Altered postural control strategies in quiet standing more than 20 years after rupture of the anterior cruciate ligament

Abstract

Aim: To explore long-term consequences of anterior cruciate ligament (ACL) rupture on postural sway and control strategies during bilateral quiet standing, in subjects treated with or without reconstructive surgery compared to uninjured controls.

Method: 70 individuals who had unilateral ACL rupture 23±2.4 years ago (33 received ACL reconstructive surgery, ACLR, and 37 had physiotherapy only, ACLPT) and 33 uninjured matched controls (CTRL) (mean age 46±5.3) stood quietly with eyes closed for 3min on a firm and on a compliant surface, respectively. Center of pressure (CoP) was registered with a force plate and postural sway was calculated from center of mass (CoM) derived from 3D kinematics. Sway density (SD) analyses of CoP assessed distance and duration of stable phases. The torque controlling postural sway was estimated from CoP-CoM.

Results: Comparisons across conditions to CTRL revealed larger CoP-CoM-area in ACLR (p=0.017, CI: 10.95, 143.10), but not in ACLPT. Mean distance between SD-peaks was greater for ACLR (p<0.001, CI: 1.73, 5.31) than for ACLPT (p=0.006, CI: 0.56, 4.12) relative to CTRL. Duration of SD-peaks was smaller for both ACLR and ACLPT (p<0.001, CI: -4.04, -1.23 and -3.82, -1.03, respectively) compared to CTRL. CoM-area in the ACL-groups did not differ from CTRL.

Conclusions: ACL-injured subjects demonstrated greater postural control efforts than CTRL but without significant differences in postural sway. Control efforts were thus not directly associated with sway and further research should be focused on variance in postural control strategies.

Keywords: Center of mass; Center of pressure; Postural sway; Sway density.