title: Non-linearity of flexion-extension characteristics in spinal segments.
abstract: Spinal biomechanics is still known just fragmentary since the only description by angle-torque characteristics without simultaneous recording of migration of the instantaneous helical axis (IHA) is not sufficient. Time-dependent flexion/extension following a cyclic laterally directed torque was measured at all six degrees of freedom by a highly precise custom-made 6D apparatus. In order to enhance the localizing resolution of IHA migration as the function of the flexional/extensional angle, small ranges of motion (ROM) were used at several degrees of pre-extension. 4 L3/L4, 3 L4/L5 and 2 T2/T3 human segments were investigated. In extensional motion, wide dorsal IHA-migrations were measured in lumbar segments and correlated with the distinct asymmetric shapes of the characteristics in extensional motion. The respective increase of differential stiffness could mainly be traced back to the enlarging geometrical moment of inertia of the segments by the dorsally migrating IHA. Both thoracic segments showed a predominant IHA-migration in cranial/caudal direction. A simple model makes it evident that the opposite curvature morphology of lumbar and thoracic joint facets conditions the different directions of IHA migration.
authors.affiliation: Department of Orthodontics, University of Göttingen, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Nägerl
authors.forename: Thelonius
authors.initials: T
authors.lastname: Hawellek
authors.forename: Andrea
authors.initials: A
authors.lastname: Lehmann
authors.forename: Jan
authors.initials: J
authors.lastname: Hubert
authors.forename: Julia
authors.initials: J
authors.lastname: Saptschak
authors.forename: Jochen
authors.initials: J
authors.lastname: Dörner
authors.forename: Björn Werner
authors.initials: BW
authors.lastname: Raab
authors.forename: Jochen
authors.initials: J
authors.lastname: Fanghänel
authors.forename: Dietmar
authors.initials: D
authors.lastname: Kubein-Meesenburg
authors.forename: Martin Michael
authors.initials: MM
authors.lastname: Wachowski
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D006801:Humans; D066298:In Vitro Techniques; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology; D008875:Middle Aged; D008954:Models, Biological; D017711:Nonlinear Dynamics; D012399:Rotation; D013131:Spine / Q000000981:diagnostic imaging / Q000502:physiology*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology; D014057:Tomography, X-Ray Computed; D019415:Torque