Do Patient-Reported Outcomes Reflect Objective Measures of Function? Implications for Total Knee Arthroplasty

Patient-reported outcomes (PROs) are used in research, clinical practice, and by federal reimbursement models to assess outcomes for patients who have knee osteoarthritis (OA) and total knee arthroplasty (TKA). We examined a large cohort of patients to determine if commonly used PROs reflect observed evaluation as measured by standardized functional tests (SFTs).

We used data from the Osteoarthritis Initiative, a 10-year observational study of knee osteoarthritis patients. Two cohorts were examined: 1) participants who received TKA (n = 281) and 2) participants who have native OA (n = 4,687). The PROs included Western Ontario and McMaster Osteoarthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS), 12-Item Short Form Health Survey (SF-12), and Intermittent and Constant Pain Score (ICOAP). The SFTs included 20 m and 400 meter (m) walks and chair stand pace. Repeated measures correlation coefficients were used to determine the relationship between PROs and SFTs.

The PROs and SFTs were not strongly correlated in either cohort. The magnitude of the repeated measures correlation (r_rm) between KOOS, WOMAC, SF-12, and ICOAP scores and SFT measurements in native knee OA patients ranged as follows: 400 m walk pace (0.08 to 0.20), chair stand pace (0.05 to 0.12), and 20 m pace (0.02 to 0.21), all with P < .05. In the TKA cohort, values ranged as follows: 400 M walk pace (0.00 to 0.29), chair stand time (0.02 to 0.23), and 20 M pace (0.03 to 0.30). Due to the smaller cohort size, the majority, but not all had P values < .05.

There is not a strong association between PROs and SFTs among patients who have knee OA or among patients who received a TKA. Therefore, PROs should not be used as a simple proxy for observed evaluation of physical function. Rather, PROs and SFTs are complementary and should be used in combination for a more nuanced and complete characterization of outcome.