Comparison of participant characteristics in each group
| Missing cases, n (%) | LOS ≥30 days (n=2793) | LOS <30 days (n=1949) | P value | |
| Age, years, median (IQR) | 0 (0) | 37 (27–49) | 34 (25–46) | <0.001 |
| Sex, male, n (%) | 1 (0.0) | 1140 (40.8) | 776 (39.8) | 0.48 |
| Medical history*, n (%) | ||||
| Psychiatric diseases | 0 (0) | 1714 (61.4) | 1191 (61.1) | 0.86 |
| COPD | 0 (0) | 4 (0.1) | 3 (0.2) | 0.92 |
| Chronic heart failure | 0 (0) | 3 (0.1) | 3 (0.2) | 0.66 |
| Cerebrovascular diseases | 0 (0) | 39 (1.4) | 18 (0.9) | 0.14 |
| CKD on HD | 0 (0) | 4 (0.1) | 3 (0.2) | 0.92 |
| Vital signs in the ED, median (IQR) | ||||
| Systolic BP, mm Hg | 56 (1.2) | 110 (91–130) | 120 (104–136) | <0.001 |
| Respiratory rate, per minute | 247 (5.1) | 23 (18–28) | 22 (18–26) | <0.001 |
| Heart rate, beats per minute | 91 (1.9) | 100 (85–119) | 93 (80–108) | <0.001 |
| Body temperature, °C | 453 (9.3) | 36.4 (35.7–36.9) | 36.5 (35.9–37.0) | <0.001 |
| GCS score | 165 (3.4) | 14 (12–15) | 14 (13–15) | <0.001 |
| RTS, median (IQR) | 350 (7.2) | 7.55 (6.61–7.84) | 7.84 (7.11–7.84) | <0.001 |
| Intubation in the ED, n (%) | 0 (0) | 841 (30.1) | 224 (11.5) | <0.001 |
| Transferred from other hospitals, n (%) | 64 (1.3) | 286 (10.4) | 192 (10.0) | 0.70 |
| Admission to trauma-specialized hospitals†, n (%) | 0 (0) | 1478 (52.9) | 997 (51.2) | 0.23 |
| Admission to non-ICU wards, n (%) | 0 (0) | 268 (9.6) | 321 (16.5) | <0.001 |
| ISS, median (IQR) | 0 (0) | 22 (13–32) | 14 (9–22) | <0.001 |
| TRISS, Ps, median (IQR) | 418 (8.6) | 0.96 (0.87–0.99) | 0.986 (0.96–0.993) | <0.001 |
| Number of regions with fractures in the spine, pelvis, and lower extremity, median (IQR) | 0 (0) | 2 (1–2) | 1 (1–2) | <0.001 |
| Spine, n (%) | 0 (0) | 1591 (57.0) | 951 (48.8) | <0.001 |
| Pelvis, n (%) | 0 (0) | 1477 (52.9) | 634 (32.5) | <0.001 |
| Lower extremity, n (%) | 0 (0) | 1638 (58.6) | 748 (38.4) | <0.001 |
| AIS score, head, n (%) | 0 (0) | <0.001 | ||
| 1 | 122 (6.3) | 103 (3.7) | ||
| 2 | 54 (2.8) | 71 (2.5) | ||
| 3 | 220 (11.3) | 374 (13.4) | ||
| 4 | 135 (6.9) | 226 (8.1) | ||
| 5 | 0 (0) | 0 (0) | ||
| 6 | 0 (0) | 0 (0) | ||
| AIS score, face, n (%) | 0 (0) | <0.001 | ||
| 1 | 175 (9) | 231 (8.3) | ||
| 2 | 159 (8.2) | 370 (13.2) | ||
| 3 | 18 (0.9) | 50 (1.8) | ||
| 4 | 1 (0.1) | 9 (0.3) | ||
| 5 | 0 (0) | 0 (0) | ||
| 6 | 0 (0) | 0 (0) | ||
| AIS score, neck, n (%) | 0 (0) | 0.73 | ||
| 1 | 8 (0.4) | 12 (0.4) | ||
| 2 | 4 (0.2) | 9 (0.3) | ||
| 3 | 2 (0.1) | 3 (0.1) | ||
| 4 | 0 (0) | 0 (0) | ||
| 5 | 1 (0.1) | 0 (0) | ||
| 6 | 0 (0) | 0 (0) | ||
| AIS score, thorax, n (%) | 0 (0) | <0.001 | ||
| 1 | 48 (2.5) | 41 (1.5) | ||
| 2 | 62 (3.2) | 81 (2.9) | ||
| 3 | 379 (19.4) | 576 (20.6) | ||
| 4 | 266 (13.6) | 516 (18.5) | ||
| 5 | 30 (1.5) | 103 (3.7) | ||
| 6 | 0 (0) | 0 (0) | ||
| AIS score, abdomen, n (%) | 0 (0) | <0.001 | ||
| 1 | 28 (1.4) | 39 (1.4) | ||
| 2 | 166 (8.5) | 286 (10.2) | ||
| 3 | 83 (4.3) | 184 (6.6) | ||
| 4 | 22 (1.1) | 81 (2.9) | ||
| 5 | 8 (0.4) | 11 (0.4) | ||
| 6 | 0 (0) | 0 (0) | ||
| AIS score, spine, n (%) | 0 (0) | <0.001 | ||
| 1 | 7 (0.4) | 2 (0.1) | ||
| 2 | 540 (27.7) | 828 (29.6) | ||
| 3 | 410 (21) | 695 (24.9) | ||
| 4 | 72 (3.7) | 159 (5.7) | ||
| 5 | 38 (1.9) | 101 (3.6) | ||
| 6 | 1 (0.1) | 2 (0.1) | ||
| AIS score, upper extremity, n (%) | 0 (0) | <0.001 | ||
| 1 | 105 (5.4) | 122 (4.4) | ||
| 2 | 295 (15.1) | 546 (19.5) | ||
| 3 | 139 (7.1) | 365 (13.1) | ||
| 4 | 0 (0) | 0 (0) | ||
| 5 | 0 (0) | 0 (0) | ||
| 6 | 0 (0) | 0 (0) | ||
| AIS score, lower extremity, pelvis, and buttocks, n (%) | 0 (0) | <0.001 | ||
| 1 | 100 (5.1) | 46 (1.6) | ||
| 2 | 578 (29.7) | 735 (26.3) | ||
| 3 | 366 (18.8) | 943 (33.8) | ||
| 4 | 96 (4.9) | 340 (12.2) | ||
| 5 | 64 (3.3) | 251 (9) | ||
| 6 | 0 (0) | 0 (0) |
*Medical history was obtained from the JTDB.
†Trauma-specialized hospitals were defined by the number of severe trauma patients with ISS ≥16 registered in the JTDB since January 1, 2004, for each participating hospital. Hospitals with the number of these trauma patients in the top half of all participating hospitals were defined as trauma-specialized hospitals.
AIS, Abbreviated Injury Scale; BP, blood pressure; CKD, chronic kidney dysfunction; COPD, chronic obstructive pulmonary disease; ED, emergency department; GCS, Glasgow Coma Scale; HD, hemodialysis; ICU, intensive care unit; ISS, Injury Severity Score; JTDB, Japan Trauma Databank; LOS, length of hospital stay; Ps, probability of survival; RTS, Revised Trauma Score; TRISS, Trauma and Injury Severity Score.