title: Investigation of impact loading rate effects on the ligamentous cervical spinal load-partitioning using finite element model of functional spinal unit C2-C3.
abstract: The cervical spine functions as a complex mechanism that responds to sudden loading in a unique manner, due to intricate structural features and kinematics. The spinal load-sharing under pure compression and sagittal flexion/extension at two different impact rates were compared using a bio-fidelic finite element (FE) model of the ligamentous cervical functional spinal unit (FSU) C2-C3. This model was developed using a comprehensive and realistic geometry of spinal components and material laws that include strain rate dependency, bone fracture, and ligament failure. The range of motion, contact pressure in facet joints, failure forces in ligaments were compared to experimental findings. The model demonstrated that resistance of spinal components to impact load is dependent on loading rate and direction. For the loads applied, stress increased with loading rate in all spinal components, and was concentrated in the outer intervertebral disc (IVD), regions of ligaments to bone attachment, and in the cancellous bone of the facet joints. The highest stress in ligaments was found in capsular ligament (CL) in all cases. Intradiscal pressure (IDP) in the nucleus was affected by loading rate change. It increased under compression/flexion but decreased under extension. Contact pressure in the facet joints showed less variation under compression, but increased significantly under flexion/extension particularly under extension. Cancellous bone of the facet joints region was the only component fractured and fracture occurred under extension at both rates. The cervical ligaments were the primary load-bearing component followed by the IVD, endplates and cancellous bone; however, the latter was the most vulnerable to extension as it fractured at low energy impact.
authors.affiliation: Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada.
authors.forename: Tanvir
authors.initials: T
authors.lastname: Mustafy
authors.affiliation: Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada. Electronic address: elrich@ualberta.ca.
authors.forename: Marwan
authors.initials: M
authors.lastname: El-Rich
authors.affiliation: Biomedical Technology Department, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Wissal
authors.initials: W
authors.lastname: Mesfar
authors.affiliation: Department of Mechanical & Aerospace Engineering, Royal Military College of Canada, Kingston, ON, Canada.
authors.forename: Kodjo
authors.initials: K
authors.lastname: Moglo
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008022:Ligaments / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D016059:Range of Motion, Articular; D016474:Weight-Bearing / Q000502:physiology; D021801:Zygapophyseal Joint / Q000502:physiology*
keywords: C2–C3 functional spinal unit; Cervical motion segment; Finite-element analysis; Impact; Intradiscal pressure; Ligament and bone failure; Load sharing; Loading rate effect