Mechanical and neurological response of cat spinal cord under static loading

doi:10.1016/0090-3019(82)90284-1

Surgical Neurology

Volume 17, Issue 3, March 1982, Pages 213-217

https://doi.org/10.1016/0090-3019(82)90284-1 Get rights and content

Abstract

The force/deformation relationship of the exposed spinal cord of cats was studied when the force was gradually applied posteriorly at T10. A linear elastic behavior was identified for deformation less than 0.5 mm, but it was not observed when the static force was no longer supported by the dural sheath. Nonlinear force/deformation relationships were observed for larger deformation, along with a strong hysteresis during a cycle of compression and decompression. The mechanical behavior remained practically the same in a repeated loading if the deformation was less than 2 mm. The motor function of cats did not recover after the cord had been compressed to 4 mm. The associated static force was about 15% of the dynamic force producing the same deformation.

References (9)

MS Albin et al.
Study of functional recovery produced by delayed localized cooling after spinal cord injury in primates
J Neurosurg
(1968)
AR Allen
Surgery of experimental lesion of the spinal cord equivalent to crush injury of fracture dislocation of spinal column
JAMA
(1911)
AR Allen
Remarks on the histopathological changes in the spinal cord due to impact
GJ Dohrmann et al.
“Standardized” spinal cord trauma: biomechanical parameters and lesion volume
Surg Neurol
(1976)

There are more references available in the full text version of this article.

Cited by (49)

Viscoelasticity of spinal cord and meningeal tissues
2018, Acta Biomaterialia
Compared to the outer dura mater, the mechanical behavior of spinal pia and arachnoid meningeal layers has received very little attention in the literature. This is despite experimental evidence of their importance with respect to the overall spinal cord stiffness and recovery following compression. Accordingly, inclusion of the mechanical contribution of the pia and arachnoid maters would improve the predictive accuracy of finite element models of the spine, especially in the distribution of stresses and strain through the cord’s cross-section. However, to-date, only linearly elastic moduli for what has been previously identified as spinal pia mater is available in the literature. This study is the first to quantitatively compare the viscoelastic behavior of isolated spinal pia-arachnoid-complex, neural tissue of the spinal cord parenchyma, and intact construct of the two. The results show that while it only makes up 5.5% of the overall cross-sectional area, the thin membranes of the innermost meninges significantly affect both the elastic and viscous response of the intact construct. Without the contribution of the pia and arachnoid maters, the spinal cord has very little inherent stiffness and experiences significant relaxation when strained. The ability of the fitted non-linear viscoelastic material models of each condition to predict independent data within experimental variability supports their implementation into future finite element computational studies of the spine.
The neural tissue of the spinal cord is surrounded by three fibrous layers called meninges which are important in the behavior of the overall spinal-cord-meningeal construct. While the mechanical properties of the outermost layer have been reported, the pia mater and arachnoid mater have received considerably less attention. This study is the first to directly compare the behavior of the isolated neural tissue of the cord, the isolated pia-arachnoid complex, and the construct of these individual components. The results show that, despite being very thin, the inner meninges significantly affect the elastic and time-dependent response of the spinal cord, which may have important implications for studies of spinal cord injury.
Comparison of in vivo and ex vivo viscoelastic behavior of the spinal cord
2018, Acta Biomaterialia
Despite efforts to simulate the in vivo environment, post-mortem degradation and lack of blood perfusion complicate the use of ex vivo derived material models in computational studies of spinal cord injury. In order to quantify the mechanical changes that manifest ex vivo, the viscoelastic behavior of in vivo and ex vivo porcine spinal cord samples were compared. Stress-relaxation data from each condition were fit to a non-linear viscoelastic model using a novel characterization technique called the direct fit method. To validate the presented material models, the parameters obtained for each condition were used to predict the respective dynamic cyclic response. Both ex vivo and in vivo samples displayed non-linear viscoelastic behavior with a significant increase in relaxation with applied strain. However, at all three strain magnitudes compared, ex vivo samples experienced a higher stress and greater relaxation than in vivo samples. Significant differences between model parameters also showed distinct relaxation behaviors, especially in non-linear relaxation modulus components associated with the short-term response (0.1–1 s). The results of this study underscore the necessity of utilizing material models developed from in vivo experimental data for studies of spinal cord injury, where the time-dependent properties are critical. The ability of each material model to accurately predict the dynamic cyclic response validates the presented methodology and supports the use of the in vivo model in future high-resolution finite element modeling efforts.
Neural tissues (such as the brain and spinal cord) display time-dependent, or viscoelastic, mechanical behavior making it difficult to model how they respond to various loading conditions, including injury. Methods that aim to characterize the behavior of the spinal cord almost exclusively use ex vivo cadaveric or animal samples, despite evidence that time after death affects the behavior compared to that in a living animal (in vivo response). Therefore, this study directly compared the mechanical response of ex vivo and in vivo samples to quantify these differences for the first time. This will allow researchers to draw more accurate conclusions about spinal cord injuries based on ex vivo data (which are easier to obtain) and emphasizes the importance of future in vivo experimental animal work.
Influence of sagittal and axial types of ossification of posterior longitudinal ligament on mechanical stress in cervical spinal cord: A finite element analysis
2015, Clinical Biomechanics
There are few studies focusing on the prediction of stress distribution according to the types of ossification of the posterior longitudinal ligament, which can be fundamental information associated with clinical aspects such as the relationship between stress level and neurological symptom severity. In this study, the influence of sagittal and axial types of ossification of the posterior longitudinal ligament on mechanical stress in the cervical spinal cord was investigated.
A three-dimensional finite element model of the cervical spine with spinal cord was developed and validated. The von Mises stresses in the cord and the reduction in cross-sectional areas and volume of the cord were investigated for various axial and sagittal types according to the occupying ratio of ossification of the posterior longitudinal ligament in the spinal canal.
The influence of axial type was less than that of the sagittal type, even though the central type showed higher maximum stresses in the cord, especially for the continuous type. With a 60% occupying ratio of ossification of the posterior longitudinal ligament, the maximum stress was significantly high and the cross-sectional area of the spinal cord was reduced by more than 30% of the intact area regardless of sagittal or axial types. Finally, a higher level of sagittal extension would increase the peak cord tissue stress, which would be related to the neurological dysfunction and tissue damage.
Quantitative investigation of biomechanical characteristics such as mechanical stress may provide fundamental information for pre-operative planning of treatment for ossification of the posterior longitudinal ligament.
Effect of bone fragment impact velocity on biomechanical parameters related to spinal cord injury: A finite element study
2014, Journal of Biomechanics
Several experimental and computational studies have investigated the effect of bone fragment impact on the spinal cord during trauma. However, the effect of the impact velocity of a fragment generated by a burst fracture on the stress and strain inside the spinal cord has not been computationally investigated, even though spinal canal occlusion and peak pressure at various impact velocities were provided in experimental studies. These stresses and strains are known factors related to clinical symptoms or injuries. In this study, a fluid-structure interaction model of the spinal cord, dura mater, and cerebrospinal fluid was developed and validated. The von-Mises stress distribution in the cord, the longitudinal strain, the cord compression and cross-sectional area at the impact center, and the obliteration of the cerebrospinal fluid layer were analyzed for three pellet sizes at impact velocities ranging from 1.5 m/s to 7.5 m/s. The results indicate that stress in the cord was substantially elevated when the initial impact velocity of the pellet exceeded a threshold of 4.5 m/s. Cord compression, reduction in cross-sectional area, and obliteration of the cerebrospinal fluid increased gradually as the velocity of the pellet increased, regardless of the size of the pellet. The present study provides insight into the mechanisms underlying spinal cord injury.
Biomechanical effects of spinal cord compression due to ossification of posterior longitudinal ligament and ligamentum flavum: A finite element analysis
2013, Medical Engineering and Physics
Citation Excerpt :
In the compression test for validation, deformation under 0.08 N was 1.59 mm as compared to 1.5 mm that was observed in a previous study [22]. In addition, the shape of the force–deformation curve for our model was consistent with that of a previous study [22] in which the relative differences in deformation under 0.02 N, 0.04 N, 0.06 N, and 0.08 N were 18.8%, 11.7%, 2.1%, and 6.0%, respectively, in comparison with the previous study (Fig. 3(a)). The stress–strain curve for the tensile test was located between those of the white matter and gray matter as shown previously depicting a typical nonlinear ‘J-shape’ for soft biological tissues [20] (Fig. 3(b)).
Ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF) have been recognized as causes of myelopathy due to thickening of the ligaments resulting in narrowing of the spinal canal and compression of the spinal cord. However, few studies have focused on predicting stress distribution under conditions of OPLL and OLF based on clinical aspects such as the relationship between level of stress and severity of neurologic symptoms because direct in vivo measurement of stress is very restrictive. In this study, a three-dimensional finite element model of the spinal cord in T12-L1 was developed based on MR images. The von-Mises stresses in the cord and the cross-sectional area of the cord were investigated for various grades and shapes of spinal cord compression in OPLL and OLF. Substantial increases in maximum stresses resulting in the manifestation of spinal cord symptoms occurred when the cross-sectional area was reduced by 30–40% at 60% compression of the antero-posterior diameter of the cord in OPLL and at 4 mm compression in OLF. These results indicate that compression greater than these thresholds may induce spinal symptoms, which is consistent with clinical observations.
Syringomyelia: A review of the biomechanics
2013, Journal of Fluids and Structures
Syringomyelia is a neurological disorder caused by the development of one or more macroscopic fluid-filled cavities in the spinal cord. While the aetiology remains uncertain, hydrodynamics appear to play a role. This has led to the involvement of engineers, who have modelled the system in silico and on the bench. In the process, hypotheses from the neurosurgical literature have been tested, and others generated, while aspects of the system mechanics have been clarified. The spinal cord is surrounded by cerebrospinal fluid (CSF) which is subject both to the periodic excitation of CSF expelled from the head with each heartbeat, and to intermittent larger transients from cough, sneeze, etc., via vertebral veins. The resulting pulsatile flow and pressure wave propagation, and their possible effects on cord cavities and cord stresses, have been elucidated. These engineering contributions are here reviewed for the first time.

View all citing articles on Scopus

^☆: This study was supported by the National Institute of Neurological and Communicative Disorders and Stroke under Grant RO1-NS-13238

^∗: Presently at Ebasco Services, Inc., World Trade Center, New York, NY.

^†: Department of Anesthesiology, The University of Texas Health and Science Center, San Antonio, TX.

View full text

Mechanical and neurological response of cat spinal cord under static loading☆

Abstract

Study of functional recovery produced by delayed localized cooling after spinal cord injury in primates

J Neurosurg

Surgery of experimental lesion of the spinal cord equivalent to crush injury of fracture dislocation of spinal column

JAMA

Remarks on the histopathological changes in the spinal cord due to impact

“Standardized” spinal cord trauma: biomechanical parameters and lesion volume

Surg Neurol