Evidence of feedforward postural adjustments to reduce knee joint loading in ACL deficient patients at cost of dynamic stability control

Abstract

The aim of this study was to examine the effect of anterior cruciate ligament (ACL) deficiency on joint kinetics and dynamic stability (DS) during landing after a single-leg hop test (SLHT). Twelve unilateral ACL deficient (ACLd) subjects performed a SLHT (both legs). Calculation of landing mechanics was done by means of a soft tissue artifact optimized rigid full body model. Margin of stability (MoS) was defined by the differences between the base of support and extrapolated centre of mass (XCoM). During landing, the ACLd leg showed a lower external knee flexion and adduction moment but generated higher ankle dorsiflexion and hip flexion moments compared to the healthy leg. The kinetic changes at the joints were explained by a increased forward lean of the trunk resulting in a more anterior position of the centre of mass causing an anterior translation of the ground reaction force vector with respect to the joints of the lower extremity in the ACLd leg. The consequence of this ACLdrelated control strategy was a greater XCoM reducing the MoS during landing. Our results give evidence of a feedforward adaptive adjustment in the ACLd leg aimed to reduce mechanical loading at the knee joint at a cost of lesser DS control. © 2011 Springer-Verlag.