Relative risk of outlet strut fracture (OSF) in Björk-Shiley convexo concave heart valves for demographic and manufacturing characteristics based on univariate Cox models
| Variable | n OSF/n at risk | Relative risk | 95% CI | p Value |
| Age at implantation (years) | ||||
| < 50 (baseline) | 30/1027 | 1.0 | – | < 0.001 |
| 50–59 | 21/1107 | 0.7 | 0.4 to 1.2 | |
| ⩾ 60 | 5/1160 | 0.2 | 0.1 to 0.4 | |
| Sex | 0.27 | |||
| Male (baseline) | 27/1411 | 1.0 | – | |
| Female | 29/1882 | 0.7 | 0.4 to 1.3 | |
| Missing data | 0/1 | |||
| Valve characteristics | ||||
| Valve size (mm) | < 0.001 | |||
| ⩽ 21 (baseline) | 1/356 | 1.0 | – | |
| 23 | 7/452 | 5.3 | 0.6 to 42.9 | |
| 25 | 1/468 | 0.8 | 0.1 to 12.0 | |
| 27 | 6/506 | 4.1 | 0.5 to 34.4 | |
| 29 | 14/700 | 7.3 | 1.0 to 55.3 | |
| 31 | 22/697 | 12.3 | 1.7 to 91.4 | |
| 33 | 5/112 | 20.2 | 2.4 to 173.1 | |
| Missing data | 0/3 | |||
| Valve position | 0.001 | |||
| Aortic (baseline) | 13/1461 | 1.0 | – | |
| Mitral | 43/1827 | 2.8 | 1.5 to 5.3 | |
| Tricuspid | 0/6 | |||
| Manufacturing period1-150 | < 0.001 | |||
| Before 1981 (baseline) | 4/757 | 1.0 | – | |
| 1981–1984 | 52/2365 | 4.8 | 1.7 to 14.3 | |
| Missing data | 0/72 | |||
| Welder group1-150 | < 0.001 | |||
| Low risk (baseline) | 11/1085 | 1.0 | – | |
| Intermediate risk | 16/518 | 2.9 | 1.4 to 6.4 | |
| High risk | 22/751 | 2.9 | 1.4 to 5.9 | |
| Missing data | 7/840 | 0.8 | 0.3 to 2.0 | |
| Shop order fracture rate1-150 1-151 | 56/3194 | 1.5 | 1.4 to 1.7 | < 0.001 |