The influence of alignment on the musculo-skeletal loading conditions at the knee

Background and aim. High tibial osteotomies attempt to recreate physiologically normal joint loading. Previous studies have discussed the influence of mal-alignment on the distribution of static loads to the medial and lateral compartments of the knee. The aim of this study was to determine the influence of mal-alignment on the tibio-femoral loading conditions during dynamic activities. Material and methods. Using a musculo-skeletal model of the lower limb, which had been previously validated with in vivo data, in this study we modified the alignment of the knee in four patients, from a normal position to the extremes of 8degrees valgus and 10degrees varus mal-alignment. The resulting tibio-femoral joint contact forces were examined while patients were walking and stair climbing. Results. Varying the mal-alignment resulted in a highly individual response in joint loads. Deviations from the normal alignment produced an increase in loading, with valgus generating a more rapid increase in loading than a varus deformity of the same amount. Varus deformities of 10degrees resulted in increases in peak contact force from an average of 3.3-times bodyweight (BW) up to a peak of 7.4 BW (+45% to +114%) while patients were walking, whilst increases of 15% up to 35% were determined for stair climbing. Increases of up to 140% were calculated at 8degrees valgus during walking and up to 53% for stair climbing. Conclusion. This study demonstrated a clear dependence of the individual joint loads on axial knee alignment. Based on the sensitivity of joint loading to valgus mal-alignment, more than 3degrees of over-correction of a varus deformity to valgus should be carefully reconsidered.