Table 2.
Baseline characteristics before matching TKRs and UKRs. Values are count (%) unless otherwise specified
| Unmatched cohort |
Matched cohort |
|||||
|---|---|---|---|---|---|---|
| TKR | UKR | TKR | UKR | |||
| Covariate | (n = 254,355) | (n = 20,347) | SMD | (n = 19,358) | (n = 19,358) | SMD |
| Admission type | ||||||
| Elective | 254,178 (100) | 20,337 (100) | 0.01 | 19,349 (100) | 19,349 (100) | 0.01 |
| Emergency | 163 (0) | 10 (0) | 8 (0) | 9 (0) | ||
| Other | 14 (0) | 0 (0) | 1 (0) | 0 (0) | ||
| Sex | ||||||
| Female | 145,049 (57) | 9,611 (47) | 0.20 | 9,083 (47) | 9,206 (48) | 0.01 |
| Male | 109,306 (43) | 10,736 (53) | 10,275 (53) | 10,152 (52) | ||
| Age at surgery, | ||||||
| mean (SD) | 70.2 (8.8) | 64.7(9.3) | 0.60 | 64.9 (9.0) | 65.1 (9.3) | 0.02 |
| BMI, n | 192,787 ( | 15,919 ( | 14,815 ( | 15,059 ( | ||
| mean (SD) | 30.9 (5.4) | 30.2 (4.9) | 0.14 | 31.0 (5.3) | 30.2 (4.9) | 0.16 |
| Primary diagnosis | ||||||
| Primary OA | 246,026 (97) | 19,993 (98) | 0.10 | 19,011 (98) | 19,013 (98) | 0.01 |
| Primary OA and other | 2,645 (1) | 129 (1) | 139 (1) | 125 (1) | ||
| Other | 5,684 (2) | 225 (1) | 208 (1) | 220 (1) | ||
| Charlson comorbidity index | ||||||
| None | 177,003 (70) | 14,997 (74) | 0.10 | 14,343 (74) | 14,245 (74) | 0.02 |
| Mild | 54,018 (21) | 3,963 (19) | 3,778 (20) | 3,787 (20) | ||
| Moderate | 16,160 (6) | 972 (5) | 857 (4) | 921 (4) | ||
| Severe | 7,174 (3) | 415 (2) | 380 (2) | 405 (2) | ||
| Ethnicity | ||||||
| White | 243,425 (96) | 19,759 (97) | 0.09 | 18,781 (97) | 18,788 (97) | 0.01 |
| Black (Caribbean) | 1,291 (1) | 70 (0) | 70 (0) | 68 (0) | ||
| Black (African) | 849 (0) | 39 (0) | 41 (0) | 39 (0) | ||
| Black (other) | 379 (0) | 19 (0) | 17 (0) | 18 (0) | ||
| Indian | 4,499 (2) | 217 (1) | 228 (1) | 213 (1) | ||
| Pakistani | 1,280 (0) | 51 (0) | 45 (0) | 50 (0) | ||
| Bangladeshi | 113 (0) | 4 (0) | 6 (0) | 4 (0) | ||
| Chinese | 175 (0) | 5 (0) | 5 (0) | 5 (0) | ||
| Other | 2,344 (1) | 183 (1) | 165 (1) | 173 (1) | ||
| Rural/urban classification | ||||||
| Urban | 187,601 (74) | 14,044 (69) | 0.12 | 13,520 (70) | 13,451 (70) | 0.008 |
| Town/fringe | 31,579 (12) | 2,612 (13) | 2,458 (13) | 2,476 (13) | ||
| Village/hamlet | 35,175 (14) | 3,691 (18) | 3,380 (17) | 3,431 (17) | ||
| Indices of multiple deprivation | ||||||
| Most deprived (20%) | 34,627 (14) | 1,961 (10) | 0.18 | 1,906 (10) | 1,917 (10) | 0.006 |
| More deprived (20–40%) | 45,285 (18) | 3,111 (15) | 3,010 (16) | 2,996 (16) | ||
| Middle-point | 56,721 (22) | 4,540 (22) | 4,295 (22) | 4,324 (22) | ||
| Less deprived (20–40%) | 60,782 (24) | 4,957 (24) | 4,779 (24) | 4,737 (24) | ||
| Least deprived (20%) | 56,940 (22) | 5,778 (29) | 5,368 (28) | 5,384 (28) | ||
| Surgeon caseload of primary knee surgery practice | ||||||
| Cases/years, mean (SD) | 80.5 (48.2) | 97.6 (50.6) | 0.35 | 96.7 (55.1) | 96.7 (50.5) | 0.001 |
| Primary complexity | ||||||
| Normal | 254,328 (100) | 20,344 (100) | 0.004 | 19,354 (100) | 19,355 (100) | 0.004 |
| Complex | 27 (0) | 3 (0) | 4 (0) | 3 (0) | ||
| ASA grade | ||||||
| 1 | 22,257 (9) | 3,646 (18) | 0.34 | 3,418 (17) | 3,294 (17) | 0.02 |
| 2 | 190,181 (75) | 14,901 (73) | 14,274 (74) | 14,297 (74) | ||
| 3 or above | 41,917 (16) | 1,800 (9) | 1,666 (9) | 1,767 (9) | ||
| VTE prophylaxis—chemical | ||||||
| LMWH (± other) | 179,562 (71) | 13,586 (67) | 0.10 | 12,708 (66) | 12,882 (67) | 0.02 |
| Aspirin only | 12,338 (5) | 1,370 (7) | 1,316 (7) | 1,283 (7) | ||
| Other | 55,739 (22) | 4,895 (24) | 4,855 (25) | 4,704 (24) | ||
| None | 6,716 (2) | 496 (2) | 479 (2) | 489 (2) | ||
| VTE prophylaxis—mechanical | ||||||
| Any | 242,433 (95) | 19,775 (97) | 0.10 | 18,781 (97) | 18,793 (97) | 0.004 |
| None | 11,922 (5) | 572 (3) | 577 (3) | 565 (3) | ||
| Fixation | ||||||
| Cemented | 246,269 (97) | 14,932 (74) | 0.70 | 15,023 (78) | 14,926 (77) | 0.01 |
| Cementless | 7,209 (3) | 4,950 (24) | 3,920 (20) | 4,014 (21) | ||
| Hybrid | 877 (0) | 465 (2) | 415 (2) | 418 (2) | ||
VTE = venous thromboemolism