Cox regression model identifying risk factors of revision after 5 years of primary total hip replacement for osteoarthritis: hospital data
| Risk factors (reference category) | Patients undergoing THR (n=142 275) HR (95% CI); p-value | ||
| Crude analysis | Adjusted analysis | Adjusted analysis (competing risk) | |
| Age at primary THR (continuous variable) | 0.98 (1.0 to 1.0); p<0.01 | 0.97 (0.97 to 0.98); p<0.01 | 0.97 (0.96 to 0.97); p<0.01 |
| Sex (women) | |||
| Men | 1.17 (1.0 to 1.4); p=0.08 | 1.22 (1.02 to 1.45); p=0.029 | 1.17 (0.98 to 1.39); p=0.088 |
| ASA grade (P1-fit and healthy) | |||
| P2-Mild disease not incapacitating | 0.93 (0.7 to 1.2); p=0.52 | 0.97 (0.76 to 1.22); p=0.77 | 0.95 (0.75 to 1.21); p=0.70 |
| P3–P5 | 0.70 (0.5 to 1.0); p=0.04 | 0.67 (0.47 to 0.94); p=0.022 | 0.58 (0.41 to 0.82); p=0.002 |
| Bearing surface (MoP) | |||
| CoC | 1.08 (0.9 to 1.3); p=0.44 | 0.73 (0.56 to 0.94); p=0.015 | p=0.02 |
| CoP | 0.93 (0.7 to 1.2); p=0.57 | 0.75 (0.57 to 0.99); p=0.039 | 0.76 (0.58 to 1.00); p=0.052 |
| CoM-MoC | 2.28 (1.3 to 4.1); p=0.01 | 1.62 (0.87 to 2.99); p=0.13 | 1.65 (0.89 to 3.05); p=0.11 |
| Head size (≤28 mm) | |||
| 32 mm | 1.28 (1.0 to 1.6); p=0.02 | 1.33 (1.07 to 1.65); p=0.012 | 1.28 (1.03 to 1.60); p=0.026 |
| 36–42 mm | 1.24 (1.0 to 1.5); p=0.05 | 1.21 (0.94 to 1.56); p=0.15 | 1.17 (0.91 to 1.51); p=0.23 |
| ≥44 mm | 3.12 (1.4 to 7.0); p=0.01 | 2.63 (1.12 to 6.19); p=0.027 | 2.56 (1.09 to 6.02); p=0.031 |
| OHS, 6-month score (0–9 points, worst score) | |||
| (10–14 points) | 0.75 (0.60 to 0.95); p=0.02 | 0.73 (0.58 to 0.91); p=0.006 | 0.73 (0.58 to 0.92); p=0.007 |
| (15–18 points) | 0.66 (0.52 to 0.83); p<0.01 | 0.61 (0.49 to 0.78); p<0.01 | 0.62 (0.49 to 0.79); p<0.01 |
| (19–23 points) | 0.39 (0.29 to 0.53); p<0.01 | 0.36 (0.26 to 0.49); p<0.01 | 0.36 (0.27 to 0.50); p<0.01 |
| (24–48 points) | 0.39 (0.30 to 0.51); p<0.01 | 0.34 (0.26 to 0.45); p<0.01 | 0.35 (0.27 to 0.46); p<0.01 |
HR represents number of times to have a revision after 5 years compared with the reference group. A value>1 indicates that the group has higher risk for revision.
Variables included in the final regression model are those with at least one category with a p-value<0.05 for a single imputed data set in a backward selection.
Bold figures represent results with p values <0.05 in the final regression model
ASA, American Society of Anaesthesiologists; CoC, ceramic-on-ceramic; CoM - MoC, ceramic-on-metal; CoP, ceramic-on-polyethylene; MoP, metal-on-polyethylene; OHS, Oxford Hip Score; THR, total hip replacement.