Towards In Vivo Wearable Diagnostics in Orthopaedics: Sensorized Bone Cement for Knee Spacer Applications

Periprosthetic joint infection (PJI) is a severe complication of total knee arthroplasty and is a leading cause of revision surgery, and is associated with significant morbidity. Two-stage exchange using antibiotic-loaded polymethylmethacrylate (PMMA) spacers remains the clinical gold standard, yet the decision to reimplant relies largely on indirect markers and clinical judgment, as no method allows continuous in situ assessment of infection resolution. Here, we report a sensorized knee spacer that transforms PMMA bone cement from a passive structural material into an active, wearable diagnostic device. A miniaturized multimodal sensor unit integrating optoelectronic and physicochemical sensing was embedded within the tibial spacer component and wirelessly coupled, enabling energy-efficient, 24/7 in vivo monitoring during the spacer interval for several months. We developed a reproducible encapsulation and integration strategy compatible with clinically realistic spatial, thermal, and mechanical constraints, without altering the established surgical workflow. The functionality of the embedded camera, spectrometer, and temperature sensors following cement integration was verified. Mechanical integrity and signal stability were confirmed under ISO-compliant dynamic biomechanical loading conditions. In vivo validation of the implantable wearable was preclinically demonstrated in a porcine model using human knee spacer dimensions. These findings establish the technical feasibility of sensor-integrated PMMA spacers and introduce bone cement as an enabling platform for smart orthopedic implants. Continuous, local monitoring of the peri-implant environment may open new pathways for evidence-based decision-making in infection management with temporary implantable wearables.