Hinge location and apical drill holes in opening wedge high tibial osteotomy: A finite element analysis

At the time of medial opening wedge high tibial osteotomy (HTO) to realign the lower limb and offload medial compartment knee osteoarthritis, unwanted fractures can propagate from the osteotomy apex. The aim of this study was to use finite element (FE) analysis to determine the effect of hinge location and apical drill holes on cortical stresses and strains in HTO. A monoplanar medial opening wedge HTO was created above the tibial tuberosity in a composite tibia. Using the FE method, intact lateral hinges of different widths were considered (5, 7.5, and 10 mm). Additional apical drill holes (2, 4, and 6 mm diameters) were then incorporated into the 10 mm hinge model. The primary outcome measure was the maximum principal strain in the cortical bone surrounding the hinge axis. Secondary outcomes included the force required for osteotomy opening, minimum principal strain, and mean cortical bone stresses (maximum principal/minimum principal/von Mises). Larger intact hinges (10 mm) were associated with higher cortical bone maximum principal strain and stress, lower minimum principal strain/stress, and required greater force to open. Lateral cortex strain concentrations were present in all scenarios, but extended to the joint surface with the 10 mm hinge. Apical drill holes reduced the mean cortical bone maximum principal strain adjacent to the hinge axis: 2 mm hole 6% reduction; 4 mm 35% reduction; and 6 mm 55% reduction. Incorporating a 4-mm apical drill hole centered 10 mm from the intact lateral cortex maintains a cortical bone hinge, minimizes cortical bone strains and reduces the force required to open the HTO; thus improving control.