Deep and superficial sensory nerve conduction to the first dorsal web space of the foot

Abstract

BackgroundPolyneuropathy tends to progress in a distal to proximal fashion beginning at the tips of the toes. Sensory nerve conduction testing in the distal foot may identify early polyneuropathic changes. Deep fibular (DFN) sensory conduction techniques have been described to assess the distal dorsal foot, however, there has been no accommodation for reported anatomic communication between the DFN and superficial fibular nerve (SFN) in the dorsal foot. This study aims to stimulate both the DFN and SFN at the ankle to evaluate the function of the observed anatomic sensory nerve variations in the first dorsal web space. Normal nerve conduction values will also be presented in a sample of young adults and sex and BMI effects will be evaluated. Materials and methodsThe study participants included 201limbs tested in 101 subjects (31 males and 70 females) between the ages of 18 and 47 (mean age 24.6 ± 4.8 years). The DFN and intermediate branch of the SFN (IDCN) were stimulated at the ankle 12 cm proximal to a surface recording electrode over the first dorsal web space of the foot. The obtained sensory nerve amplitude and latency values were recorded and velocity values were calculated. ResultsThe current study identified a first dorsal web space response in 78% of limbs tested. Web space responses were variable in origin with SFN only, DFN only and both SFN and DFN recorded responses in the web space. The mean DFN peak to trough amplitude was 5.8 ± 2.3 μV, while the peak velocity was 31.2 ± 2.9 m/s. The mean SFN-IDCN peak to trough amplitude was 5.9 ± 2.3 μV and the mean peak velocity was 32.1 ± 3.8 m/s. There was a statistically significant sex effect for SFN-IDCN onset latency and velocity with women demonstrating shorter onset latencies and faster velocities than the men. There was a significant SFN-IDCN BMI effect for onset latency and velocity, such that those with low BMI had shorter latency and faster nerve conduction values. A significant DFN sex effect was also identified for amplitude with males and females demonstrating a mean amplitude of 5.4 μV and 6.0 μV, respectively. ConclusionsThere is a high degree of anatomic and functional variability in sensory supply to the first dorsal web space of the foot requiring exploration of the DFN and SFN when assessing focal nerve entrapments or generalized polyneuropathy. A general dorsal foot sensory velocity and amplitude value may serve as an index for evaluation of early polyneuropathy.