Sress distribution in varus knee after operative correction of its mechanical axis

An analysis of the results of 121 minus-valgizing osteotomies in genu varum performed in the years 1985-1998 allowed the authors to conclude that the recommended by most researchers hyper-corrective valgus positioning of the knee's mechanical axis after an osteotomy resulted in increased postoperative valgity in 12 cases. This complication nullified the intended effect of the operation and required another corrective procedure. Clinical observations showed that the probable causes of the complications could be different, e.g. a significant decrease of bone density in the joint's exterior section, taking over the body-weight load, and the patient's considerable overweight. Whereas the presumptive cause was a limited capability of remodelling of the overloaded exterior section of the joint. In order to determine the magnitude and distribution of static forces in the knee's articular ends, a series of measurements were made using spatial photoelastic models as exact geometrical copies of specimens from autopsy. The measurements have shown that in the case of the hypercorrective position of the joint's axis, an extremely heavy concentration of forces occurs on the relatively small bearing surface of the outer condyle of the tibia. This creates adverse mechanical conditions and makes it impossible to obtain the intended correction angle.