Methods for locating the tibio-femoral contact pathway in total knee replacements using marker-based gait analysis and standard radiography.

INTRODUCTION: The purpose of this study was to develop and test techniques for tracking the path of contact between the tibial and femoral total knee replacement components during level over-ground walking. The tibio-femoral path of contact could be an indicator of the in vivo performance of a total knee replacement as an estimator of areas of contact between the implant components. A longer contact path, indicative of more sliding between the implant components during walking, could indicate an implant at risk for increased wear. In addition, the tibio-femoral contact path determines the position and length of the muscle and ligament lever arms about the knee, and can subsequently influence knee contact force calculations.
METHODS: Two methods were developed to predict the tibio-femoral contact pathways for total knee replacement devices. Both methods used patient-specific knee kinematics obtained during gait analysis, standard radiographs obtained during clinical follow-ups, and point-clouds of the tibial and femoral bearing surfaces. The validity of the techniques was evaluated with knee wear simulator tests and comparisons to wear scars on postmortem retrieved tibial components.
RESULTS: The average total anterior-posterior distance covered by the contact path for ten patients implanted with a total knee replacement was 29.01 mm on the lateral side, and 21.80 mm on the medial side. Both methods for predicting the tibiofemoral contact pathways yielded similar results, and fell within the wear scars of simulator-tested and postmortem retrieved implants.
CONCLUSIONS: The methods for predicting the tibio-femoral contact pathway using marker-based gait analysis and standard clinical radiographs are computationally simple, and reliably predict contact path characteristics as evaluated against wear scars from knee wear simulator tests and postmortem retrieved implants.