title: Three-dimensional intervertebral range of motion in the cervical spine: Does the method of calculation matter?
abstract: Intervertebral range of motion (ROM) is commonly calculated using ordered rotations or projection angles. Ordered rotations are sequence-dependent, and projection angles are dependent upon on which orientation vectors are projected. This study assessed the effect of calculation method on intervertebral ROM in the subaxial cervical spine (C3-C7) during in vivo dynamic, three-dimensional, functional movement. Biplane radiographs were collected at 30 images per second while 29 participants performed full ROM flexion/extension, axial rotation and lateral bending movements of their cervical spine. In vivo bone motion was tracked with sub-millimeter accuracy using a validated volumetric model-based tracking technique. Intervertebral rotations were calculated using six Cardan angle sequences and two projection angle combinations. Within-subject comparisons revealed significant differences in intervertebral ROM among calculation methods (all p<0.002). Group mean ROM differences were small, but significantly different among calculation methods (p<0.001). A resampling technique demonstrated that as group size increases, the differences between calculation methods decreases substantially. It is concluded that the method used to calculate intervertebral rotations of the sub-axial cervical spine can significantly affect within-subject and between group comparisons of intervertebral ROM.
authors.affiliation: Department of Orthopaedic Surgery, Biodynamics Lab, University of Pittsburgh, 3820 South Water Street, Pittsburgh, PA 15203, USA. Electronic address: anderst@pitt.edu.
authors.forename: William J
authors.initials: WJ
authors.lastname: Anderst
authors.affiliation: Department of Bioengineering, University of Pittsburgh, USA.
authors.forename: Yashar
authors.initials: Y
authors.lastname: Aucie
mesh_terms: D000328:Adult; D002574:Cervical Vertebrae / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement; D016059:Range of Motion, Articular; D013223:Statistics as Topic / Q000379:methods*; D055815:Young Adult
keywords: Cardan angles; Euler angles; Kinematics; Ordered rotation; Projection angles; Spine