Contribution of the sural nerve to postural stability and cutaneous sensation of the lower limb.

Abstract

The sural nerve is a cutaneous nerve of the lower limb that innervates the posterolateral aspect of the lower leg, ankle, and foot. Considering this pattern, it is plausible that it contributes to the maintenance of postural stability. However, the implications of sensory loss following sural nerve injury have yet to be thoroughly investigated. Therefore, the aim of this study was to investigate the immediate effect of sural nerve sensory loss on postural stability and its variability of innervation to the lower limb. Twenty-five healthy adult subjects participated in an observational study with a repeated-measures design. Each participant underwent a postural stability assessment using the Neurocom Balance Master under 2 conditions: 1) with the sural nerve functioning normally and 2) following a bilateral ultrasound-guided sural nerve block. The cutaneous distribution of the sural nerve was mapped for descriptive purposes. There were no statistically significant differences between conditions for the primary outcome measure (unilateral stance on the dominant leg with eyes closed). A statistically significant reduction in postural stability was detected during unilateral stance on the nondominant leg (with eyes closed) following the nerve block (mean increase, 2.25 deg/s; 95% confidence interval, -0.48 to 2.91; t = 2.75; df = 24; P = .01). The mean area of plantar skin innervated by the sural nerve was 17% ± 11%, and the mean area of lateral skin was 50% ± 6%. Our findings demonstrate that a loss in sural nerve function is unlikely to reduce postural stability during daily activities. The sural nerve has a variable innervation pattern that can involve the third digit and the plantar medial border of the heel. Practitioners should consider this variability when assessing for potential sensory deficits and when planning procedures requiring anesthesia to the plantar surface of the foot.