Biomechanics of high tibial osteotomy

This paper is a review of the biomechanical principles that support limb realignment surgery via osteotomy around the knee, principally high (proximal) tibial osteotomy. The basic biomechanical principles have been described, and the related literature examined for evidence to support the recommendations made. The forces on the knee when walking are shown to lead to most of the load acting through the medial compartment, the most frequent site of degeneration of the knee, due to the adduction moment that acts during the weight-acceptance phase. Realignment of the limb to move the mechanical axis to a desired point within the knee is described, and the resulting joint contact pressures in the medial and lateral compartments are shown to be higher in the less-congruent lateral articulation when the load passes through the centre of the knee. At the same time, there can be changes of the posterior slope of the tibial plateau, and a slope of ten degrees can induce a shearing force, which stretches the ACL, of 0.5 body weight when the knee force is 3 times body weight. The options regarding tibial or femoral or even double osteotomies are discussed in relation to medial-lateral slope of the joint line. Secondary effects such as alteration of collateral ligament tension or of the height of the patella are described. Critical review of the publications supporting osteotomy surgery suggests that many of the accepted 'rules' have little scientific evidence to show that they represent the best practise for long-term preservation of the joint.