Strength-Duration Curves of the Common Fibular Nerve Show Hypoexcitability in People With Functional Ankle Instability

Abstract

Background: Some motor impairments, such as decreased reaction of peroneal muscles, altered kinematics, or poor postural control, have been described in people with functional ankle instability. Evidence shows a possible relationship between fibular nerve impairments and functional ankle instability.

Objective: To investigate the electrophysiologic excitability of the common fibular nerve, as measured by strength-duration curves, in subjects with functional ankle instability compared with a control group without ankle impairment.

Design: A cross-sectional study.

Setting: University Research laboratory.

Participants: Fifty subjects with functional ankle instability (35 men, 15 women; ages 24.36 ± 5.01 years) and 63 uninjured control patients (44 men, 19 women; ages 22.67 ± 4.85 years) were recruited by convenience sampling.

Interventions: Not applicable.

Main outcome measures: Strength-duration curves of the common fibular nerve were made in all participants. Rheobase, chronaxie, Bawen index, accommodation index, galvano-tetanic threshold, and intensity thresholds for different pulse durations were obtained and compared between the 2 groups.

Results: Subjects with functional ankle instability show increased values of chronaxie (0.58 ± 0.24 ms versus 0.47 ± 0.16 ms; P = .004), Bawen index (1.53 ± 0.24 versus 1.39 ± 0.21; P = .002), and intensity thresholds for pulse durations ≤2 ms both for rectangular and triangular pulse wave forms. The accommodation index was smaller in subjects with functional ankle instability than controls (3.7 ± 0.72 versus 4.05 ± 0.98; P = .036). The remaining parameters did not show significant differences between groups.

Conclusions: These findings suggest that subjects with functional ankle instability show a decreased excitability in their common fibular nerve when compared with subjects without ankle injuries.