Abstract
Total knee arthroplasty (TKA) implanted in the context of severe arthritis are associated with substantial functional outcomes, pain relief and improvements in range of motion. While patellofemoral complications are among the most frequent reasons for dissatisfaction and revisions, adverse patellofemoral outcomes after TKA are always difficult to predict. As such, patellofemoral biomechanics data are necessary to understand anterior knee pain and residual patellofemoral symptoms in regards to implantation techniques.Historically, a neutral postoperative coronal alignment of the lower limb (180°±3) has been considered as a goal to achieve for mechanically aligned TKA, in spite of possible postoperative changes in femoral phenotype due to the femoral component implantation. A preliminary clinical study performed at our department, including a cohort of 163 patients who underwent a primary TKA in the context of varus deformity, aimed to investigate the influence of postoperative changes in femoral joint line obliquity (JLO) on functional outcomes after TKA. Patients with substantial changes in femoral JLO were associated with lower patient-reported outcomes scores (HSS Patella score, KOOS-12, FJS-12) at mean 34-month follow-up. A mean drop of 2.5 points for each score was found per each degree of changes in femoral JLO.While several well-known surgical factors usually lead to the occurrence of anterior knee pain during flexion, little is known about the role of tensile forces in patellar retinaculum as the capability to flex and bend the knee during squatting is commonly related to satisfactory clinical outcomes for patients. There is limited amount of data about patellofemoral biomechanics in TKA from computational analysis using finite element modeling, with different boundary conditions and loads. As such, this study aimed to develop and validate a new finite element model which can be used to investigate the influence of TKA implantation techniques on patellofemoral stress during squatting simulation.First, a fixed-bearing posterior stabilized TKA was implanted in a knee finite element model. A constant load of 130N was applied at the center of the TKA in order to reproduce boundary conditions of bipodal squatting. We evaluated quadricipital force, medial and lateral tibio-femoral contact forces and patellofemoral Von Mises stress from extension to 100° of flexion. Quadricipital force increased during flexion, up to 6 times the initial load. Patellofemoral stress also increased during flexion, up to 16 MPa at 100° of flexion. Overall, contact forces and post-cam engagement angle were consistent with several published computational simulation.Secondly, the same TKA design was implanted in the context of a varus knee deformity with femoral JLO using mechanical alignment and kinematic alignment techniques. The same boundary conditions were applied to compare patellofemoral stress and lateral retinaculum forces at 60° and 100° of flexion. In mechanically aligned TKA setup, change in JLO was associated with increased lateral retinaculum forces and patellofemoral contact surface, which both can lead to anterior knee pain. However, kinematically-aligned TKA showed increased stress peak during flexion, disregarding the restitution of the femoral JLO and raising the lack of specific femoral component design dedicated to this implantation technique