The Effect of Valgus Bracing and Lateral Wedge Orthotics on Intra-articular Knee Loads During Gait

Abstract

PURPOSE: Tibiofemoral load in the medial compartment of the knee is determined mainly by the ground reaction force and the resulting external adduction moment. Applying an abduction moment about the knee with valgus bracing may shift tibiofemoral load from the medial compartment to the lateral compartment by reducing varus malalignment and/or by applying an abduction moment to resist the external adduction moment. Alternatively, shifting the COP laterally under the foot with lateral wedge orthotics may reduce the resultant GRF moment arm about the knee, and thereby reduce the external adduction moment. Most in vivo studies show a positive correlation between these conservative approaches to medial compartment OA, pain relief, and a reduced adductor moment. METHODS: A computer model of the knee and the lower limb was used to calculate the reduction of medial tibiofemoral joint load that might be achieved by using a valgus moment knee brace. The analysis was performed for the instant of opposite toe off, when peak medial compartment load occurs during normal gait. Medial compartment load was calculated as the abduction moment applied by a simulated valgus brace was increased in 1 Nm increments, starting from the value for normal walking. To evaluate the affects of lateral wedges, a separate analysis was performed in which the COP under the foot was shifted laterally in increments of 1 mm. RESULTS: A 3 Nm brace abduction moment at the knee reduced the total adduction moment at the knee by 8% and the peak medial compartment load by 3%. Medial compartment load decreased as a linear function of the abduction moment applied by the brace. Valgus angle decreased by less than 1o when a 3 Nm abduction moment was applied to the knee. Medial compartment load was reduced mainly by the decrease in the external adduction moment, and not by a change in the varus alignment of the leg. A 3 mm lateral shift in COP reduced the total knee adduction moment by 5% and the peak medial compartment load by 2%. Medial compartment load decreased linearly with lateral displacement of the COP. CONCLUSIONS: Our results help to explain the reduction in knee pain obtained with valgus bracing and foot orthoses, and provide quantitative estimates of the reduction in medial compartment load during gait, estimates that cannot be obtained from an inverse dynamics analysis alone.