The sural nerve was studied orthodromically using the near-nerve technique in 273 normal subjects (155 females, 118 males) aged 5 to 90 years. The sensory action potential (SAP), evoked at the dorsum of the foot, was recorded at the lateral malleolus and midcalf, and at the midcalf when evoked at the lateral malleolus. In addition, the SAP was recorded at intermediate distal sites and at proximal sites at the popliteal fossa, the gluteal fold, and the S-1 root. The amplitude of the SAP recorded at midcalf was 32% higher in females than in males. This was probably due to volumeconduction properties, as differences between genders were less noticeable at more distal recording sites. The amplitude decreased steeply and exponentially with age. Conduction distance had a strong influence on the amplitude of the SAP, which decreased with increasing distance following a power relationshipwith an exponent of 1.4 to 1.7. This decrease was due to temporal dispersion with decreased summation and increased phase cancellation. The conduction velocity was slightly lower along the very distal course of the nerve than along more proximal segments. Key words: sural nerve action potential amplitude conduction velocity. gender MUSCLE & NERVE 15:374383 1992

CONDUCTION STUDIES OF THE NORMAL SURAL NERVE STEVEN H. HOROWITZ, MD, and CHRISTIAN KRARUP, MD

Because of its accessibility for morphological studies,' the sural nerve is the sensory nerve in the lower extremity most often studied electrophysiologically in patients with peripheral nerve disorders, allowing correlation between pathological and pathophysiological findings.".' * Using near-nerve e l e ~ t r o d e ,our ~ purpose was to update values in normal subjects, and to investigate the effects of stimulation and recording from different sites on the amplitude, duration, and conduction velocity. The sural nerve was stimulated and evoked compound sensory action poFrom the Laboratories of Clinical Neurophysiology, Department of Neurology, Long Island Jewish Medical Center, Long Island Campus for the Albert Einstein College of Medicine, New York (Dr. Horowitz), and Department of Medicine (Neurology), Brigham and Women's Hospital, and the Department of Neurology, Harvard Medical School, Boston, Massachusetts, and the Department of Clinical Neurophysiology, Rigshospitaiet, Copenhagen, Denmark (Dr. Krarup) Presented in part at the Vlllth International Congress of Electromyography and Related Clinical Neurophysiology, Sorrento, Italy, May, 1987. Acknowledgments: We are indebted to F Buchthal, MD and W. Trojaborg, MD for their comments and criticism. We thank Professor A. Rosenfalck for allowing us to include recordings performed in collaboration with Alborg University. Address reprint requests to C. Krarup, MD, Department of Clinical Neurophysiology, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark.

tentials (SAP) were recorded at various sites from the distal foot to the first sacral root. The advantages of the technique have been delineated5,6: these are the precise determinations of the sites of stimulation and recording along the nerve and detailed resolution of evoked responses.

MATERIALS AND METHODS

The sural nerve was studied in 273 subjects: 155 females (F), aged 5 to 80 years; 118 males (M), aged 8 to 90 years. The age distribution of females (average 42.9 years) was not significantly different from that of males (average 40.9 years) (Mann- Whitney U test). The subjects were either paid volunteers or patients without symptoms or signs of generalized neuropathy. We included patients referred for mononeuropaties in the upper extremities and lower back pain without evidence of radiculopathy. All patients had clinical evaluation of sensory function and motor function, tendon reflexes, and supplementary EMG and nerve conduction studies appropriate for their complaints. Only those patients without clinical and electrophysiological signs of neuropathy or radiculopathy were included in the study. Subjects.

Accepted for publication June 1, 1991 CCC 0148-639)(/92/030374- 10 $04.00 0 1992 John Wiley & Sons, Inc.

374

Sural Nerve Conduction Studies

Orthodromic conduction along various segments of the sural nerve

Electrophysiological Methods.

MUSCLE 8, NERVE

March 1992

I

I

c I

S 1 root

I I

I I t

Gluteal fold. GF

I I I I

I I I

# I

__-'

Popliteal fossa, PF

Upper calf. UC Midcalf. MC Intermediate calf, IC Low calf. LC Malleolus Lateralis. ML

Dorsum pedis. DP

FIGURE 1. Schematic representation of sites of recording and stimulation of the sural nerve between the dorsum of the foot and the S1 root. The distance from DP to ML was 80 to 100 mm, from ML to LC 70 mrn, from LC to IC 30 mm, from 1C to MC 30 mm, and from MC to UC 30 to 50 mrn. Distances proximal to MC varied among subjects.

was studied (Fig. 1). The basic principles of the near-nerve technique have been d e ~ c r i b e d . ~ Stimulation and Recording Electrodes. For stimulation and recording, a 0.7-mm diameter insulated needle with a 3-mm bared tip was placed close to the nerve. The anode or reference electrode was another needle with a 5-mm bared tip placed at a medial transverse distance of 25 to 35 mm. At the dorsum of the foot, the stimulating electrodes were placed at a longitudinal distance of 10 to 15 mm. The stimulus was a 0.2-ms rectangular pulse from a constant current stimulator. The cathode was placed close to the nerve by means of a threshold of

Conduction studies of the normal sural nerve.

The sural nerve was studied orthodromically using the near-nerve technique in 273 normal subjects (155 females, 118 males) aged 5 to 90 years. The sen...
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