# Transfer of patients’ tibiofemoral kinematics and loads to a six-degree-of-freedom (6-DOF) joint simulator under consideration of virtual ligaments

## TL;DR

This study improves preclinical testing of knee implants by simulating real-life activities and ligament effects using a 6-DOF joint simulator.

## Contribution

A novel method for transferring real patient data to a joint simulator with virtual ligaments for testing knee replacements.

## Key findings

- Tibiofemoral contact area is more influenced by dynamics than kinematics.
- Virtual PCL resection caused posterior tibial shift and increased abduction.
- Squat and sit-to-stand showed similar patterns, unlike other activities.

## Abstract

Preclinical testing of total knee replacements (TKR) is crucial for evaluating new implant designs. Dynamic experimental testing focus mostly on level walking and squats, failing to represent a full range of daily activities. Moreover, the contribution of the ligament apparatus is often simplified. Therefore, this study transferred five daily activity load cases—level walking, downhill walking, stair descent, squat, and sit-to-stand—onto a six-degree-of-freedom (6-DOF) joint simulator with a cruciate-retaining bicondylar TKR and a virtual ligament apparatus. Forces and kinematics were based on telemetric data from an ultra-congruent TKR. The resulting kinematics, kinetics, and tibiofemoral contact surfaces were evaluated. Additionally, variations of the virtual ligament apparatus on the joint simulator, e.g. resection of the posterior cruciate ligament (PCL), have been used to assess its influence on the resulting joint dynamics. Results showed that tibiofemoral contact area was more influenced by dynamics than kinematics. Virtual PCL resection shifted the tibia posteriorly (up to 3 mm) and increased abduction (up to 0.5°). Different results were seen across all load cases. The exceptions are the squat and sit-to-stand load cases with similar patterns. Thus, cruciate-retaining TKR can be tested using telemetric data from ultra-congruent TKR, aiding in comprehensive evaluations.

The online version contains supplementary material available at 10.1038/s41598-025-95400-4.