Contribution of geometric design parameters to knee implant performance: Conflicting impact of conformity on kinematics and contact mechanics

Background: Articular geometry of knee implant has a competing impact on kinematics and contact mechanics of total knee arthroplasty (TKA) such that geometry with lower contact pressure will impose more constraints on knee kinematics. The geometric parameters that may cause this competing effect have not been well understood. This study aimed to quantify the underlying relationships between implant geometry as input and its performance metrics as output. Methods: Parametric dimensions of a fixed-bearing cruciate retaining implant were randomized to generate a number of perturbed implant geometries. Performance metrics (i.e., maximum contact pressure, anterior-posterior range of motion [A-P ROM] and internal-external range of motion [I-E ROM]) of each randomized design were calculated using finite element analysis. The relative contributions of individual geometric variables to the performance metrics were then determined in terms of sensitivity indices (SI). Results: The femoral and tibial distal or posterior radii and femoral frontal radius are the key parameters. In the sagittal plane, distal curvature of the femoral and tibial influenced both contact pressure, i.e., SI = 0.57; SI = 0.65, and A-P ROM, i.e., SI = 0.58; SI = 0.6, respectively. However, posterior curvature of the femoral and tibial implants had a smaller impact on the contact pressure, i.e., SI = 0.31; SI = 0.23 and a higher impact on the I-E ROM, i.e., SI =0.72; SI = 0.58. It is noteworthy that in the frontal plane, frontal radius of the femoral implant impacted both contact pressure (SI = 0.38) and I-E ROM (SI = 0.35). Conclusion: Findings of this study highlighted how changes in the conformity of the femoral and tibial can impact the performance metrics.