Quantitative evaluation of facet deflection, stiffness, strain and failure load during simulated cervical spine trauma

Abstract

Traumatic cervical facet dislocation (CFD) is often associated with devastating spinal cord injury. Facet fractures commonly occur during CFD, yet quantitative measures of facet deflection, strain, stiffness and failure load have not been reported. The aim of this study was to determine the mechanical response of the subaxial cervical facets when loaded in directions thought to be associated with traumatic bilateral CFD - anterior shear and flexion. Thirty-one functional spinal units (6 × C2/3, C3/4, C4/5, and C6/7, 7 × C5/6) were dissected from fourteen human cadaver cervical spines (mean donor age 69 years, range 48-92; eight male). Loading was applied to the inferior facets of the inferior vertebra to simulate the in vivo inter-facet loading experienced during supraphysiologic anterior shear and flexion motion. Specimens were subjected to three cycles of sub-failure loading (10-100 N, 1 mm/s) in each direction, before being failed in a randomly assigned direction (10 mm/s). Facet deflection, surface strains, stiffness, and failure load were measured. Linear mixed-effects models (α = 0.05; random effect of cadaver) accounted for variations in specimen geometry and bone density. Specimen-specific parameters were significantly associated with most outcome measures. Facet stiffness and failure load were significantly greater in the simulated flexion loading direction, and deflection and surface strains were higher in anterior shear at the non-destructive analysis point (47 N applied load). The sub-failure strains and stiffness responses differed between the upper and lower subaxial cervical regions. Failure occurred through the facet tip during anterior shear loading, while failure through the pedicles was most common in flexion.

The effect of axial compression and distraction on cervical facet mechanics during anterior shear, flexion, axial rotation, and lateral bending motions

“…Maximum principal and shear facet surface strains (for the neutral condition) were larger than those observed at the bilateral facet bases during loading of isolated subaxial cervical facets that simulated non-destructive anterior shear motions (maximum principal: 216±39 vs 124±16 µε; maximum shear: 602±121 vs 206±29 µε) and flexion rotations (maximum principal: 336±72 vs 70±8 µε; maximum shear: 712±144 vs 109±15 µε) (Quarrington et al, 2018). Maximum and minimum principal strains during anterior shear translations were also generally larger for the current study compared to those measured at the postero-lateral surface of subaxial cervical superior facets during unconstrained anterior shear (Cripton, 1999), despite larger intervertebral shear displacement (mean 2 mm) in the latter study.…”

“…Facet surface strains have been measured during non-traumatic anterior shear motion of cervical functional spinal units (FSUs) (Cripton, 1999), but have not been reported for other intervertebral motions. In a recent study, surface strain, deflection, stiffness and failure load of the subaxial inferior facets were quantified during uni-axial loading that simulated physiologic intervertebral flexion and anterior shear motions (Quarrington et al, 2018); however, point loads were applied to the articular facet surfaces, which may not accurately represent in-vivo conditions. The response of the cervical facets to axial rotation and lateral bending has not been investigated.…”

Predicting the loss of correction after isolated anterior stabilization in the surgical treatment of subaxial cervical dislocations

“…Стоит отметить, что при анализе современных отечественных и зарубежных публикаций, посвященных лечению вывихов шейных позвонков, в первую очередь обращает на себя внимание терминологическое несоответствие: один и тот же с морфологической точки зрения тип повреждения обозначается разными дефинициями. Тем не менее в англоязычной литературе вывихи шейных позвонков именуются термином «cervical facet dislocation», в случае двусторонней дислокации -«bilateral facet dislocation», в случае односторонней -«unilateral facet dislocation» [1,25]. В структуре повреждений шейных позвонков на долю переломовывихов приходится до 36,3 % [26].…”

“…По мнению исследователей, эти факторы следует считать неблагоприятными, усложняющими получение стабильности после вентральных операций. Не менее половины повреждений спинного мозга, сопровождающихся полным или неполным неврологическим дефицитом, являются следствием переломовывихов на уровне сегментов С 5 -С 6 , С 6 -С 7 [25]. При этом более тяжелые разрушения спинного мозга возникают при двусторонних переломовывихах.…”

Experimental analysis of the lower cervical spine in flexion with a focus on facet tracking

“…As such, it appears important to analyze lone FSUs without dynamic or muscular effects in order to assess the structural influence on facet kinematics. Furthermore, as dislocations are often associated with facet fractures [Foster et al, 2012], Quarrington et al [2018Quarrington et al [ , 2019 studied facet deflections and strains under low speed loading.…”