Patellofemoral mechanics after uniplane open wedge high tibial osteotomy is superior to those after biplane open wedge high tibial osteotomy.

Background: It is known that open wedge high tibial osteotomy (OWHTO) may lead to progression of patellofemoral degeneration due to descent of the patellar height. However, the difference in patellofemoral joint (PFJ) loads with normal daily activity between uniplane and biplane osteotomies is unclear. The purpose of this study was to reveal the differences in PFJ biomechanics between uniplane and biplane OWHTO using finite element analysis (FEA).

Methods: In this study, a finite element model of the knee joint was established using computed tomography (CT) and magnetic resonance imaging (MRI) data from a healthy volunteer, and a 10° varus deformity of the proximal tibia was simulated. Under the guidance of experienced orthopedic surgeons, simulations of both uniplane and biplane open wedge high tibial osteotomy procedures were conducted. The maximum stress and contact area of the PFJ at knee flexion angles of 90°, 60°, 30°, and 0° during sitting-to-standing and walking were measured in the three finite element models (normal knee joint model, uniplane OWHTO model, and biplane OWHTO model).

Results: In all models, the peak value of von-mises stress (VMS) occurred at 90 degrees of knee flexion. At 90 degrees of knee flexion, the biplane OWHTO model exhibited the highest PFJ stress, measuring 9.664 MPa. As the knee joint extended from 90 degrees of flexion to 0 degrees of extension, the PFJ stress gradually decreased in all three models. The decrease was most pronounced in the uniplane OWHTO model, although it remained higher than in the normal model.

Conclusion: Uniplane OWHTO would induce lower contact stress and larger contact area on the patellofemoral surface than biplane OWHTO during walking and sitting-to-standing, which may cause less mechanical pain and secondary damage to the articular cartilage. Therefore, uniplane OWHTO might be a better option for patients with anterior knee pain and/or PFJ degeneration.