Background/Purpose: Previous studies show differences between self-report measures and performance/functional measures following total knee arthroplasty (TKA). We investigated the hypothesis that this trend would hold true in a large prospective cohort of patients (no exclusion criteria) undergoing primary unilateral TKA.  

Methods: De-identified data from 345 patients (age 63.8 y/o, 44% male, BMI of 32.37), undergoing primary unilateral TKA, were included in this study. Data were drawn from a clinical registry of all patients seeking rehabilitation services at ATI Physical Therapy, (Greenville, SC) from January 2014-January 2016. The performance measure used was the Timed Up and Go (TUG). The self-report measure used was the disability subscale of the Western Ontario and McMaster Universities Arthritis Index (WOMAC). All measures were collected at baseline (pre-TKA), early post-TKA (<20 days after TKA) and later post-TKA (30 to 45 days after TKA). One-way repeated measure ANOVA’s were then performed on each outcome (TUG and WOMAC separately) to test for the effect of time. Post-hoc contrasts compared the change in outcomes from baseline scores. Secondarily, Pearson product moment correlations were calculated by using change scores from baseline ([initial-final/initial]*100) to evaluate the relationship across time points between TUG and WOMAC disability subscale.

Results: TKA resulted in a significant worsening of mean TUG times from baseline to early post-TKA (3.16 sec; p<0.001), while WOMAC disability subscale scores demonstrated functional improvement (-5.22; p<0.005). At the later post-TKA time point, mean TUG times significantly improved from baseline (-2.56 sec; p<0.001) and WOMAC disability subscale scores had a large significant improvement (-20.52; p<0.001). Pearson product moment correlations revealed that change in the WOMAC total disability subscale was not significantly correlated (p>0.05) with change in TUG times from baseline to the early or later post-TKA time points.

Conclusion: At early post-TKA, patients reported improved scores from baseline on the WOMAC while poorer times were observed on the TUG. Similarly, for later post-TKA, the lack of correlation between changes in WOMAC and TUG measures from baseline, further suggests that patient-reported and performance outcomes may be measuring different constructs. Therefore, they should both be used for assessment as they provide different, but complementary information. Using only patient-reported outcomes is likely to disguise critical deficits impairing patient function. This is particularly true during the early post-TKA period when patients perception of their physical function (self-report) contrasts with more objective assessments (performance testing). Failure to identify underlying functional deficits, not captured using self-report measures, may result in inappropriate discharge planning and long term functional decline.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/using-a-large-prospective-cohort-of-patients-to-examine-differences-in-performance-and-self-reported-outcomes-following-total-knee-replacement/