Optimizing the technique for eliciting antidromic sural and superficial fibular sensory nerve action potentials.

Abstract

Lower limb sensory nerve action potentials are an important component of nerve conduction studies. Most testing of the sural and superficial fibular nerves involves antidromic techniques above the ankle, which result in a falsely unobtainable response in 2%-6% of healthy people. Cadaver, surgical, and more recent ultrasound series suggest this may relate to the site of fascia penetration of the nerve, and it is hypothesized that a modified technique may be more likely to produce reliable responses and reduce false-negative errors. This article evaluates a variety of recording distances for both nerves in 100 healthy controls, including varying recording electrode positions and techniques, to provide the optimal electrodiagnostic information in healthy control subjects. Shorter stimulation distances produce higher-amplitude responses but become confounded by increasing stimulation artifact at very short distances, with the best balance found at around 10 cm. In both sural and superficial fibular nerves, amplitude increases by approximately 10%/cm compared with the standard 14 cm distance. The Daube superficial fibular technique produced a higher amplitude than the Izzo Intermediate technique (by 22.46%, p < .001). The calculated upper limit of normal for side-to-side variation in amplitude was around 50% in the sural nerve but over 70% in the superficial fibular nerve. It is proposed that the 10 cm recording distance for both nerves is optimal, with minimal false-negatives and a higher amplitude elicited than with existing techniques.