Cervical Spine Disc Deformation During In Vivo Three-Dimensional Head Movements.

P8. Correlations between sagittal plane disc dimensions and principal surface strains across the L3-4 intact IVD during in vitro multidirectional loading

Intervertebral disc (IVD) degeneration is the main cause of neck pain. Although conventional magnetic resonance imaging can detect morphological changes in intervertebral disc degeneration, it cannot provide accurate and objective evaluations. Magnetic resonance diffusion tensor imaging (DTI) reflects the microstructural changes in tissues by describing the diffusion of water molecules. It was initially applied to the evaluation of lumbar disc degeneration; however, no study has used DTI to evaluate cervical disc degeneration. To conduct a prospective study to evaluate the efficacy and feasibility of DTI in quantifying cervical disc degeneration by correlating the main parameters of axial DTI of intervertebral discs, namely fractional anisotropy (FA) and mean diffusivity (MD) values, using the Pfirrmann grade. The cervical discs of 30 symptomatic volunteers with neck pain and 20 asymptomatic volunteers were assessed using a 3.0 T magnetic resonance scanner. We evaluated intervertebral discs from C3/4 to C6/7 in each volunteer. The Pfirrmann grades, FA value, and MD value on the conventional magnetic resonance imaging were evaluated. The Kruskal-Wallis test and Wilcoxon rank-sum test were used to compare the FA and MD values of subjects with different degeneration levels. Statistical analysis showed that the FA value of the nucleus pulposus in patients group was significantly higher than that in the asymptomatic volunteers, and the MD value of the nucleus pulposus was significantly lower than that in the asymptomatic volunteers, and the difference was significant (P < 0.05). In the study group, with an increase in cervical intervertebral disc grade, the FA value of the nucleus pulposus also showed a gradual upward trend, and this difference was significant (P < 0.05). The MD value of the nucleus pulposus showed a gradual downward trend, except between grades I and II, which indicates that the axial FA value can better show the early pathological changes of the cervical intervertebral disc. The FA and MD values of the cervical intervertebral disc can quantitatively evaluate the degree of degeneration of the cervical intervertebral disc; axial DTI imaging technology can provide a good theoretical basis for the imaging diagnosis of cervical intervertebral disc degeneration and has important clinical application value.

A biomimetic artificial intervertebral disc system composed of a cubic three-dimensional fabric

Segmental motion and bone-implant interface stresses were analyzed at C5-C6 levels with Bryan, Prestige LP, and ProDisc-C cervical disc prostheses using an image-based finite element modeling technique. To predict stress patterns at the interface between prosthesis and lower vertebral end plate to better understand the underlying mechanisms of subsidence and how the load transfer pattern of each disc design affects segmental motion. Subsidence is one of the most commonly reported device-related complications in intervertebral disc arthroplasty. Although clinical outcomes have been reported regarding many types of cervical prostheses, few reports have analyzed the effects of stress from cervical artificial discs to the vertebral end plate. Three-dimensional voxel finite elements were built for C5-C6 spine unit based on computed tomography images acquired from a patient with indication for cervical disc arthroplasty. Models of facet joints and uncovertebral joints were added and artificial disc designs were placed in the intervertebral disc space. Static analyses were conducted under normal physiologic loads in flexion, extension, and lateral bending with precompression. Bryan disc recovered highest range of motion (4.75 degrees ) due to the high elastic nucleus, and therefore imposed the lowest stresses superior to C6. The ProDisc-C and Prestige LP discs caused high stress concentrations around their central fins or teeth, and may initiate bone absorption. Analysis of Prestige LP disc may indicate possible subsidence posteriorly caused by the rear-positioned metal-to-metal joint. Rigidity of the cores ("nuclei") in Prestige LP and ProDisc-C prostheses guarantee initial maintenance of disc height, but high contact stress takes place at the bone-end plate interface if they are improperly placed or undersized. Anchorage designs add an additional factor that may increase propensity of subsidence, indicated by the high contact stress occurring at the end plate flanges of Prestige LP, and at midline keel fixation on the end plate of ProDisc-C. Although Bryan disc differs in these 2 concerns, it also creates much larger displacement during motion with more variation in disc height that may theoretically increase the load sharing of facet and/or uncovertebral joints compared to more rigid artificial discs.

Uniaxial low-cycle fatigue and creep-fatigue tests have been carried out on hollow alloy 800 specimens that were filled with steam. Two testing temperatures were employed, each with its own steam condition. These temperatures and steam conditions were 650/sup 0/F with saturated steam (5% liquid, 95% vapor) and 1200/sup 0/F with superheated steam at 2200 psi. The low-cycle fatigue tests were carried out at both 650/sup 0/F and 1200/sup 0/F by cycling the strain between equal tensile and compressive magnitudes until specimen failure or until it was no longer practical to continue the test. The creep-fatigue tests were carried out to failure by cycling the strain in the same fashion as in the low-cycle fatigue tests but with holds imposed at either the peak tensile strain or the peak compressive strain or at both peak tensile and compressive strains in each loading cycle.

The biomechanical impact of facet tropism on the intervertebral disc and facet joints in the cervical spine

Normative Magnetic Resonance Imaging Data of Age-Related Degenerative Changes in Cervical Disc Morphology

The fastigial nucleus (FN) receives vestibular information predominantly from Purkinje cells of the vermis. FN in the monkey can be divided in a rostral part, related to spinal mechanisms, and a caudal part with oculomotor functions. To understand the role of FN during movements in space, single-unit activity in alert monkeys was recorded during passive three-dimensional head movements from rostral FN. Seated monkeys were rotated sinusoidally around a horizontal earth-fixed axis (vertical stimulation) at different orientations 15 degrees apart (including roll, pitch, vertical canal plane and intermediate planes). In addition, sinusoidal rotations around an earth-vertical axis (yaw stimulus) included different roll and pitch positions (+/-10 degrees, +/-20 degrees). The latter positions were also used for static stimulation. One hundred fifty-eight neurons in two monkeys were modulated during the sinusoidal vertical search stimulation. The vast majority showed a uniform response pattern: a maximum at a specific head orientation (response vector orientation) and a null response 90 degrees apart. Detailed analysis was obtained from 111 neurons. On the basis of their phase relation during dynamic stimulation and their response to static tilt, these neurons were classified as vertical semicircular canal related (n = 79, 71.2%) or otolith related (n = 25; 22.5%). Only seven neurons did not follow the usual response pattern and were classified as complex neurons. For the vertical canal-related neurons (n = 79) all eight major response vector orientations (ipsilateral or contralateral anterior canal, posterior canal, roll, and nose-down and nose-up pitch) were found in Fn on one side. Neurons with ipsilateral orientations were more numerous and on average more sensitive than those with contralateral orientations. Twenty-eight percent of the vertical canal-related neurons also responded to horizontal canal stimulation. None of the vertical canal-related neurons responded to static tilt. Otolith-related neurons (n = 25) had a phase relation close to head position and were considerably less numerous than canal-related neurons. Except for pitch, all other response vector orientations were found. Seventy percent of these neurons responding during dynamic stimulation also responded during static tilt. The sensitivity during dynamic stimulation was always higher than during static stimulation. Sixty-one percent of the otolith-related neurons responded also to horizontal canal stimulation. These results show that in FN, robust vestibular signals are abundant. Canal-related responses are much more common than otolith-related responses. Although for many canal neurons the responses can be related to single canal planes, convergence between vertical canals but also with horizontal canals is common.

Intervertebral disc (IVD) degeneration is a complex pathology, involving alterations in mechanical and biological function. Mechanical injury to IVDs may contribute to the development of IVD degeneration, and can arise following excessive loading or repeated exposure to loading levels which are not instantaneously damaging. Lateral bending and flexion produced the highest maximum shear strains in human IVDs and are considered the motions that place the IVD at greatest risk of injury (1). The biological response of the IVD to combined bending and compression has been examined in vivo in rat and mouse tail bending models demonstrating structural disruption, apoptosis and remodeling (2,4). However, there are practical limitations to current in vivo studies, as it can be difficult to apply repeated bending loads to the disc in vivo, and few large animal models exist capable of tracking the early biological, structural and compositional changes from asymmetrical loading. IVD organ culture allows control over mechanical boundary conditions and investigation of cellular responses to loading while the IVD remains largely intact, and allows the use of large animal models which more closely mimic the nutritional and compositional nature of human IVDs.

The annulus fibrosus (AF) of the intervertebral disc (IVD) consists of a set of concentric layers composed of a primary circumferential collagen fibers arranged in an alternating oblique orientation. Moreover, there exists an additional secondary set of radial translamellar collagen fibers which connects the concentric layers, creating an interconnected fiber network. The aim of this study was to investigate the mechanical role of the radial fiber network. Toward that goal, a three-dimensional (3D) finite element model of the L3-L4 spinal segment was generated and calibrated to axial compression and pure moment loading. The AF model explicitly recognizes the two heterogeneous networks of fibers. The presence of radial fibers demonstrated a pronounced effect on the local disc responses under lateral bending, flexion, and extension modes. In these modes, the radial fibers were in a tensile state in the disc region that subjected to compression. In addition, the circumferential fibers, on the opposite side of the IVD, were also under tension. The local stress in the matrix was decreased in up to 9% in the radial fibers presence. This implies an active fiber network acting collectively to reduce the stresses and strains in the AF lamellae. Moreover, a reduction of 26.6% in the matrix sideways expansion was seen in the presence of the radial fibers near the neutral bending axis of the disc. The proposed biomechanical model provided a new insight into the mechanical role of the radial collagen fibers in the AF structure. This model can assist in the design of future IVD substitutes.

In vitro experiment using bone morphogenetic protein-2 (BMP-2) and cells from the nucleus pulposus (NP), transitional zone (TZ), and anulus fibrosus (AF) of the human intervertebral disc (IVD). To demonstrate the differential effect of BMP-2 on DNA synthesis, proteoglycan synthesis, and osteocalcin mRNA expression in human IVD cells from the NP, TZ, and AF, respectively. BMP-2 has been proven to be effective in stimulating proteoglycan synthesis in articular chondrocytes and IVD cells from the NP. Nevertheless, the effect of BMP-2 on cells from different regions of the IVD has not yet been thoroughly elucidated. Human IVDs were harvested from surgical disc procedures and tissue from the NP, TZ, and AF was obtained. Disc tissue was enzymatically digested, and IVD cells were cultured three-dimensionally in alginate beads. Then IVD cell cultures from the NP, TZ, and AF were exposed to BMP-2. DNA synthesis and newly synthesized proteoglycan were measured. Reverse transcription-polymerase chain reaction for mRNA expression of bone sialoprotein, DLX5, osteocalcin, and collagen type I, was performed. Cells from the AF responded to BMP-2 with mitogenesis. There was no significant increase in DNA synthesis in cultures from the NP and TZ treated with BMP-2. Only cells from the NP showed a significant increase in newly synthesized proteoglycan in response to BMP-2. IVD cells from all zones demonstrated no significant expression of bone sialoprotein, DLX5, osteocalcin mRNA after treatment with BMP-2. BMP-2 clearly exerted a mitogenic effect on AF cells, and stimulated proteoglycan synthesis in NP cells. However, BMP-2 did not have an osteogenic effect in any IVD region. Taken together, these results confirm that BMP-2 can be used as an anabolic agent for mitogenesis in AF cells and NP cell matrix regeneration without the possibility of osteogenesis.

Cervical herniated disc tissue obtained at surgery for myelopathy and intervertebral discs from autopsy cases were examined histologically. To clarify the characteristic histology of cervical disc herniation and the processes by which herniated masses are produced. Except for nucleus pulposus or anulus fibrosus, no other disc tissue has been described histologically in the cervical spine. Twenty-one herniated cervical discs from 20 surgical cases (patients aged 37-68 years) and mid-sagittal slabs of 135 cervical discs from 41 autopsy cases (aged 20-85 years) were examined histologically. All the surgical specimens had cartilaginous endplate fragments together with nucleus pulposus or anulus fibrosus. Of the autopsy disc specimens, 61% had a horizontal cleft longer than two thirds of the anteroposterior diameter of the disc, and 49% had one or more vertical clefts extending to the cartilaginous endplate. Thirty-three percent showed separation of the cartilaginous endplate, and 15% had a herniated mass including parts of the cartilaginous endplate. These abnormal features increased with aging. The same order of decreasing frequency from horizontal cleft formation through herniation was observed in all decades. The cartilaginous endplate-type of herniation is the predominant type of herniation in the cervical spine. It results from horizontal and vertical cleft formations of the disc.

IntroductionMesenchymal stem cells (MSCs) have been proposed for the purposes of tissue engineering and repair of intervertebral disk (IVD) tissue. These cells would be induced to differentiate into cells with a disc-cell like phenotype, as an alternative treatment for against disk degeneration. One major drawback is that there currently exists no simple way to distinguish a nucleus pulposus (NP) cell from its annulus fibrosus (AF) or hyaline cartilage counterparts. In addition, immature NP cells produce similar macromolecules to those of hyaline cartilage1; therefore, it is difficult to confirm MSCs differentiation into a disk cell phenotype. Our previous studies have shown that surfaces rich in primary amines, -NH2, can influence the adhesion properties of cells.2 In this study, we created reproducible NH2-rich surfaces by low-pressure plasma polymerization of ethylene-ammonia mixture (so-called “L-PPE: N”) to test the hypothesis that selective adhesion of disk cells can be used to distinguish between an NP and an AF phenotype. This would serve as a marker to distinguish an appropriate NP, generated by tissue engineering techniques, from other cartilaginous phenotypes that may be inappropriate for function in the disc.Materials and MethodsSurface preparation L-PPE: N coatings approximately 100 nm thick were prepared as previously described.3 These deposits, which contain about 7.5% NH2, were deposited on poly(ethylene terephthalate) (PET) film in a low-pressure (L) capacitively coupled radio-frequency glow-discharge plasma reactor. However, half of the films' surfaces were masked, so as to remain uncoated, bare PET.Cell isolation and culture Adult bovine tails (2 to 3 years old) were obtained 2 hours after slaughter at a local abattoir. The IVDs were dissected from their adjacent vertebral bodies and separated into nucleus pulposus (NP) and AF. Both tissues of the AF and the NP were first weighed (wet weight) and then subjected to a pronase digestion (0.2% W/V), followed by a digestion of collagenase 1A (0.04% W/V) for NP tissue and collagenase II (0.04% W/V) for AF tissue. After isolation, the AF cells and the NP cells were separately cultured on the half-coated surfaces in DMEM high glucose, supplemented with 10% FBS and 1% penicillin/streptomycin in a concentration of 1 × 106 cells/mL. Regular polystyrene culture dishes (TCPS) were used as a control. After 4 days of culture, cells were washed with ddH20, fixed and stained with Safranin-O. Images were captured of both cell types before and after wash, using an optical microscope.ResultsAF cells adhered preferentially to the L-PPE: N-coated surface, but did not adhere to the bare part of the PET surface (Fig. 1). NP cells, however, indiscriminately adhered to both PET and L-PPE: N surfaces. Both NP and AF cells adhered to regular TCPS dishes after 4 days. After washing with ddH20, which was meant to remove any nonadherent cells, and to provide a clearer image to be captured, AF cells remained bound to L-PPE:N surfaces; however, NP cells were completely removed from both surfaces.ConclusionIn this study, we show that AF cells adhered preferentially to the substrate's portion that was L-PPE: N-coated, whereas NP cells did not manifest any preference to coated or uncoated portions. This preferential attachment to an amine-containing surface can be used to distinguish NP from AF cells; together with the production of a high GAG-to-hydroxyproline (proteoglycan-to-collagen) ratio by NP cells, it could help in identifying an NP-like phenotype.I confirm having declared any potential conflict of interest for all authors listed on this abstractYesDisclosure of InterestNone declaredMwale F, et al. European Cells and Materials 2004;8:58–64Girard-Lauriault PL, et al. Macromolecular Bioscience 2009;9:911–921Girard-Lauriault PL, et al. Plasma Processes and Polymers 2005;2:263–270

Quantifying the ranges of relative motions of the intervertebral discs and facet joints in the normal cervical spine

Magnetic Resonance Imaging of the Cervical Spine: Frequency of Degenerative Changes in the Intervertebral Disc with Relation to Age