Design and Evaluation of an Integrated Piezoelectric Force Sensing Total Knee Replacement

With patient dissatisfaction rates in total knee arthroplasty currently at 20%, smart knee technology seeks to provide an in vivo method for tracking postoperative joint forces, which could aid in early diagnosis of postoperative complications and provide key data to help improve implant designs and surgical procedures. This study investigates the design, simulation, and experimental evaluation of a piezoelectric force sensing system integrated into a commercially available knee implant that preserves the overall implant geometry. Finite element simulation and parametric analysis are used to identify the transducer arrangement with the lowest error in sensing compartmental joint contact forces. A prototype is then subjected to an axial load profile simulating walking using a joint motion simulator. Total and compartmental contact forces are evaluated, and accuracy of compartmental center of pressure localization is evaluated via ±3 mm and ±6 mm anterior-posterior translations. Results show the ability to track the axial force profile and demonstrate center of pressure deviations of ∼1 mm or better at 3-A and 3-P translations and ∼3-4 mm at 6-A and 6-P translations. Error of the order of ∼15% is observed in the total force measurement at maximum load. Suspected sources of error include plastic deformation of the tibial bearing insert and high stress levels in the piezoelectric transducers that suggest partial depolarization. Overall, our piezoelectric smart knee replacement shows promise for in vivo joint sensing, and this work marks a path for further development for integration into commercial knee replacement components.