Postural Control in Single-limb Stance. In Individuals with Anterior Cruciate Ligament Injury and Uninjured Controls

Abstract: The overall aims of this work were to evaluate a method of assessing postural control, measured by balance in single-limb stance on a force platform, and to study balance in single-limb stance in individuals with non-operated anterior cruciate ligament (ACL) injury in comparison with that of uninjured controls. Ninety-nine patients (99) with ACL injury and 141 uninjured subjects were included in the studies. The tests included in the various studies were: balance in single-limb stance (amplitude and average speed of center of pressure (CP) movements), the one-leg hop test for distance, proprioception, knee muscle strength, knee joint laxity, subjective estimation of extremity function, and short-duration sub-maximal cycling. The training methods used were neuromuscular, and self-monitored training. Balance in single-limb stance and the one-leg hop test were found to be reliable and appropriate tests for distinguishing between groups of subjects (Papers I and IV). Relatively large differences in an individual’s balance measurements would, however, be required to confidently state that a change is real (Paper IV). Balance in single-limb stance and the one-leg hop test were influenced by age and sex (Paper II). When comparing patients with uninjured subjects these factors were, therefore, matched. The patients seemed to exhibit larger CP movements at a lower speed (Paper III) or CP movements at a lower speed with retained amplitude (Paper V) compared with the uninjured subjects. Regardless of training method and therapeutic approach, CP amplitude was persistently higher in both legs during the follow-up compared with uninjured subjects (Paper III). However, functional performance, as measured with the one-leg hop test for distance, was restored by neuromuscular training, but not by self-monitored training (Paper III). Higher values of CP movements were found in the patients and the uninjured subjects after short-duration, sub-maximal cycling, indicating compensatory mechanisms aimed at maintaining balance in single-limb stance, or a decreased ability to maintain balance (Papers IV and V). The injured leg in the patients was more affected by cycling than the legs of the control group (Paper V). Anterior knee laxity, proprioception, and muscle strength seem to play a role in maintaining balance in single-limb stance in patients with ACL injury (Paper VI). Low amplitudes of CP movements correlated with better subjective extremity function, whereas no correlation was found between average speed of CP movements and subjective function (Paper VI). Thus, the method studied for assessing postural control in single-limb stance can be useful in the evaluation of neuromuscular function after knee injury.