Impact of Test Speed and Lubrication Conditions on Dynamic Testing of Total Knee Endoprostheses

Preclinical testing is essential for evaluating new implant designs and materials for total knee replacement (TKR). Standardized wear tests, such as ISO 14243, are widely accepted but only partially represent physiological kinematics and kinetics, as they do not account for all six degrees of freedom of the knee joint. More advanced setups, including robotic systems and joint simulators, enable complex load cases; however, the influence of lubrication conditions and testing speeds remains insufficiently standardized. This study investigated the kinematic and kinetic effects of different lubrication conditions (dry, synthetic synovial fluid, silicone oil) and speeds (static, 10%, 50%, 100% of normal gait) in a joint simulator setup using a posterior cruciate ligament-retaining TKR during level walking. Complementary pin-on-disk measurements revealed significant dependencies on both lubrication and speed. During joint simulator tests, omitting lubrication resulted in more than double the maximum flexion–extension moment, while the range of anterior–posterior femoral translation increased by approximately 73%. At 50% and 100% speed, silicone lubrication yielded results comparable to static tests, in contrast to the dry and synthetic synovial fluid conditions. These findings demonstrate that physiologically relevant lubrication and appropriate test speeds are essential for obtaining reliable results in experimental studies of TKR dynamics.