Measurement device for ankle joint kinematic and dynamic characterisation

The paper describes a measurement device for obtaining the kinematic characterisation and isometric loading of ankle joints under different working conditions. Non-invasive, in vivo experiments can be conducted with this experimental apparatus, the potential of which could be usefully exploited in basic biomedical research, prosthesis design, clinical applications, sports medicine and rehabilitation. The device determines the 3D movement of the foot with respect to the shank and evaluates the torques and moments around the three articular axes in relation to any desired angular position of the ankle complex. When integrated with superficial electromyographic techniques and electrical stimulation, it allows the assessment of the functionality of the lower leg in both mechanical and myo-electrical terms. The paper reports the main mechanical and electronic features of the device (high linearity; maximum moment ranges +/-300Nm for flexion-extension, +/-35Nm for both pronation-supination and internal-external rotation; angular ranges: 1000 of dorsi-plantar flexion, +/-50degrees of internal-external rotation and prono-supination; linear ranges: +/-25mm along each axis). Results from a healthy volunteer, under voluntary or stimulated conditions, helped in testing its operatability, reliability,. robustness, repeatability and effectiveness. Preliminary simplified protocols have been also applied to 20 healthy volunteers, and the main results were 80.8+/-11.9degrees of internal-external rotation, 46.2+/-9.1degrees of prono-supination and 74.6+/-13.1degrees of flexion-extension. Torques and moments were normalised with respect to a body mass index of 30. The maximum plantar flexion moment (57.5+/-21.3 Nm) was measured with the foot at 150 of dorsal flexion; the maximum dorsal flexion moment (50.2+/-20.3Nm) was measured with the foot at 15degrees of plantar flexion.