Bony Endplate Research Articles

Preparation of Intact Bovine Tail Intervertebral Discs for Organ Culture

The intervertebral disc (IVD) is the joint of the spine connecting vertebra to vertebra. It functions to transmit loading of the spine and give flexibility to the spine. It composes of three compartments: the innermost nucleus pulposus (NP) encompassing by the annulus fibrosus (AF), and two cartilaginous endplates connecting the NP and AF to the vertebral body on both sides. Discogenic pain possibly caused by degenerative intervertebral disc disease (DDD) and disc herniations has been identified as a major problem in our modern society. To study possible mechanisms of IVD degeneration, in vitro organ culture systems with live disc cells are highly appealing. The in vitro culture of intact bovine coccygeal IVDs has advanced to a relevant model system, which allows the study of mechano-biological aspects in a well-controlled physiological and mechanical environment. Bovine tail IVDs can be obtained relatively easy in higher numbers and are very similar to the human lumbar IVDs with respect to cell density, cell population and dimensions. However, previous bovine caudal IVD harvesting techniques retaining cartilaginous endplates and bony endplates failed after 1-2 days of culture since the nutrition pathways were obviously blocked by clotted blood. IVDs are the biggest avascular organs, thus, the nutrients to the cells in the NP are solely dependent on diffusion via the capillary buds from the adjacent vertebral body. Presence of bone debris and clotted blood on the endplate surfaces can hinder nutrient diffusion into the center of the disc and compromise cell viability. Our group established a relatively quick protocol to "crack"-out the IVDs from the tail with a low risk for contamination. We are able to permeabilize the freshly-cut bony endplate surfaces by using a surgical jet lavage system, which removes the blood clots and cutting debris and very efficiently reopens the nutrition diffusion pathway to the center of the IVD. The presence of growth plates on both sides of the vertebral bone has to be avoided and to be removed prior to culture. In this video, we outline the crucial steps during preparation and demonstrate the key to a successful organ culture maintaining high cell viability for 14 days under free swelling culture. The culture time could be extended when appropriate mechanical environment can be maintained by using mechanical loading bioreactor. The technique demonstrated here can be extended to other animal species such as porcine, ovine and leporine caudal and lumbar IVD isolation.

Preparation of Intact Bovine Tail Intervertebral Discs for Organ Culture

The intervertebral disc (IVD) is the joint of the spine connecting vertebra to vertebra. It functions to transmit loading of the spine and give flexibility to the spine. It composes of three compartments: the innermost nucleus pulposus (NP) encompassing by the annulus fibrosus (AF), and two cartilaginous endplates connecting the NP and AF to the vertebral body on both sides. Discogenic pain possibly caused by degenerative intervertebral disc disease (DDD) and disc herniations has been identified as a major problem in our modern society. To study possible mechanisms of IVD degeneration, in vitro organ culture systems with live disc cells are highly appealing. The in vitro culture of intact bovine coccygeal IVDs has advanced to a relevant model system, which allows the study of mechano-biological aspects in a well-controlled physiological and mechanical environment. Bovine tail IVDs can be obtained relatively easy in higher numbers and are very similar to the human lumbar IVDs with respect to cell density, cell population and dimensions. However, previous bovine caudal IVD harvesting techniques retaining cartilaginous endplates and bony endplates failed after 1-2 days of culture since the nutrition pathways were obviously blocked by clotted blood. IVDs are the biggest avascular organs, thus, the nutrients to the cells in the NP are solely dependent on diffusion via the capillary buds from the adjacent vertebral body. Presence of bone debris and clotted blood on the endplate surfaces can hinder nutrient diffusion into the center of the disc and compromise cell viability. Our group established a relatively quick protocol to "crack"-out the IVDs from the tail with a low risk for contamination. We are able to permeabilize the freshly-cut bony endplate surfaces by using a surgical jet lavage system, which removes the blood clots and cutting debris and very efficiently reopens the nutrition diffusion pathway to the center of the IVD. The presence of growth plates on both sides of the vertebral bone has to be avoided and to be removed prior to culture. In this video, we outline the crucial steps during preparation and demonstrate the key to a successful organ culture maintaining high cell viability for 14 days under free swelling culture. The culture time could be extended when appropriate mechanical environment can be maintained by using mechanical loading bioreactor. The technique demonstrated here can be extended to other animal species such as porcine, ovine and leporine caudal and lumbar IVD isolation.

Postoperative Imaging of Spinal Disk Arthroplasty Devices

Cervical and lumbar arthroplasty is being increasingly used over the past decade for the management of degenerative spinal disease with multiple varied devices available worldwide. As more experience is obtained with the devices currently available, the need for postoperative imaging has heightened. Plain x-rays are still useful for the assessment of device positioning, determination of range of motion, and to rule out potential device migration. Computed tomography scanning can be combined with this, but incorporation of newer devices into bony endplates is difficult to visualize. In cases where neural structures need to be assessed at operated or adjacent levels, magnetic resonance (MR) scanning is suitable in most titanium-based or nonmetallic devices but produces significant artifact in cobalt-chromium alloy-based devices. In this latter group, computed tomography myelography, which is more invasive than MR scanning, will need to be used. In time, it would be envisioned that nonmetallic devices made of plastics should allow for acceptable postoperative MR imaging. As our experience with the devices and their imaging increases, these recommendations may change; however, material properties play a greater role in the decision making of type of modality used for postoperative imaging in scenarios where interbody fusion is performed.

The Effects of Age, Sex, Ethnicity, and Spinal Level on the Rate of Intervertebral Disc Degeneration

A gross anatomic and magnetic resonance imaging study of intervertebral disc (IVD) degeneration in fresh cadaveric lumbar spines. The purpose of this study was to find the rate of IVD degeneration. Age, sex, race, and lumbar level are among some of the factors that play a role in IVD degeneration. The rate at which IVDs degenerate is unknown. Complete lumbar spine segments (T11/T12 to S1) were received within 24 hours of death. The nucleus pulposus, anulus fibrosus, cartilaginous and bony endplate, and the peripheral vertebral body were assessed with magnetic resonance imaging and IVD degeneration was graded by two observers from grade 1 (nondegenerated) to grade 5 (severely degenerated) on the basis of a scale developed by Tanaka et al. The specimens were then sectioned and gross anatomic evaluation was performed according to Thompson et al. RESULTS.: A total of 433 donors and 1712 IVDs were analyzed. There were 366 whites, 47 Africans, 16 Hispanics, 4 Asian. There were 306 male and 127 female donors. The age range was 14 to 81 years, (average: 60.5 ± 11.3). For donors greater than age 40, the L5/S1 IVD degenerated at a significantly faster rate of 0.043 per year compared to 0.031, 0.034, 0.033, 0.027 for L1/L2, L2/L3, L3/L4, L4/L5, respectively. For donors younger than 40, L5/S1 IVD degenerated at a significantly faster rate of 0.141/y compared to 0.033, 0.021, 0.031, 0.050 for L1/L2, L2/L3, L3/L4, L4/L5, respectively. Multiple regression analysis revealed that sex had no significant effect on IVD degeneration whereas African ethnicity was associated with lower Thompson score at L1/L2, L2/L3, L3/L4, L4/L5 when compared with whites. The relatively early degeneration at L5-S1 in all races and lower Thompson grade in donors of African ethnicity needs further investigation. Factors such as sagittal alignment, facet joint arthritis, and genetics potentially play a role in IVD degeneration.

In silico evaluation of a new composite disc substitute with a L3–L5 lumbar spine finite element model

When the intervertebral disc is removed to relieve chronic pain, subsequent segment stabilization should restore the functional mechanics of the native disc. Because of partially constrained motions and the lack of intrinsic rotational stiffness ball-on-socket implants present many disadvantages. Composite disc substitutes mimicking healthy disc structures should be able to assume the role expected for a disc substitute with fewer restrictions than ball-on-socket implants. A biomimetic composite disc prototype including artificial nucleus fibre-reinforced annulus and endplates was modelled as an L4-L5 disc substitute within a L3-L5 lumbar spine finite element model. Different device updates, i.e. changes of material properties fibre distributions and volume fractions and nucleus placements were proposed. Load- and displacement-controlled rotations were simulated with and without body weight applied. The original prototype reduced greatly the flexibility of the treated segment with significant adjacent level effects under displacement-controlled or hybrid rotations. Device updates allowed restoring large part of the global axial and sagittal rotational flexibility predicted with the intact model. Material properties played a major role, but some other updates were identified to potentially tune the device behaviour against specific motions. All device versions altered the coupled intersegmental shear deformations affecting facet joint contact through contact area displacements. Loads in the bony endplates adjacent to the implants increased as the implant stiffness decreased but did not appear to be a strong limitation for the implant biomechanical and mechanobiological functionality. In conclusion, numerical results given by biomimetic composite disc substitutes were encouraging with greater potential than that offered by ball-on-socket implants.

Biomechanical comparison of the end plate design of three vertebral body replacement systems

Compression fractures at the thoracolumbar junction are frequently treated by reconstruction with vertebral body replacement systems. Modern cage implants have been developed which respect the anatomy and angulation of the adjacent bony endplates. The objective of this study was to investigate the biomechanical performance of anatomic endplate design and variable endplate angulation. Three cage systems [Hydrolift (HYL), Aesculap; Synex II (SYN), Synthes; Obelisc (OBC), Ulrich] were compared employing a composite bone substitute material at two levels of endplate angulation (0°, 3°). Their load-bearing capacity was assessed in a physiologic test with human vertebral specimens in a misalignment situation (3°). The HYL and SYN offered anatomically shaped endplates. The endplates of the HYL had variable angulation during insertion and were then mechanically fixated. The OBC had fixed and circular endplates. The load to failure and system stiffness were evaluated by an axial compression test. The bone mineral density (BMD) and the area of the bony endplates were measured via CT. None of the mechanical properties differed between 0° and 3° for the HYL cage using bone substitute material, while the OBC lost 19% of the failure load (p = 0.001) and 55% of stiffness (p = 0.001) in case of misalignment. In human bone specimens, failure loads were comparable among all implants (p > 0.1) with the HYL showing the largest system stiffness (p < 0.05). Furthermore, a strong correlation between stiffness and BMD (R(2) = 0.82) and failure load and BMD (R(2) = 0.87) was found. Anatomically shaped and continuously variable endplates provide mechanical advantages under imperfect alignment and may thus reduce secondary dislocation and the loss of correction. This is achieved by retaining an optimal contact area between the implant and the bony endplates. Conventional cage design with circular endplates offer adequate stability in optimal contact situations.

Development of an intact intervertebral disc organ culture system in which degeneration can be induced as a prelude to studying repair potential

The present work describes a novel bovine disc organ culture system with long-term maintenance of cell viability, in which degenerative changes can be induced as a prelude to studying repair. Discs were isolated with three different techniques: without endplates (NEP), with bony endplates (BEP) and with intact cartilage endplates (CEP). Swelling, deformation, and cell viability were evaluated in unloaded cultures. Degeneration was induced by a single trypsin injection into the center of the disc and the effect on cell viability and matrix degradation was followed. Trypsin-treated discs were exposed to TGFβ to evaluate the potential to study repair in this system. NEP isolated discs showed >75% maintained cell viability for up to 10days but were severely deformed, BEP discs on the other hand maintained morphology but failed to retain cell viability having only 27% viable cells after 10days. In CEP discs, both cell viability and morphology were maintained for at least 4weeks where >75% of the cells were still viable. To mimic proteoglycan loss during disc degeneration, a single trypsin injection was administered to the center of the disc. This resulted in 60% loss of aggrecan, after 7days, without affecting cell viability. When TGFβ was injected to validate that the system can be used to study a repair response following injection of a bio-active substance, proteoglycan synthesis nearly doubled compared to baseline synthesis. Trypsin-treated bovine CEP discs therefore provide a model system for studying repair of the degenerate disc, as morphology, cell viability and responsiveness to bio-active substances were maintained.

Micro-CT quantification of subchondral endplate changes in intervertebral disc degeneration

The intervertebral disc (IVD) is dependent on nutrient provision through a cartilage layer with underlying subchondral bone, analogous to joint cartilage. In the joint, subchondral bone remodeling has been associated with osteoarthritis (OA) progression due to compromised nutrient and gas diffusion and reduced structural support of the overlaying cartilage. However, subchondral bone changes in IVD degeneration have never been quantified before. The aim of this study is to determine the subchondral bone changes at different stages of IVD degeneration by micro-CT. Twenty-seven IVDs including the adjacent vertebral endplates were obtained at autopsy. Midsagittal slices, graded according the Thompson score, were scanned. Per scan 12 standardized cylindrical volumes of interest (VOI) were selected. Six VOIs contained the bony endplate and trabeculae (endplate VOIs) and six accompanying VOIs only contained trabecular bone (vertebral VOIs). Bone volume as percentage of the total volume (BV/TV) of the VOI, trabecular thickness (TrTh) and connectivity density (CD) were determined. An increase in BV/TV and TrTh was found in endplate VOIs of IVDs with higher Thompson score whereas these values remained stable or decreased in the vertebral VOIs. The increase in bone volume combined with the increase in TrTh in endplate VOIs strongly suggest that the subchondral endplate condenses to a more dense structure in degenerated IVDs. This may negatively influence the diffusion and nutrition of the IVD. The endplate differences between intact and mild degenerative IVDs (grade II) indicate an early association of subchondral endplate changes with IVD degeneration.

Development of a whole disc organ culture system to study human intervertebral disc

Study type: Basic scienceObjective: Low back pain is one of the most common health problems1 and is strongly associated with intervertebral disc degeneration, (IVD). Current treatments remove the symptoms without reversing or even retarding the underlying problem. Development of new therapy for the regeneration of the degenerative IVD is complicated by the lack of a validated long-term organ culture model in which therapeutic candidates can be studied. The object of this study was to develop, optimize, and validate an organ culture model for human IVD, allowing for the study of degeneration and the potential for regeneration of the human IVD.Methods: From eleven donors, an average of 5–6 IVDs were obtained. Inclusion criteria were; age between 50 and 70 years old, no history of cancer, chemotherapy, diabetes, or liver cirrhosis. An x-ray of the harvested spine was done to assess the grade of degeneration. Three different methods for isolating the discs were studied: with bony endplate (BEP), without endplate (NEP), and with cartilage endplate (CEP). Discs were cultured for 4 weeks without external load, in Dulbecco's modified eagle media with glucose and fetal bovine serum (FBS). Four different combinations of concentrations of glucose and FBS were compared: low glucose-low FBS, low glucose-high FBS, high glucose-low FBS, and high glucose-high FBS.2 Short-term cultures (1 week) were performed to compare the cell viability of the three methods of isolating the discs. Swelling potential on NEP and CEP discs from the same donor were evaluated. After four weeks of culture, a 4 mm punch was taken from CEP discs and cell viability was evaluated using a live/dead assay with confocal microscopy.Results: Analyzing the potential of swelling in CEP discs, there was an increase in volume to a maximum of 25% and retention of shape and morphology. Whereas in NEP discs, there was an excessive deformation and a two-fold time increase in volume than CEP discs. The cell viability in short-term cultures is around 40%–50% in the BEP model, 50%–60% in the NEP model and > 96% in the CEP model. BEP isolated discs show endplate necrosis that begins after 4 days of culture. Cell viability in CEP discs was evaluated at 4 weeks in three different areas of the disc: nucleus pulposus, inner annulus fibrosus, and outer annulus fibrosus. We found no difference in live cells (> 96%) between the four different concentrations of FBS and glucose (Table 1).Table 1Cell visibility after 4 weeks of organ culture under different glucose and FBS* concentrationsCulture ConditionNP (%) viabilityiAF (%) viabilityoAF (%) viabilityCell visibility after four weeks of organ culture under different glucose and FBS concentrations*FBS = Fetal bovine serumHIGH GLUCOSE + HIGH FBS98.44 ± 1.6097.42 ± 2.7598.06 ± 3.58HIGH GLUCOSE + LOW FBS97.61 ± 1.5897.37 ± 0.9396.05 ± 2.75LOW GLUCOSE + LOW FBS97.18 ± 1.2297.81 ± 0.6896.23 ± 2.51LOW GLUCOSE + HIGH FBS96.38 ± 2.4897.10 ± 1.8597.19 ± 1.95Conclusions: We have developed a novel method to isolate human IVDs and optimized the culture conditions. The CEP method has been proven to be superior to the previous models (NEP and BEP) in cell viability and maintaining physiologic swelling.3 In the long-term cultures, the CEP system maintained sufficient nutrient supply and high cell survival in all regions of the discs even with low concentrations of FBS and glucose. The availability of an intact disc organ culture system has a considerable advantage over the culture of isolated disc cells, as it maintains the cells in their unique microenvironment, making any response to catabolic or anabolic agents more physiologically relevant.

Comparison of SpineJet™ XL and Conventional Instrumentation for Disk Space Preparation in Unilateral Transforaminal Lumbar Interbody Fusion

Although unilateral transforaminal lumbar interbody fusion (TLIF) is widely used because of its benefits, it does have some technical limitations. Removal of disk material and endplate cartilage is difficult, but essential, for proper fusion in unilateral surgery, leading to debate regarding the surgery's limitations in removing the disk material on the contralateral side. Therefore, authors have conducted a randomized, comparative cadaver study in order to evaluate the efficiency of the surgery when using conventional instruments in the preparation of the disk space and when using the recently developed high-pressure water jet system, SpineJet XL. Two spine surgeons performed diskectomies and disk preparations for TLIF in 20 lumbar disks. All cadaver/surgeon/level allocations for preparation using the SpineJet XL (HydroCision Inc., Boston, MA, USA) or conventional tools were randomized. All assessments were performed by an independent spine surgeon who was unaware of the randomizations. The authors measured the areas (cm(2)) and calculated the proportion (%) of the disk surfaces. The duration of the disk preparation and number of instrument insertions and withdrawals required to complete the disk preparation were recorded for all procedures. The proportion of the area of removed disk tissue versus that of potentially removable disk tissue, the proportion of the area of removed endplate cartilage, and the area of removed disk tissue in the contralateral posterior portion showed 74.5 +/- 17.2%, 18.5 +/- 12.03%, and 67.55 +/- 16.10%, respectively, when the SpineJet XL was used, and 52.6 +/- 16.9%, 22.8 +/- 17.84%, and 51.64 +/- 19.63%, respectively, when conventional instrumentations were used. The results also showed that when the SpineJet XL was used, the proportion of the area of removed disk tissue versus that of potentially removable disk tissue and the area of removed disk tissue in the contralateral posterior portion were statistically significantly high (p < 0.001, p < 0.05, respectively). Also, compared to conventional instrumentations, the duration required to complete disk space preparation was shorter, and the frequency of instrument use and the numbers of insertions/withdrawals were lower when the SpineJet XL was used. The present study demonstrates that hydrosurgery using the SpineJet XL unit allows for the preparation of a greater portion of disk space and that it is less traumatic and allows for more precise endplate preparation without damage to the bony endplate. Furthermore, the SpineJet XL appears to provide tangible benefits in terms of disk space preparation for graft placement, particularly when using the unilateral TLIF approach.

Pro-inflammatory, Pleiotropic, and Anti-inflammatory TNF-α, IL-6, and IL-10 in Experimental Porcine Intervertebral Disk Degeneration

The aim of this study was to check the balance between tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-10 (IL-10) in well-developed end-stage disk disease in the disk itself as well as in paradiskal spine. In 6 domestic pigs the cranial bony end plate of the L4 vertebra was perforated to the nucleus pulposus. At 3 months the degenerated experimental and contiguous control disks, together with the adjoining bony and cartilaginous vertebral end plates, bone marrow, and spinal ligaments, were excised and used for immunohistochemical analysis. In general, there were more TNF-alpha and in particular IL-10 positive cells in the degenerated disks than in the control disks, whereas the number of IL-6 labeled cells did not differ among sites or between control and experimental intervertebral disks. These results suggest that TNF-alpha and IL-10 are involved in the late reparatory phases of the experimental disk lesion. Use of an experimental model showed that strictly disk-directed manipulation and degeneration are also reflected in the contiguous vertebrae, including adjoining cartilage, bone, marrow, and ligaments.

The implications of stress patterns in the vertebral body under axial support of an artificial implant

Clinical studies show an association between changed load patterns both in the disc and its adjacent vertebral body, with painful degenerated discs. This suggests that failure to restore the normal loading pattern on implantation of a disc replacement could be a cause of lower clinical success rate. In the present study the variations of load patterns in the vertebra after disc implantation was studied using a simplified finite element models of natural and artificial discs. The effect of implant size and presence of voids at the implant–bony endplate interface were studied, for the worst case scenario of no bone remodelling. An altered stress pattern was observed in the vertebrae of implanted segments. The use of smaller size implants and presence of voids at the interface caused localized stress concentration in the endplate and adjacent cancellous bone. The study results support the hypothesis that current implants fail to restore normal loading patterns in the vertebral body, and the localized high stress regions could be the source of pain, and the cause of low success rate of TDRs.

Dependency of disc degeneration on shear and tensile strains between annular fiber layers for complex loads

Background One of the first signs of disc degeneration is the formation of circumferential tears within the annulus fibrosus. It is assumed that high shear and tensile strains between the lamellae mainly cause the initiation of these failures. However, it is not known which load application and which degree of disc degeneration could lead to the highest strains and therefore, might induce the formation of tears. Therefore, the aim of this finite element (FE) study was, to find load combinations that would yield highest shear and tensile strains in differently degenerated discs. Materials and methods A three-dimensional FE-model of a motion segment L4-5 was utilized in different degrees of disc degeneration (healthy, mild, moderate, and severe). The degenerated models consider the reduction of disc height, endplate curvatures, the osteophyte formation, the increase of nucleus compressibility, and the decrease of fiber and ligament stiffness. An axial compression load of 500 N together with moments of 7.5 Nm in single and combined load directions were simulated. Results High strains for the healthy and degenerated discs were predicted for load combinations, particularly for the combination of lateral bending plus flexion or extension. The maximum strains were located in the postero-lateral region of the disc. In comparison to the healthy disc, the maximum strains increased slightly for the mildly and moderately degenerated disc. Strains decreased strongly for the severely degenerated disc. With progressive degeneration, the size of the region of maximum strains diminished and the location transferred from the inner annulus to the adjacent bony endplates. Conclusions The results could be a possible explanation for the initiation of circumferential tears. The mildly degenerated disc model, which represents early stages of life, suggests that circumferential tears could primarily occur at these stages, especially for the load combinations of lateral bending plus axial rotation and lateral bending plus flexion.

Clinical Results of Posterior Lumbar Interbody Fusion Using Titanium Intervertebral Spacers in Elderly Patients over 70 Years

Study Design : Retrospective study. Objective : To report the clinical and radiological results of posterior lumbar interbody fusion (PLIF) using titanium intervertebral spacers in elderly patients over 70 years. Summary of Background Data : PLIF with intervertebral spacers has been introduced to treat degenerative lumbar disorders. However, in the elderly patients, it is concerned that there are several possible complications that can be associated with the use of interbody support in anterior column reconstruction under weak bone quality. There were few reports about the results of PLIF using titanium intervertebral spacers in elderly patients. Methods : Twenty-six patients with mean age of 73 years (range, 70-78) underwent one or two-level PLIF using titanium intervertebral blocks combined with posterior instrumentation, with minimum 2-year follow-up (average 49 months ; range, 25-88). Radiographic and clinical outcomes analysis was performed. Results : The sagittal alignment (regional lordosis) of the operative segments averaged 7.4° before surgery, 12.7° at discharge, 11.1° post-op 1-year, and 11.8° at the final follow-up. The percentage of posterior disc height was 14.1% before surgery, and was significantly improved after the surgery to 26.9% at discharge and 21.8% at the final follow-up. In 18 patients with spondylolisthesis, the percentage of slip averaged 18.9% before surgery, and was significantly improved after the surgery to 6.8% at discharge and maintained until the final follow-up. All patients had radiographic fusion at the follow-up. The average JOA score was 12.6 points before surgery, and increased significantly to 23.1 points at the final follow-up. Conclusion : Posterior lumbar interbody fusion using titanium spacers is valuable even in the elderly patients. The preservation of bony endplate of vertebral body, and the insertion of spacers as antero-lateraly as possible in the intervertebral space, are important for successful fusion.

Herniated and spondylotic intervertebral discs of the human cervical spine: histological and immunohistological findings in 500 en bloc surgical samples

In this paper the authors' goal was to identify histological and immunohistochemical differences between cervical disc hemrniation and spondylosis. A total of 500 cervical intervertebral discs were excised from 364 patients: 198 patients with disc herniation and 166 patients with spondylosis. We examined en bloc samples of endplate-ligament-disc complexes. Types of herniation and graded degrees of disc degeneration on MR images were examined histologically and immunohistochemically. The herniated discs showed granulation tissue, newly developed blood vessels, and massive infiltration of CD68-positive macrophages, which surrounded the herniated tissue mainly in the ruptured outer layer of the anulus fibrosus. The vascular invasion was most significant in uncontained (extruded)-type herniated discs. Chondrocytes positive for matrix metalloproteinase (MMP)-3, tumor necrosis factor (TNF)-alpha, basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) were abundant in both herniated and spondylotic discs. Free nerve fibers, positive for nerve growth factor (NGF), neurofilament 68, growth-associated protein (GAP)-43, and substance P, were strongly apparent in and around the outer layer of uncontained (extruded)-type herniated discs, with enhanced expression of NGF. The authors observed that herniated discs showed more advanced degeneration in the outer layer of the anulus fibrosus around the granulation tissue than spondylotic discs. On the other hand, spondylotic discs showed more advanced degeneration in the cartilaginous endplate and inner layer of the anulus fibrosus than herniated discs. Spondylotic discs also had thicker bony endplates and expressed TNFalpha and MMP-3 more diffusely than herniated discs, especially in the inner layer of the anulus fibrosus. The authors' results indicate that herniated and spondylotic intervertebral discs undergo different degenerative processes. It is likely that TNFa, MMP-3, bFGF, and VEGF expression is upregulated via the herniated mass in the herniated intervertebral discs, but by nutritional impairment in the spondylotic discs. Macrophage accumulation around newly formed blood vessels in the herniated disc tissues seemed to be regulated by MMP-3 and TNFalpha expression, and both herniated and spondylotic discs exhibited marked neoangiogenesis associated with increased bFGF and VEGF expression. Nerve fibers were associated with NGF overexpression in the outer layer of the anulus fibrosus as well as in endothelial cells of the small blood vessels.

Tissue engineered intervertebral disc repair in the pig using injectable polymers

The intervertebral disc (IVD) has a central nucleus pulposus (NP) able to resist compressive loads and an outer annulus fibrosus which withstands tension and gives mechanical strength. The tissue engineering of a disc substitute represents a challenge from mechanical and biological (nutrition and transport) points of view. Two hyaluronan-derived polymeric substitute materials, HYAFF 120, an ester and HYADD 3, an amide were injected into the NP of the lumbar spine of female pigs (11.1 +/- 1.0 Kg) in which a nucleotomy had also been performed. Homologous bone marrow stem cells, obtained from the bone marrow three weeks before spinal surgery, were included in the HYADD 3 material (1x 10(6) cells/ml). Two lumbar discs were operated in each animal. Control discs received a nucleotomy only. The animals were killed after 6 weeks and the lumbar spines recovered for histopathological study. Nucleotomy resulted in loss of normal IVD structure with narrowing, fibrous tissue replacement and disruption of the bony end-plates (4/4). By contrast, both HYAFF 120 (4/4) and HYADD 3 (4/4) treatment prevented this change. The injected discs had a central NP-like region which had a close similarity to the normal biconvex structure and contained viable chondrocytes forming matrix like that of normal disc.

Compressive loading at the end plate directly regulates flow and deformation of the basivertebral vein: an analytical study

BackgroundMetastatic diseases and infections frequently involve the spine. This is the result of seeding of the vertebral body by tumor cells or bacteria delivered by venous blood from Batson's plexus, which is hypothesized to enter the vertebral body via the epidural veins. Isolated spinal segments deform significantly at the bony end plate when under compression. This deformation could cause a volume change of the vertebral body and may be accompanied by retrograde flow of venous blood. To date, this process has not been investigated quantitatively. The purpose of this study was to determine the volume changes of the vertebral body and basivertebral vein for a vertebral body under compression.MethodsA three-dimensional finite element mesh model of the L4 segment with both adjacent discs was modified from a 3-D computed tomography scan image. An octagon representing the basivertebral vein was introduced into the center of the vertebral body in the model. Four compressive orientations (1500 N) were applied on the top disc. The volume change of the vertebral body model and the basivertebral vein were then computed.ResultsThe volume change of the vertebral body was about 0.1 cm3 (16.3% of the basivertebral vein) for the four loading conditions. The maximum cross-sectional area reductions of the basivertebral vein and volume reduction were 1.54% and 1.02%, for uniform compression.ConclusionOur study quantified the small but significant volume change of a modeled vertebral body and cross-sectional areas and that of the basivertebral vein, due to the inward bulging of the end plate under compression. This volume change could initiate the reverse flow of blood from the epidural venous system and cause seeding of tumors or bacterial cells.

Disc Replacement: Postoperative Imaging

Cervical arthroplasty is being increasingly used for the management of degenerative spinal disease. As more experience is obtained with the devices currently available, the need for postoperative imaging has heightened. Plain X-rays are still useful for the assessment of device positioning and range of motion and to rule out potential device migration. CT scanning can be combined with this but incorporation of newer devices into bony endplates is difficult to visualize. In cases where neural structures need to be assessed at operated or adjacent levels MR scanning is suitable in most titanium-based devices but produces significant artifact in cobalt-chromium alloy-based devices. In this latter group CT myelography, more invasive than MR scanning, will need to be utilized. As our experience with the devices and their imaging increases, these recommendations may change but material properties play a greater role in the decision-making of type of modality used for postoperative imaging in scenarios where interbody fusion is performed.

Coblation of spinal endplates in preparation for interbody spinal fusion

Posterior lumbar interbody fusion (PLIF) and anterior lumbar interbody fusion (ALIF) have become routine alternatives to intertransverse process fusion. The use of Coblation ® (ArthroCare Corporation, Sunnyvale, CA) allows for routine and reproducible removal of cartilaginous endplate down to the bony endplate. Our experience with this new technology is reviewed. The authors used Coblation ® to prepare endplates of 10 consecutive patients undergoing interbody fusion. The results were compared to the following 10 consecutive patients undergoing interbody fusion with endplates prepared in the standard fashion with curettes and rongeurs. The same interbody grafts and instrumentation were used in all patients. Follow-up X-rays were done at 1 week, 6 weeks, 6 months, 1 year, and then each year thereafter. The 20 patients were reviewed along with their films. In each patient the disk spaces and the ALIF/PLIF cages appeared to be fused by 6 months. There was one superficial wound infection in each group. In each of the cases in which PLIF was performed, the cages were augmented by posterior lateral graft and pedicle screw fixation. All patients in both groups reported improvement in pain and/or neurologic symptoms by 6 months. The patients were followed for 4.6 years in the Coblation ® group and 4.1 years in the standard group. Disk space height was measured in all patients at 6 months. In the Coblation ® group, average disk space height was 9.0 mm compared to 8.2 mm in the standard group ( p < 0.1). We feel that the maintenance of normal structures within the lumbar spine with anterior/posterior lumbar interbody fusions and non-mechanical means of preparing the endplates are advantageous. Clearly, the number of patients involved and the length of follow-up limit this study, but it serves as an early indicator that endplate preparation may play a role in graft subsidence and fusion rates. Additional study is warranted.

A theoretical study of the distribution of insulin-like growth factor in human articular cartilage

We present a mathematical simulation which integrates the mechanisms that are currently believed to govern the concentration of the growth factor, IGF1, in cartilage. Articular cartilage is treated as a two-layer continuum: a thin surface layer, exposed to synovial fluid, with a higher cell density, and a deeper layer with impermeable bony endplate. A system of differential equations accounts for diffusion of IGF1 from synovial fluid into, and throughout, the cartilage; IGF1 synthesis, its reactions with soluble binding protein, with cell receptors, and with immobile binding sites on the extracellular matrix. We have collected all available physiologic data relevant to the solution of these equations and used it to compute numerical solutions that yield time dependent profiles for free and complex IGF1 throughout the depth of normal cartilage. Equations for osteoarthritic cartilage were formulated as well. Numerical results indicate a time-scale of several days for IGF1 profiles to settle down after a disturbance. The number of cell receptors for IGF1 appears to be more important than their rate of internalization. There is a lower bound to the number of cell receptors and of immobile binding sites. Parameters that await experimental determination are identified.