Table 1 Intra-rater reliability of the visual FPI, Kinect and Vicon systems for each item of the FPI

FPI 1 Talar head

  Day 1 median (IQR)

0 (0 to 1)

  Day 2 median (IQR)

1 (0 to 1)

N/A

N/A

  Spearman’s rho

0.38*

FPI 2 Lateral curvature

  Day 1 median (IQR)

0 (0 to 1)

−1.55 (−3.40 to 0.75)

−1.32 (−5.06 to 0.93)

  Day 2 median (IQR)

0 (0 to 1)

−0.97 (−4.29 to 0.74)

−2.83 (−4.06 to 0.51)

  Spearman’s rho

0.52*

0.78*

0.73*

FPI 3 Calcaneal inv/ev

  Day 1 median (IQR)

0 (0 to 1)

10.03 (7.54 to 11.71)

9.77 (6.82 to 12.98)

  Day 2 median (IQR)

1 (0 to 1)

11.34 (9.32 to 14.26)

10.73 (7.57 to 12.18)

  Spearman’s rho

0.42*

0.30

0.37

FPI 4 TNJ bulging

  Day 1 median (IQR)

1 (0 to 1)

−17.00 (−22.00 to −13.00)

−12.93 (−15.86 to −8.52)

  Day 2 median (IQR)

1 (0 to 1)

−16.50 (−19.25 to −13.00)

−11.63 (−16.22 to −8.71)

  Spearman’s rho

0.17

0.62*

0.79*

FPI 5 Congruence of MLA/Arch height

  Day 1 median (IQR)

1 (0 to 2)

49.35 (39.94 to 61.36)

26.75 (22.19 to 31.12)

  Day 2 median (IQR)

1 (0 to 1)

46.28 (40.33 to 58.88)

28.82 (23.86 to 32.72)

  Spearman’s rho

0.63*

0.72*

0.78*

FPI 5 Arch peak

  Day 1 median (IQR)

17.65 (15.69 to 32.65)

42.67 (38.25 to 45.03)

  Day 2 median (IQR)

N/A

24.20 (15.56 to 35.76)

42.41 (34.59 to 46.53)

  Spearman’s rho

0.66*

0.13

FPI 6 Forefoot ab/add

  Day 1 median (IQR)

1 (0 to 2)

−3.00 (−6.00 to 3.00)

2.87 (−0.71 to 7.88)

  Day 2 median (IQR)

1 (0.75 to 1)

0.00 (−6.00 to 6.50)

4.19 (−1.15 to 8.75)

  Spearman’s rho

0.29

0.21

0.55*

FPI total score

  Day 1 median (IQR)

3 (2 to 6)

  Day 2 median (IQR)

4 (2 to 5.25)

N/A

N/A

  ICC

0.87*