Tibial slope changes following dome-type high tibial osteotomy

The tibial slope is essential in knee biomechanics, both for ligament function and knee kinematics. High tibial osteotomy (HTO) designed primarily to correct frontal plane malalignment in osteoarthritis of the knee joint can cause unintentional tibial slope changes. We evaluated tibial slope changes in 40 knees in patients with medial compartment osteoarthritis treated by dome-type HTO and external fixation on one side, and followed up for 55 months on average. Four different tibial slope measurement methods (anterior tibial cortex, proximal tibial anatomic axis, posterior tibial cortex, and proximal fibular anatomic axis) were used preoperatively and postoperatively on both sides. Patients were allocated into three groups according to their final frontal plane alignment of the knee joint (hypercorrection, normo-correction, and undercorrection groups) based on tibiofernoral anatomic axis angle. As a whole, preoperative slope values (11.2degrees, 7.5degrees, 5.6degrees, and 8.2degrees for the four methods, respectively) displayed a significant decrease postoperatively (on average 7.9degrees, 4.8degrees, 2.2degrees, and 3.7degrees, respectively). Patients with undercorrection (or recurrence of deformity) had a more remarkable decrease in slope than those with normocorrection or hypercorrection. The higher the degree of postoperative mechanical axis valgus, the higher the degree of posterior tibial slope that resulted. Sagittal plane changes after dome-type HTO basically decreasing the tibial slope should be taken into account for subsequent reconstructive procedures such as total knee arthroplasty.