The anterior cruciate ligament-deficient knee with varus alignment: An analysis of gait adaptations and dynamic joint loadings

Abstract

Thirty-two patients with an ACL-deficient knee and lower limb varus alignment and 16 healthy controls were analyzed during level walking using a force-plate and optoelectronic system. The forces and moments of the lower limb and knee joint were measured and knee joint loads and ligament tensile forces were cal culated using a mathematical model. The majority of patients (20 of 32) had an abnormally high adduction moment at the affected knee. The ad duction moment showed a statistically significant cor relation to high medial tibiofemoral compartment loads and high lateral soft tissue forces, but not to the degree of varus alignment on standing roentgenograms. Fif teen of 32 knees had abnormally high lateral soft tissue forces. We interpreted these gait findings as indicative of a medial shift in the center of maximal joint pressure and an increase in lateral soft tissue forces to achieve coronal plane stability. Further, there is the likelihood of separation of the lateral tibiofemoral joint and "con dylar lift-off" during periods of the stance phase. If this occurs, all of the load-bearing forces would shift to the medial tibiofemoral joint and relatively large tensile forces would occur in the lateral soft tissue restraints. The flexion moment, as related to the quadriceps muscle force, was significantly lower than the control knees in 40% of the involved knees, and the extension moment, as related to the hamstring muscle force, was significantly higher in 50% of the involved knees. We interpret this finding as a gait adaptation tending to diminish quadriceps muscle activity and enhance ham string muscle activity to provide dynamic anteroposte rior stability of the knee joint. The fundamental assumption of this paper is that any combination of conditions leading to higher medial joint forces is associated with factors leading to more rapid degeneration of the medial compartment in patients with ACL deficiency, varus deformity, and lax lateral ligaments.