A total knee replacement (TKR) restores range of motion and provides pain relief primarily for patients suffering from osteoarthritis. While durability has improved significantly, these implants can still fail prematurely, especially because of improper soft tissue balancing or overloading if the patient exceeds exercise limitations. These failures could be mitigated by intra- and post-operative load sensing, respectively. The development of a sensor system capable of measuring and reporting forces transmitted through TKR is one of the next logical evolutions of these implants. While some sensor systems have been proposed, they all require external power provided via induction coils or an internal battery that will eventually become depleted. We propose that energy can be harvested from the loads passing through the joint during the activities of daily living using the triboelectric effect. The triboelectric effect is a newly discovered transduction mechanism for converting mechanical energy into electrical energy. It has a higher power density than other mechanisms such as electromagnetic and piezoelectric transduction, and therefore allows a smaller overall form factor. This means the sensor can be installed between the tibial tray and UHMWPE bearing component of any TKR without any modifications. The objective of the proposed research is to create a self-powered load measurement system for TKR. Studies will focus on i) developing a model that can accurately predict the output power of the energy harvester, ii) manufacturing a physical prototype as a proof-of- concept, and iii) comprehensive testing. The model will enable optimizing the energy harvester design to maximize power generation. We will integrate the energy harvester into a low-power sensing and telemetry system capable of transmitting the measured data wirelessly to an external receiver. The integrated system will be tested by a joint simulator under typical knee loading. The sensor accuracy in measuring the load will be quantified. Load imbalances such as improper soft tissue tensions or implant component misalignment will be simulated and the sensor's capability in detecting these issues will be determined. Because the sensor will interface directly with other implant components, we will also perform long-term durability studies to rule out any potential detrimental effects on implant longevity as a result of introducing our sensor. Once developed and tested, our sensor will offer an option for continuous monitoring of TKR health.
Failure of total knee replacement can occur as a result of improper joint alignment or overloading. Our objective is to create a self-powered load sensor that continuously monitors and reports these loads. This capability would allow surgeons to align the joint more accurately, and to warn patients when they are performing activities that could lead to premature implant failure.
