TABLE III.
Results of the Random-Effects Analysis Comparing C-C and M-HXLPE Implants
| Hazard Ratio (95% CI)* |
||
| >28-mm C-C, Relative to All M-HXLPE† | ≤28-mm C-C, Relative to All M-HXLPE‡ | |
| Time in yr | ||
| 0 to 1 | Ref. | Ref. |
| 1 to 2 | 6.59 (4.98-8.71) | 5.94 (4.35-8.11) |
| 2 to 3 | 8.09 (6.08-10.76) | 7.27 (5.31-9.95) |
| 3 to 4 | 9.66 (7.25-12.88) | 8.29 (6.05-11.37) |
| 4 to 5 | 10.59 (7.94-14.13) | 9.15 (6.67-12.56) |
| 5 to 6 | 11.82 (8.84-15.80) | 10.14 (7.37-13.94) |
| 6 to 7 | 12.74 (9.49-17.11) | 10.85 (7.88-14.96) |
| 7 to 8 | 14.82 (10.93-20.09) | 12.63 (9.08-17.56) |
| 8 to 9 | 15.45 (11.10-21.52) | 13.11 (9.07-18.94) |
| 9 to 10 | NA | 14.74 (9.52-22.82) |
| Sex | ||
| Male | Ref. | Ref. |
| Female | 1.08 (0.93-1.27) | 0.97 (0.80-1.18) |
| Age in yr | ||
| 45 to 54 | Ref. | Ref. |
| 55 to 64 | 0.81 (0.68-0.97) | 0.87 (0.70-1.10) |
| Bearing surface and size | ||
| Overall | NA | 1.10 (0.43-2.85) |
| 0 to 2 yr§ | 0.80 (0.67-0.96) | NA |
| 2 to 6 yr§ | 0.92 (0.78-1.08) | NA |
| 6 to 9 yr§ | 0.96 (0.81-1.15) | NA |
Results are based on an iterative solution that updates the residual covariances until convergence. Confidence intervals for the C-C >28-mm model are based on a Z distribution. Our simulations indicated that an optimal strategy for CI construction in the presence of random effects was to use tκ − 1 for fixed parameters with corresponding random effects and to use tn − p otherwise (where κ − 1 and n − p indicate the degrees of freedom for the t distribution, κ is the number of registries, n is the number of observations, and p is the number of fixed effects); this is the approach taken in construction of the CIs for the C-C ≤28-mm model. NA = not applicable.
The estimated intercept was −5.69 (SE, 1.17).
The estimated intercept was −5.56 (SE, 0.18), and the bearing surface random effect was 0.08 (SE, 0.12).
The bearing effects over time are based on a combination of the main and interaction effects from the model.