Understanding the ideal ligamentous balance to be achieved during surgery is considered by many the Holy Grail of total knee arthroplasty (TKA). Balance of the compartmental forces in artificial knees is a critical factor in surgical outcomes related to performance and lifespan of knee replacements and to patient satisfaction. Improperly balanced knees result in accelerated wear of the articular surfaces, reduced range of motion, and patient discomfort and pain due to osteolysis. Current surgical practices for the balance of ligamentous forces rely heavily on the surgeon's experience and use qualitative methods to achieve proper balance. The lack of quantitative measures for intraoperative balancing of forces presents a gap in the current scientific knowledge of TKA, thus revealing a need to measure tibiofemoral forces in vivo to develop improved surgical procedures and implant designs. Current methods for in vivo load sensing require external power sources for charging internal batteries as well as modifications to existing total knee replacement geometries. The goal of this work is to investigate the use of piezoelectric materials embedded in total knee replacement (TKR) bearings in order to sense tibiofemoral forces in vivo and to convert knee loads into usable electrical energy to power the embedded sensor, thereby preserving existing implant designs and creating a self-powered solution. Additionally, the use of the embedded sensors to perform in vivo implant wear and loosening monitoring will be investigated, which has not been addressed by current methods.
Aim 1 will identify the effects of embedding piezoelectric transducers on the fatigue life of the bearings and determine the ability of embedded transducers to accurately sense tibiofemoral forces through both multiphysics finite element simulation and experimental fatigue testing that subjects the instrumented implant to realistic load profiles experienced in the knee.
Aim 2 will develop sensing techniques for in vivo implant wear and loosening monitoring based on existing methods used in the structural health monitoring field using experimental techniques.
Aim 3 will determine the amount of energy that can be converted and stored by the piezoelectric transducers to power the implantable device through multiphysics simulation and experimental compression testing. This research supports the NIH mission by 1) furthering the understanding of the effects of mechanical forces on implant wear and loosening, 2) advancing the development of data-driven approaches to improve implant performance, and 3) progressing the development of in vivo wear measurements in total knee replacements; all of which have been identified by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) as long-range research goals. The ability to continuously measure tibiofemoral forces both intra- and postoperatively will allow much needed insight into the progression of forces in artificial knees, furthering the understanding of ideal practices for surgical procedures and TKR designs. Advancements in in vivo measurement technology from this work can be applied to other orthopedic applications including hip and spine implantation.

Public Health Relevance

Currently over 700,000 patients receive total knee replacements in the United States each year, most of which result in restored knee function, however, not all operations are successful and all knee replacements eventually wear out. Current surgical practices rely heavily on the surgeon's experience to achieve the optimal 'balance' of knee forces that results in a successful operation and there is no current means of reliably recording data of the forces and wear in knee implants after surgery. The purpose of this study is to determine if sensors can be embedded into knee replacements to record force and wear data in a nonintrusive manner, which can be used to develop better surgical procedures and better implant designs in order to improve surgical outcomes and ultimately public health.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Academic Research Enhancement Awards (AREA) (R15)
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Special Emphasis Panel (ZRG1-SBIB-G (83)A)
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Washabaugh, Charles H
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Tennessee Technological University
Engineering (All Types)
Schools of Engineering
United States
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