Deviating from mechanical alignment in total knee arthroplasty: are native kinematic and ligament strain restoration...

The main proposed targets for implant alignment in total knee arthroplasty (TKA) include restoration of native knee kinematics and/or ligament strains. These two targets may be inherently interchangeable, yet the extent of their relationship remains to be determined. For a single osteoarthritic patient, we used a previously established workflow to generate a personalized musculoskeletal model of the native knee and, subsequently, an implanted model configuration according to mechanical alignment (MA) principles. In the mechanically aligned model, the rotational alignment of the components was systematically varied within ± 4° relative to MA position in 2° increments/decrements, resulting in a total of 5⁶(15,625) simulated positions. Of these, 1103 positions more closely reproduced native kinematics compared with MA, and 84% of these also resulted in ligament strains closer to the native state. About three-times more positions (3294) were favorable when considering ligament strains, but only 28% of these also resulted in improved kinematics. There was a moderate positive correlation between the two targets (Pearson'sr= 0.607,R²= 0.369), suggesting they are related but not completely interchangeable. Although targeting restoration of native knee kinematics is generally expected to facilitate restoration of ligament strains, and vice versa, both objectives should be considered within a unified objective function to better achieve reconstruction of native biomechanical conditions after TKA.