A "safe zone" in medial open-wedge high tibia osteotomy to prevent lateral cortex fracture

The purpose of this cadaveric study was to study the effect of plane of osteotomy on incidence of lateral cortex fracture and to define a "safe zone" through which medial open-wedge high tibial osteotomy (HTO) could be performed with minimal risk of lateral cortex fracture. Medial open HTO was performed in nine fresh frozen human cadavers (18 knees) with each specimen randomly assigned to a "safe zone" osteotomy (group A, between the tip of the fibular head and the circumference line of the fibular head,) or a lower level osteotomy (group B, distal to the circumference line of the fibular head). Six out of nine knees developed lateral cortex fracture in group B compared to none in group A (P = 0.009) when the osteotomy site was distracted to a maximum of 20 mm. Directing the plane of the osteotomy toward the "safe zone" significantly reduces the risk of lateral cortex fracture compared to an osteotomy, which is directed at a lower level. Confining the plane of a medial open HTO to within the "safe zone" can prevent lateral cortex fracture and subsequent loss of correction.