Parametric Testing of Surrogate Knee Replacement Bearings With Embedded Piezoelectric Transducers

In the United States, Total Knee Replacement (TKR) is a surgery many people go through, but frequently, patients find that they are unhappy post-surgery due to misalignment and loosening of the knee. An estimated 20% of knee replacement recipients report discomfort or undesired functionality within their first few years after surgery. Surgical techniques currently rely heavily on experience and tactile feedback to correctly align the knee replacement. If surgical teams were to have access to data regarding compartmental forces within the knee over the life of the implant, then a more precise balancing procedure could be implemented. As it stands, the only way to obtain this in vivo data is for patients to undergo post-operative fluoroscopy procedures; unfortunately, patients have no incentive to undergo this process. This study tests the capabilities of knee bearings embedded with piezoelectric transducers to estimate the magnitude and location of loading given certain inputs. The prototype is fabricated from ultra high molecular weight (UHMW) polyethylene using Computer Numerical Control (CNC) machining. For this study, to simulate loads under both normal and irregular knee positions, a custom fixture is designed and fabricated for use in a uniaxial load frame. The problem at hand necessitates a more realistic knee testing environment that can simulate the loading types of both balanced and imbalanced knees. Thus, the fixture permits various degrees of internal and external rotation. Additionally, through use of an X-Y translational table, the setup allows for in-plane translation between the condyles of the femoral component and the bearing prototype. This study compares values of force location from the piezoelectric sensors to measurements from pressure sensitive film. The piezoelectric knee bearing is tested to lay the groundwork for in vivo testing. Future work expanding upon this research would include designing and optimizing an in vivo knee bearing replacement to facilitate force location and magnitude data collection in a system free from external power sources by utilizing the energy harvesting capabilities of piezoelectrics.