Table 1 Baseline characteristics of children with juvenile idiopathic arthritis (JIA) and healthy controls tested for dynamic joint function

Gender, male: female

21:33

Median age in years (range)

11.3 (5.7 – 19.6)

Mean disease duration in month (range)

20.9 (0 – 161)

JIA subtypes

 • Oligoarticular arthritis

18

 • Polyarticular arthritis

5

 • Systemic arthritis

4

 • Psoriatic arthritis

6

 • Enthesitis-related arthritis

6

 • Unclassified arthritis

5

Non-JIA rheumatic diseases

 • Dermatomyositis with arthritis

2

 • Other

8

JIA cohort N = 36

Gender, male: female

12: 24

Median age in years (range)

12.3 (5.7 – 19.6)

Mean disease duration in month (range)

25.8 (0 – 161)

JIA subtypes

 • Oligoarticular arthritis

   ◦Extended

6

   ◦Persistent

9

 • Polyarticular arthritis

4

 • Systemic arthritis

3

 • Psoriatic arthritis

5

 • Enthesitis-related arthritis

5

 • Unclassified arthritis

4

Joint status (66 knee joints tested)

 • active arthritis

14

 • inactive arthritis, history of arthritis

28

 • unaffected joints

24

Current treatments

 • methotrexate

10

 • oral corticosteroidssteroids

5

 • NSAIDs

15

 • untreated

12

Inception cohort N = 8

Gender male: female

2: 6

Median age in years (range)

10.5 (6.6 - 14.8)

Median height in cm (range)

141.8 (116.7 - 163.0)

Median weight in kg (range)

35.9 (20.7 - 57.1)

Handedness right/left/both

7/0/1

JIA disease duration after diagnosis

   ≤1 month

4

   >1 month

4

JIA subtypes

 • Oligoarticular arthritis

4

 • Psoriatic arthritis

1

 • Enthesitis-related arthritis

2

 • Unclassified arthritis

1

Side of affected knee joint right: left

4: 4

Current treatments

 • NSAID

3

 • untreated

5

Controls N = 9, 18 joints tested

Gender male: female

5 4

Median age in years (range)

12.1 (7.3 – 19.3)

Median height in cm (range)

156.0 (130.0 - 168.1)

Median weight in kg (range)

42.9 (25.2 – 73.1)

Handedness right/left/both

7/1/1