Tibial nerve motor conduction to the abductor hallucis.

Abstract

Tibial motor studies to the abductor hallucis are commonly performed in electrodiagnosis. Numerous authors have investigated this nerve to derive the normal ranges for latency, amplitude, and nerve conduction velocity (NCV). Many of the studies were performed without regard to temperature control, fixed distance measurement, and demographic characteristics such as age, gender, and height, which are known to affect nerve conduction studies. They often used small sample sizes, and some did not use true normal controls. This study was performed to create an expanded database of normative values for the tibial nerve. In this study, 250 asymptomatic subjects without risk factors for neuropathy were recruited and tested for their tibial motor response. Latency, amplitude, area, duration, and NCV were recorded. A repeated measures analysis of variance was performed with the waveform measures as the dependent variables and age, gender, and height as independent variables. Factors that were significant at the P < or = 0.01 level were used to create separate normative databases. Age was found to be associated with different results for amplitude, area, and NCV. Height was found to be associated with different results for NCV. Once these statistically significant factors were determined, Tukey-adjusted pair-wise comparisons of least squares means were used to collapse categories (by decade for age) that were not significantly different from each other at the P < or = 0.05 level. Side-to-side and proximal-to-distal differences were analyzed. The normal range was derived as mean +/- 2 standard deviations (SD) and at the 97th (third) percentiles of observed values. Mean onset latency was 4.5 ms (SD, 0.8). Mean amplitude was 15.3 mV (SD, 4.5), 12.9 mV (SD, 4.5), and 9.8 mV (SD, 4.2) for the respective age groups of 19-29, 30-59, and 60-79 yr. Nerve conduction velocity ranged from a mean of 44 to 51 m/s depending on the demographic groups of various ages and heights. The upper limit of side-to-side latency variation was 1.4 ms (at the 97th percentile), and the upper limit of normal amplitude difference from side to side was 50% (at the 97th percentile). The other measures are presented in the article.