A Novel Smart Implantable Device Demonstrates Early Gait Decline as a Marker of Periprosthetic Joint Infection After Total Knee Arthroplasty

Background Periprosthetic joint infection (PJI) remains a major cause of early failure after total knee arthroplasty (TKA), yet early diagnosis is difficult and often delayed. Continuous physiologic monitoring from smart implantable devices may offer earlier insight into functional changes preceding clinical recognition. Methods A retrospective analysis linked insurance claims to gait and activity data collected by a smart implantable device (SID). Patients with a primary PJI diagnosis and SID transmissions spanning 14 days before and 14 days after diagnosis were included. Gait parameters and qualified step count were aligned to the diagnosis date, three-day moving averages were analyzed, and within-patient changes from day −7 to day −1 were assessed. Results Thirty-three SID-TKA patients met inclusion criteria (16 intravenous-antibiotics; 17 revision/DAIR/removal). Step count declined significantly before diagnosis in both groups, with a 55–58% reduction by day −1. The revision group also showed significant pre-diagnostic decreases across all gait parameters, whereas changes were smaller and not statistically significant in the intravenous-antibiotics group. Case reviews illustrated variable patterns of early functional decline among individuals. Conclusion Continuous implant-derived gait monitoring detected functional deterioration in some patients in the days preceding clinical PJI diagnosis. These findings support the potential role of smart implants as an adjunct to existing diagnostic pathways and highlight the need for prospective evaluation of early gait deviations as a marker of evolving infection.