropathy, careful documentation of the muscles involved often delineates the site of compres-sion. Vital to this differentiation is the knowledge that the brachioradialis, extensor carpi radialis brevis, and exten-sor carpi radialis longus are innervated proximal to the radial tunnel, whereas the extensor carpi ulnaris, extensor digitorum communis, extensor pollicis longus, and extensor pollicis brevis are all innervated distal to it by the posterior interosseous nerve. Strength testing of these muscles is described in Chapter 4, Hand and Wrist. In the presence of an apparent radial nerve palsy, therefore, doc-

Figure 3-48. Long finger extension test.

umentation of weakness of the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis indicates that the site of compression is proximal to the radial tunnel. Severe compression of the posterior interosseous nerve at the radial tunnel leaves those three muscles unaffected but may produce weakness of the extensor digitorum communis, the extensors pollicis longus and brevis, and the extensor carpi ulnaris. In such a patient, the wrist deviates to the radial side when the patient is instructed to actively extend it because the radial wrist extensors are functioning but the extensor carpi ulnaris is not.

Pronator Syndrome. As ałready mentioned, the most common site of median nerve compression in the forearm is the point at which the nerve passes between the two heads of the pronator teres. Pronator syndrome is much less common than compression of the medial nerve at the carpal tunnel and is difficult to diagnose. As noted in the Palpation section, the reproduction of the patients symptoms by dircct pressurc over the pronator teres during resisted forearm pronation is the most reli-able screening test for pronator syndrome. If pronator syndrome is suspcctcd, the effect of prolongcd resisted pronation should also be investigated. This test is per-formed in the same manner described for testing pronation strength (see Fig. 3-40). In this case, however, the examiner resists the patient s attempts at pronation for 60 seconds or morę. Reproduction of the patienfs symptoms by this maneuver further reinforces the possibility of pronator syndrome.

Other Sites of Median Nerve Compression. Several other less common sites of median nerve compression about the elbow and in the forearm are possible. At the elbow, the median nerve may be compressed by the lacer-tus fibrosus. If this is the case, the patient s symptoms may usually be reproduced by prolonged resisted elbow flexion and resisted forearm supination.

The median nerve may also be compressed by the origin of the flexor digitorum superficialis. In this case, the resisted long finger PIP flexion test will sometimes reproduce the patients symptoms. In this test, which is analogous to the long finger extension test, the patient is asked to flex the fingers of the involved hand with the forearm supinated. The examiner’s finger is then hookcd under the middle phalanx of the patient s long finger, and the examiner attempts to extend the PIP joint while the patient resists as strongly as possible (Fig. 3-49). Reproduction of the patient s symptoms by this maneu-ver suggests median nerve compression by the flcxor digitorum superficialis.

The site of a median nerve injury can usually be defincd by the muscles that are affected. An injury proxi-mal to the elbow affects all median-innervated functions, including wrist flexion, finger flexion, thumb flexion, and thumb opposition. If the nerve is injured in the proximal