Comparison of previous and present study
| Previous study 1958–1989, % | Present study 2010–2012, % | Risk difference % (CI) | p Value | |
|---|---|---|---|---|
| Revision | 48.3 | 42.6 | −5.7 (−11.5 to 0.20) | 0.060 |
| Before 1970 | 58.4 | −15.8 (−25.4 to −6.1) | 0.001 | |
| 1970–79 | 54.6 | −12.0 (−19.3 to −4.6) | 0.001 | |
| 1980–89 | 33.7 | 9.0 (2.1 to 15.8) | 0.010 | |
| Infection | 7.4 | 5.5 (4.1*) | −1.8 (−4.7 to 1.1) | 0.261 (0.039*) |
| Before 1970 | 2.7 | 2.8 (−1.0 to 6.7) | 0.238 | |
| 1970–79 | 8.6 | −3.1 (−7.0 to 0.9) | 0.126 | |
| 1980–89 | 8.0 | −2.5 (−6.2 to 1.2) | 0.192 | |
| Acute infection | 6.1 | 3.2 | −2.9 (−5.3 to −0.42) | 0.037 |
Pairwise comparison of the proportions is reported as risk difference with related p values indicating significant difference or not.
*To estimate the effect of antibiotic prophylaxis, all patients in present study with no antibiotic prophylaxis (n=44) were excluded resulting in a significant difference (p 0.039) in risk of infection for all patients who followed the current regimen.
As well as comparing the 2010–2012 cohort with the entire 1958–1989 cohort, the new cohort is compared to three individual time periods in the previous study and presented in the table in italics. The rate of revision was significantly higher (p 0.001) in the first two time periods compared to the 2010–2012 cohort, but it was significantly lower in the latest decade (p 0.010). Though the rate of infection was remarkably lower in the earliest time period, compared to the 2010–2012 cohort none of the three time periods had a significantly different rate of infection.