Table 4

 Prevalence of joint effusion on ultrasonography in subjects with painful knee osteoarthritis

Ultrasonographic joint effusion*p Value†
*Joint effusion was defined as present if depth ⩾4 mm; †p values refer to comparisons between subgroups with or without joint effusion. (Student’s t test for quantitative variables and χ2 test for qualitative variables); ‡missing data for one patient.
Subjects, No (%)‡338 (56.4)261 (43.6)
Maximal effusion depth (mm)<0.0001
    Mean (SD)1.3 (1.4)7.5 (5)
    Median (range)1.2 (0–4)6.3 (4–71)
Synovial thickness (mm)<0.0001
    Mean (SD)1.1 (1.5)3.3 (2.9)
    Median (range)0.6 (0–10.2)2.9 (0–29)
Appearance of synovial tissue, No (%)<0.0001
    Normal231 (68.3)47 (18.0)
    Nodular34 (10.1)97 (37.2)
    Diffuse73 (21.6)117 (44.8)