Table 4. Kneea- Univariate linear mixed regression models of WOMAC-function or–pain stratified by high/low pre-operative group profiles.
| Low groupb | High groupc | Low vs Highd | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Coef. | 95% CI | p-value | Coef. | 95% CI | p-value | Diff. | 95% CI | p-value | ||||
| WOMAC-function | ||||||||||||
| Pre-operative scoree | -0.555 | (-0.733, | -0.378) | <0.001 | 0.995 | (0.819, | 1.172) | <0.001 | -1.551 | (-1.802, | -1.300) | <0.001 |
| Short-term changef | 0.373 | (0.286, | 0.459) | <0.001 | 0.229 | (0.173, | 0.285) | <0.001 | 0.144 | (0.041, | 0.247) | 0.006 |
| Long-term changef | 0.000 | (-0.001, | 0.001) | 0.827 | 0.001 | (-0.000, | 0.001) | 0.179 | -0.001 | (-0.002, | 0.001) | 0.350 |
| WOMAC-pain | ||||||||||||
| Pre-operative scoree | -0.595 | (-0.770, | -0.420) | <0.001 | 0.962 | (0.802, | 1.122) | <0.001 | -1.557 | (-1.794, | -1.319) | <0.001 |
| Short-term changef | 0.464 | (0.355, | 0.572) | <0.001 | 0.299 | (0.225, | 0.372) | <0.001 | 0.165 | (0.034, | 0.296) | 0.014 |
| Long-term changef | 0.000 | (-0.001, | 0.001) | 0.737 | 0.001 | (-0.000, | 0.002) | 0.074 | -0.001 | (-0.002, | 0.001) | 0.388 |
Coefficient with p-value<0.05 are highlighted in bold. WOMAC- function and–pain are modelled as standardized outcomes.
a. The regression coefficients are derived from random intercept and slope models adjusted for time of assessment parameterised as two linear splines (short-term changes and long-term changes). The variances of random effects and correlation coefficients are not presented but are available on request. High/low function status defined on pre-operative WOMAC-function or -pain using their median scores (51 and 45) as cut-points.
b. The low group refers to participants with low functional ability or high level of pain.
c. The high group refers to participants with high level of function or low level of pain before surgery.
d. Difference between the low and high groups’ regression coefficients assessed with linear contrasts.
e. Intercept: Estimated mean function or pain standardised score on the day of surgery.
f. Short-term and long-term changes: Estimated monthly mean change in function or pain standardised scores between the pre-operative and first post-operative assessments (~3 months) or between the first and second post-operative assessments (~3 and ~12 months), respectively.