Effect of tibial tray backside design on stress transfer and micromotion in uncemented posterior-stabilized TKA: A finite element study.

Purpose: The uncemented posterior-stabilized total knee arthroplasty (PS-TKA) gained increasing acceptance as younger and active patients have higher requirements for the lifespan and functionality of prostheses, because their frequent gait and deep-flexion activities may amplify tibial implant-bone interface micromotion and increase the risk of early tibial loosening. The purpose of this study is to evaluate the biomechanical fixation effects of three different tibial tray backside designs, with the aim of informing surgeons in selecting the most appropriate fixation strategy for uncemented PS-TKA. Methods: The finite element and micromotion models were developed to quantify the tibial von Mises stress and interface micromotion under the knee loading conditions. The effects of three common tibial tray backside designs, including a cylindrical stem with a triple flat keel (CS-TFK), a tapered stem with a double flat keel (TS-DFK) and a cylindrical stem with a double serrated keel (CS-DSK), on stress transfer and interface micromotion were compared. Results: During walking, all designs exhibited similar stress and micromotion patterns, with minimal risk for prostheses instability. During squatting, the cylindrical stem with double serrated keel design exhibited the highest proximal tibial stress (124.03 MPa) and the lowest maximum micromotion (361.91 µm), resulting in the largest area suitable for bone ingrowth (42.53%). In contrast, the tapered stem with double flat keel design had the lowest stress (90.70 MPa), and its area at risk for poor osseointegration (micromotion >150 µm) increased by 44.70% compared with the cylindrical stem with double serrates keel design. Discussion: The tibial tray backside design influenced its primary fixation. Among the evaluated designs, the CS-DSK balanced stress transfer and interface micromotion, suggesting it may be favored for uncemented PS-TKA in younger, active patients to lower the likelihood of early tibial aseptic loosening. CS-DSK favored early ingrowth but produced higher local stresses, so overload risk should be monitored in older patients with osteoporosis. Level of Evidence: N/A.