Table 5 Patient baseline characteristics associated with significant pain variability based on discrete-time frailty model (recurrent outcome)

Male gender

Female

1.30

(0.86, 1.97)

1.40

(0.93, 2.09)

Age (years)

per year

0.95

(0.92, 0.98)

0.94

(0.91, 0.98)

Body mass index (kg/m²)

per kg/m²

1.07

(1.02, 1.12)

1.04

(1.00, 1.08)

Occupational class

Managerial/professional

Intermediate

0.95

(0.53, 1.70)

Routine and manual

0.77

(0.49, 1.22)

PF-10 physical function (0–100)

per unit

0.99

(0.99, 0.99)

ns

ns

WOMAC knee pain (0–20)

per unit

1.12

(1.04, 1.21)

1.10

(1.03, 1.17)

WOMAC knee function (0–68)

per unit

1.03

(1.01, 1.05)

mc

mc

Compartmental distribution of radiographic OA^b

Normal

Isolated tibiofemoral

1.05

(0.49, 2.24)

Isolated patellofemoral

0.93

(0.62, 1.40)

Combined tibiofemoral and patellofemoral

1.07

(0.75, 1.53)

Overall severity of radiographic OA^b

Normal

Mild

0.93

(0.63, 1.36)

Mod/severe

1.10

(0.77, 1.57)

HADS anxiety (0–21)

per unit

1.05

(1.00, 1.10)

mc

mc

HADS depression (0–21)

per unit

1.11

(1.02, 1.21)

ns

ns

Previous knee injury

No

ns

ns

Unilateral

1.27

(0.92, 1.76)

Bilateral

1.96

(1.02, 3.79)

Time since onset of knee problem^b

<1 year

1 year to < 5 years

2.38

(1.14, 4.97)

2.23

(1.11, 4.46)

5 years to < 10 years

2.32

(1.10, 4.89)

2.20

(1.08, 4.48)

≥10 years

2.40

(1.18, 4.92)

2.11

(1.12, 4.05)

Duration of morning stiffness^b

None

≤30 min

2.23

(1.17, 4.23)

1.67

(1.07, 2.61)

>30 min

3.75

(1.16, 12.16)

1.71

(0.73, 3.98)

Knee given way during past month

No

1.42

(1.06, 1.90)

ns

ns

Seen hospital doctor about knee

No

1.89

(1.41, 3.13)

ns

ns

Severity of effusion

None

Mild

0.99

(0.69, 1.42)

Moderate/gross

1.18

(0.72, 1.92)

Nodal symptomatic hand OA

No

0.80

(0.48, 1.35)

Frequent sedentary activity

No

2.00

(0.96, 4.19)

Frequent moderate activity

No

0.79

(0.56, 1.13)

Frequent vigorous activity

No

0.79

(0.51, 1.23)