Total knee replacement: Are there any baseline factors that have influence in patient reported outcomes?

Background: There is conflicting evidence about what factors influence outcomes after total knee replacement (TKR). The objective is to identify baseline factors that differentiate patients who achieve both, minimal clinically important difference (MCID) and a patient acceptable symptom state (PASS) in pain and function, measured by WOMAC, after TKR from those who do not attain scores above the cutoff in either of these dimensions.

Methods: One-year prospective multicentre study. Patients completed WOMAC, SF-12, EQ-5D, expectations, other joint problems and sociodemographic data while in the waiting list, and 1-year post-TKR. Dependent variable was a combination of MCID and PASS in both dimensions (yes/no). Univariate analysis was performed to identify variables associated. Exploratory factor analysis (EFA) was performed to study how these variables grouped into different factors.

Results: Total sample comprised 492 patients. Mean (SD) age was 71.3 (6.9), and there were a 69.7% of women. Of the total, 106 patients did not attain either MCID or PASS in either dimension, and 230 exceeded both thresholds in both dimensions. In the univariate analysis, 13 variables were associated with belonging to one group or another. These 13 variables were included in EFA; 3 factors were extracted: expectations, mental health, and other joints problems. The percentage of variance explained by the 3 factors was 80.4%.

Conclusion: We have found 2 modifiable baseline factors, expectations and mental health, that should be properly managed by different specialist. Indication of TKR should take into account these modifiable factors for improving outcomes after TKR.