Postural control capability of ACL-deficient knee after sudden tilting

Loss of neurophysiological function in an anterior cruciate ligament (ACL)-deficient knee leads to irregularities in neuromuscular coordination, and any sudden change in circumstances is believed to contribute to deterioration in postural control. The aim of this study was to investigate differences between ACL-deficient patients and healthy subjects through examination of postural control in response to perturbation. Twelve patients awaiting ACL reconstruction were compared with 12 healthy athletes. Subjects were instructed to stand on an unstable board that was then tilted suddenly from behind. The stepping power and reaction time of subjects to this perturbation were measured through accelerometers attached to both the unstable board and the subjects' knees. In healthy athletes, stepping power was stronger on the tilted side than on the opposing side, while their step reaction, as part of anticipatory postural control, was faster on the opposing side than on the tilted side. In patients with ACL-deficient knees, the opposite was true; stepping power was no stronger on the tilted side, while their step reaction was no faster on the opposing side. In terms of postural control capability, both the affected and the healthy knee of ACL-deficient patients were impaired as a result of control patterns that differed from the usual model.