Effect of displacement rate on the tensile mechanics of pediatric cervical functional spinal units

Nuckley, David J.; Hertsted, Suzanne M.; Eck, Michael P.; Ching, Randal P.

doi:10.1016/j.jbiomech.2004.09.021

Cited by 32 publications

(17 citation statements)

References 34 publications

(73 reference statements)

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“…To compute the facet kinematics, it was assumed that the motion tracking flag and vertebra constitute a rigid body. Rigid fixation of the vertebrae within the mounts using screws and wiring [19] (Fig. 2) ensured no loosening at the vertebrae-mount interfaces.…”

Section: Discussionmentioning

confidence: 99%

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Cervical facet joint kinematics during bilateral facet dislocation

et al. 2007

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Previous biomechanical models of cervical bilateral facet dislocation (BFD) are limited to quasi-static loading or manual ligament transection. The goal of the present study was to determine the facet joint kinematics during high-speed BFD. Dislocation was simulated using ten cervical functional spinal units with muscle force replication by frontal impact of the lower vertebra, tilted posteriorly by 42.5°. Average peak rotations and anterior sliding (displacement of upper articulating facet surface along the lower), separation and compression (displacement of upper facet away from and towards the lower), and lateral shear were determined at the anterior and posterior edges of the right and left facets and statistically compared (P < 0.05). First, peak facet separation occurred, and was significantly greater at the left posterior facet edge, as compared to the anterior edges. Next, peak flexion rotation and anterior facet sliding occurred, followed by peak facet compression. The highest average facet translation peaks were 22.0 mm for anterior sliding, 7.9 mm for separation, 9.9 mm for compression and 3.6 mm for lateral shear. The highest average rotation of 63°occurred in flexion, significantly greater than all other directions. These events occurred, on average, within 0.29 s following impact. During BFD, the main sagittal motions included facet separation, flexion rotation, anterior sliding, followed by compression, however, non-sagittal motions also existed. These motions indicated that unilateral dislocation may precede bilateral dislocation.

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Section: Discussionmentioning

confidence: 99%

“…Each FSU was mounted in resin at the upper and lower vertebrae such that the superior endplate of the lower vertebra was tilted anteriorly by 12.5°(SD 6.2°). The vertebrae were rigidly secured within the mounts using screws and wiring [19], as shown in the lateral radiograph (Fig. 2).…”

Section: Specimen Preparationmentioning

confidence: 99%

Cervical facet joint kinematics during bilateral facet dislocation

et al. 2007

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“…Several studies on pediatric cervical spine have been conducted using animal surrogates as an alternative to pediatric cadavers (Aldman et al 1974;Backaitis et al 1975;Ching et al 2001;Clarke et al 2007;Hilker et al 2002;Mertz et al 1982;Nuckley et al 2005Nuckley et al , 2007Pintar et al 2000;Prasad and Daniel 1984;Schreck and Patrick 1975). Animal surrogate studies provide valuable insights into the biomechanical response of the cervical spine but are limited by interspecies differences between the animal surrogate and human pediatric cervical spines.…”

Section: Introductionmentioning

confidence: 99%

Importance of Muscle Activations for Biofidelic Pediatric Neck Response in Computational Models

Dibb¹,

Cox²,

Nightingale³

et al. 2013

Traffic Injury Prevention

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Objective: During dynamic injury scenarios, such as motor vehicle crashes, neck biomechanics contribute to head excursion and acceleration, influencing head injuries. One important tool in understanding head and neck dynamics is computational modeling. However, realistic and stable muscle activations for major muscles are required to realize meaningful kinematic responses. The objective was to determine cervical muscle activation states for 6-year-old, 10-year-old, and adult 50th percentile male computational head and neck models. Currently, pediatric models including muscle activations are unable to maintain the head in an equilibrium position, forcing models to begin from nonphysiologic conditions. Recent work has realized a stationary initial geometry and cervical muscle activations by first optimizing responses against gravity. Accordingly, our goal was to apply these methods to Duke University's head-neck model validated using living muscle response and pediatric cadaveric data.Methods: Activation schemes maintaining an upright, stable head for 22 muscle pairs were found using LS-OPT. Two optimization problems were investigated: a relaxed state, which minimized muscle fatigue, and a tensed activation state, which maximized total muscle force. The model's biofidelity was evaluated by the kinematic response to gravitational and frontal impact loading conditions. Model sensitivity and uncertainty analyses were performed to assess important parameters for pediatric muscle response. Sensitivity analysis was conducted using multiple activation time histories. These included constant activations and an optimal muscle activation time history, which varied the activation level of flexor and extensor groups, and activation initiation and termination times.Results: Relaxed muscle activations decreased with increasing age, maintaining upright posture primarily through extensor activation. Tensed musculature maintained upright posture through coactivation of flexors and extensors, producing up to 32 times the force of the relaxed state. Without muscle activation, the models fell into flexion due to gravitational loading. Relaxed musculature produced 28.6-35.8 N of force to the head, whereas tensed musculature produced 450-1023 N. Pediatric model stiffnesses were most sensitive to muscle physiological cross-sectional area.Conclusions: Though muscular loads were not large enough to cause vertebral compressive failure, they would provide a prestressed state that could protect the vertebrae during tensile loading but might exacerbate risk during compressive loading. For example, in the 10-year-old, a load of 602 N was produced, though estimated compressive failure tolerance is only 2.8 kN. Including muscles and time-variant activation schemes is vital for producing biofidelic models because both vary by age. The pediatric activations developed represent physiologically appropriate sets of initial conditions and are based on validated adult cadaveric data.

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“…Ching and Nuckley utilized an immature baboon model to evaluate cervical spine biomechanics [143,[146][147][148]. Isolated functional spinal units from specimens ranging in age from 2 to 26 human equivalent years were tested in tension [143].…”

Section: Structural Response: Animal Cadaveric Specimensmentioning

confidence: 99%

“…A decreasing trend in tensile failure load was observed when moving from the upper to lower cervical spine except for the youngest age group which demonstrated no difference across spinal level. The effect of loading rate on these findings was further examined using specimens of 10 human equivalent years subjected to tensile loading at rates from 0.5 to 5,000 mm/s [147]. Metrics of tensile mechanics (stiffness: 2×, failure load: 4×) increased with loading rate according to a power relationship.…”

Section: Structural Response: Animal Cadaveric Specimensmentioning

confidence: 99%

Pediatric Biomechanics

Arbogast¹,

Maltese²

2014

Accidental Injury

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During the human postnatal developmental process, extensive tissue and morphological changes occur. Many take place in the first few years of life but substantial development for several body regions continues well into young adulthood. Along with overall change in size, these material and structural changes influence the biomechanical response of child such that they respond differently to traumatic load than an adult. Understanding the unique biomechanical response of the child is challenging, as compared to the wealth of biomechanical data on the adult response to trauma, pediatric biomechanical data are relatively sparse. As a result, quantitative scaling relationships based on anatomical and material differences have been historically used to understand the biomechanics of the child. The last decade, however, has seen a tremendous increase in contributions to the biomechanics literature based upon pediatric subjects -volunteers, postmortem human subjects, and animal models -thus increasing our knowledge of how to design injury mitigation systems to protect the young.In this chapter, aspects of developmental anatomy and biomechanical knowledge are reviewed to provide context for pediatric human injury prediction. Emphasis is initially placed on the head and brain as this body region represents the most common seriously injured body region for children in virtually all unintentional injury modes. Specifically, head injuries are particularly relevant clinically as the developing brain is difficult to evaluate and treat, and even mild brain injuries in childhood can lead to deficits that remain long after the injury. Discussion follows on the cervical spine and thorax as these body regions are not only important from an injury mitigation standpoint but they govern the kinematics of the head during traumatic loading and therefore play a role in head injury protection. A brief description follows for the other body regions: the abdomen

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Effect of displacement rate on the tensile mechanics of pediatric cervical functional spinal units

Cited by 32 publications

References 34 publications

Cervical facet joint kinematics during bilateral facet dislocation

Cervical facet joint kinematics during bilateral facet dislocation

Importance of Muscle Activations for Biofidelic Pediatric Neck Response in Computational Models

Pediatric Biomechanics

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