Table 1.
Characteristics of 4498 participants aged 45-79 from the Osteoarthritis Initiative (OAI). Figures are medians (interquartile range) for continuous variable and numbers (percentage) for categorical variables
| Variables | High risk cohort (n=3171) |
Knee osteoarthritis cohort (n=1327) | P value |
|---|---|---|---|
| Age (years) | 61 (53-69) | 61 (54-69) | 0.77 |
| Age group (years): | |||
| <55 | 934 (29) | 378 (28) | 0.76 |
| 55-64 | 1033 (33) | 432 (33) | |
| >64 | 1204 (38) | 517 (39) | |
| Men | 1302 (41) | 577 (43) | 0.14 |
| Ethnicity: | |||
| White | 2626 (83) | 942 (71) | <0.001 |
| Black or African-American | 466 (15) | 344 (26) | |
| Asian | 30 (1) | 11 (1) | |
| Other | 45 (1) | 30 (2) | |
| Missing | 4 (0) | 0 (0) | |
| Annual income level ($): | |||
| <10 000 | 84 (3) | 64 (5) | <0.001 |
| 10 000-<25 000 | 276 (9) | 148 (11) | |
| 25 000-<50 000 | 741(23) | 337 (25) | |
| 50 000-<100 000 | 1111 (35) | 407 (31) | |
| >100 000 | 740 (23) | 259 (20) | |
| Missing | 219 (7) | 112 (8) | |
| Education level: | |||
| Less than high school graduate | 84 (3) | 65 (5) | <0.001 |
| High school graduate | 371 (12) | 201 (15) | |
| Some college | 719 (23) | 363 (27) | |
| College graduate | 686 (22) | 256 (20) | |
| Some graduate school | 263 (8) | 106 (8) | |
| Graduate degree | 1026 (32) | 319 (24) | |
| Missing | 22 (1) | 17 (1) | |
| BMI | 27.8 (24.6-31.1) | 29.7 (26.6-33.4) | <0.001 |
| Missing | 1 (0) | 3 (0) | |
| Modified Charlson comorbidity index: | |||
| 0 | 2431 (77) | 914 (69) | <0.001 |
| 1 | 453 (14) | 234 (18) | |
| 2 | 172 (5) | 99 (7) | |
| 3 | 46 (1) | 40 (3) | |
| ≥4 | 38 (1) | 13 (1) | |
| Missing | 31 (1) | 27 (2) | |
| Kellgren-Lawrence grade: | |||
| 0 | 1076 (34) | 69 (5) | <0.001 |
| 1 | 579 (18) | 90 (7) | |
| 2 | 923 (29) | 408 (31) | |
| 3 | 393 (12) | 481 (36) | |
| 4 | 81 (3) | 211 (16) | |
| Missing | 119 (4) | 68 (5) | |
| Self reported diagnosis of osteoarthritis in 12 months before baseline: | |||
| Yes | 472 (15) | 542 (41) | <0.001 |
| No | 2568 (81) | 689 (52) | |
| Missing | 131 (4) | 96 (7) | |
| Previous knee injury at baseline: | |||
| Yes | 1275 (40) | 625 (47) | <0.001 |
| No | 1878 (59) | 687 (52) | |
| Missing | 18 (1) | 15 (1) | |
| Previous knee surgery at baseline: | |||
| Yes | 549 (17) | 450 (34) | <0.001 |
| No | 2619 (83) | 875 (66) | |
| Missing | 3 (0) | 2 (0) | |
| SF-12* score: | |||
| Physical component summary (PCS) | 52.8 (46.4-56.1) | 46.2 (38.0-52.9) | <0.001 |
| Mental component summary (MCS) | 55.3 (50.4-58.3) | 55.7 (48.8-59.7) | 0.11 |
| Missing | 36 (1) | 21 (2) | — |
| SF-6D* utility index | 0.86 (0.72-0.92) | 0.78 (0.66-0.86) | <0.001 |
| Missing | 36 (1) | 23 (2) | — |
| WOMAC* total score | 6.1 (1.0-17.0) | 24.1 (13.0-39.0) | <0.001 |
| Missing | 14 (0) | 19 (1) | — |
| KOOS* quality of life | 75.0 (62.5-87.5) | 50.0 (37.5-62.5) | <0.001 |
| Missing | 1 (0) | 0 (0) | — |
| Use of pain medication for osteoarthritis: | |||
| Yes | 1016 (32) | 620 (47) | <0.001 |
| No | 2154 (68) | 706 (53) | |
| Missing | 1 (0) | 1 (0) | |
| Use of non-pharmacological treatment: | |||
| Yes | 284 (9) | 169 (13) | <0.001 |
| No | 2883 (91) | 1156 (87) | |
| Missing | 4 (0) | 2 (0) | |
| Missed work days in last 3 months†: | |||
| Yes | 64 (3) | 69 (8) | <0.001 |
| No | 1928 (97) | 750 (92) | |
| No of work days missed if ≥1 | 2.5 (2.0-5.2) | 3.0 (2.0-5.0) | 0.5 |
BMI=body mass index; WOMAC=Western Ontario and McMaster Universities arthritis index; KOOS=knee injury and osteoarthritis outcome score.
*Range of scales: SF-6D, 0-1 scale (higher scores indicate better health); SF-12, 0-100 scale (higher scores indicate less severe symptoms); WOMAC, 0-100 scale (higher scores indicate more severe symptoms); KOOS quality of life, 0-100 scale (higher scores indicate less severe symptoms).
†Measured only in those who reported being employed: n=1992 in high risk cohort and 819 in knee osteoarthritis cohort.