Table 1.
Characteristics of total study sample and according to hospital and surgeon volume groups.
| Covariates | Whole sample (N = 62,906) | Hospital volume of procedures |
Surgeon volume of procedures |
||||
|---|---|---|---|---|---|---|---|
| <7 per mo (N = 4467) | 7-15 per mo (N = 17,399) | >15 per mo (N = 41,040) | <1.5 per mo (N = 3417) | 1.5-4 per mo (N = 45,348) | >4 per mo (N = 14,141) | ||
| Patients | |||||||
| Gender, n (%) | |||||||
| Men | 26,861 (43) | 1929 (43) | 7321 (42) | 17,611 (43) | 1459 (43) | 19,451 (43) | 5951 (42) |
| Women | 36,045 (57) | 2538 (57) | 10,078 (58) | 23,429 (57) | 1958 (57) | 25,897 (57) | 8190 (58) |
| Mean age (std error), y | 69 (11) | ||||||
| Age category, n (%) | |||||||
| 40-60 y | 11,677 (19) | 803 (18) | 3069 (18) | 7805 (19) | 703 (21) | 8330 (18) | 2644 (19) |
| 60-75 y | 28,565 (45) | 1858 (42) | 7840 (45) | 18,867 (46) | 1456 (43) | 20,436 (45) | 6673 (47) |
| ≥75 y | 22,664 (36) | 1806 (40) | 6490 (37) | 14,368 (35) | 1258 (37) | 16,582 (37) | 4824 (34) |
| Deprivation index, n (%) | |||||||
| 1 | 10,617 (17) | 742 (17) | 3197 (18) | 6678 (16) | 831 (24) | 7462 (16) | 2324 (16) |
| 2 | 11,510 (18) | 833 (19) | 2973 (17) | 7704 (19) | 667 (20) | 8283 (18) | 2560 (18) |
| 3 | 11,662 (19) | 888 (20) | 2596 (15) | 8178 (20) | 498 (15) | 8399 (19) | 2765 (20) |
| 4 | 11,947 (19) | 748 (17) | 3443 (20) | 7756 (19) | 542 (16) | 8855 (20) | 2550 (18) |
| 5 | 12,388 (20) | 685 (15) | 3965 (23) | 7738 (19) | 566 (17) | 8948 (20) | 2874 (20) |
| Missing | 4782 (8) | 571 (13) | 1225 (7) | 2986 (7) | 313 (9) | 3401 (7) | 1068 (8) |
| Diabetes, n (%) | 6925 (11) | 590 (13) | 2057 (12) | 4278 (10) | 405 (12) | 5128 (11) | 1392 (10) |
| Morbid obesity, n (%) | 105 (0) | ||||||
| Benzodiazepines, n (%) | 23,988 (38) | 1691 (38) | 6742 (39) | 15,555 (38) | 1419 (42) | 17,411 (38) | 5158 (36) |
| Antihypertensives, n (%) | 37,130 (59) | 2691 (60) | 10,619 (61) | 23,820 (58) | 1990 (58) | 26,998 (60) | 8142 (58) |
| Antidepressants, n (%) | 9259 (15) | 704 (16) | 2614 (15) | 5941 (14) | 560 (16) | 6775 (15) | 1924 (14) |
| Antiosteoporotics, n (%) | 5376 (9) | 429 (10) | 1492 (9) | 3455 (8) | 311 (9) | 3881 (9) | 1184 (8) |
| Steroids, n (%) | 9934 (16) | 757 (17) | 2801 (16) | 6376 (16) | 588 (17) | 7262 (16) | 2084 (15) |
| Lipid-lowering medication, n (%) | 24,420 (39) | 1734 (39) | 6976 (40) | 15,710 (38) | 1279 (37) | 17,729 (39) | 5412 (38) |
| Prosthesis | |||||||
| Bearing surface, n (%) | |||||||
| MoP | 18,601 (30) | 1716 (38) | 5441 (31) | 11,444 (28) | 1141 (33) | 13,955 (31) | 3505 (25) |
| CoC | 28,721 (46) | 1712 (38) | 7380 (42) | 19,629 (48) | 1524 (45) | 19,918 (44) | 7279 (51) |
| CoP | 13,936 (22) | 984 (22) | 4093 (24) | 8859 (22) | 707 (21) | 10,094 (22) | 3135 (22) |
| MoM | 1648 (3) | 55 (1) | 485 (3) | 1108 (3) | 45 (1) | 1381 (3) | 222 (2) |
| Fixation type, n (%) | |||||||
| No cement | 47,734 (76) | 3552 (80) | 13,420 (77) | 30,762 (75) | 2510 (73) | 34,955 (77) | 10,269 (73) |
| No antibiotics | 2063 (3) | 217 (5) | 441 (3) | 1405 (3) | 104 (3) | 1523 (3) | 436 (3) |
| Antibiotics | 13,109 (21) | 698 (16) | 3538 (20) | 8873 (22) | 803 (24) | 8870 (20) | 3436 (24) |
| Hospital stays | |||||||
| Mean length of stay (std error), d | 8.6 (2.9) | ||||||
| Length of stay category, n (%) | |||||||
| <8 d | 21,952 (35) | 953 (21) | 5034 (29) | 15,965 (39) | 853 (25) | 14,296 (32) | 6803 (48) |
| 8-9 d | 26,659 (42) | 1812 (41) | 7227 (42) | 17,620 (43) | 1410 (41) | 19,817 (44) | 5432 (38) |
| >9 d | 14,295 (23) | 1702 (38) | 5138 (30) | 7455 (18) | 1154 (34) | 11,235 (25) | 1906 (13) |
| Median hospital volume (interquartile range), acts/mo | 12 (6-19) | ||||||
| Hospital volume category, n (%) | |||||||
| <7 per mo | 4467 (7) | 984 (29) | 3469 (8) | 14 (0) | |||
| 7-15 per mo | 17,399 (28) | 1345 (39) | 15,602 (34) | 452 (3) | |||
| >15 per mo | 41,040 (65) | 1088 (32) | 26,277 (58) | 13,675 (97) | |||
| Median surgeon volume (interquartile range), acts/mo | 2.6 (1.1-5.2) | ||||||
| Surgeon volume category, n (%) | |||||||
| <1.5 per mo | 3417 (5) | 984 (22) | 1345 (8) | 1088 (3) | |||
| 1.5-4 per mo | 45,348 (72) | 3469 (78) | 15,602 (90) | 26,277 (64) | |||
| >4 per mo | 14,141 (22) | 14 (0) | 452 (3) | 13,675 (33) | |||
CoP, ceramic-on-polyethylene; MoM, metal-on-metal; MoP, metal-on-polyethylene; std, standard.