Recurrent varus angulation after high tibial osteotomy: an anatomic analysis.

Recurrent varus deformity and an associated lateral instability are a common and perplexing concern after high tibial osteotomy. An anatomic study using fresh cadaver specimens was done to delineate the cause of this complication. A closing wedge osteotomy was done on four cadaveric knees, which then were subjected to a small varus load to simulate the adduction moment experienced by the knee during normal gait. The osteotomy was progressively closed in 5 degree increments and the angular alignment of the knee was measured with each incremental change. Experimental results identified postosteotomy angular corrections to be 50%, or less, of the predicted value. As the osteotomy was closed progressively the lateral joint space increased concomitantly, creating an effective lateral instability and negating much of the angular correction afforded by the osteotomy. At osteotomy angles greater than 10 degrees the lateral collateral ligament was rendered nonfunctional with the lateral capsule and the anterior cruciate ligament assuming the primary function of stabilizing the lateral side of the knee. As commonly done, a closing wedge valgus tibial osteotomy does not alter the lateral collateral tension, which allows the knee to swing back toward native alignment when subjected to a varus load.