A new protocol from real joint motion data for wear simulation in total knee arthroplasty: stair climbing.

In its normal lifespan, a knee prosthesis must bear highly demanding loading conditions, going beyond the sole activity of level walking required by ISO standard 14243. We have developed a protocol for in vitro wear simulation of stair climbing on a displacement controlled knee simulator. The flexion/extension angle, intra/extra rotation angle, and antero/posterior translation were obtained in patients by three-dimensional video-fluoroscopy. Axial load data were collected by gait analysis. Kinematics and load data revealed a good consistence across patients, in spite of the different prosthesis size. The protocol was then implemented and tested on a displacement controlled knee wear simulator, showing an accurate reproduction of stair climbing waveforms with a relative error lower than 5%.