High tibial osteotomy: an operation based on a spurious mechanical concept. A theoretic treatise.

The biomechanical basis for high tibial osteotomy (HTO) is erroneously conceived, in that to unload the medial side of the knee, an osteotomy would have to be performed of sufficient magnitude to shift the lateral side of the knee joint far enough medially to intersect the dynamic axis, not the mechanical axis. The resulting angular deformity would be functionally and cosmetically unacceptable in the eyes of most patients and surgeons. To corroborate these theoretic considerations, and to define the angular deformity necessary to unload the medial side of the knee joint during the midstance phase of gait, a cadaver osteotomy model was used with compartmental loading defined by direct observation, as well as by load-sensitive film. As predicted, medial compartment unloading did not occur until the lateral side of the joint crossed the dynamic axis. In both cadavers tested, the extremity alignment necessary to unload the medial side was approximately 25 degrees valgus. The efficacy of HTO should be re-examined, as its biomechanical basis is fundamentally flawed.