Improving physiological fidelity of in vitro knee simulators through bidirectional optimized muscle control

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Robotics

Background:

• Existing in vitro knee simulators lack the physiological fidelity needed for comprehensive surgical intervention evaluation due to limited motion and agonist-antagonist co-contraction.
• Current simulators often require activity-specific hardware modifications, hindering versatile testing.

Purpose of the Study:

• To develop a generalizable control framework for in vitro knee simulators that integrates bidirectional actuation and force optimization.
• To enhance physiological relevance in knee simulator testing by enabling active agonist-antagonist co-contraction and a wider range of motion.
• To create a versatile platform capable of replicating diverse daily living activities for biomechanical evaluation.

Main Methods:

• Developed a novel control framework for the BiOME knee simulator, incorporating bidirectional sagittal-plane control via coordinated ankle translation.
• Integrated feedback position/force loops with a model-based feedforward estimator and an optimization routine for quadriceps-hamstring co-contraction.
• Implemented and benchmarked five control strategies for squatting motion on a phantom knee against in vivo and in vitro data.

Main Results:

• The feedforward block significantly improved vertical ground reaction force (GRF) tracking accuracy by 48% and flexion-angle accuracy by 80%.
• Optimized bidirectional control restored physiological ankle dorsiflexion and reduced peak quadriceps loads by 37%, aligning better with literature.
• The generalizable framework demonstrated high repeatability and accuracy, requiring only activity-specific data (force plate, motion capture) for diverse activity replication.

Conclusions:

• The developed generalizable control framework significantly enhances the physiological fidelity and accuracy of in vitro knee simulators.
• This approach enables testing across a wide range of daily activities without hardware redesign, advancing biomechanical evaluation of surgical techniques and implants.
• The BiOME simulator, with its optimized bidirectional control, offers a more realistic and versatile platform for orthopedic research.