On the consequences of intra-operative release versus over-tensioning of the posterior cruciate ligament in total knee arthroplasty

Intra-operative tensioning of the posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) is commonly based on the surgeon's experience, resulting in a possibly loose or overly tight PCL. To date, the consequences of different PCL tensioning scenarios for the post-operative biomechanics of the knee remain unclear. Using a comprehensive musculoskeletal modelling approach that allows predictive joint kinematic and kinetic balance, we assessed variations in the movement and loading patterns of the knee as well as changes in ligament and muscle forces during walking in response to systematic variations in the PCL reference strain. The results indicate only small differences in the tibiofemoral and patellofemoral kinematics and kinetics for scenarios involving up to 10% release of the PCL (relative to the baseline reference scenario with 2% residual strain). These observations remain valid for simulations performed with high- as well as with low-conformity implant designs. However, over-tensioning of the ligament was found to considerably overload the tibiofemoral joint, including altered contact mechanics, and may therefore shorten the implant longevity. Finally, no meaningful impact of the PCL reference strain on the muscle force patterns was observed. This study therefore favours balancing the knee with a slightly loose rather than tense PCL, if appropriate intra-operative PCL tension cannot be objectively achieved.