Table 3. Characteristics of the Total Hip Arthroplasty Cohort Before and After Matching.
| Characteristic | Prior to Matching | After Matching | |||||
|---|---|---|---|---|---|---|---|
| All Patients | Overlapping | Nonoverlapping | P Value | Overlapping | Nonoverlapping | Standardized Difference | |
| Patients, No. | 52 869 | 1560 | 51 309 | 1456 | 1456 | ||
| Demographics | |||||||
| Age, median (IQR), y | 68 (60-76) | 66 (57-74) | 68 (60-76) | <.001 | 66 (58-74) | 66 (58-74) | 0 |
| Female, No. (%) | 28 836 (54.5) | 817 (52.4) | 28 019 (54.6) | .08 | 767 (52.7) | 767 (52.7) | 0 |
| Income quintile, No. (%) | .003 | 0.03 | |||||
| Lowest | 8093 (15.3) | 234 (15.0) | 7859 (15.3) | 219 (15.0) | 201 (13.8) | 0.04 | |
| 2 | 9782 (18.5) | 256 (16.4) | 9526 (18.6) | 243 (16.7) | 238 (16.3) | 0.01 | |
| 3 | 10 147 (19.2) | 261 (16.7) | 9886 (19.3) | 244 (16.8) | 270 (18.5) | 0.05 | |
| 4 | 11 377 (21.5) | 357 (22.9) | 11 020 (21.5) | 332 (22.8) | 314 (21.6) | 0.03 | |
| Highest | 13 293 (25.1) | 447 (28.7) | 12 846 (25.0) | 413 (28.4) | 430 (29.5) | 0.03 | |
| Comorbidities, No. (%) | |||||||
| Previous MI | 1802 (3.4) | 38 (2.4) | 1764 (3.4) | .03 | 35 (2.4) | 45 (3.1) | 0.04 |
| CHF | 2713 (5.1) | 83 (5.3) | 2630 (5.1) | .73 | 78 (5.4) | 67 (4.6) | 0.03 |
| Cerebrovascular disease | 559 (1.1) | 12 (0.8) | 547 (1.1) | .26 | 12 (0.8) | 19 (1.3) | 0.05 |
| COPD | 4027 (7.6) | 95 (6.1) | 3932 (7.7) | .02 | 93 (6.4) | 99 (6.8) | 0.02 |
| Dementia | 900 (1.7) | 14 (0.9) | 886 (1.7) | .01 | 12 (0.8) | 23 (1.6) | 0.07 |
| Diabetes | 10 921 (20.7) | 283 (18.1) | 10 638 (20.7) | .01 | 271 (18.6) | 251 (17.2) | 0.04 |
| Chronic renal failure | 1621 (3.1) | 45 (2.9) | 1576 (3.1) | .67 | 43 (3.0) | 45 (3.1) | 0.01 |
| Frailty | 2410 (4.6) | 76 (4.9) | 2334 (4.5) | .55 | 71 (4.9) | 63 (4.3) | 0.03 |
| Charlson score | .06 | ||||||
| No prior admission | 36 390 (68.8) | 1093 (70.1) | 35 297 (68.8) | 1021 (70.1) | 993 (68.2) | 0.04 | |
| 0 | 9807 (18.5) | 286 (18.3) | 9521 (18.6) | 261 (17.9) | 279 (19.2) | 0.03 | |
| 1 | 3069 (5.8) | 71 (4.6) | 2998 (5.8) | 70 (4.8) | 77 (5.3) | 0.02 | |
| 2 | 2123 (4.0) | 75 (4.8) | 2048 (4.0) | 70 (4.8) | 65 (4.5) | 0.02 | |
| ≥3 or more | 1480 (2.8) | 35 (2.2) | 1445 (2.8) | 34 (2.3) | 42 (2.9) | 0.03 | |
| Admission characteristics | |||||||
| Teaching hospital, No. (%) | 19 134 (36.2) | 1104 (70.8) | 18 030 (35.1) | <.001 | 1033 (70.9) | 1033 (70.9) | 0 |
| Surgical assistant, No. (%) | 40 287 (76.2) | 1104 (70.8) | 39 183 (76.4) | <.001 | 446 (30.6) | 473 (32.5) | 0.04 |
| Family physician | 25 042 (47.4) | 441 (28.3) | 24 601 (47.9) | 420 (28.8) | 374 (25.7) | 0.07 | |
| Nonorthopedic surgeon | 6624 (12.5) | 165 (10.6) | 6459 (12.6) | 144 (9.9) | 149 (10.2) | 0.01 | |
| Orthopedic surgeon | 8621 (16.3) | 498 (31.9) | 8123 (15.8) | 446 (30.6) | 460 (31.6) | 0.02 | |
| Surgeon volume, median (IQR) | 59 (40-88) | 82 (49-126) | 59 (40-87) | <.001 | 87 (53-130) | 86 (52-132) | 0.01 |
| Hospital volume, median (IQR) | 265 (181-496) | 415 (273-550) | 263 (180-487) | <.001 | 456 (275-553) | 435 (276-550) | 0.05 |
| Characteristic | Total | Overlapping | Nonoverlapping | P Value | Overlapping | Nonoverlapping | P Value |
| Surgical complication, No. (%) | 1145 (2.2) | 36 (2.3) | 1109 (2.2) | .70 | 34 (2.3) | 20 (1.4) | .052 |
| Dislocation | 267 (0.5) | 6 (0.4) | 261 (0.5) | .50 | NA | 6 (0.4) | .76 |
| Infection | 251 (0.5) | 8 (0.5) | 243 (0.5) | .82 | 7 (0.5) | 6 (0.4) | .78 |
| Revision | 845 (1.6) | 25 (1.6) | 820 (1.6) | >.99 | 24 (1.6) | 17 (1.2) | .26 |
| Duration of surgery, median (IQR), min | 108 (92-127) | 120 (99-142) | 107 (92-127) | <.001 | 119 (99-140) | 109 (91-132) | <.001 |
| Death within 90 d, No. (%) | 108 (0.2) | 6 (0.4) | 102 (0.2) | .11 | 6 (0.4) | NA | .53 |
Abbreviations: CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; IQR, interquartile range; MI, myocardial infarction; NA, not applicable (<5 events).