Changes in motor-flexibility following anterior cruciate ligament reconstruction as measured by means of a leg-amplitude differentiation task with haptic and visual feedback.

Background: In the current study changes in lower-limb motor flexibility of patients undergoing Anterior Cruciate Ligament Reconstruction were evaluated in relation to fear of harm.

Methods: Fourteen patients were measured pre- and post-surgery, and data were compared to those of a single measurement in fifteen controls. Lower-limb motor-flexibility was assessed in treadmill-walking and a cyclic leg-amplitude differentiation task augmented with haptic or visual feedback. Flexibility was captured by determining the between-leg coordination-variability (SD of relative phase) and each leg's temporal variability (sample entropy). Patients were post hoc divided into a higher-fear-group (pre-surgery: n = 6, post-surgery: n = 7) and a lower-fear-group (pre-surgery: n = 6, post-surgery: n = 7) by means of a median split of their scores on a self-reported fear of harm scale. Differences in flexibility-measures between the higher-fear-group and the lower-fear-group were also assessed.

Findings: No pre- and post-surgery differences, nor differences with the control group, were found in motor-flexibility during treadmill-walking but the post-surgery higher-fear-group did show lower values of SD relative phase. In the leg-amplitude differentiation task the SD of the relative phase decreased but sample entropy increased post-surgery towards levels of the control-group. The pre-surgery higher-fear-group showed lower values of sample entropy in visual conditions.

Interpretation: While gait kinematics may not show motor-flexibility changes following anterior cruciate ligament reconstruction, a leg-amplitude differentiation task does show such changes. Differentiating patients on a fear-of-harm scale revealed subtle differences in motor-flexibility. Challenging patients with non-preferred movements such as amplitude differentiation may be a promising tool to evaluate motor-flexibility following ACLR.