A new protocol for wear testing of total knee prostheses from real joint kinematic data: Towards a scenario of realistic simulations of daily living activities.

A new tendency in the field of wear testing of total knee replacements is represented by realistic simulations of various motor tasks of daily living (chair sitting and rising, squat, stair ascent, etc.). Various studies have shown in fact the limits of the ISO 14243 standards, in particular the concern about the ability of the level walking simulations to recreate the main wear mechanisms which occur on the knee implant during its in vivo lifespan. The recently proposed protocols for the simulation of these motor tasks still lack accuracy and consistency between the various degrees of freedom, which are necessary for a good replication of the mechanical behavior in a replaced knee. In the present study a realistic scenario for simulation of various motor tasks using a displacement controlled wear testing machine is presented. Stair climbing, chair sit/stand cycle, and squat cycle were analyzed through video-fluoroscopy in a population of knee replacement patients to extract flexion/extension and intra/extra rotation angles, together with anterior/posterior translation. Corresponding axial load data were arranged by gait analysis from a control population. The proposed protocol was tested on a displacement controlled wear simulator. Kinematic and load data revealed good consistency across subjects. The knee simulator showed an accurate reproduction of the various motion and load patterns, with average error lower than 5%. The obtained dataset for wear simulator, containing all the displacement and loading parameters for stair climbing, chair sit/stand and squat activities, is fully reported.