Table 1 Clinical characteristics of early knee OA and healthy control groups

Age, years

73.5 ± 6.6

73.8 ± 6.3

72.9 ± 7.3

0.882

Sex [women], n (%)

23 (46.0%)

14 (45.2%)

9 (47.4%)

0.879

Body mass index, kg/m²

20.8 ± 2.4

20.9 ± 2.2

20.7 ± 2.7

0.859

KSS function, /100

91.6 ± 12.5

95.5 ± 6.6

85.2 ± 16.8

0.003

KSS symptom, /25

22.7 ± 3.5

24.5 ± 0.9

19.8 ± 4.2

 < 0.001

Total of WORMS

18.6 ± 13.1

17.8 ± 13.2

20.0 ± 13.3

0.563

OA severity; KL grade = 0, n (%)

19 (38.0%)

12 (38.7%)

7 (36.8%)

0.895

Muscle volume, cm³

 Quadriceps femoris

1108.4 ± 277.0

1093.2 ± 259.7

1133.2 ± 308.8

0.624

  Rectus femoris

154.0 ± 40.8

149.4 ± 40.6

161.7 ± 41.1

0.305

  Vastus intermedius

317.7 ± 85.6

320.3 ± 82.2

313.6 ± 93.0

0.792

  Vastus lateralis

359.4 ± 92.8

348.6 ± 80.3

377.0 ± 110.4

0.298

  Vastus medialis

277.2 ± 71.4

274.9 ± 69.9

281.0 ± 75.6

0.775

Intramuscular fat, %

 Quadriceps femoris

7.1 ± 1.8

6.7 ± 1.2

7.7 ± 2.3

0.073

  Rectus femoris

5.7 ± 1.4

5.5 ± 1.1

6.1 ± 1.8

0.196

  Vastus intermedius

7.6 ± 1.9

7.4 ± 1.4

7.9 ± 2.5

0.354

  Vastus lateralis

8.2 ± 2.2

8.0 ± 1.8

8.5 ± 2.8

0.409

  Vastus medialis

6.8 ± 2.2

6.0 ± 1.2

8.2 ± 2.8

 < 0.001

Gait speed, m/s

1.6 ± 0.2

1.6 ± 0.2

1.5 ± 0.2

0.093

Chair stand-30, repetitions

27.2 ± 6.4

26.3 ± 7.1

28.6 ± 4.8

0.214

Knee extension strength, Nm/kg

2.3 ± 0.6

2.3 ± 0.6

2.4 ± 0.6

0.703

Steps (average 1000 steps per day)

8.3 ± 3.7

8.2 ± 3.4

8.4 ± 4.3

0.796