Methods for determining spinal flexion/extension, lateral bending, and axial rotation from marker coordinate data: Analysis and refinement

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Angular coupling patterns in the spine are often described by quantifying flexion/extension, lateral bending, and axial rotation angles as functions of one another. The most common methods for calculating these angles from marker coordinate data are the Euler method and the projection method. Both methods have the problem that they may be applied to spinal motion in a variety of ways, depending on the sequence chosen for Euler rotations or the vectors chosen for projection. The spinal angles calculated by each permutation of both methods vary significantly, leading to difficulties in reporting and comparing results between studies. The ambiguities of the Euler and projection techniques may be resolved and the two techniques standardized for application to the spine by considering vertebral symmetry. Using symmetry considerations, unique vectors may be chosen for determining the planar projection angles that best describe coupling in the spine. Because of the close relationship, presented herein, between projection angles and Euler angles, the same considerations allow one Euler rotation sequence to be chosen over the five alternate sequences. To validate the need for standardization of these techniques and to demonstrate the utility of the method presented, the results from a published study describing angular coupling patterns in the upper cervical spine are reexpressed in terms of the newly chosen Euler sequence and projection angle set. The reevaluated angles are consistent in both methods and lead to a conclusion different from the published conclusion with regard to the pattern of lateral bending coupling at C1-C2 during axial rotation.

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Human Movement Science







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