Preoperative varus laxity correlates with overcorrection in medial opening wedge high tibial osteotomy

Medial opening wedge high tibial osteotomy (HTO) is a realignment of the lower limb. Despite accurate preoperative planning and careful surgical techniques, many HTOs result in alignment correction errors. These alignment correction errors may be due to soft tissue laxity around the knee such as varus or valgus laxity. The purpose of this study was to examine the relationship of varus and valgus laxity of the knee and alignment correction errors, and to have a formula to predict the subsequent degree of these correction errors. Fifty knees from 41 patients undergoing opening wedge HTO for knee osteoarthritis were involved. Standing full-length anteroposterior radiographs of the lower limb and the tibia, and varus and valgus stress radiographs of the knee were used to evaluate alignment and joint laxity. Parameters were global correction (the change in the hip-knee-ankle angle), bony correction (the change in the medial proximal tibial angle), and soft tissue correction (global correction - bony correction). The average of global correction, bony correction, and soft tissue correction were 12.8A degrees A A +/- A 4.3A degrees, 9.4A degrees A A +/- A 3.2A degrees, and 3.4A degrees A A +/- A 2.5A degrees, respectively. Preoperative varus laxity was moderately correlated with soft tissue correction (R = 0.58), and in which the slope of the line in the scatter plot represented 0.59, implying that soft tissue correction increases by 0.59A degrees for every 1A degrees of preoperative varus laxity. Preoperative varus laxity is correlated with soft tissue correction, suggesting that more accurate alignment correction could be achieved by surgical planning taking into account preoperative varus laxity as a factor of soft tissue correction.