In vivo human cervical spinal cord deformation and displacement in flexion

Effect of sagittal alignment on spinal cord biomechanics in the stenotic cervical spine during neck flexion and extension

Spinal cord stress and strain contribute to degenerative cervical myelopathy (DCM), while cervical kyphosis is known to negatively impact surgical outcomes. In DCM, the relationship between spinal cord biomechanics, sagittal alignment, and cord compression is not well understood. Quantifying this relationship can guide surgical strategies. A previously validated three-dimensional finite element model of the human cervical spine with spinal cord was used. Three models of cervical alignment were created: lordosis (C2-C7 Cobb angle: 20°), straight (0°), and kyphosis (- 9°). C5-C6 spinal stenosis was simulated with ventral disk protrusions, reducing spinal canal diameters to 10 mm, 8 mm, and 6 mm. Spinal cord pre-stress and pre-strain due to alignment and compression were quantified. Cervical flexion and extension were simulated with a pure moment load of 2 Nm. The Von Mises stress and maximum principal strain of the whole spinal cord were calculated during neck motion and the relationship between spinal cord biomechanics, alignment, and compression was analyzed using linear regression analysis. Spinal cord pre-stress and pre-strain were greatest with kyphosis (7.53 kPa, 5.4%). Progressive kyphosis and stenosis were associated with an increase in spinal cord stress (R2 = 0.99) and strain (R2 = 0.99). Cervical kyphosis was associated with greater spinal cord stress and strain during neck flexion-extension and the magnitude of difference increased with increasing stenosis. Cervical kyphosis increases baseline spinal cord stress and strain. Incorporating sagittal alignment with compression to calculate spinal cord biomechanics is necessary to accurately quantify spinal stress and strain during neck flexion and extension.

The biomechanical implications of neck position in cervical contusion animal models of SCI

Large animal contusion models of spinal cord injury are an essential precursor to developing and evaluating treatment options for human spinal cord injury. Reducing variability in these experiments has been a recent focus as it increases the sensitivity with which treatment effects can be detected while simultaneously decreasing the number of animals required in a study. Here, we conducted a detailed review to explore if head and neck positioning in a cervical contusion model of spinal cord injury could be a factor impacting the biomechanics of a spinal cord injury, and thus, the resulting outcomes. By reviewing existing literature, we found evidence that animal head/neck positioning affects the exposed level of the spinal cord, morphology of the spinal cord, tissue mechanics and as a result the biomechanics of a cervical spinal cord injury. We posited that neck position could be a hidden factor contributing to variability. Our results indicate that neck positioning is an important factor in studying biomechanics, and that reporting these values can improve inter-study consistency and comparability and that further work needs to be done to standardize positioning for cervical spinal cord contusion injury models.

Effects of cervical rotatory manipulation on the cervical spinal cord complex with ossification of the posterior longitudinal ligament in the vertebral canal: A finite element study

Background: There are few studies focusing on biomechanism of spinal cord injury according to the ossification of the posterior longitudinal ligament (OPLL) during cervical rotatory manipulation (CRM). This study aimed to explore the biomechanical effects of CRM on the spinal cord, dura matter and nerve roots with OPLL in the cervical vertebral canal. Methods: Three validated FE models of the craniocervical spine and spinal cord complex were constructed by adding mild, moderate, and severe OPLL to the healthy FE model, respectively. We simulated the static compression of the spinal cord by OPLL and the dynamic compression during CRM in the flexion position. The stress distribution of the spinal cord complex was investigated. Results: The cervical spinal cord experienced higher von Mises stress under static compression by the severe OPLL. A higher von Mises stress was observed on the spinal cord in the moderate and severe OPLL models during CRM. The dura matter and nerve roots had a higher von Mises stress in all three models during CRM. Conclusion: The results show a high risk in performing CRM in the flexion position on patients with OPLL, in that different occupying ratios in the vertebral canal due to OPLL could significantly increase the stress on the spinal cord complex.

Spinal cord bioelectronic interfaces: opportunities in neural recording and clinical challenges

Bioelectronic stimulation of the spinal cord has demonstrated significant progress in restoration of motor function in spinal cord injury (SCI). The proximal, uninjured spinal cord presents a viable target for the recording and generation of control signals to drive targeted stimulation. Signals have been directly recorded from the spinal cord in behaving animals and correlated with limb kinematics. Advances in flexible materials, electrode impedance and signal analysis will allow SCR to be used in next-generation neuroprosthetics. In this review, we summarize the technological advances enabling progress in SCR and describe systematically the clinical challenges facing spinal cord bioelectronic interfaces and potential solutions, from device manufacture, surgical implantation to chronic effects of foreign body reaction and stress-strain mismatches between electrodes and neural tissue. Finally, we establish our vision of bi-directional closed-loop spinal cord bioelectronic bypass interfaces that enable the communication of disrupted sensory signals and restoration of motor function in SCI.

Effects of cervical rotatory manipulation on the cervical spinal cord: a finite element study

BACKGROUND

Little information is available concerning the biomechanism involved in the spinal cord injury after cervical rotatory manipulation (CRM). The primary purpose of this study was to explore the biomechanical and kinematic effects of CRM on a healthy spinal cord.

METHODS

A finite element (FE) model of the basilaris cranii, C1-C7 vertebral bodies, nerve root complex and vertebral canal contents was constructed and validated against in vivo and in vitro published data. The FE model simulated CRM in the flexion, extension and neutral positions. The stress distribution, forma and relative position of the spinal cord were observed.

RESULTS

Lower von Mises stress was observed on the spinal cord after CRM in the flexion position. The spinal cord in CRM in the flexion and neutral positions had a lower sagittal diameter and cross-sectional area. In addition, the spinal cord was anteriorly positioned after CRM in the flexion position, while the spinal cord was posteriorly positioned after CRM in the extension and neutral positions.

CONCLUSION

CRM in the flexion position is less likely to injure the spinal cord, but caution is warranted when posterior vertebral osteophytes or disc herniations exist.

Cervical disc degeneration: important considerations for the manual therapist

Cervical disc degeneration (CDD) is a progressive, age-related occurrence that is frequently associated with neck pain and radiculopathy. Consistent with the majority of published clinical practice guidelines (CPG) for neck pain, the 2017 American Physical Therapy Association Neck Pain CPG recommends cervical manipulation as an intervention to address acute, subacute, and chronic symptoms in the 'Neck Pain With Mobility Deficits' category as well for individuals with 'Chronic Neck Pain With Radiating Pain'. While CPGs are evidence-informed statements intended to help optimize care while considering the relative risks and benefits, these guidelines generally do not discuss the mechanical consequences of underlying cervical pathology nor do they recommend specific manipulation techniques, with selection left to the practitioner's discretion. From a biomechanical perspective, disc degeneration represents the loss of structural integrity/failure of the intervertebral disc. The sequelae of CDD include posterior neck pain, segmental hypermobility/instability, radicular symptoms, myelopathic disturbance, and potential vascular compromise. In this narrative review, we consider the mechanical, neurological, and vascular consequences of CDD, including information on the anatomy of the cervical disc and the mechanics of discogenic instability, the anatomic and mechanical basis of radiculitis, radiculopathy, changes to the intervertebral foramen, the importance of Modic changes, and the effect of spondylotic hypertrophy on the central spinal canal, spinal cord, and vertebral artery. The pathoanatomical and biomechanical consequences of CDD are discussed, along with suggestions which may enhance patient safety.

Cervical Canal Morphology: Effects of Neck Flexion in Normal Condition: New Elements for Biomechanical Simulations and Surgical Management

STUDY DESIGN

Continuous measurements and computation of absolute metrics of cervical subarachnoid space (CSS) and spinal cord (SC) geometries proposed are based on in vivo magnetic resonance imaging and 3D reconstruction.

OBJECTIVE

The aim of the study is to offer a new methodology to continuously characterize and to quantify the detailed morphology of the CSS and the cervical SC in 3D for healthy subjects in both neutral supine and flexion.

SUMMARY OF BACKGROUND DATA

To the best of our knowledge, no study provides a morphological quantification by absolute indices based on the 3D reconstruction of SC and CSS thanks to in vivo magnetic resonance imaging. Moreover, no study provides a continuous description of the geometries.

METHODS

Absolute indices of SC (cross-sectional area, compression ratio, position in the canal, length) and of CSS (cross-sectional area, occupational ratio, lengths) were computed by measures from 3D semi-automatic reconstructions of high resolution in vivo magnetic resonance images (3D T2-SPACE sequence) on healthy subjects (N = 11) for two postures: supine neutral and flexion neck positions. The variability induced by the semi-automatic reconstruction and by the landmarks positioning were investigated by preliminary sensitivity analyses. Inter and intra-variability were also quantified on a randomly chosen part of our population (N = 5).

RESULTS

The length and cross-sectional area of SC are significantly different (P < 0.05) in flexion compared with neutral neck position. Spinal cord stays centered in the canal for both postures. However, the cross-sectional area of CSS is submitted to low variation after C3 vertebra for both postures. Occupational ratio (OR) and compression ratio (CR) after C3 are significantly lower in flexion.

CONCLUSION

This study presented interpretations of morphological measures: (1) left-right stability (described by the Left-Right eccentricity index) ensured by the denticulate ligaments and the nerve roots attached to the dural sheaths, (2) a Poisson effect of the SC was partially notified through its axial (antero-posterior [AP] diameter, OR, CR) and its longitudinal geometrical descriptions (length of spinal cord [LSC]). Such morphological data can be useful for geometrical finite element modeling and could now be used to compare with injured or symptomatic subjects.

LEVEL OF EVIDENCE

3.

Impact of K-Line (-) in the Neck-Flexion Position on Patient-reported Outcomes After Cervical Laminoplasty For Patients With Ossification of the Posterior Longitudinal Ligament

STUDY DESIGN

This study was a post hoc analysis of prospective data.

OBJECTIVE

The objective of this study was to investigate whether K-line (-) in the neck-flexion position [f-K-line (-)] affects patient-reported outcome measures after cervical laminoplasty for patients with ossification of the posterior longitudinal ligament (OPLL).

SUMMARY OF BACKGROUND AND DATA

The f-K-line was recently proposed as a predictor of poor outcomes after laminoplasty for patients with OPLL. However, its impact on patient-reported outcome measures remains to be elucidated.

PATIENTS AND METHODS

We analyzed prospectively collected data from 68 patients with cervical myelopathy due to OPLL who underwent double-door laminoplasty between 2008 and 2015. Patients were categorized into f-K-line (-) and f-K-line (+) groups on a baseline neck-flexion radiograph. Outcome measures included the Japanese Orthopaedic Association score, EuroQol 5-Dimensional Questionnaire, the Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire, and 11-point Numerical Rating Scale for pain. The degree of satisfaction with the outcome was assessed at the 2-year follow-up using a 7-point Numerical Rating Scale.

RESULTS

Of the 68 patients, 22 (32%) and 46 (68%) were grouped into the f-K-line (-) and f-K-line (+) groups, respectively. The 2 groups showed no significant difference in baseline functions. The f-K-line (-) group showed a significantly lower recovery rate of the Japanese Orthopaedic Association score and a significantly lower gain in EuroQol 5-Dimensional Questionnaire score than compared with the f-K-line (+) group at the 2-year follow-up. Among the 5 domains of the Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire, cervical function, and upper extremity function were significantly lower in the f-K-line (-) group than in the f-K-line (+) group. Patients in the f-K-line (-) group also reported a significantly higher pain intensity in the upper and lower extremities and a significantly lower degree of satisfaction compared with those in the f-K-line (+) group.

CONCLUSION

The f-K-line (-) was significantly associated with poorer functional recovery, higher pain intensity in the extremities, and lower patient satisfaction after cervical laminoplasty for patients with OPLL.

Measurement of in vivo spinal cord displacement and strain fields of healthy and myelopathic cervical spinal cord

OBJECTIVE

Cervical myelopathy (CM) is a common and debilitating form of spinal cord injury caused by chronic compression; however, little is known about the in vivo mechanics of the healthy spinal cord during motion and how these mechanics are altered in CM. The authors sought to measure 3D in vivo spinal cord displacement and strain fields from MR images obtained during physiological motion of healthy individuals and cervical myelopathic patients.

METHODS

Nineteen study participants, 9 healthy controls and 10 CM patients, were enrolled in the study. All study participants had 3T MR images acquired of the cervical spine in neutral, flexed, and extended positions. Displacement and strain fields and corresponding principal strain were obtained from the MR images using image registration.

RESULTS

The healthy spinal cord displaces superiorly in flexion and inferiorly in extension. Principal strain is evenly distributed along the spinal cord. The CM spinal cord displaces less than the healthy cord and the magnitude of principal strain is higher, at the midcervical levels.

CONCLUSIONS

Increased spinal cord compression during cervical myelopathy limits motion of the spinal cord and increases spinal cord strain during physiological motion. Future studies are needed to investigate how treatment, such as surgical intervention, affects spinal cord mechanics.

Concussion with primary impact to the chest and the potential role of neck tension

Objectives

Most biomechanical research on brain injury focuses on direct blows to the head. There are a few older studies that indicate craniocervical stretch could be a factor in concussion by causing strain in the upper spinal cord and brainstem. The objectives of this study are to assess the biomechanical response and estimate the strain in the upper cervical spine and brainstem from primary impact to the chest in American football.

Methods

Impact testing was conducted to the chest of a stationary unhelmeted and helmeted anthropomorphic test device (ATD) as well as the laboratory reconstruction of two NFL game collisions resulting in concussion. A finite element (FE) study was also conducted to estimate the elongation of the cervical spine under tensile and flexion loading conditions.

Results

The helmeted ATD had a 40% (t=9.84, p<0.001) increase in neck tensile force and an 8% (t=7.267, p<0.001) increase in neck flexion angle when compared with an unhelmeted ATD. The case studies indicated that the neck tension in the injured players exceeded tolerable levels from volunteer studies. The neck tension was combined with flexion of the head relative to the torso. The FE analysis, combined with a spinal cord coupling ratio, estimated that the strain along the axis of the upper cervical spinal cord and brainstem was 10%–20% for the combined flexion and tension loading in the two cases presented.

Conclusion

Strain in the upper spinal cord and brainstem from neck tension is a factor in concussion.

The Transverse Isotropy of Spinal Cord White Matter Under Dynamic Load

The rostral-caudally aligned fiber-reinforced structure of spinal cord white matter (WM) gives rise to transverse isotropy in the material. Stress and strain patterns generated in the spinal cord parenchyma following spinal cord injury (SCI) are multidirectional and dependent on the mechanism of the injury. Our objective was to develop a WM constitutive model that captures the material transverse isotropy under dynamic loading. The WM mechanical behavior was extracted from the published tensile and compressive experiments. Combinations of isotropic and fiber-reinforcing models were examined in a conditional quasi-linear viscoelastic (QLV) formulation to capture the WM mechanical behavior. The effect of WM transverse isotropy on SCI model outcomes was evaluated by simulating a nonhuman primate (NHP) contusion injury experiment. A second-order reduced polynomial hyperelastic energy potential conditionally combined with a quadratic reinforcing function in a four-term Prony series QLV model best captured the WM mechanical behavior (0.89 < R2 < 0.99). WM isotropic and transversely isotropic material models combined with discrete modeling of the pia mater resulted in peak impact forces that matched the experimental outcomes. The transversely isotropic WM with discrete pia mater resulted in maximum principal strain (MPS) distributions which effectively captured the combination of ipsilateral peripheral WM sparing, ipsilateral injury and contralateral sparing, and the rostral/caudal spread of damage observed in in vivo injuries. The results suggest that the WM transverse isotropy could have an important role in correlating tissue damage with mechanical measures and explaining the directional sensitivity of the spinal cord to injury.

Mechanical and cellular processes driving cervical myelopathy

Cervical myelopathy is a well-described clinical syndrome that may evolve from a combination of etiological mechanisms. It is traditionally classified by cervical spinal cord and/or nerve root compression which varies in severity and number of levels involved. The vast array of clinical manifestations of cervical myelopathy cannot fully be explained by the simple concept that a narrowed spinal canal causes compression of the cord, local tissue ischemia, injury and neurological impairment. Despite advances in surgical technology and treatment innovations, there are limited neuro-protective treatments for cervical myelopathy, which reflects an incomplete understanding of the pathophysiological processes involved in this disease. The aim of this review is to provide a comprehensive overview of the key pathophysiological processes at play in the development of cervical myelopathy.

Volume change theory for syringomyelia: A new perspective

Background:

The etiopathogenesis of syringomyelia is still an enigma. The authors present a novel theory based on fluid dynamics at the craniovertebral (CV) junction to explain the genesis of syringomyelia (SM). The changes in volume of spinal canal, spinal cord, central canal and spinal subarachnoid space (SSS) in relation to the posterior fossa have been analysed, specifically during postural movements of flexion and extension. The effect of fluctuations in volume of spinal canal and its contents associated with cerebrospinal fluid (CSF) flow dynamics at the CV junction have been postulated to cause the origin and propagation of the syringomyelia. The relevant literature on the subject has been reviewed and the author's theory has been discussed.

Conclusion:

Volume of spinal canal in flexion is always greater than that in extension. Flexion of spine causes narrowing of the ventral subarachnoid space (SAS) and widening of dorsal SAS while extension causes reverse changes leading to fluid movement in dorsal spinal SAS in flexion and ventral spinal SAS in extension. Cervical and lumbar spinal region with maximum bulk hence maximum area and volume undergo maximum deformation during postural changes. SSS CSF is the difference between the volume of spinal canal and spinal cord, varies in flexion and extension which is compensated by changes in posterior fossa (CSF) volume in normal circumstances. Blocked SAS at foramen magnum donot permit spinal SAS CSF exchange which during postural changes is compensated by cavitatory/cystic (syrinx) change at locations in cervical and lumbar spine with propensity for maximum deformation. Augmentation of posterior fossa volume by decompression helps by normalization of this CSF exchange dynamics but immobilizing the spinal movement theoretically will cease any dynamic volume changes thereby minimizing the destructive influence of the fluid exchange on the cord. Thus, this theory strengthens the rational of treating patients by either methodology.

A flexible base electrode array for intraspinal microstimulation

In this paper, we report the development of a flexible base array of penetrating electrodes which can be used to interface with the spinal cord. A customizable and feasible fabrication protocol is described. The flexible base arrays were fabricated and implanted into surrogate cords which were elongated by 12%. The resulting strains were optically measured across the cord and compared to those associated with two types of electrodes arrays (one without a base and one with a rigid base connecting the electrodes). The deformation behavior of cords implanted with the flexible base arrays resembled the behavior of cords implanted with individual microwires that were not connected through a base. The results of the strain test were used to validate a 2-D finite element model. The validated model was used to assess the stresses induced by the electrodes of the three types of arrays on the cord, and to examine how various design parameters (thickness, base modulus, etc.,) impact the mechanical behavior of the electrode array. Rigid base arrays induced higher stresses on the cord than the flexible base arrays which in turn imposed higher stresses than the individual microwire implants. The developed flexible base array showed improvement over the rigid base array; however, its stiffness needs to be further reduced to emulate the mechanical behavior of individual microwire arrays without a base.

Development of surrogate spinal cords for the evaluation of electrode arrays used in intraspinal implants

We report the development of a surrogate spinal cord for evaluating the mechanical suitability of electrode arrays for intraspinal implants. The mechanical and interfacial properties of candidate materials (including silicone elastomers and gelatin hydrogels) for the surrogate cord were tested. The elastic modulus was characterized using dynamic mechanical analysis, and compared with values of actual human spinal cords from the literature. Forces required to indent the surrogate cords to specified depths were measured to obtain values under static conditions. Importantly, to quantify surface properties in addition to mechanical properties normally considered, interfacial frictional forces were measured by pulling a needle out of each cord at a controlled rate. The measured forces were then compared to those obtained from rat spinal cords. Formaldehyde-crosslinked gelatin, 12 wt% in water, was identified as the most suitable material for the construction of surrogate spinal cords. To demonstrate the utility of surrogate spinal cords in evaluating the behavior of various electrode arrays, cords were implanted with two types of intraspinal electrode arrays (one made of individual microwires and another of microwires anchored with a solid base), and cord deformation under elongation was evaluated. The results demonstrate that the surrogate model simulates the mechanical and interfacial properties of the spinal cord, and enables in vitro screening of intraspinal implants.

Changes in level of the conus after corrective surgery for scoliosis: MRI-based preliminary study in 31 patients

BACKGROUND

Detection of postoperative spinal cord level change can provide basic information about the spinal cord status, and electrophysiological studies regarding this point should be conducted in the future.

METHODS

To determine the changes in the spinal cord level postoperatively and the possible associated factors, we prospectively studied 31 patients with scoliosis. All the patients underwent correction and posterior fusion using pedicle screws and rods between January 2008 and March 2009. The pre- and postoperative conus medullaris levels were determined by matching the axial magnetic resonance image to the sagittal scout image. The patients were divided according to the change in the postoperative conus medullaris level. The change group was defined as the patients who showed a change of more than one divided section in the vertebral column postoperatively, and the parameters of the change and non-change groups were compared.

RESULTS

The mean pre- and postoperative Cobb's angle of the coronal curve was 76.80° ± 17.19° and 33.23° ± 14.39°, respectively. Eleven of 31 patients showed a lower conus medullaris level postoperatively. There were no differences in the pre- and postoperative magnitude of the coronal curve, lordosis and kyphosis between the groups. However, the postoperative degrees of correction of the coronal curve and lumbar lordosis were higher in the change group. There were also differences in the disease entities between the groups. A higher percentage of patients with Duchenne muscular dystrophy had a change in level compared to that of the patients with cerebral palsy (83.3% vs. 45.5%, respectively).

CONCLUSIONS

The conus medullaris level changed postoperatively in the patients with severe scoliosis. Overall, the postoperative degree of correction of the coronal curve was higher in the change group than that in the non-change group. The degrees of correction of the coronal curve and lumbar lordosis were related to the spinal cord level change after scoliosis correction.

Poisson's ratio and strain rate dependency of the constitutive behavior of spinal dura mater

Knowledge of the mechanical behavior of spinal dura mater is important for a number of applications including the experimental and computational modeling of physiological phenomena and spinal cord trauma. However, mechanical characterization of dura mater is relatively sparse and is further compounded by the use of the tangent modulus as the sole measure of stiffness. This study aims to provide a more complete description of the mechanical properties of spinal dura mater, including the effect of strain rate. Bovine dura mater was tested under uniaxial tension in both the longitudinal and the circumferential directions at three different strain rates; 0.01, 0.1, and 1.0 s(-1). An Ogden model was fitted to the resulting stress-stretch data. The morphology of the dura mater was assessed using Sirius red and H&E staining. No significant effect of the strain rate was found for the Ogden model parameters. Longitudinal specimens were significantly stronger and more deformable than circumferential samples, probably due to the structural arrangement of the collagen fibers. At low strains, however, the circumferential specimens were stiffer than the longitudinal ones. The findings of this study will allow more complete representations of the spinal dura mater to be developed.

Cervical spondylotic myelopathy associated with kyphosis or sagittal sigmoid alignment: outcome after anterior or posterior decompression

Object

The effects of sagittal kyphotic deformities or mechanical stress on the development of cervical spondylotic myelopathy, or the reduction and fusion of kyphotic sagittal alignment have not been consistently documented. The aim in this study was to determine the effects of kyphotic sagittal alignment of the cervical spine in terms of neurological morbidity and outcome after 2 types of surgical intervention.

Methods

The authors retrospectively reviewed the records of 476 patients who underwent cervical spine surgeries for spondylotic myelopathy between 1993 and 2006 at their university medical center. Among these were identified 43 patients—30 men and 13 women, with a mean age of 58.8 years—who had cervical kyphosis exceeding 10° on preoperative sagittal lateral radiographs obtained in the neutral position, and their cases were analyzed in this study. Anterior decompression with interbody fusion was conducted in 28 patients, and en bloc open-door C3–7 laminoplasty in 15 patients. Both pre- and postoperative neurological, radiographic, and MR imaging findings were assessed in both surgical groups.

Results

The mean preoperative kyphotic angle in all 43 patients was 15.9 ± 5.9° in the neutral position. Segmental instability was noted in 26 patients (61%) and reversed dynamic spinal canal stenosis at the level above the local kyphosis in 22 (51%). Preoperative T2-weighted MR images showed high-intensity signal within the cord at and around the level of maximal compression or segmental instability in 28 patients (65%). The mean kyphotic angle in both the neutral and flexion positions was significantly smaller at 4–6 weeks after surgery in the anterior spondylectomy group than in the laminoplasty group (p < 0.001). Furthermore, the angle in the neutral position was significantly smaller on follow-up in the anterior spondylectomy group than in the laminoplasty group (p = 0.034). The transverse area of the spinal cord was significantly larger in the anterior spondylectomy group than in the laminoplasty group on follow-up (p = 0.037). Preoperative neurological scores (assessed using the Japanese Orthopaedic Association scale) and improvement on follow-up ≥ 2 years after treatment (average 3.3 years) were not significantly different between the 2 groups; however, there was a significant difference in Japanese Orthopaedic Association score at 4–6 weeks postoperatively (p = 0.047).

Conclusions

Kyphotic deformity and mechanical stress in the cervical spine may play an important role in neurological dysfunction. In a select group of patients with kyphotic deformity ≥ 10°, adequate correction of local sagittal alignment may help to maximize the chance of neurological improvement.

The effect of bone fragment size and cerebrospinal fluid on spinal cord deformation during trauma: an ex vivo study

Object

The purpose of the study was to assess the effect of CSF and the size of the impacting bone fragment area on spinal cord deformation during trauma.

Methods

A transverse impact rig was used to produce repeated impacts on bovine and surrogate cord models. Tests were recorded with high-speed video and performed on specimens with and without CSF and/or dura mater and with 3 different impactor areas.

Results

The CSF layer was found to reduce the maximum cord deformation significantly. A 50% reduction in impact area significantly increased the maximum cord deformation by 20–30%. The surrogate model showed similar trends to the bovine model but with lower absolute deformation values.

Conclusions

Cerebrospinal fluid protects the cord during impact by reducing its deformation. A smaller bone fragment impact area increases the deformation of the cord, in agreement with clinical results, where a higher impact energy—possibly giving rise to smaller fragments—results in a worse neurological deficit.

Probing the influence of myelin and glia on the tensile properties of the spinal cord

Although glia have been historically classified as the structurally supporting cells of the central nervous system, their role in tissue mechanics is still largely unstudied. The influence of myelin and glia on the mechanical properties of spinal cord tissue was examined by testing embryonic day 18 chick embryo spinal cords in uniaxial tension following disruption of the glial matrix using either ethidium bromide (EB) or an antibody against galactocerebroside (alphaGalC) in the presence of complement. Demyelination was confirmed by myelin basic protein immunoreactivity and quantified using osmium tetroxide staining. A substantial loss of astrocytes and oligodendrocytes concurrent with demyelination was observed following EB injection but not alphaGalC injection. No morphological changes were observed following injection of saline or IgG with complement as controls for EB and alphaGalC. Demyelinated spinal cords demonstrated significantly lower stiffness and ultimate tensile stress than myelinated spinal cords. No significant differences were observed in the tensile response between the two demyelinating protocols. The results demonstrate that the glial matrix provides significant mechanical support to the spinal cord, and suggests that myelin and cellular coupling of axons via the glial matrix in large part dictates the tensile response of the tissue.

Relative shortening and functional tethering of spinal cord in adolescent scoliosis - Result of asynchronous neuro-osseous growth, summary of an electronic focus group debate of the IBSE

There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an on-line Delphi discussion. The Statement for this debate was written by Dr WCW Chu and colleagues who examine the spinal cord to vertebral growth interaction during adolescence in scoliosis. Using the multi-planar reconstruction technique of magnetic resonance imaging they investigated the relative length of spinal cord to vertebral column including ratios in 28 girls with AIS (mainly thoracic or double major curves) and 14 age-matched normal girls. Also evaluated were cerebellar tonsillar position, somatosensory evoked potentials (SSEPs), and clinical neurological examination. In severe AIS compared with normal controls, the vertebral column is significantly longer without detectable spinal cord lengthening. They speculate that anterior spinal column overgrowth relative to a normal length spinal cord exerts a stretching tethering force between the two ends, cranially and caudally leading to the initiation and progression of thoracic AIS. They support and develop the Roth-Porter concept of uncoupled neuro-osseous growth in the pathogenesis of AIS which now they prefer to term 'asynchronous neuro-osseous growth'. Morphological evidence about the curve apex suggests that the spinal cord is also affected, and a 'double pathology' is suggested. AIS is viewed as a disorder with a wide spectrum and a common neuroanatomical abnormality namely, a spinal cord of normal length but short relative to an abnormally lengthened anterior vertebral column. Neuroanatomical changes and/or abnormal neural function may be expressed only in severe cases. This asynchronous neuro-osseous growth concept is regarded as one component of a larger concept. The other component relates to the brain and cranium of AIS subjects because abnormalities have been found in brain (infratentorial and supratentorial) and skull (vault and base). The possible relevance of systemic melatonin-signaling pathway dysfunction, platelet calmodulin levels and putative vertebral vascular biology to the asynchronous neuro-osseous growth concept is discussed. A biomechanical model to test the spinal component of the concept is in hand. There is no published research on the biomechanical properties of the spinal cord for scoliosis specimens. Such research on normal spinal cords includes movements (kinematics), stress-strain responses to uniaxial loading, and anterior forces created by the stretched cord in forward flexion that may alter sagittal spinal shape during adolescent growth. The asynchronous neuro-osseous growth concept for the spine evokes controversy. Dr Chu and colleagues respond to five other concepts of pathogenesis for AIS and suggest that relative anterior spinal overgrowth and biomechanical growth modulation may also contribute to AIS pathogenesis.

Positional cervical spinal cord compression and fibromyalgia: a novel comorbidity with important diagnostic and treatment implications

The variable presentation and treatment response of fibromyalgia (FM) may be related to comorbidities, including positional cervical cord compression (PC3). Prevalence of PC3 among routine referrals for rheumatology consultation was assessed over 2 random months (January and February 2006) from a 4-year experience of 1100 patients. PC3 was defined as cord abutment, compression or flattening with a spinal canal diameter of <10 mm by magnetic resonance sagittal flexion, neutral, and extension images. Of 107 referrals, 53 had FM, 32 had a connective tissue disease (CTD) without FM, and 22 had chronic widespread pain (CWP) without FM criteria. The dynamic cervical spine images were obtained in 70 patients: 49 of 53 with FM, 20 of 22 with CWP and 1 of 32 with CTD, based on history and examination. Among those who received magnetic resonance imaging [MRI], 52 patients met PC3 criteria (71% of FM group [35/49], 85% of CWP group [17/20]). Two patients had a Chiari malformation (FM), 1 had multiple sclerosis (CWP), and 1 had multiple myeloma (CWP). Extension views were required for diagnosis for 37 of these 52 (71%) subjects, as well as for 8 patients who also had cervical spinal cord flattening. The pilot data suggest that further evaluation of PC3 in a controlled trial is warranted among patients with FM and CWP.

PERSPECTIVE

Fibromyalgia is complex and poorly understood. Recognition of unsuspected, comorbid cervical cord compression may provide new insight into its variable presentation, leading to novel treatment considerations. Also, dissemination of this dynamic MRI protocol may promote further study of this emerging concept of cervical cord irritation.

Surgical management of cervical myelopathy: indications and techniques for laminectomy and fusion

BACKGROUND

Cervical spondylotic myelopathy (CSM) is a commonly encountered surgical disease that may be approached through a variety of operative techniques. Operative goals in the treatment of CSM include effective neural element decompression and maintaining spinal stability to avoid delayed deformity progression and neurologic compromise. Determining the most appropriate operative approach requires careful consideration of the patient's clinical presentation and radiographic imaging.

PURPOSE

To review the indications and techniques for multilevel laminectomy and fusion in the treatment of CSM.

CONCLUSIONS

When indications permit, a multilevel laminectomy is an effective and safe method of neural element decompression. Recognizing the potential for spinal instability is essential to prevent neurologic compromise and intractable axial neck pain caused by deformity progression. A variety of techniques have been described to supplement the posterior tension band after laminectomy; however, lateral mass fixation has evolved into the preferred stabilization technique. Although clinical success is well documented, a successful outcome is dependent on a comprehensive, individualized evaluation of each patient presenting with CSM.

The length of the cervical cord: effects of postural changes in healthy volunteers using positional magnetic resonance imaging

STUDY DESIGN

The length of the cervical cord in healthy volunteers was measured in the supine and erect position using positional magnetic resonance imaging (MRI).

OBJECTIVE

To assess the relationship between the length of the cervical cord and cervical posture in healthy volunteers.

SUMMARY OF BACKGROUND DATA

A number of detailed descriptions of the normal morphologic features of the cervical cord have been published. However, to our knowledge, there is no report to compare the relationship between the length of the cervical cord and cervical posture in healthy volunteers using positional MRI.

METHODS

This study was performed on 20 healthy volunteers using positional MRI. The subjects were studied in the supine and erect positions. The recumbent series consisted of 3 positions: neutral, flexion, and extension. The erect series consisted of 3 positions: neutral, flexion, and extension. On the midsagittal image, the length of the cervical cord from C1 to C7 was measured at the anterior, middle, and posterior line. The angle of the lower-endplate of C2 and C7 was measured. The results were compared with each series.

RESULTS

In the recumbent and erect series, the mean length of the cervical cord in flexion was longer than in neutral and extension at the anterior, middle, and posterior line. There were significant differences between the length of the cervical cord in flexion, neutral, and extension. The mean length of the cervical cord in extension was shorter than in neutral and flexion at the anterior, middle, and posterior line. There were significant differences between length of the cervical cord in extension, neutral, and flexion.

CONCLUSIONS

We found posture-dependent differences of the length of the cervical cord in the recumbent and erect series. These results may be important when assessing the dynamic factor in cervical spondylotic myelopathy.

The biomechanical response of spinal cord tissue to uniaxial loading

The spinal cord is an integral component of the spinal column and is prone to physical injury during trauma or more long-term pathological insults. The development of computational models to simulate the cord-column interaction during trauma is important in developing a proper understanding of the injury mechanism. Such models would be invaluable in seeking both preventive strategies that reduce the propensity for injury and identifying specific treatment regimes. However, these developments are hampered by the limited information available on the structural and mechanical properties of this soft tissue owing to the difficulty in handling this material in a cadaveric situation. The purpose of the present paper is to report the rapid deterioration in the quality of the tissues once excised, which provides a further challenge to the successful elucidation of the structural properties of the tissue. In particular, the tangent modulus of the tissue is seen to increase sharply over a period of 72 h.

Biomechanical Aspects of the Cervical Cord: Effects of Postural Changes in Healthy Volunteers Using Positional Magnetic Resonance Imaging

STUDY DESIGN

The area in cross-sectional view of the cervical cord (ACSCC) at each disc levels was measured in supine and erect positions using positional magnetic resonance imaging (pMRI).

OBJECTIVES

To assess the relationship between ACSCC and cervical posture in healthy volunteers using pMRI.

SUMMARY OF BACKGROUND DATA

There have been few detailed descriptions of the normal morphologic features of the cervical cord. However, there is no report to compare the relationship between ACSCC and cervical posture in healthy volunteers.

METHODS

The study was performed on 20 healthy volunteers. The subjects were studied with pMRI in the supine and erect positions. The recumbent series and the erect series consist of 3 positions each: neutral, flexion and extension. On axial images, ACSCC was measured at the C2/3, C3/4, C4/5, C5/6, and C6/7 disc levels. On midsagittal image, the angle of the lower-endplate of C2 and C7 was measured. The results were compared between each series.

RESULTS

In the recumbent and erect series, ACSCC was larger in extension than in neutral and flexion at all levels. There were significant differences between ACSCC in extension, neutral and flexion. ACSCC was smaller in flexion than in neutral and extension at all levels. There were significant differences between ACSCC in flexion, neutral and extension.

CONCLUSIONS

We found posture-dependent differences of ACSCC in the recumbent and erect series. These results may be valuable for identifying a dynamic factor in patients with cervical spondylotic myelopathy.

Effect of spinal flexion on the conus medullaris: a case series using magnetic resonance imaging

Anatomy textbooks state that the conus medullaris moves cephalad when the vertebral column is flexed. This could confer protection against spinal cord damage during dural puncture, but has not been demonstrated in vivo. We therefore imaged the spine of 10 volunteers using magnetic resonance imaging to determine if such movement occurs with the spine in the neutral and flexed positions. The position of the conus medullaris in relation to the superior endplate of the L1 vertebra was determined. On spinal flexion, the conus medullaris moved cephalad in three subjects and caudad in three subjects, with no change in the remaining four. The median overall movement (95% CI [range]) was 0 mm (4 mm caudad to 1 mm cephalad [3 mm caudad to 1 mm cephalad]; p = 1.0). Whilst spinal flexion may facilitate needle insertion during dural puncture, it is unlikely to confer extra protection against spinal cord damage.

The mechanical properties of rat spinal cord in vitro

Freshly excised rat spinal cords were tested in uniaxial tension, in vitro, at strain rates ranging from 0.002 to 0.2 s-1. Stress relaxation tests were performed for a range of strains from 2% to 5%, with the relaxation behaviour being recorded for a period of at least 30 min. Samples exhibited a characteristic "J" shaped non-linear stress-strain response, with stiffness increasing with applied strain. The cords were labelled with rows of small markers and the uniaxial tension tests were recorded via video. Subsequent image analysis enabled the distribution of strain on the cord surface to be determined. Viscoelastic models were developed to model the mechanical behaviour of the specimens and were found to adequately describe the material behaviour.

Modification of stretch tolerance in a stooping position

A stooping (slump) position is believed to add tension to the nerve tissue complex. This study was designed to determine whether this position would have an effect on the stretch tolerance in a passive knee extension. Thirteen healthy individuals were tested. The knee extension was stopped by the subjects at "onset of pain". Joint range of motion and passive resistance to the extension were recorded in four test situations: upright sitting and stooping position, with the ankle joint in either the neutral or maximal dorsi-flexed position. A significant decrease in range of motion was seen when shifting from upright to stooping position: Delta angle -2.4 degrees (P<0.01). According to this, the passive tissue tension was accepted at significantly lower values in stooping position: Delta torque -1.2 N m (P<0.01). Testing with maximal dorsi-flexion of the ankle showed more pronounced changes: Delta angle -3.4 degrees (P<0.001); Delta torque -2.3 N m (P<0.001), but the effect of foot position was not significant. Knee joint range of motion was acutely diminished in a stooping position. Thus, stretch tolerance was affected by manipulation of structures, which were not directly mechanically related to this joint. An influence from the nerve tissue complex must be considered to be a factor when describing the mechanisms behind altered stretch tolerance.

MRI-based technique for determining nonuniform deformations throughout the volume of articular cartilage explants

Articular cartilage is critical to the normal function of diarthrodial joints. Despite the importance of the tissue and the prevalence of cartilage degeneration (e.g., osteoarthritis), the technology required to noninvasively describe nonuniform deformations throughout the volume of the tissue has not been available until recently. The objectives of the work reported in this paper were to 1) describe a noninvasive technique (termed the cartilage deformation by tag registration (CDTR) technique) to determine nonuniform deformations in articular cartilage explants with the use of specialized MRI tagging and image processing methods, 2) evaluate the strain error of the CDTR technique using a custom MRI-compatible phantom material, and 3) demonstrate the applicability of the CDTR technique to articular cartilage by determining 3D strain fields throughout the volume of a bovine articular cartilage explant. A custom MRI pulse sequence was designed to tag and image articular cartilage explants at 7 Tesla in undeformed and deformed states during the application of multiple load cycles. The custom pulse sequence incorporated the "delays alternating with nutations for tailored excitation" (DANTE) pulse sequence to apply tags. This was followed by a "fast spin echo" (FSE) pulse sequence to create images of the tags. The error analysis using the phantom material indicated that deformations can be determined with an error, defined as the strain precision, better than 0.83% strain. When this technique was applied to a single articular cartilage explant loaded in unconfined compression, hetereogeneous deformations throughout the volume of the tissue were evident. This technique potentially can be applied to determine normal cartilage deformations, analyze degenerated cartilage, and evaluate cartilage surgical repair and treatment methodologies. In addition, this technique may be applied to other soft tissues that can be appropriately imaged by MR.

Acute brainstem dissection of syringomyelia associated with cervical intramedullary neurinoma

Intramedullary tumors and syringomyelia typically present with slowly progressing deficits. More rarely, they are characterized by acute presentation or worsening, at times mimicking other more common etiologies. The acute onset of syringomyelia is most likely attributable to an acute increase in cerebrospinal fluid and epidural venous pressure that results in impulsive fluid movement and, ultimately, in the rupture of the syrinx and dissection into the spinal cord or brainstem. Reported here is a case of acute presentation of a small cervical intramedullary neurinoma due to the upward dissection of its associated syrinx. Critical questions are: (1) how can a small tumor produce a large syrinx? and (2) in the absence of craniospinal interferences, which mechanism underlies the acute expansion of the cavity, resulting in a rapid onset? The authors examined the pathophysiology of syrinx formation and enlargement in intramedullary tumors and reviewed the literature, emphasizing the relationship between spinal cord movements and intramedullary pressure. On the basis of current pathogenetic concepts, the authors concluded that tumor-related syringomyelia might be caused by an association of mechanisms, both from within (obstruction of perivascular spaces; increase in extracellular fluid viscosity due to the tumor itself; intramedullary pressure gradients among different cord levels and between the cord and the subarachnoid space) and from without (the cerebrospinal fluid entering the tissue). All these factors may be amplified, as in the reported case, by a tumor located dorsally at the cervical level. Abnormal postures of the spine, such as a prolonged and excessive flexed neck position, may ultimately contribute to the acute dissection of the syrinx.

In vivo measurements of human brain displacement

Finite element models are increasingly important in understanding head injury mechanisms and designing new injury prevention equipment. Although boundary conditions strongly influence model responses, only limited quantitative data are available. While experimental studies revealed some motion between brain and skull, little data exists regarding the base of the skull. Using magnetic resonance images (MRI) of the caudal brain regions, we measured in vivo, quasi-static angular displacement of the cerebellum (CB) and brainstem (BS) relative to skull, and axial displacement of BS at the foramen magnum in supine human subjects (N=5). Images were obtained in flexion (7 degrees - 54 degrees ) and neutral postures using SPAMM tagging technique (N=47 pairs). Rigid body skull rotation angle from neutral posture (theta, degrees) was determined by extracting the edge feature points of the skull, and rotating and displacing the coordinates in one image until they matched those in the other. Tissue rotation was obtained by comparing tag lines in image pairs before and after flexion, and the motion of BS and CB were expressed relative to skull rotation and displacement. During flexion, the CB rotated in the flexion direction, exceeding the skull rotation, but relative BS rotations were negligible. Meanwhile, the BS moved caudally toward the foramen magnum. With a flexion angle of 54 degrees , the 95% confidence interval for the relative CB rotation was 2.7 degrees - 4.3 degrees , and 0.8 - 1.6mm for the relative BS axial displacement. Albeit quasi-static, this study provides important data that can be implemented to create more life-like boundary conditions in human finite element models.

Effect of Acute Calcium Influx after Mechanical Stretch InjuryIn Vitroon the Viability of Hippocampal Neurons

We use a new in vitro model to examine the effect of mechanical deformation on neurons. We examined acute changes in cytosolic calcium concentrations ([Ca(2+)](i)) caused by a rapid stretch of cultured hippocampal neurons, using mechanical loading conditions that mimic brain deformations during trauma. We found that stretch-injury of neurons induces a strain-dependent increase in [Ca(2+)](i). Remarkably, the extent of this calcium response exceeded the levels initiated by chemical toxicity with NMDA (100 microM) or glutamate (5 mM) exposure. Propidium iodide labeling at 24 h following stretch showed neuronal death occurred only at the most severe level of mechanical injury. Although NMDA-induced toxicity could be inhibited in calcium free media or by treatment with MK-801, stretch-induced neuronal death was not similarly reduced with either treatment. Unexpectedly, reduction of the acute stretch-induced calcium transient with calcium-free media or MK-801 resulted in an increase in neuronal death at lower stretch levels. These data suggest that mechanical stretch can initiate calcium influx in hippocampal neurons, but substantially modulating the early calcium flux from the extracellular space or through the NMDA channel does not provide an effective means for improving neuronal survival.

Biomechanical dynamics of the heart with MRI

Magnetic resonance imaging (MRI) provides a noninvasive way to evaluate the biomechanical dynamics of the heart. MRI can provide spatially registered tomographic images of the heart in different phases of the cardiac cycle, which can be used to assess global cardiac function and regional endocardial surface motion. In addition, MRI can provide detailed information on the patterns of motion within the heart wall, permitting calculation of the evolution of regional strain and related motion variables within the wall. These show consistent patterns of spatial and temporal variation in normal subjects, which are affected by alterations of function due to disease. Although still an evolving technique, MRI shows promise as a new method for research and clinical evaluation of cardiac dynamics.

Differential Diagnosis and Management of Spinal Nerve Root-related Pain

Pain originating from spinal nerve roots demonstrates multiple pathogeneses. Distinctions in the patho-anatomy, biomechanics, and pathophysiology of spinal nerve roots contribute to pathology, diagnosis, and management of root-related pain. Root-related pain can emerge from the tension events in the dura mater and nerve tissue associated with primary disc related disorders. Conversely, secondary disc-related degeneration can produce compression on the nerve roots. This compression can result in chemical and mechanical consequences imposed on the nervous tissue within the spinal canal, lateral recess, intervertebral foramina, and extraforminal regions. Differences in root-related pathology can be observed between lumbar, thoracic, and cervical spinal levels, meriting the implementation of different diagnostic tools and management strategies.

Mechanisms of neurovascular compression within the spinal and intervertebral canals

OBJECTIVE

To describe some possible causes of encroachment on human spinal and intervertebral canal (foramen) neurovascular II structures. DATA SELECTION AND SYNTHESIS: A review of some imaging films of patients aged 38 to 52 years and some human autopsy histopathologic sections from 40- to 60-year-old cadavers to determine what structures may be responsible for neurovascular compression in individuals in this relatively young-to-middle-age group and to illustrate some examples.

RESULTS

Stenosis of the spinal and intervertebral canal neurovascular structures can be caused by various bony and soft-tissue structures. Stenosis can be related to osteophytosis of the vertebral body, uncoverte-intervertebral disc protrusion, ossification of the posterior longitudinal ligament, and ligamentum flavum hypertrophy or buckling.

DISCUSSION

Various forms of spinal and intervertebral canal stenosis can cause compression of neurovascular structures that may, in turn, be responsible for symptomatology. Of course, autopsy findings cannot be equated with painful syndromes in patients.

A review of biomechanics of the central nervous system--part II: spinal cord strains from postural loads

OBJECTIVE

To review spinal cord strains arising from postural loads.

DATA COLLECTION

A hand search of available reference texts and a computer search of literature from the Indexed Medicus sources were collected, with special emphasis placed on spinal cord strains caused by various postural rotations and translations of the skull, thorax, and pelvis

RESULTS

All spinal postures will deform the neural elements within the spinal canal. Flexion causes the largest canal length changes and, hence, the largest nervous system deformations. Neural tissue strains depend on the spinal level, the spinal movement generated, and the sequence of movements when more than one spinal area is moved.

CONCLUSIONS

Rotations of the global postural components (head, thoracic cage, pelvis, and legs) cause stresses and strains in the central nervous system and peripheral nervous system. Translations of the skull, thorax, and pelvis, as well as combined postural loads, need to be studied for their effects on the spinal canal and neural tissue deformations. Flexion of any part of the spinal column may generate axial tension in the entire cord and nerve roots. Slight extension is the preferred position of the spine as far as reducing the magnitude of mechanical stresses and strains in the central nervous system is concerned.

Nerve trunk pain: physical diagnosis and treatment

The management of peripheral neuropathic pain or nerve trunk pain relies upon accurate differential diagnosis. In part neurogenic pain has been attributed to increased activity in, as well as to abnormal processing of non-nociceptive input from, the nervi nervorum. For neurogenic pain to be identified as the dominant feature of a painful condition there should be evidence of increased nerve trunk mechanosensitivity from all aspects of the physical examination procedure. Consistent dysfunction should be identified on key active and passive movements, neural tissue provocation tests as well as nerve trunk palpation. A local cause for the neurogenic pain disorder should also be identified if the condition is to be treated by manual therapy. A treatment approach is presented which has been shown to have efficacy in the relief of pain and restoration of function in cervicobrachial pain disorders where there is evidence according to the outlined examination protocol of nerve trunk pain.