‘Mean axis of rotation of the midtarsal joint’ NESTER et al.

Why would the authors of, “Kinematics of the Midtarsal Joint During Standing Leg Rotation” include in Fig. 2 a, “Mean axis of rotation of the midtarsal joint projected on transverse and sagittal plane”.

Why would the authors of, “Kinematics of the Midtarsal Joint During Standing Leg Rotation” include in Fig. 2 a, “Mean axis of rotation of the midtarsal joint projected on transverse and sagittal plane”.

Taken from:
‘Mean axis of rotation of the midtarsal joint’ NESTER et al.