Proprioceptive deficits of the lower limb following anterior cruciate ligament deficiency affect whole body steering control

The role of lower limb proprioception in the steering control of locomotion is still unclear. The purpose of the current study was to determine whether steering control is altered in individuals with reduced lower limb proprioception. Anterior cruciate ligament deficiency (ACLD) results in a decrease in proprioceptive information from the injured knee joint (Barrack et al. 1989). Therefore the whole body kinematics were recorded for eight unilateral ACLD individuals and eight CONTROL individuals during the descent of a 20° incline ramp followed by either a redirection using a side or cross cutting maneuver or a continuation straight ahead. Onset of head and trunk yaw, mediolateral displacement of a weighted center of mass (COM_HT) and mediolateral displacement of the swing foot were analyzed to evaluate differences in the steering control. Timing analyses revealed that ACLD individuals delayed the reorientation of body segments compared to CONTROL individuals. In addition, ACLD did not use a typical steering synergy where the head leads whole body reorientation; rather ACLD individuals reoriented the head, trunk and COM_HT in the new direction at the same time. These results suggest that when lower limb proprioceptive information is reduced, the central nervous system (CNS) may delay whole body reorientation to the new travel direction, perhaps in order to integrate existing sensory information (vision, vestibular and proprioception) with the reduced information from the injured knee joint. This control strategy is maintained when visual information is present or reduced in a low light environment. Additionally, the CNS may move the head and trunk segments as, effectively, one segment to decrease the number of degrees of freedom that must be controlled and increase whole body stability during the turning task.