An improved technique for radial nerve conduction studies.

A technique for recording evoked sensory potentials from the radial nerve has already been reported by us (Downie and Scott, 1964). This technique, although reliable, is time consuming and occasionally difficult and the amplitude of potentials may be as low as 1 to 2 microvolts. The purpose of this communication is to describe a simpler technique by which potentials of greater amplitude can be obtained. In addition, the segment of nerve tested is one which can be readily identified and biopsied if so desired without causing unpleasant or disturbing sensory loss to the subject. The location of a nerve which is to be tested is usually determined by stimulating its motor fibres and finding the stimulus site from which maximal muscle contraction is obtained. In the case of pure sensory nerves, electrodes of rather wide extent are used, such as ring electrodes for the digital nerves, or the broad electrode around the radial aspect of the wrist as described in the previous report (Downie and Scott, 1964). In studying the anatomy of the superficial terminal branches of the radial nerve it can be seen that one or more branches pass superficial to the tendon of extensor pollicis longus. In most people these can be palpated by running an examining finger along the tendon. Active extension of the thumb makes such examination easier. The largest branch crosses the tendon about 1 cm. distal to the extensor retinaculum. This site is sufficiently constant to allow accurate placement of an active recording electrode even when the nerve cannot be palpated. Proximally the superficial branches of the radial nerve merge and run along the radial border of the forearm on its flexor surface in close apposition to the cephalic vein to a point just distal to the mid forearm where the nerve passes more deeply.