title: The application of physiological loading using a dynamic, multi-axis spine simulator.
abstract: In-vitro testing protocols used for spine studies should replicate the in-vivo load environment as closely as possible. Unconstrained moments are regularly employed to test spinal specimens in-vitro, but applying such loads dynamically using an active six-axis testing system remains a challenge. The aim of this study was to assess the capability of a custom-developed spine simulator to apply dynamic unconstrained moments with an axial preload. Flexion-extension, lateral bending, and axial rotation were applied to an L5/L6 porcine specimen at 0.1 and 0.3Hz. Non-principal moments and shear forces were minimized using load control. A 500N axial load was applied prior to tests, and held stationary during testing to assess the effect of rotational motion on axial load. Non-principal loads were minimized to within the load cell noise-floor at 0.1Hz, and within two-times the load-cell noise-floor in all but two cases at 0.3Hz. The adoption of position control in axial compression-extension resulted in axial loads with qualitative similarities to in-vivo data. This study successfully applied dynamic, unconstrained moments with a physiological preload using a six-axis control system. Future studies will investigate the application of dynamic load vectors, multi-segment specimens, and assess the effect of injury and degeneration.
authors.affiliation: Centre for Orthopaedic Biomechanics, Department of Mechanical Engineering, University of Bath, Bath, BA1 7AY, UK ; College of Engineering, Mathematics & Physical Sciences, University of Exeter, Harrison Building, Streatham Campus, North Park Road, Exeter, EX4 4QF, UK. Electronic address: t.holsgrove@exeter.ac.uk.
authors.forename: Timothy Patrick
authors.initials: TP
authors.lastname: Holsgrove
authors.affiliation: Centre for Orthopaedic Biomechanics, Department of Mechanical Engineering, University of Bath, Bath, BA1 7AY, UK.
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Miles
authors.affiliation: Centre for Orthopaedic Biomechanics, Department of Mechanical Engineering, University of Bath, Bath, BA1 7AY, UK.
authors.forename: Sabina
authors.initials: S
authors.lastname: Gheduzzi
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D008159:Lumbar Vertebrae / Q000502:physiology*; D008422:Materials Testing / Q000295:instrumentation*; D012399:Rotation; D013552:Swine; D016474:Weight-Bearing
keywords: Dynamic; Physiological testing; Preload; Six-axis; Spine biomechanics