Finite Helical Axis Behavior In Cervical Kinematics

Cattrysse, Erik and Cescon, Corrado and Clijsen, Ron and Barbero, Marco (2013) Finite Helical Axis Behavior In Cervical Kinematics. In: XXIV Congress of the International Society of Biomechanics, August 4-9, Natal, Rio Grande do Norte - Brazil.

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SUMMARY The Finite Helical Axis (FHA) is still confronted with representational difficulties. The present study investigates the applicability of the Minimum Convex Hull (MCH) method and the angle dispersion method to represent cervical kinematics. INTRODUCTION Although a far more stable approach and very common in spacecraft dynamics and graphic imaging, the FHA struggles with interpretational and representational difficulties compared to a six degrees of freedom analysis especially in clinical context and among medical professionals. The dispersion of the 3D-motion axis has been used previously to express the stability of the motion in cervical kinematics for whiplash patients (Osterbauer et al. 1992; Panjabi 1979; Woltring et al. 1985). However, graphical representations do not allow for mathematical and statistical comparison of data in larger dataset. It may as well cause difficulties to establish reproducibility measures and to set normative data for comparison in clinical cases. The present study investigates the applicability of a method to represent cervical kinematics and to quantify FHA behavior. METHODS A sample of 10 healthy subjects was studied, five males and five females, ranging in age from 21.5 to 28.9 years (24.4 ±1.8 years).Subjects were not considered if they had a history of headache or neck surgery or had received treatment for neck or shoulder conditions within the past three months. Cervical movements were registered with the Polhemus-G4, a non-invasive 3D-electromagnetic device, which tracks the positions and attitude of sensors relative to a source (120Hz). The subjects were asked to perform three series of movements of the head at a natural spontaneous speed (Cattrysse et al., 2012). Each series consisted of five consecutive pair of opposite planar movements (flexion- extension, left-right rotation, left-right lateral bending). Each movement was portioned in 4 phases, between neutral and extreme left and right rotation. Minimum Convex Hull method and the angle between IHA (instantaneous Helical axis) and FHA were calculated as a measure of dispersion. The effect of angle steps was calculated on the estimation global FHA-parameters. RESULTS Figure 1 shows the effect of angle intervals on the estimation of global parameters extracted from groups helical axis: mean angle between each axis and the main axis (Mean Angle), convex hull area (area CH). The mean angle between the main helical axis and each of the helical axis computed with different angle intervals did not depend from the angle interval. The convex hull area dramatically decreased with increasing angle steps. The optimal compromise, which was selected for further analysis was a 10 degree angle.

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