sign in sign up
<<
Home , Saphenous nerve

Tohoku J. exp. Med., 1983, 140, 67-71

Saphenous Conduction in Healthy Subjects

ITARU K.IMURA,*D. RAM AYYAR and JAMES C. MCVEETY Department of Neurology, University of Miami School of Medicine, Miami, Florida 33101, USA

KIMURA, I., AYYAR, D.R. and MCVEETY, J.C. Saphenous Nerve Conduction in Healthy Subjects. Tohoku J. exp. Med., 1983, 140 (1), 67-71 Saphenous nerve conduction was studied in 40 healthy subjects utilizing a slight modification of the method described by Wainapel et al. The mean values obtained were as follows: distal sensory latency, 2.9+0.3 msec for 10 cm distance; conduction velocity, 46.6+3.5 m/sec; and amplitude of sensory nerve action potential, 10.7+4.3 µV. The technique should be useful in the electro- diagnostic differentiation between lumbar root (L3, L4) lesions and postganglionic lesions such as and lesions and entrapment neuropathy of the saphenous nerve. --- sensory nerve conduction; lumbar ; saphenous nerve; electrodiagnosis

Saphenous nerve, the largest branch of the femoral nerve is a purely sensory nerve. It arises from the third and fourth lumbar roots, traverses the internal aspect of thigh and leg and terminates in the medial aspect of the . The nerve lies lateral to the in the distal part of the femoral triangle from where it descends into the subsartorial or Hunter's canal by piercing its roof and descends to the medial aspect of the . From here it takes a downward course along the medial aspect of the leg in the company of the long saphenous vein. The nerve ends by dividing into branches that supply the medial side of the leg and foot. The length of the nerve and its superficial location, particularly in the leg, make it an ideal choice to be used for nerve conduction studies. In spite of this saphenous nerve conduction studies are not frequently utilized in many laboratories. Different methods have been described and of these the one described by Wainapel et al. (1978) appears to be the least demanding technically. We are herein describing a simple method which is a slight modification of the method described by Wainapel et al.

MATERIALS AND METHODS Forty adults (20 men and 20 women) from 19 to 79 years of age (mean age 42.2) were studied. All subjects were screened by history and physical examination to exclude those with any suspicion of underlying neurological disease.

Received for publication, August 12, 1982. * Present address: Department of Neurology, Institute of Brain Diseases, Tohoku University School of Medicine, 1-1 Seiryo-Machi, Sendai 980, Japan. 67 68 I. Kimura et al.

A TECA TE4 electromyograph (White Plains, New York) was used to elicit and record responses on photosensitive paper for measurement. Rectangular pulse stimuli of 0.1 msec duration were used for percutaneous nerve stimulation. The high-cut filter and low-cut filter were set at 3.2 kHz and 32 Hz, respectively. Room temperature was thermostatically maintained at 26.8 degrees Centigrade during all examinations, and subjects' limbs were kept warm and the limb temperature was maintained at or above 33.0 degrees Centigrade. Electrode setting in this study is shown in Fig. 1. Surface electrode (TECA, 6030) of 10 mm in diameter was placed just anterior to the anterior border of medial malleolus, in

Fig . 1. Electrode setting for antidromic sphaneous nerve conduction studies. Recording electrode (a), medial malleolus (m), ground electrode (g) and three points of nerve stimulation (b, c, d).

the space between the malleolus and the medial border of the tibialis anterior tendon as a recording electrode (a). The reference electrode was located 3.0 cm distally from the recording electrode along the saphenous vein. The sites of stimulation were located 10, 15 and 20 cm above the recording electrode along the medial border of the (b, c, d). Firm pressure was exerted on the stimulating probe, pushing it between muscle belly of the medial head of gastrocnemius and the tibia. The subject lies on his side with the knee slightly bent. We also measured sural sensory nerve conduction according to the antidromic method described by DiBenetto (1970). Stimulating points along the nerve were at 7,14 and 21 cm above the recording electrode. The recording electrode was placed 2.0 cm below and behind the lateral malleolus and the reference electrode was placed 3.0 cm in front of it. Sensory nerve conduction velocity (SCV) was calculated by the equation: SCV = (L1-L2)J(D1-D2) where L1 and L2 represent proximal and distal latencies (msec) measured from the stimulus artifact to the initial rising point of the response and D1-D2, distance (mm) from proximal to distal stimulation. Distal sensory latency (msec) was measured from the stimulus artifact to the peak of the first negative deflection of the response and amplitude was measured from negative to positive peaks.

RESULTS Table 1 summarizes the results of our saphenous and conduction studies and compares them with Wainapel's results. Conduction velocity exceeded 40 m/sec in all of the 40 subjects. At the significance level p=0.05 we found no statistical difference in distal sensory latency, conduction velocity or amplitude of Saphenous Nerve Conduction in Healthy Subjects 69

TABLE 1. Normal values of distal latency, nerve conduction velocity and amplitude of sensory action potentials in the saphenous nerve and sural nerve in 40 healthy subjects

Fig .2. Histogram of mean values for sensory conduction velocity (A) and amplitude of sensory action potentials (B) of the saphenous nerve in 40 healthy subjects. 70 I. Kimura et al. sensory nerve action potential related to either right and left sides or sex. Values in TABLE 1 represent averaged values (mean±s.D.) of two sides. There was no statistically significant difference in these three parameters related to age. The use of electronic averager was not necessary, since only one subject showed a response with amplitude lower than 5 , tV. Fig. 2 shows the histogram of mean values for conduction velocity (A) and amplitude of sensory action potential (B) of the saphenous nerve in 40 subjects. Ocassionally, some difficulty was noted in visualizing the saphenous nerve response owing to artifact from muscle contraction and stimulus artifact. The problem could be eliminated by scrupulously observing the correct leg and foot posi- tion and with suitable filter setting as well as rotation of the anode of the stimulating probe without moving the cathode for eliminating the stimulus artifact.

DISCUSSION Antidromic technique for measurement of the sensory nerve action potential, especially in the distal part of the saphenous nerve, offers the following advantage when compared with orthodromic method originally reported by Ertekin (1969) and Stohr et al. (1978). 1) The mean amplitude of the evoked saphenous sensory potentials are much bigger than those obtained using orthodromic stimulation. 2) The technique is simple and can be used in routine electrodiagnostic studies. 3) There is no need to insert needle electrodes to record sensory responses or for nerve stimulation. However, our method does not study conduction in the proximal segment of the saphenous nerve whereas some of the other methods described do (Ertekin 1969; Stohr et al. 1978). It would appear unnecessary to assess proximal saphenous conduction in all patients, since there is a close correlation between the conduction velocity in the proximal (knee to ) and the distal ( to knee) segments of this nerve (Stohr et al. 1978). The amplitude of the saphenous nerve action potential is significantly lower than the amplitude of the sural nerve action potential (p<0.01). This easily performed and reproducible antidromic method for measurement of the saphenous nerve conduction should be useful in differentiating between third and fourth lumbar root lesions and more distal lesions including lumbar plexus, femoral nerve lesions and entrapment neuropathy of the saphenous nerve. Entrap- ment neuropathy of this nerve at the Hunter's canal presents with persistent pain in the lower part of the thigh and leg and is aggravated by walking or effort (Mores et al. 1975). This syndrome can be easily differentiated from other causes of leg pain such as chronic venous insufficiency, arterial disease in lower extremity or lumbar root compression, by comparing the saphenous nerve sensory action potentials of both sides. This technique is also valuable in the evaluation of those patients with "diabetic amyotrophy" who do not have associated peripheral neuropathy . Sural nerve conduction studies are most commonly utilized in studying Saphenous Nerve Conduction in Healthy Subjects 71 patients with peripheral neuropathy. However, if the sural nerve action potential is absent in a patient with peripheral neuropathy, saphenous nerve conduction studies may help in categorizing the type of peripheral neuropathy. Of course if the peripheral neuropathy is extensive saphenous sensory nerve action potential will be absent as well. In this situation studying the saphenous sensory nerve conduction in the proximal segment may prove to be helpful.

References

1) DiBenetto, M. (1970) Sensory nerve conduction in lower extremities. Arch. phys. med. Rehabil., 51, 253-258. 2) Ertekin, C. (1969) Saphenous nerve conduction in man. J. Neurol. Neurosurg. Psychiat., 32, 530-540. 3) Mores, M., Ouaknine, G. & Nathan, H. (1975) Saphenous nerve entrapment simulating vascular disorder. Surgery, 77, 299-303. 4) Stohr, M., Schumm, F. & Ballier, R. (1978) Normal sensory conduction in the saphenous nerve in man. Electroenceph. din. Neurophysiol., 44, 172-178. 5) Wainapel, S.F., Kim, D.J. & Ebel, A. (1978) Conduction studies of the saphenous nerve in healthy subjects. Arch. phys. med. Rehabil., 59, 316-319.