Exploring contactless vibro-acoustic implant stability monitoring for a solid femoral stem

Vibro-acoustic methods allow monitoring the fixation of orthopedic implants, such as hip implants. However, their clinical application is challenged by damping effects from surrounding soft tissues, particularly hindering measurements at higher frequencies. Previous studies have shown that these effects can be mitigated using an instrument that attaches to a modular femoral stem, altering the dynamic properties of the bone-implant system. This study explores the feasibility of further improving clinical applicability by implementing contactless excitation and response acquisition. An instrument designed for solid stems was tested on an artificial bone-implant structure with artificial soft tissues. Contactless methods included electromagnetic excitation and laser vibrometry for dynamic response measurement. Acoustic excitation using piezoelectric speakers (AT-1440, Pui Audio, Ohio, USA; SPS-68, Sonitron, St-Niklaas, Belgium) was introduced as an alternative to electromagnetic excitation. Considering the sound pressure levels of each speaker, accelerometers detected 100 and 93.3% of the structure’s resonance frequencies in the target frequency range, respectively. Solid femoral stem insertion was successfully monitored using contactless excitation and response techniques, even in the presence of artificial soft tissue. The instrument permitted monitoring of resonance frequencies converging at 1.1, 2.3, and 5.5 kHz. [Work supported by Internal Funds KU Leuven and FWO grant 1S35424N.]