The Recording of Lateral Popliteal Nerve

It has been shown by Dawson and Scott (1949) that when the median or ulnar nerve is stimulated with a brief shock at the wrist an action potential can be recorded from the nerve at a higher level in the arm through electrodes placed on the skin over the course of the nerve. This technique has proved to be of considerable practical value in the assessment of patients with ulnar nerve lesions at the elbow (Gilliatt and Thomas, 1960). The advantages of recording the nerve action potential are twofold. In the first place, the potential depends upon the passage of a synchronous volley of impulses under the recording electrodes, and it is thus highly sensitive to dispersion of impulses in different fibres of the nerve. In this way abnormalities of the nerve action potential may be detected when the degree of nerve damage is insufficient to affect conduction velocity in all the constituent fibres. The technique is thus more sensitive than conventional estimation of motor conduction velocity in which measurements of latency are made for the fastest surviving fibre. The second advantage of recording from the nerve itself is that impulses in sensory fibres make a substantial contribution to the action potential. The relative contributions of motor and sensory fibres vary in different nerves, but for the median and ulnar nerves it has been shown by Dawson (1956) that a substantial afferent volley in sensory fibres can be obtained by stimulation below or close to the motor threshold. Recording the nerve action potential may thus be expected to provide information about the behaviour of both motor and sensory fibres in a mixed nerve. The work to be described in the present paper has been concerned with the recording of nerve action potentials from the lateral popliteal (peroneal) nerve. In general we found lateral popliteal nerve action potentials to be smaller than those seen in the upper limb but, once initial technical difficulties had