Dissociation Between Instrumented Mobility and Self-Reported Function in Adults Aged 70 Years or Older After Unilateral Total Knee Arthroplasty: A Preliminary Longitudinal Study Using an Inertial Sensor and the WOMAC

Background and Objectives: Total knee arthroplasty (TKA) reliably reduces pain and improves self-reported function, yet objective mobility may remain impaired in older adults. We examined the relationship between inertial-sensor-based mobility and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) in adults aged 70 years or older after unilateral TKA.

Methods

In this observational longitudinal study, 25 participants were assessed at up to three postoperative time points (M1, first available assessment; M2, 2024 follow-up; M3, 2025 follow-up). Outcomes were the instrumented Timed Up and Go (TUG) test with segmented turning variables, the 2-Minute Walk Test (2MWT), spatiotemporal gait variables recorded with a trunk-mounted inertial measurement unit, and the WOMAC. Paired changes in the instrumented outcomes were tested with Wilcoxon signed-rank tests under Benjamini–Hochberg false-discovery-rate (FDR) control and are reported with bootstrap confidence intervals (CIs); longitudinal change in the WOMAC was not tested, because the response format used at the first assessment could not be established from the available records, so WOMAC scores are used only within time point; associations used Spearman correlations with bootstrap CIs and leave-one-out influence diagnostics. Individual-level agreement was examined by standardising each of three externally validated objective outcomes against the inverted WOMAC total score within time point and classifying discordance across a range of cut-offs. Observed changes in the instrumented outcomes were benchmarked against published minimal detectable change (MDC) values.