Abstract
Background
In-vitro testing of knee joints remains vital in the understanding of knee surgery and arthroplasty. However, based on the design philosophy of the original Oxford knee simulator, this in-vitro testing has mainly focused on squatting motion. As the activities of daily living might drastically differ from this type of motion, both from a kinematic and kinetic point of view, a new knee simulator is required that allows studying more random motion patterns. This paper describes a novel knee simulator that overcomes the limitations of traditional Oxford simulators, providing both kinematic and kinetic freedom with respect to the applied boundary conditions.
Methods
This novel test simulator keeps the hip at a fixed position, only providing a single rotational degree of freedom (DOF) in the sagittal plane. In addition, the ankle holds four DOF, including all rotational DOF and the translation along the medio-lateral axis. Combining these boundary conditions leaves five independent DOF to the knee; the knee flexion angle is actively controlled through the positioning of the ankle joint in the antero-posterior and proximal-distal direction. The specimens' quadriceps muscle is actively controlled, the medial and lateral hamstrings are passively loaded. To validate the performance of this simulator, two fresh frozen specimens have been tested during normal squatting and cycling. Their kinematic patterns have been compared to relevant literature data.
Results
Kinematic patterns in line with literature data are observed for the squatting motion, e.g. displaying femoral rollback for both specimens. In contrast, the kinematic patterns that are observed during cycling differ remarkably from the patterns of the squatting movement.
Conclusion
The results provide confidence in the working principle of the presented knee simulator, the mechanical design and all processing steps. In addition, the remarkable differences observed in kinematic patterns between different studied motions indicate the need for broadening the research view to relevant motion patterns, beyond squatting.
