Table 1.
Baseline characteristics of knee OA patients according to the use of opioids as the first analgesic treatment
| Variable | Opioid users§ | Opioid non-users | ||
|---|---|---|---|---|
| Total (n = 348,516) | Tramadol (n = 346,544) | Stronger opioids (n = 1972) | (n = 2,509,483) | |
| N (%) | N (%) | N (%) | N (%) | |
| Age, years (mean ± SD) | 64.2 ± 9.9 | 64.1 ± 9.8 | 68.3 ± 11.0 | 64.0 ± 9.8 |
| 50–59 | 137,190 (39.4) | 136,658 (39.4) | 532 (27.0) | 997,164 (39.7) |
| 60–69 | 107,022 (30.7) | 106,485 (30.7) | 537 (27.2) | 781,375 (31.1) |
| ≥ 70 | 104,304 (29.9) | 103,401 (9.8) | 903 (45.8) | 730,944 (29.1) |
| Sex (female) | 195,021 (56.0) | 193,960 (56.0) | 1061 (53.8) | 1,562,071 (62.2) |
| Health insurance | ||||
| National insurance | 323,934 (92.9) | 322,308 (93.0) | 1626 (82.5) | 2,352,280 (93.7) |
| Medical aid | 22,104 (6.3) | 21,809 (6.3) | 295 (15.0) | 136,862 (5.5) |
| Veterans | 2478 (0.7) | 2427 (0.7) | 51 (2.6) | 20,341 (0.8) |
| Type of institution† | ||||
| Tertiary hospital | 5597 (1.6) | 5119 (1.5) | 478 (24.2) | 33,123 (1.3) |
| General hospital | 29,424 (8.4) | 28,395 (8.2) | 1029 (52.2) | 182,805 (7.3) |
| Hospital | 54,905 (15.8) | 54,519 (15.7) | 386 (19.6) | 336,196 (13.4) |
| Clinic | 253,698 (72.8) | 253,624 (73.2) | 74 (3.8) | 1,684,123 (67.1) |
| Oriental medical hospital | 74 (0.0) | 74 (0.0) | – | 222,631 (8.9) |
| Others | 4818 (1.4) | 4813 (1.4) | 5 (0.3) | 50,605 (2.0) |
| Type of department† | ||||
| Internal medicine | 33,778 (9.7) | 33,420 (9.6) | 358 (18.2) | 219,877 (8.8) |
| Orthopedics | 244,305 (70.1) | 243,184 (70.2) | 1121 (56.8) | 1,588,219 (63.3) |
| Rehabilitation | 5480 (1.6) | 5424 (1.6) | 56 (2.8) | 46,811 (1.9) |
| Oriental medicine | – | – | – | 226,250 (9.0) |
| Others | 64,953 (18.6) | 64,516 (18.6) | 437 (22.2) | 428,326 (17.1) |
| Elixhauser score | 4.5 ± 6.4 | 4.5 ± 6.3 | 10.3 ± 10.6 | 4.4 ± 6.2 |
| Comorbidity†† | ||||
| Congestive heart failure | 16,502 (4.7) | 16,294 (4.7) | 208 (10.5) | 112,668 (4.5) |
| Cardiac arrhythmias | 12,515 (3.6) | 12,364 (3.6) | 151 (7.7) | 92,539 (3.7) |
| Peripheral vascular disorders | 54,070 (15.5) | 53,668 (15.5) | 402 (20.4) | 356,803 (14.2) |
| Hypertension, uncomplicated | 158,773 (45.6) | 157,611 (45.5) | 1162 (58.9) | 1,125,517 (44.9) |
| Hypertension, complicated | 17,426 (5.0) | 17,263 (5.0) | 163 (8.3) | 123,765 (4.9) |
| Paralysis | 3317 (1.0) | 3232 (0.9) | 85 (4.3) | 22,838 (0.9) |
| Other neurological disorders | 14,069 (4.0) | 13,860 (4.0) | 209 (10.6) | 97,410 (3.9) |
| Chronic pulmonary disease | 104,644 (30.0) | 103,822 (30.0) | 822 (41.7) | 734,749 (29.3) |
| Diabetes, uncomplicated | 67,736 (19.4) | 67,064 (19.4) | 672 (34.1) | 478,114 (19.1) |
| Diabetes, complicated | 37,415 (10.7) | 37,046 (10.7) | 369 (18.7) | 259,686 (10.3) |
| Hypothyroidism | 14,665 (4.2) | 14,546 (4.2) | 119 (6.0) | 120,335 (4.8) |
| Renal failure | 5111 (1.5) | 5023 (1.4) | 88 (4.5) | 36,877 (1.5) |
| Liver disease | 73,216 (21.0) | 72,548 (20.9) | 668 (33.9) | 522,157 (20.8) |
| Peptic ulcer disease excluding bleeding | 80,772 (23.2) | 80,162 (23.1) | 610 (30.9) | 542,506 (21.6) |
| Metastatic cancer | 1614 (0.5) | 1386 (0.4) | 228 (11.6) | 10,203 (0.4) |
| Solid tumor without metastasis | 17,432 (5.0) | 17,016 (4.9) | 416 (21.1) | 136,534 (5.4) |
| Weight loss | 3000 (0.9) | 2847 (0.8) | 153 (7.8) | 19,827 (0.8) |
| Fluid and electrolyte disorders | 13,631 (3.9) | 13,341 (3.8) | 290 (14.7) | 88,210 (3.5) |
| Deficiency anemia | 15,807 (4.5) | 15,513 (4.5) | 294 (14.9) | 115,735 (4.6) |
| Alcohol abuse | 7674 (2.2) | 7593 (2.2) | 81 (4.1) | 48,089 (1.9) |
| Depression | 41,634 (11.9) | 41,113 (11.9) | 521 (26.4) | 277,119 (11.0) |
| Musculoskeletal disorders | ||||
| Low back pain | 187,194 (53.7) | 185,990 (53.7) | 1204 (61.1) | 1,257,774 (50.1) |
| Intervertebral disc disorder | 69,342 (19.9) | 68,789 (19.9) | 553 (28.0) | 413,702 (16.5) |
| Spinal stenosis | 74,070 (21.3) | 73,357 (21.2) | 713 (36.2) | 405,241 (16.1) |
| Fibromyalgia | 6576 (1.9) | 6532 (1.9) | 44 (2.2) | 39,799 (1.6) |
| Medication† | ||||
| NSAIDs | 246,933 (70.9) | 245,578 (70.9) | 1355 (68.7) | 1,492,548 (59.5) |
| Nonselective | 233,275 (66.9) | 232,418 (67.1) | 857 (43.5) | 1,372,520 (54.7) |
| Cox-2 inhibitor use | 14,793 (4.2) | 14,175 (4.1) | 618 (31.3) | 123,006 (4.9) |
| Acetaminophen | 7909 (2.3) | 7589 (2.2) | 320 (16.2) | 143,820 (5.7) |
| SYSADOA* | 78,876 (22.6) | 78,593 (22.7) | 283 (14.4) | 554,849 (22.1) |
| Steroid | 15,561 (4.5) | 15,443 (4.5) | 118 (6.0) | 59,245 (2.4) |
| GI-protective agents¶ | 217,241 (62.3) | 215,953 (62.3) | 1288 (65.3) | 976,102 (38.9) |
OA osteoarthritis, NSAIDs nonsteroidal anti-inflammatory drugs, SYSADOA symptomatic slow-acting drugs for OA, GI gastrointestinal
†Type of institution, department, and medication were determined at the index date
††Comorbidities with more than 3% prevalence
*SYSADOA includes diacerein, avocado, glucosamine, sadenin, chondroitin sulfate, and herbal SYSADOA such as Layla, Joins, and Shinbaro
¶GI protective agents include proton pump inhibitors, H2 blockers, rebamipide, teprenone, and Artemisia asiatica
§Opioid user includes combination products of acetaminophen