Responsiveness of the Stair Climb Test Across Follow‐Up Periods and Baseline Severity in Knee Osteoarthritis

BACKGROUND AND PURPOSE: The properties of the Stair Climb Test (SCT) remain to be determined in patients with knee osteoarthritis. Thus, this study aimed to evaluate the responsiveness and clinically meaningful improvement of the SCT across different follow-up periods and baseline severity in patients with knee osteoarthritis. METHODS: A prospective longitudinal observational study was conducted. Fifty-six adults with knee osteoarthritis (63.8 ± 10.6 y; 52% women) were included. Participants were stratified according to baseline WOMAC score into mild (< 30 points; n = 29) and severe (≥ 30 points; n = 27) groups. Patients participated in a 32-week home-based exercise program including progressive strengthening and balance exercises performed three times per week. SCT and 30STS were assessed. Responsiveness was quantified using the standardized response mean (SRM) during the early (0-8 weeks), late (8-32 weeks), and overall (0-32 weeks) follow-up periods. Clinically meaningful improvement was evaluated using an anchor-based approach, with responders defined as participants achieving an increase of ≥ 2 repetitions on the 30STS. Receiver operating characteristic analyses were used to estimate preliminary anchor-derived thresholds for meaningful functional change and to assess discriminative ability. RESULTS: The SCT showed numerically higher responsiveness estimates during the early follow-up period in participants with higher baseline disability (SRM = -0.59), while the corresponding estimate in the mild group was lower (SRM = -0.46). Numerically lower responsiveness estimates were observed during the late follow-up period (SRM = 0.10 and -0.33 for severe and mild groups, respectively). The 30STS showed relatively consistent SRM estimates across follow-up periods (SRM range: 0.26-0.62). The SCT showed poor discriminative ability during the early phase (AUC = 0.54; 95% CI: 0.38-0.70), whereas discrimination was numerically higher during the late phase (AUC = 0.64; 95% CI: 0.48-0.79). A preliminary anchor-derived threshold for meaningful functional change of -1.6 seconds identified during the late phase was associated with higher odds of responder classification according to the 30STS anchor (OR = 2.6). CONCLUSIONS: The responsiveness and clinical interpretability of the SCT may vary according to the follow-up period and baseline severity in knee osteoarthritis.