Electrodiagnostic testing of neurologic injuries in athletes.

In this article the value and limitations of the EMG examination in assessing patients with known or suspected sports-related nerve injuries is reviewed. The basic components of the EMG examination--the nerve conduction studies (NCS) and the needle electrode examination (NEE)--are described, and their components are defined. The types of pathophysiology produced by focal nerve lesions is detailed, and their effects on the various portions of the EMG examination are described. Of note is that the two processes that cause clinical weakness, conduction block and conduction failure (axon loss), both alter the NCS amplitudes, without having any appreciable effect on the rate of impulse conduction along the nerve fibers that can still conduct across the lesion site. For this reason, the most widely known NCS parameter, the conduction velocity, is of very little value with the acute type of nerve lesion usually encountered in sports. The fact that fibrillation potentials, seen on NEE, are the most sensitive indicator of motor axon loss, is noted, as is the fact that they do not appear until some 3 weeks following nerve injury. Our EMG laboratory experience with sports-related nerve injuries is reviewed. The majority of patients were engaged in contact sports (especially football). The majority of lesions affected primarily the shoulder girdle region, although a variety of disorders (radiculopathies, brachial plexopathies, various mononeuropathies) were found. Some of the difficulties in the EMG assessment of this region are reviewed, as well as the clinical and EMG findings with three entities, "burners," acute brachial neuropathy, and rotator cuff tears, which affect it and which occur in athletes.