Table 1. Characteristics of participants and risk factors for knee pain.
| Total | Knee Pain | No Pain | P Value* | |
|---|---|---|---|---|
| Patient number | 3,278 | 721 | 2,577 | |
| Age (years) | 61.27 ± 0.24 | 65.14 ± 0.44 | 60.25 ± 0.23 | < 0.001 |
| Female, n (%) | 1,757 (49.5) | 547 (73.4) | 1,210 (43.2) | < 0.001 |
| Height (cm) | 160.75 ± 0.21 | 156.67 ± 0.38 | 161.83 ± 0.21 | < 0.001 |
| Weight (kg) | 62.28 ± 0.23 | 60.31 ± 0.46 | 62.79 ± 0.26 | < 0.001 |
| BMI (kg/m2), n (%) | <0.001 | |||
| < 25 | 2,140 (64.5) | 419 (58.9) | 1,721 (66.0) | |
| ≥25 - <30 | 1,041 (32.6) | 251 (33.8) | 790 (32.2) | |
| ≥30 | 97 (2.9) | 51 (7.2) | 46 (1.7) | |
| Obesity (%)† | 1,138 (34.7) | 302 (41.0) | 836 (33.9) | < 0.001 |
| Waist circumference (cm) | 84.02 ± 0.23 | 84.93 ± 0.45 | 83.78 ± 0.25 | 0.014 |
| Current smoker, n (%) | 556 (21.0) | 73 (12.7) | 483 (23.2) | < 0.001 |
| Income status, n (%)‡ | < 0.001 | |||
| Low | 817 (26.0) | 217 (30.4) | 600 (24.9) | |
| Moderate | 1,650 (50.7) | 362 (49.2) | 1,288 (51.0) | |
| High | 811 (23.3) | 142 (20.4) | 669 (24.1) | |
| Education level, n (%)§ | < 0.001 | |||
| Low (0–6 years) | 1,529 (44.6) | 503 (69.2) | 1,026 (38.1) | |
| Moderate (7–12 years) | 1,378 (43.7) | 188 (26.6) | 1,190 (48.2) | |
| High (≥ 13 years) | 371 (11.7) | 30 (4.2) | 341 (13.6) | |
| Stiffness, n (%)|| | 370 (121.3) | 297 (41.2) | 73 (2.8) | < 0.001 |
| Vitamin D insufficiency, n (%)¶ | 2,047 (61.4) | 457 (62.7) | 1,590 (61.1) | 0.552 |
| Osteoporosis, n (%) | 715 (19.5) | 244 (31.1) | 471 (16.5) | < 0.001 |
| Bed rest, n (%) | 266 (7.8) | 126 (18.0) | 140 (5.2) | < 0.001 |
| Days of bed rest | 0.57 ± 0.07 | 1.70 ± 0.24 | 0.28 ± 0.05 | < 0.001 |
| LE fat mass (kg) | 5.00 ± 0.05 | 5.58 ± 0.10 | 4.85 ± 0.05 | < 0.001 |
| LE fat percentage (%) | 26.79 ± 0.24 | 30.78 ± 0.49 | 25.75 ± 0.24 | < 0.001 |
| LEM (kg) | 13.15 ± 0.08 | 11.83 ± 0.13 | 13.50 ± 0.08 | < 0.001 |
| LMI (LEM/weight x 100, %) | 21.03 ± 0.08 | 11.83 ± 0.13 | 13.50 ± 0.08 | < 0.001 |
| DLEM, n (%)** | 237 (6.4) | 85 (10.7) | 152 (5.2) | < 0.001 |
| K/L grade, n (%) | < 0.001 | |||
| Normal | 1,210 (39.9) | 138 (22.0) | 1,072 (44.6) | |
| K/L grade 1 | 834 (25.4) | 131 (17.0) | 703 (27.6) | |
| K/L grade 2 | 459 (12.4) | 87 (10.2) | 372 (12.9) | |
| K/L grade 3 | 511 (15.1) | 185 (26.2) | 326 (12.2) | |
| K/L grade 4 | 264 (7.3) | 180 (24.6) | 84 (2.7) | |
| Radiographic knee OA, n (%) | 1,234 (34.7) | 452 (61.0) | 782 (27.8) | < 0.001 |
a Categorical variables are presented as number (weighted %), and continuous variables as mean ± SD, unless otherwise indicated.
*P values are the results of comparisons between participants with knee pain and participants without knee pain. P < 0.05 was considered significant. BMI = Body mass index; DLEM = Decreased lower extremity muscle mass; K/L = Kellgren and Lawrence; LE = Lower extremity; LEM = Lower extremity muscle mass; LMI = Lower extremity muscle mass index; OA = Osteoarthritis.
† Obesity was defined as BMI > 25 kg/m2.
‡ Income status was categorized into three groups (low, less than 670 USD dollars a month; moderate, less than 2,200 USD dollars a month; high, more than 2,200 USD dollars a month).
§ Education level was categorized into three groups (low, less than elementary school; moderate, middle and high school; high, more than university).
|| Stiffness was defined as the presence of morning stiffness of the knee for more than 30 days during the past 3 months.
¶ Vitamin D insufficiency was defined as serum 25(OH) D level < 20 ng/ml.
** Lower extremity muscle mass and fat mass were evaluated by dual x-ray absorptionmetry. DLEM was defined as an LMI was 2 standard deviations below the mean in a sex-matched young reference group.