Total Knee Replacement (TKR) is an important and in-demand procedure for the aging population of the United States. In recent decades, the number of TKR procedures performed has shown an increase. This pattern is expected to continue in the coming decades. Despite medical advances in orthopedic surgery, a high number of patients, approximately 20%, are dissatisfied with their procedure outcomes. Common causes that are suggested for this dissatisfaction include loosening of the implant components as well as infection. To eliminate loosening as a cause, it is necessary to determine the state of the implant both intra- and post-operatively. Previous research has focused on passively sensing the compartmental loads between the femoral and tibial components. Common methods include using strain gauges or even piezoelectric transducers to measure force. An alternative to this is to perform real-time structural health monitoring (SHM) of the implant to determine changes in the state of the system. A commonly investigated method of SHM, referred to as the electromechanical impedance (EMI) method, involves using the coupled electromechanical properties of piezoelectric transducers to measure the host structure’s condition. The EMI method has already shown promise in aerospace and infrastructure applications, but has seen limited testing for use in the biomechanical field. This work is intended to validate the EMI method for use in detecting damage in cemented bone-implant interfaces, with TKR being used as a case study to specify certain experimental parameters. An experimental setup which represents the various material layers found in a bone-implant interface is created with various damage conditions to determine the ability for a piezoelectric sensor to detect and quantify the change in material state. The objective of this work is to provide validation as well as a foundation on which additional work in SHM of orthopedic implants and structures can be performed.

Total Knee Replacement (TKR) is a common procedure that is gaining importance with the aging American population. Although TKR is common, about 20% of patients report being unhappy with their results. Previous research has pointed to misalignment and loosening as contributing factors to negative outcomes. What is lacking in the field of TKR is a sensory system that can determine the internal loads of the knee in a direct manner. Implant bearings embedded with piezoelectric transducers have already shown promise in providing accurate sensing data. To perform further experimentation, prototype implant bearings that can be accurately and efficiently produced are needed. This work investigates various fabrication processes and possible materials to provide a foundation for developing surrogate biomechanical implants, especially those with integrated smart sensors. In this study, an original knee bearing is scanned and the resulting geometries used to generate prototypes. The prototypes are fabricated using a variety of methods including CNC machining and additive manufacturing. The prototypes are then tested to determine load distribution, active sensor performance, as well as kinematic performance under loading. The results of this study show that FDM printing provides quick and affordable results but is not ideal for rigorous experimentation. SLA printed prototypes are improved in final quality with an increase in fabrication time. Lastly, CNC machined processes are more labor intensive but can provide the best material characteristics. The findings from this study aim to have an impact not only on researchers studying biomedical sensing, but on the field of biomechanical implants.

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Total Knee Arthroplasty (TKA) continues to be a common and important orthopedic procedure for many in the United States. Despite recent medical advancements and increasing knowledge in the orthopedic community, it has been determined that 20% of TKA patients are still dissatisfied with their knee replacements. Causes of this failure include septic loosening and wear on the bearing component of the implant. Another cause of failure that has received specific attention from the mechanical community is aseptic loosening, which has been attributed to unbalanced ligaments or misalignment of the implant components. Previous efforts have been made to detect loosening by using passive force sensors such as piezoelectric transducers or strain gauges to detect misalignment. An alternative to this is to perform active sensing or structural health monitoring to evaluate possible loosening before it becomes a critical concern to the patient. One method of structural health monitoring, called the electromechanical impedance (EMI) method, is particularly attractive as it can use a single, compact piezoelectric transducer to determine the state of the host structure. This work is intended to evaluate the ability of the EMI method in sensing loosening between the cement and bone of a TKA tibial tray. This work will utilize real tibial trays implanted into synthetic bone (Sawbone) to evaluate the feasibility of detecting loosening using the EMI method. The intention of this work is to serve as a foundation for further in-vivo and intraoperative studies.