In vitro strain distribution in the proximal tibia. Effect of varus-valgus loading in the normal and osteoarthritic knee.

Six human cadaver legs were tested with strain-gauge rosettes to determine the effects of varus/valgus loading on the distribution of strain on the cortical bone of the proximal tibia at loads of up to 250 kg. Changes in the femorotibial angle of 1.5 degrees and 3.1 degrees, to create varus/valgus deformities, produced significant unloading of the opposite aspect of the normal leg. A varus deformity of 3.1 degrees in the medial compartment osteoarthritic model virtually unloaded the lateral compartment and, because of the bending effect, placed the whole of the lateral aspect of the leg into axial tension. Under these conditions, the axial strains in almost the whole of the medial aspect of the tibia were doubled, from an initial value of 250 microstrain (compressive) to a value of approximately 500 microstrain (compressive). While a change in load-action, to simulate a 3.1 degrees valgus deformity in the medial compartment osteoarthritic model, did not completely unload the medial plateau of the tibia, it was suggested that such unloading could be achieved with slightly greater valgus loading. Successful clinical results, employing valgus osteotomies in patients with medial compartment osteoarthritis, are obtained by unloading the medial compartment while markedly increasing compressive loads on the whole of the lateral aspect of the leg.