Correlation between smartwatch-measured daily walking steps and patient-reported functional outcomes following total knee arthroplasty: a prospective cohort study

Abstract

BACKGROUND: Patient-reported outcome measures (PROMs) are the clinical standard for assessing recovery after total knee arthroplasty (TKA) which reflect patients' perceived function, whereas smartwatch step counts capture real-world activity. Whether their changes align after TKA is uncertain. We therefore assessed correlations between changes in daily steps and changes in PROMs. METHODS: In this prospective single-centre cohort, 86 patients undergoing unilateral primary TKA received a consumer-grade smartwatch (Polar A370™). Daily steps and PROMs were recorded 1 month pre-operatively and at 3 and 6 months post-operatively. PROMs comprised the Oxford Knee Score (OKS; 0-48, higher = better) and the KOOS-Physical Function Short-form (KOOS-PS; 0-28, higher = worse). Change scores were computed so that positive values indicated improvement. Pearson correlations assessed associations between change in steps and change in PROMs; paired t-tests compared pre-operative with 6-month values. RESULTS: Of 96 enrolled patients, 86 (89.6%) completed the 6-month follow-up. At 6 months, functional outcomes improved substantially: OKS increased from 26.4 (6.6) to 38.4 (5.8) (p < 0.001), and KOOS-PS decreased from 14.1 (4.3) to 9.8 (2.7) (p < 0.001). Daily steps increased modestly from 6651 (4,294) to 7807 (4,363) (p = 0.008). Correlations between change in steps and change in PROMs were negligible: OKS r = 0.055 (95% CI - 0.159 to 0.264) and KOOS-PS r = 0.071 (95% CI - 0.143 to 0.279). CONCLUSIONS: Although PROMs improved markedly after TKA, they showed little correlation with smartwatch-measured step counts. Patient-reported outcomes and objective activity data reflect different aspects of recovery and should be interpreted as complementary rather than hierarchical measures. IRB approval: Si COA 582/2022.