Introduction
Background
Aim of the study
Materials and methods
Study design
Instruments
Standardised questionnaire
Partially standardised telephone interview
Patient record
Recruitment and inclusion criteria of cases and controls
General inclusion criteria
Additional criteria for the case group
Additional criteria for the control group
Power of the dataset
Analysis
Ethics
Results
Description of the sample
Age at inclusion in study (years) | Age used for exposure analysis (years) | |||||
---|---|---|---|---|---|---|
Gender |
n
| Mean | Standard deviation | Mean | Standard deviation | |
Cases | Female | 438 | 62.0 | 9.6 | 59.6 | 9.8 |
Male | 301 | 60.0 | 11.1 | 57.1 | 11.2 | |
Controls | Female | 303 | 57.8 | 11.8 | 54.8 | 11.8 |
Male | 268 | 53.9 | 12.7 | 50.9 | 12.7 |
Results of exposure assessment
Exposed | Not exposed | No indication | ||||||
---|---|---|---|---|---|---|---|---|
Exposure | Gender | Controls/cases |
n
|
%
|
n
| % |
n
| % |
Sitting | Female | Controls | 261 | 86.2 | 28 | 9.2 | 14 | 4.6 |
Cases | 367 | 83.8 | 60 | 13.7 | 11 | 2.5 | ||
Male | Controls | 228 | 85.1 | 34 | 12.7 | 6 | 2.2 | |
Cases | 239 | 79.4 | 53 | 17.6 | 9 | 3.0 | ||
Standing | Female | Controls | 240 | 79.2 | 49 | 16.2 | 14 | 4.6 |
Cases | 363 | 82.9 | 64 | 14.6 | 11 | 2.5 | ||
Male | Controls | 226 | 84.4 | 36 | 13.4 | 6 | 2.2 | |
Cases | 249 | 82.7 | 43 | 14.3 | 9 | 3.0 | ||
Walking | Female | Controls | 249 | 82.2 | 40 | 13.2 | 14 | 4.6 |
Cases | 381 | 87.0 | 46 | 10.5 | 11 | 2.5 | ||
Male | Controls | 241 | 90.0 | 21 | 7.8 | 6 | 2.2 | |
Cases | 266 | 88.4 | 26 | 8.6 | 9 | 3.0 | ||
Kneeling, squatting | Female | Controls | 113 | 37.3 | 176 | 58.1 | 14 | 4.6 |
Cases | 215 | 49.1 | 212 | 48.4 | 11 | 2.5 | ||
Male | Controls | 118 | 44.1 | 144 | 53.7 | 6 | 2.2 | |
Cases | 163 | 54.5 | 129 | 42.5 | 9 | 3.0 | ||
Climbing stairs | Female | Controls | 186 | 61.4 | 104 | 34.3 | 13 | 4.3 |
Cases | 317 | 72.4 | 111 | 25.3 | 10 | 2.3 | ||
Male | Controls | 181 | 67.6 | 81 | 30.2 | 6 | 2.2 | |
Cases | 220 | 73.1 | 75 | 24.9 | 6 | 2.0 | ||
Jumping | Female | Controls | 46 | 15.3 | 244 | 80.5 | 13 | 4.2 |
Cases | 91 | 20.8 | 337 | 76.9 | 10 | 2.3 | ||
Male | Controls | 79 | 29.5 | 183 | 68.3 | 6 | 2.2 | |
Cases | 120 | 39.8 | 173 | 57.5 | 8 | 2.7 | ||
Lifting/carrying of loads | Female | Controls | 101 | 32.0 | 144 | 47.5 | 62 | 20.5 |
Cases | 152 | 35.7 | 190 | 43.4 | 96 | 21.9 | ||
Male | Controls | 162 | 60.4 | 87 | 32.5 | 19 | 7.1 | |
Cases | 196 | 65.1 | 83 | 27.6 | 22 | 7.3 |
Controls | Cases | Total | |||||
---|---|---|---|---|---|---|---|
Gender | Exposure |
n
|
%
|
n
|
%
|
n
| % |
Female | No sports | 94 | 31.0 | 143 | 32.6 | 237 | 32.0 |
Sports - cumulative exposure could be calculated | 170 | 56.1 | 237 | 54.1 | 407 | 54.9 | |
Sports - no cumulative exposure could be calculated | 39 | 12.9 | 58 | 13.2 | 97 | 13.1 | |
Male | No sports | 41 | 15.3 | 39 | 13.0 | 80 | 14.1 |
Sports - cumulative exposure could be calculated | 201 | 75.0 | 241 | 80.1 | 442 | 77.7 | |
Sports - no cumulative exposure could be calculated | 26 | 9.7 | 21 | 7.0 | 47 | 8.3 | |
Female | No leisure time activities | 173 | 57.1 | 239 | 54.6 | 412 | 55.6 |
Leisure time activities - cumulative exposure could be calculated | 97 | 32.0 | 169 | 38.6 | 266 | 35.9 | |
Leisure time activities - no cumulative exposure could be calculated | 33 | 10.9 | 30 | 6.8 | 63 | 8.5 | |
Male | No leisure time activities | 154 | 57.5 | 154 | 51.2 | 308 | 54.1 |
Leisure time activities - cumulative exposure could be calculated | 90 | 33.6 | 130 | 43.2 | 220 | 38.7 | |
Leisure time activities - no cumulative exposure could be calculated | 24 | 9.0 | 17 | 5.6 | 41 | 7.2 |
Tertile split | |||
---|---|---|---|
First tertile | Second tertile | Third tertile | |
Smoking (package-years) | |||
Female | <9 | 9 to 20 | >20 |
Male | <16.5 | 16.5 to 27 | >27 |
Kneeling/squatting (hours/life) | |||
Female | <3,542 | 3,542 to 8,934 | >8,934 |
Male | <3,573 | 3,573 to 12,243 | >12,243 |
Sitting (hours/life) | |||
Female | <16,031 | 16,031 to 33,119 | >33,119 |
Male | <15,180 | 15,180 to 34,960 | >34,960 |
Median split
| |||
Low exposure
|
High exposure
| ||
Lifting and carrying (tons/life) | |||
Female | <1,088 | ≥1,088 | |
Male | <2,214 | ≥2,214 | |
Sports with risk for unapparent trauma (hours/life) | |||
Female | <1,440 | ≥1,440 | |
Male | <3,232 | ≥3,232 |
Predictors of symptomatic knee OA: models
Item |
n
tot
| Cases (n) | Controls (n) | Pvalue | Odds ratio | 95% confidence interval | |
---|---|---|---|---|---|---|---|
Knee pain during childhood | No (R) | 623 | 361 | 262 | 1.00 | - | |
Yes | 59 | 41 | 18 | <0.05 | 2.08 | 1.01 to 4.26 | |
Knee OA in relatives | No (R) | 408 | 216 | 192 | 1.00 | - | |
Yes | 205 | 142 | 63 | <0.001 | 2.17 | 1.40 to 3.37 | |
Malalignment of the knee | No (R) | 624 | 336 | 288 | 1.00 | - | |
Yes | 90 | 83 | 7 | <0.001 | 11.54 | 4.65 to 28.66 | |
Body mass index | 18.5 to <25 kg/m2 (R) | 255 | 97 | 158 | 1.00 | - | |
≥25 to <30 kg/m2 | 249 | 163 | 86 | <0.001 | 3.21 | 2.09 to 4.96 | |
≥30 to <35 kg/m2 | 149 | 107 | 42 | <0.001 | 3.55 | 2.12 to 5.94 | |
≥35 to <40 kg/m2 | 55 | 49 | 6 | <0.001 | 11.58 | 4.38 to 30.63 | |
≥40 kg/m2 | 23 | 20 | 3 | <0.001 | 17.65 | 4.50 to 69.23 | |
Smoking | No (R) | 391 | 255 | 136 | 1.00 | - | |
Yes, <9 package-years | 117 | 63 | 54 | NS | 0.69 | 0.40 to 1.17 | |
Yes, 9 to 20 package-years | 114 | 64 | 50 | NS | 1.16 | 0.67 to 2.03 | |
Yes, >20 package-years | 115 | 54 | 61 | <0.01 | 0.43 | 0.26 to 0.73 | |
Occupation: kneeling or squatting | No (R) | 388 | 212 | 176 | 1.00 | - | |
Yes, <3,542 hours/life | 109 | 62 | 47 | NS | 1.50 | 0.83 to 2.69 | |
Yes, 3,542 to 8,934 hours/life | 110 | 68 | 42 | NS | 1.36 | 0.78 to 2.37 | |
Yes, >8,934 hours/life | 109 | 85 | 24 | <0.01 | 2.52 | 1.35 to 4.68 | |
Occupation: sitting | No (R) | 88 | 60 | 28 | 1.00 | - | |
Yes, <16,032 hours/life | 209 | 127 | 82 | NS | 0.72 | 0.37 to 1.40 | |
Yes, 16,032 to 33,119 hours/life | 209 | 122 | 87 | <0.05 | 0.51 | 0.26 to 0.99 | |
Yes, >33,119 hours/life | 210 | 118 | 92 | <0.01 | 0.39 | 0.20 to 0.76 | |
Occupation: lifting and carrying | No (R) | 263 | 139 | 124 | 1.00 | - | |
sometimes | 65 | 37 | 28 | NS | 0.88 | 0.44 to 1.77 | |
Yes, <1,088 tons/life | 122 | 69 | 53 | NS | 0.69 | 0.38 to 1.24 | |
Yes, ≥1,088 tons/life | 121 | 92 | 29 | <0.01 | 2.13 | 1.14 to 3.98 | |
Sports with risk for unapparent trauma | No (R) | 570 | 342 | 228 | 1.00 | - | |
Yes, <1,440 hours/life | 81 | 41 | 40 | NS | 0.92 | 0.48 to 1.75 | |
Yes, ≥1,440 hours/life | 78 | 50 | 28 | <0.01 | 2.47 | 1.31 to 4.65 |
Item |
n
tot
| Cases (n) | Controls (n) | Pvalue | Odds ratio | 95% confidence interval | |
---|---|---|---|---|---|---|---|
Knee OA in relatives | No (R) | 367 | 170 | 197 | 1.00 | - | |
Yes | 109 | 76 | 33 | <0.01 | 2.37 | 1.41 to 3.98 | |
Body mass index | 18.5 to <25 kg/m2 (R) | 157 | 48 | 109 | 1.00 | - | |
≥25 to <30 kg/m2 | 240 | 133 | 107 | <0.001 | 2.26 | 1.43 to 3.57 | |
≥30 to <35 kg/m2 | 128 | 84 | 44 | <0.001 | 4.00 | 2.30 to 6.94 | |
≥35 kg/m2 | 40 | 35 | 5 | <0.001 | 12.56 | 4.40 to 36.86 | |
Occupation: kneeling or squatting | No (R) | 272 | 128 | 144 | 1.00 | - | |
Yes, <3,574 hours/life | 94 | 48 | 46 | NS | 1.70 | 0.96 to 3.00 | |
Yes, 3,574 to 12,244 hours/life | 94 | 55 | 39 | <0.01 | 2.16 | 1.24 to 3.77 | |
Yes, >12,244 hours/life | 94 | 61 | 33 | <0.01 | 2.47 | 1.41 to 4.32 | |
Sports with risk for unapparent trauma | No (R) | 218 | 109 | 109 | 1.00 | - | |
Yes, <3,232 hours/life | 168 | 82 | 86 | NS | 1.57 | 0.98 to 2.52 | |
Yes, ≥3,232 hours/life | 168 | 104 | 64 | <0.01 | 2.58 | 1.59 to 4.17 |