Table 2 WOMAC pain, function and total score for different BMI groups (pre-surgery: all scales N = 1565; 12-month: pain N = 1311, function N = 1308, total N = 1308)

WOMAC pain

normal: < 25

45.2 (38.7–51.7)

10.7 (2.9–18.5)

34.5 (31.9–37.1)

pre-obesity: 25–30

45.9 (39.3–52.6)

9.8 (3.7–16.0)

36.1 (34.1–38.1)

class I obesity: 30–35

50.5 (43.7–57.2)

10.1 (3.6–16.6)

40.4 (38.0–42.7)*

class II obesity: 35–40

54.3 (41.8–66.8)

10.2 (0.0–22.9)

44.2 (40.3–48.0)*

class III obesity: ≥ 40

54.9 (39.1–70.7)

12.6 (0.0–29.2)

42.3 (36.7–48.0)*

Group

Time

Group-by-time interaction

F = 6.1; p < 0.001

F = 2458.4; p < 0.001

F = 6.7; p < 0.001

WOMAC function

normal: < 25

52.6 (50.6–54.6)

16.2 (14.0–18.4)

36.4 (33.8–39.1)

pre-obesity: 25–30

54.5 (53.0–56.0)

15.5 (13.9–17.1)

39.0 (37.0–41.0)

class I obesity: 30–35

57.7 (56.0–59.5)

16.2 (14.3–18.1)

41.6 (39.2–43.9)*

class II obesity: 35–40

61.1 (58.2–63.9)

18.7 (15.6–21.9)

42.3 (38.5–46.2)*

class III obesity: ≥ 40

62.8 (58.6–67.1)

22.4 (17.8–27.0)

40.4 (34.8–46.1)

Group

Time

Group-by-time interaction

F = 8.0; p < 0.001

F = 2497.6; p < 0.001

F = 2.7; p = 0.030

WOMAC total

normal: < 25

50.9 (49.0–52.8)

15.1 (13.1–17.2)

35.8 (33.3–38.3)

pre-obesity: 25–30

52.6 (51.1–54.0)

14.5 (13.0–16.0)

38.1 (36.2–39.9)

class I obesity: 30–35

56.0 (54.3–57.6)

14.9 (13.1–16.7)

41.0 (38.8–43.2)^a

class II obesity: 35–40

59.1 (56.4–61.8)

16.7 (13.7–19.6)

42.4 (38.8–46.1)^a

class III obesity: ≥ 40

60.8 (56.8–64.8)

20.2 (15.8–24.5)

40.6 (35.3–46.0)

Group

Time

Group-by-time interaction

F = 7.4; p < 0.001

F = 2739.4; p < 0.001

F = 3.6; p = 0.006