Table 2.
Results from multivariable mixed-effects regression models (patients nested within surgeons) of age, gender, categorised BMI, ASA grade and source of funding on stem age and cup age, with category proportions
| Stems | Cups | |||||||||
| Established (n=4 18 831) |
New (n=13 124) |
OR* | (95% CI) | P value | Established (n=4 06 072) |
New (n=25 883) |
OR* | (95% CI) | P value | |
| Age | ||||||||||
| <55 years old | 43 780 (10.5%) |
2793 (21.3%) |
1.83 | 1.73 to 1.93 | <0.001 | 42 752 (10.5%) |
3821 (14.8%) |
1.31 | 1.25 to 1.37 | <0.001 |
| 55–80 (ref) | 312 205 (74.5%) |
9246 (70.5%) |
1 | – | – | 302 823 (74.6%) |
18 628 (72.0%) |
1 | – | – |
| ≥80 years old | 62 846 (15.0%) |
1085 (8.3%) |
0.60 | 0.56 to 0.64 | <0.001 | 60 497 (14.9%) |
3434 (13.3%) |
0.91 | 0.87 to 0.95 | <0.001 |
| Gender | ||||||||||
| Male (ref) | 165 607 (39.5%) |
5768 (44.0%) |
1 | – | – | 161 248 (39.7%) |
10 127 (39.1%) |
1 | – | – |
| Female | 253 224 (60.5%) |
7356 (56.0%) |
0.87 | 0.84 to 0.90 | <0.001 | 244 824 (60.3%) |
15 756 (60.9%) |
1.06 | 1.03 to 1.09 | <0.001 |
| BMI | ||||||||||
| Underweight and normal (ref.) | 95 306 (22.8%) |
2911 (22.2%) |
1 | – | – | 91 863 (22.6%) |
6354 (24.5%) |
1 | – | – |
| Overweight | 165 849 (39.6%) |
5138 (39.1%) |
1.02 | 0.97 to 1.08 | 0.373 | 160 834 (39.6%) |
10 153 (39.2%) |
0.95 | 0.91 to 0.99 | 0.007 |
| Class I obese | 105 670 (25.2%) |
3391 (25.8%) |
1.06 | 1.00 to 1.12 | 0.067 | 102 781 (25.3%) |
6280 (24.3%) |
0.93 | 0.90 to 0.97 | 0.001 |
| Class II obese | 38 995 (9.3%) |
1276 (9.7%) |
1.10 | 1.02 to 1.19 | 0.011 | 37 977 (9.4%) |
2294 (8.9%) |
0.94 | 0.89 to 1.00 | 0.042 |
| Class III obese | 13 011 (3.1%) |
408 (3.1%) |
0.99 | 0.87 to 1.11 | 0.808 | 12 617 (3.1%) |
802 (3.1%) |
0.94 | 0.86 to 1.02 | 0.135 |
| ASA grade | ||||||||||
| I (ref) | 60 022 (14.3%) |
2661 (20.3%) |
1 | – | – | 58 265 (14.3%) |
4418 (17.1%) |
1 | – | – |
| II | 293 142 (70.0%) |
8940 (68.1%) |
0.81 | 0.77 to 0.86 | <0.001 | 284 437 (70.0%) |
17 645 (68.2%) |
0.98 | 0.95 to 1.03 | 0.461 |
| III | 63 904 (15.3%) |
1482 (11.3%) |
0.66 | 0.61 to 0.72 | <0.001 | 61 681 (15.2%) |
3705 (14.3%) |
1.00 | 0.94 to 1.05 | 0.935 |
| IV+V | 1763 (0.4%) |
41 (0.3%) |
0.64 | 0.46 to 0.90 | 0.010 | 1689 (0.4%) |
115 (0.4%) |
1.02 | 0.82 to 1.26 | 0.881 |
| Source of funding | ||||||||||
| NHS | 364 928 (87.1%) |
10 553 (80.4%) |
1 | – | – | 354 642 (87.3%) |
20 839 (80.5%) |
1 | – | – |
| Private | 53 903 (12.9%) |
2571 (19.6%) |
1.02 | 0.95 to 1.08 | 0.642 | 51 430 (12.7%) |
5044 (19.5%) |
1.09 | 1.04 to 1.14 | <0.001 |
*ORs, 95% CI and p values are from mixed-effects logistic regression models adjusted for all exposure variables.
ASA, American Society of Anaesthesiologists; BMI, body mass index; NHS, National Health Service.