Table 2 Synovial histologic features of osteoarthritis vs rheumatoid arthritis

 Lymphocytic inflammation

<0.001

  None

43 (29.3%)

7 (11.7%)

  Mild (0–1 perivascular aggregates per low power field)

64 (43.5%)

20 (33.3%)

  Moderate (>1 perivascular aggregate + focal interstitial infiltration)

30 (20.4%)

14 (23.3%)

  Marked (both perivascular and widespread interstitial aggregates)

9 (6.1%)

15 (25.0%)

  Band-like

1 (0.7%)

4 (6.7%)

 Lining hyperplasia

<0.001

  Normal lining

10 (6.8%)

0 (0.0%)

  2–3 cells thick

97 (66.0%)

16 (26.7%)

  3–4 cells thick

38 (25.9%)

26 (43.3%)

  > 4 cells thick

2 (1.4%)

18 (30.0%)

 Neutrophils

1 (0.7%)

13 (21.7%)

<0.001

 Plasma cells (×25 mag)

<0.001

  < 10% plasma cells within lymphocytic aggregates

125 (85.0%)

33 (55.0%)

  < 50% plasma cells

18 (12.2%)

17 (28.3%)

  >50% plasma cells

4 (2.7%)

10 (16.7%)

 Binucleate plasma cells

16 (10.9%)

19 (31.7%)

<0.001

 Russell bodies

13 (8.8%)

13 (21.7%)

0.019

 Sub-lining giant cells

2 (1.4%)

9 (15.0%)

<0.001

 Synovial giant cells

25 (17.0%)

22 (36.7%)

0.003

  Missing

0 (0.0%)

2 (3.3%)

 Fibrin

13 (8.8%)

27 (45.0%)

<0.001

 Detritus

62 (42.2%)

42 (70.0%)

<0.001

 Computer vision quantification of cell density, mean

2900

4196

<0.001

 Fibrosis

<0.001

  None

7 (4.8%)

40 (66.7%)

  Focal

85 (57.8%)

16 (26.7%)

  Widespread or band-like

55 (37.4%)

4 (6.6%)

 Mast cells

146 (99.3%)

22 (36.7%)

<0.001

  Missing

0 (0.0%)

1 (1.7%)

 Synovial mucoid change

0.73

  None

6 (4.1%)

5 (8.3%)

  Slight (perivascular or focal interstitial)

63 (42.9%)

22 (36.7%)

  Moderate (perivascular or focal interstitial)

50 (34.0%)

22 (36.7%)

  Marked (perivascular or focal interstitial)

17 (11.6%)

6 (10.0%)

  Myxomatous

11 (7.5%)

4 (6.7%)

  Missing

0 (0.0%)

1 (1.7%)

 Germinal centers

1 (0.7%)

2 (3.3%)

0.20