Thermo-mobility coupling: continuous knee temperature-step interaction patterns predict functional recovery after total knee arthroplasty.

Abstract

Wearables increasingly quantify mobility after total knee arthroplasty (TKA), but local joint inflammation is still evaluated intermittently. It is unknown whether the interaction between knee temperature and free-living activity predicts recovery. To determine whether early thermo-mobility coupling (TMC), defined as the temporal relationship between peri-patellar skin temperature and step-derived mobility, predicts 12-week functional outcomes after primary total knee arthroplasty (TKA). In a prospective cohort at a tertiary center, adults undergoing unilateral primary TKA wore a peri-patellar temperature patch and thigh-mounted accelerometer continuously for 6 weeks postoperatively. Daily temperature metrics and step-based mobility measures were derived. TMC indices included within-day temperature-activity cross-correlation and the temperature load index (TLI), a step-weighted measure of peri-patellar thermal elevation. The primary outcome was the Knee Injury and Osteoarthritis Outcome Score-Activities of Daily Living (KOOS-ADL) at 12 weeks. Secondary outcomes included knee flexion range of motion (ROM), Timed Up-and-Go (TUG), and time to opioid cessation. Among 142 patients (mean age 67 ± 8 years, 64% women), higher maladaptive TMC during postoperative weeks 2-4 was independently associated with worse KOOS-ADL (- 8.1 points per SD), reduced flexion ROM (- 6.2°), slower TUG (+ 2.1 s), and delayed opioid cessation (hazard ratio 0.71), after adjustment for covariates. Patients in the most adaptive TMC quartile more often achieved clinically important KOOS-ADL improvement than those in the least adaptive quartile (78% vs. 43%). Continuous thermo-mobility coupling profiles carried prognostic information on early postoperative functional recovery after TKA and may help identify patients with potentially maladaptive recovery trajectories. Longer-term validation is required to determine whether early TMC patterns predict sustained functional outcomes beyond the 12-week postoperative period.