This study defines the normal range of motor conduction velocities and distal latencies in nerves to various leg and foot muscles, and in the proximal and distal segments of the same nerve to the foot muscles. The significance of differences in temperature in individual variations in nerve conduction velocity has been evaluated.A series of patients with various diseases of the sciatic nerve or its branches has been similarly investigated. The pattern of abnormality in nerve conduction has been found to be of considerable assistance in clinical evaluation. METHODS AND MATERIALThe sciatic nerve was stimulated proximally in the buttock or upper thigh in its position either between the greater trochanter of the femur and the tuberosity of the ischium, or directly below the middle of this position on a line drawn downwards to the apex of the popliteal fossa. The lower position of stimulation of the sciatic nerve was in the apex of the popliteal fossa at the level of the upper border of the femoral condyles. At the ankle the posterior tibial nerve was stimulated posterior to the middle part of the medial malleolus, and the anterior tibial nerve at a line joining the upper part of the malleoli. The conduction velocity was determined between the points of stimulation, and the latency of response from the distal stimulating point. Action potentials were recorded intramuscularly from the tibialis anticus, gastrocnemius, and soleus in the leg, and from the extensor digitorum brevis and abductor hallucis in the foot.The stimulating electrode at all positions, other than the proximal stimulating point in the thigh, was a bipolar surface electrode with a diameter of 6 mm. for each electrode and a centre-to-centre separation of 25 mm. (DISA 13K62). The surface of the skin was prepared by gentle abrasion and rubbing with ether. Needle electrodes were used for the stimulation in the upper thigh or buttock. The needles were 0 4 mm. in diameter and 8 cm. in length, stainless steel and non-insulated. The needles were placed 2 5 cm. apart, at a depth of 3 to 6 cm., in the same position as that of the bipolar surface stimulating electrode. A thin flat lead plate, ground 3 x 8 cm., was placed between the stimulating and recording electrodes. The stimulus was a rectangular pulse of 0-7 msec. duration. It was obtained from a stimulator (DISA) with a double shielded output transformer (Buchthal, Guld, and Rosenfalck, 1955). The output impedance was 15kfQ and the maximum output current 15 mA. The stimulating current was 2 mA at threshold and 4 to 6 mA with supramaximal stimulation, both with surface and with needle electrodes; this current was obtained with 10 and 25 V between the electrodes. A 50 ,usec. signal was introduced to indicate the onset of the stimulus. The recording electrodes were three concentric needles with an external diameter of 0 45 mm.; the leading-off area of the core was 0 07 mm.2 (DISA 13K50).In five subjects an electrode convertible from bipolarity to unipolarity was used in recording from the gastrocnemius and sol...

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