Plantar Sensation and Muscle Activity During a Step on Various Textured Unstable Surfaces in Patients with Anterior...

After anterior cruciate ligament reconstruction (ACLR), patients have been found to have reduced plantar sensation, which may result in reduced afferent input to the central nervous system and thus contribute to motor deficits. Textured surfaces are thought to have a beneficial neurosensory effect. The aim of this cross-sectional study was to compare plantar sensation and leg muscle activity while stepping on different textured surfaces between patients after ACLR and healthy controls.Plantar cutaneous thresholds to light touch were measured in 10 patients at least 6 months after ACLR and in 10 healthy controls. Patients or controls were asked to step forward on the centre of a force plate with the affected (ACLR) or randomly assigned (healthy controls) leg and maintain the single-legged stance for 10 seconds (floor condition). They were instructed to perform the same task on a balance board with a textured surface, the same balance board with a smooth surface, and a balance pad in random order. Muscle activity of four leg muscles was recorded using surface electromyography. The significance of differences in plantar sensation and mean muscle activity within three time frames between and within ACLR patients and healthy controls was analysed using non-parametric statistical tests with Bonferroni correction (p < 0.05).There were no significant differences between patients with ACLR and healthy controls in plantar sensation and muscle activity for all unstable surface conditions (p > 0.05). Friedman tests revealed significant differences in the activities of all muscles between surface conditions at the first peak of the vertical ground reaction force (vGRF) after the rapid increase in the force-time curve (transition from early lifting phase to late lifting phase) within both groups (p < 0.01). Post-hoc Wilcoxon signed-rank tests showed significantly altered activity for most muscles between the smooth and textured balance board conditions only at the first vGRF peak (p ≤ 0.01) in both patients and healthy controls.Although plantar sensation and muscle activity did not differ between patients with ACLR and healthy controls, altered muscle activity in both groups, especially during the transition from the early to the late lifting phase of stepping on a textured unstable surface, may indicate an acute change in the afferent input of plantar mechanoreceptors in response to the surface stimulus. In addition, it may indicate an acute change in motor output caused by a beneficial neurosensory effect. This effect should be considered with caution due to the small sample size.