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Table 1 Characteristics of the study subjects

From: The complement system is activated in synovial fluid from subjects with knee injury and from patients with osteoarthritis

Main diagnostic groups Subgroups of injury Duration, range (median) n (% women) Age in years, median (range) Differences in age, p value
Reference subjects NA 23 (22) 26 (15–58)
Osteoarthritisa 0–14.8 years (2.7) 24 (42) 64 (36–86) <0.001
Rheumatoid arthritisb 0–43.0 years (10) 32 (63) 64 (32–83) <0.001
Pyrophosphate arthritis 0–9.8 years (0.01) 25 (40) 75 (41–92) <0.001
Knee injuryc 0–36.9 years (0.02) 294 (27) 29 (13–65) 0.842
  Recent injury 0–83 days (4) 219 (25) 26 (13–64) 0.705
  Recent injury, substratification 0 days (0) 35 (23) 30 (14–47) 0.991
1 day (1) 39 (21) 24 (13–57) 0.211
2–3 days (3) 31 (29) 26 (16–54) 0.914
4–7 days (5) 46 (28) 25 (14–64) 0.492
8–22 days (11) 44 (30) 23 (14–57) 0.151
23–83 days (32) 24 (13) 38 (21–59) 0.033
  Old injuryd 1–36.9 years (3.3) 75 (33) 32 (18–65) 0.090
  Old injury, substratification 1–3 years (2.0) 35 (40) 33 (18–61) 0.149
   3.01–36.9 years (5.1) 40 (28) 30 (18–65) 0.121
  1. The injury groups are presented with stratification based on time between injury and synovial fluid aspiration. Differences in age between patients and reference groups were analysed using Student’s t test, and significant values (p < 0.05) are indicated by boldface type. Duration refers to time between injury or onset of disease and sampling. NA Not applicable
  2. aSymptomatic and/or radiographically diagnosed idiopathic osteoarthritis (with no history of knee trauma), with information of disease duration from 17 of 24 patients. The OA score for the OA group was as follows: median = 7, range = 3–9 (information from 15 of 24 patients)
  3. bRheumatoid arthritis, with information of disease duration from 29 of 32 patients, taking the following medications: no information (n = 1), no medication (n = 3), non-steroidal anti-inflammatory and/or disease-modifying drugs (n = 28)
  4. cThe clinical diagnosis of the subjects with knee injury was as follows: isolated anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) injuries (ACL n = 39, PCL n = 4), ACL injury with meniscal tear (n = 69), ACL injury with meniscal tear and other ligament injuries (n = 37), ACL injury with other ligament injuries (n = 47), isolated meniscal tear (n = 58), meniscal tear with other (not ACL) ligament injuries (n = 7), patellar dislocation with or without soft tissue injuries (n = 13), other types of injuries (medial or lateral collateral ligament tears n = 7, give-way n = 2), no signs of soft tissue injury (n = 10)
  5. dSix patients in the old injury group had post-traumatic OA (based on OA score ≥5 [20]), and the group had the following OA score: median = 2, range = 1–8 (information from 63 of 75 patients)