Pattern of conduction times in the distribution of the radial nerve

THE RADIAL NERVE is one of the most frequently injured nerves and may be the site of a specific mononeuritis or may be affected in polyneuritis. The clinical criteria for the diagnosis of the site of a lesion of the radial nerve are based largely on the serial branching of the nerve, the localization depending on the involvement of the distal branches and preservation of the proximal branches. However, the clinical localization of the lesion is not always clear. Thus, the degree of involvement of the individual fibers in a high lesion may vary considerably; in a funiculitis of the nerve, because of the maintenance of fiber distribution for some distance proximal to the entry of a nerve branch, it is possible to have a lesion somewhat above the presumed level of the lesion determined clinically,l and the motor fibers are frequently more susceptible to compression than the sensory fibers.2$3 Electrical excitation of nerve can be of considerable help in the investigation of a nerve lesion. The retention of nervous excitability below the level of a lesion, even in a complete palsy, is a sign of preservation of continuity and lack of degeneration of nerve fibers, whereas loss of excitability is the earliest sign of a degenerative lesion of the nerve. Electrical excitation is useful in conjunction with electromyography in the diagnosis and in following the course of reinnervation. The involvement of the nerve in a mononeuritis or in the course of a polyneuritis can be confirmed by the demonstration of slowing of conduction velocity or an increase in latency. However, there have been few reports of electrical excitation of the radial nerve. Dejerine and Bernheim4 in 1899 stimulated the