The effect of axial compression and distraction on cervical facet mechanics during anterior shear,flexion, axial rotation,and lateral bending motions |
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| Institution: | 1. Department of Orthopedic Surgery, MGH/BWH Orthopedic Spine Surgery Fellowship Program, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA;2. Department of Orthopedic Surgery, Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA;3. The Spine Journal, North American Spine Society, 7075 Veterans Boulevard, Burr Ridge, IL 60527, USA;1. Department of Mechanical Engineering, University of Sheffield, United Kingdom;2. INSIGNEO Institute for in silico Medicine, University of Sheffield, United Kingdom;3. Medical Device Research Institute, College of Science and Engineering, Flinders University, Tonsley, SA, Australia;4. Centre for Orthopaedic and Trauma Research, The University of Adelaide, Adelaide, SA, Australia;5. Department of Orthopaedics and Trauma, Royal Adelaide Hospital, Adelaide, SA, Australia;6. School of Mechanical Engineering, University of Adelaide, Adelaide, SA 5005, Australia |
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| Abstract: | The subaxial cervical facets are important load-bearing structures, yet little is known about their mechanical response during physiological or traumatic intervertebral motion. Facet loading likely increases when intervertebral motions are superimposed with axial compression forces, increasing the risk of facet fracture. The aim of this study was to measure the mechanical response of the facets when intervertebral axial compression or distraction is superimposed on constrained, non-destructive shear, bending and rotation motions. Twelve C6/C7 motion segments (70 ± 13 yr, nine male) were subjected to constrained quasi-static anterior shear (1 mm), axial rotation (4°), flexion (10°), and lateral bending (5°) motions. Each motion was superimposed with three axial conditions: (1) 50 N compression; (2) 300 N compression (simulating neck muscle contraction); and, (3) 2.5 mm distraction. Angular deflections, and principal and shear surface strains, of the bilateral C6 inferior facets were calculated from motion-capture data and rosette strain gauges, respectively. Linear mixed-effects models (α = 0.05) assessed the effect of axial condition. Minimum principal and maximum shear strains were largest in the compressed condition for all motions except for maximum principal strains during axial rotation. For right axial rotation, maximum principal strains were larger for the contralateral facets, and minimum principal strains were larger for the left facets, regardless of axial condition. Sagittal deflections were largest in the compressed conditions during anterior shear and lateral bending motions, when adjusted for facet side. |
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| Keywords: | Cervical spine Biomechanics Facet joint Distraction Compression |
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