The effects of dual-tasking on postural control in people with unilateral anterior cruciate ligament injury

Several studies have investigated postural control in anterior cruciate ligament (ACL) deficient patients; yet the contribution of cognitive processing (attention) in the postural control of these patients is still unclear. A dual-task design was used to determine the effects of a concurrent digit span memory task on standing balance in a group of ACL patients (n=27) compared with a group of matched, healthy participants (n=27). In double limb stance, three levels of postural difficulty were studies on a force platform (rigid surface with eyes open, rigid surface with eyes closed, and foam surface with eyes closed). There were three cognitive conditions (no cognitive task, easy cognitive task and difficult cognitive task). For double limb stance, a mixed model analysis of variance showed that in the presence of a cognitive task, postural control was compromised yet there was no interaction between cognitive task difficulty and group (ACL or control). For single limb stance, the more difficult cognitive tasks were associated with lower standard deviations for velocity in the antero-posterior direction and the phase plane portraits. This cognitive task did not appear to compromise postural control in ACL injured patients to a greater extent than unimpaired people. Future studies should examine ACL patients with more severe disabilities and expose them to more demanding dynamic balance conditions to further explore dual-tasking effects.