Purpose: 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.
Methods: 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).
Results: 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.
Conclusion: 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.