Simple Smart Implants: Simultaneous Monitoring of Loosening and Temperature in Orthopaedics With an Embedded Ultrasound Transducer

Abstract

Implant failure can have devastating consequences on patient outcomes following joint replacement. Time to diagnosis affects subsequent treatment success, but current diagnostics do not give early warning and lack accuracy. This research proposes an embedded ultrasound system to monitor implant fixation and temperaturea potential indicator of infection. Requiring only two implanted components: a piezoelectric transducer and a coil, pulse-echo responses are elicited via a three-coil inductive link. This passive system avoids the need for batteries, energy harvesters, and microprocessors, resulting in minimal changes to existing implant architecture. Proof-of-concept was demonstrated in vitro for a titanium plate cemented into synthetic bone, using a small embedded coil with 10mm diameter. Gross looseningsimulated by completely debonding the implant-cement interfacewas detectable with 95% confidence at up to 12 mm implantation depth. Temperature was calibrated with root mean square error of 0.19 o C at 5 mm, with measurements accurate to ±1 o C with 95% confidence up to 6 mm implantation depth. These data demonstrate that with only a transducer and coil implanted, it is possible to measure fixation and temperature simultaneously. This simple smart implant approach minimises the need to modify well-established implant designs, and hence could enable mass-market adoption.

Best practice in digital orthopaedics

“…The sensor must be compact to avoid relevant changes in the original architecture of the implant, but it still must be able to harvest and store energy or to provide a self-powering system ( 13 ). Hall et al recently presented an in vitro trial to test an alternative for ultrasound-guided implant sensor that is able to detect loosening and temperature changes even though this technology does not expire ( 14 ). This leads to biocompatibility that is also an important aspect of implantables.…”

Bioelectronic multifunctional bone implants: recent trends

“…It is true that extracorporeal therapeutic ultrasound stimulation is widely used for bone growth and/or fracture healing of peri-implant regions (Palanisamy et al 2022 ). Recent advances already succeeded to incorporate ultrasound systems inside implants, but their performances as stimulation systems have never been tested so far (Hall et al 2021 ). Electromagnetic-stimulating implant systems are promising technologies towards the delivery of controllable stimuli to target regions (Peres et al 2022a ).…”

“…3 a) (Marschner et al 2009 ). A simple ultrasonic sensor was designed for smart implants to monitor implant fixation states, intracorporeally only requiring a piezoelectric transducer and a coil (Hall et al 2021 ). Another impacting technology uses extracorporeal magnetic induction to excite magnetic oscillators inside instrumented implants, such that extracorporeal mechanical transduction (using inercial sensors) can be performed (Fig.…”

“Smart Knee Implants: An Overview of Current Technologies and Future Possibilities”

“…Loosening is a frequent cause for TKR failure [ 1 , 10 ]. Early detection of implant loosening, or bone resorption could be achieved by measuring temperature around the implant [ 58 ], by using mechanical magnetic sensors with an oscillating membrane [ 59 ] or with an embedded ultrasound system [ 60 ].…”

“…Several sensor technologies have been explored to facilitate early infection detection. The simplest approach is to measure the temperature of implant components or the surrounding tissue [ 60 , 65 ]. More advanced approaches involve the analysis of bodily fluids with biosensors [ 20 ].…”