Current concepts in intervertebral disc restoration

Biomechanical tests and finite element analyses of pelvic stability using bilateral single iliac screws with different channels in lumbo-iliac fixation

Background

In lumbo-iliac fixation, the iliac screw can be placed in several locations and directions. There is no uniform standard for the placement of a single iliac screw. Biomechanical tests and finite element analyses were used to compare the effect of bilateral single iliac screws with three channels on pelvic stability to determine the best channel.

Methods

Five embalmed adult cadaver pelvic specimens were selected. An unstable Tile C1 pelvic injury model was established. Lumbo-iliac fixation for the treatment of left sacral Denis II fracture includes the following: three channels of bilateral, single iliac screws (channel A from posterior superior iliac spine (PSIS) to anterior inferior iliac spine (AIIS), channel B from 1 cm medial and 1 cm caudal of PSIS to AIIS, and channel C from 2 cm below PSIS to AIIS). Biomechanical testing was performed for stiffness evaluations. A finite element model was established to study the stress distribution of the model and the maximum von Mises stress of internal fixation.

Results

Biomechanical tests revealed that under vertical compression loading. The compressive stiffness fixed by channel B (246.15 ± 27.85 N/mm) was better than that fixed by channel A and channel C. Under torsional load, the torsional stiffness fixed by channel B (2.234 ± 0.223 N·m/°) was stronger than that fixed by channel A and channel C. However, there was no significant difference in terms of compressive and torsional stiffness between channel B and channel A (P > 0.05). Finite element analyses conformed that the maximum von Mises stress of the internal fixator fixed in channel B under the conditions of vertical, forwards bending, backwards extension, left bending, left rotating, and right bending (213.98 MPa, 338.96 MPa, 100.63 MPa, 297.06 MPa, 200.95 MPa and 284.75 MPa, respectively) was significantly lower than those fixed in channel A and channel C.

Conclusions

The construct stiffness of the channel from 1 cm medial and 1 cm caudal of PSIS to AIIS is better than that of the other two channels. This channel has the advantages of good biomechanical stability, small maximum von Mises stress of internal fixation.

Correlation between bone mineral density of different sites and lumbar disc degeneration in postmenopausal women

Osteoporosis and lumbar disc degeneration (LDD) have been common causes that make increasing patients suffer from different degrees of low back pain. At present, whether osteoporosis degenerates or protects disc is still controversial, and the correlation between hip bone mineral density (BMD) and LDD still remains unclear. Our study aims to analyze the correlation between BMD of different sites and LDD in postmenopausal women, and explore the potential pathophysiological mechanism of them.One hundred ninety-five postmenopausal female patients were enrolled and divided into osteoporosis, osteopenia, and normal bone mass groups. Their BMD and lumbar spine magnetic resonance imaging were retrospectively analyzed. Two spine surgeons were selected to assess LDD according to Pfirrmann grading system.Based on lumbar BMD, LDD of normal bone mass group was more severe than the other 2 groups in L1/2 and L2/3 segments (P < .05). Based on hip BMD, LDD of each disc from L1/2 to L5/S1 had no significant difference among the 3 groups (P > .05). Lumbar BMD (L1-L4) was positively correlated with corresponding degree of LDD (L1/2-L4/5) (P < .05), whereas there was no correlation between hip BMD and degree of LDD (P = .328).There is a positive correlation between lumbar BMD and LDD in postmenopausal women, which is more obvious in the upper lumbar spinal segments (L1, L2). However, there is no correlation between hip BMD and LDD, suggesting that in postmenopausal women with lumbar degenerative disease, hip BMD is more suitable for the diagnosis of osteoporosis.

Laser Reconstruction of Spinal Discs Experiments and Clinic

Degenerative disease of the intervertebral discs (DDD) is currently a serious problem facing the world community. The surgical methods and conservative therapy used today, unfortunately, do not stop the pathological process, but serve as a palliative method that temporarily relieves pain and improves the patient’s quality of life. Therefore, at present, there is an active search for new methods of treating DDD. Among new techniques of treatment, biological methods, and minimally invasive surgery, including the use of laser radiation, which, depending on the laser parameters, can cause ablative or modifying effects on the disc tissue, have acquired considerable interest. Here, we analyze a new approach to solving the DDD problem: laser tissue modification. This review of publications is focused on the studies of the physicochemical foundations and clinical applications of a new method of laser reconstruction of intervertebral discs. Thermomechanical action of laser radiation modifies tissue and leads to its regeneration as well as to a long-term restoration of disc functions, elimination of pain and the return of patients to normal life.

Two dimensional automatic active shape model of degenerative disc repaired by low-intensity laser

OBJECTIVE

Intervertebral disc degeneration is the main factor causing low back pain, and the related long-term treatment can improve the situation of degeneration. This study aimed to investigate the effect of low-intensity laser irradiation on the repair of degenerative intervertebral disc by two dimensional automatic active shape model (2D-AASM).

METHODS

Nine Bama miniature pigs were randomly divided into three groups: control group (Con), model group (Mod) and laser treatment group (Las). After one month, the discs were treated with low-energy laser for another month. MRI was performed for one month, and the statistical shape model and 2D-AASM of intervertebral disc were established based on the minimum description length method.

RESULTS

The model established by the proposed method is more accurate and the segmentation result is more accurate. From the segmented T2-weighted image, the signal intensity of the Mod group decreased significantly, and the signal intensity in the Las group was moderate and high compared with the Mod group. The HE staining display the structure of Con group was damaged, and the construction of Las group was restored compared with Mod group.

CONCLUSIONS

The 2D-AASM method effectively improves the accuracy of intervertebral disc segmentation. The low-intensity laser has a protective effect on the repair of the degenerative intervertebral disc.

Advanced Strategies for the Regeneration of Lumbar Disc Annulus Fibrosus

Damage to the annulus fibrosus (AF), the outer region of the intervertebral disc (IVD), results in an undesirable condition that may accelerate IVD degeneration causing low back pain. Despite intense research interest, attempts to regenerate the IVD have failed so far and no effective strategy has translated into a successful clinical outcome. Of particular significance, the failure of strategies to repair the AF has been a major drawback in the regeneration of IVD and nucleus replacement. It is unlikely to secure regenerative mediators (cells, genes, and biomolecules) and artificial nucleus materials after injection with an unsealed AF, as IVD is exposed to significant load and large deformation during daily activities. The AF defects strongly change the mechanical properties of the IVD and activate catabolic routes that are responsible for accelerating IVD degeneration. Therefore, there is a strong need to develop effective therapeutic strategies to prevent or reconstruct AF damage to support operational IVD regenerative strategies and nucleus replacement. By the way of this review, repair and regenerative strategies for AF reconstruction, their current status, challenges ahead, and future outlooks were discussed.

The Role of Two-Step Blending in the Properties of Starch/Chitin/Polylactic Acid Biodegradable Composites for Biomedical Applications

The current research trend for excellent miscibility in polymer mixing is the use of plasticizers. The use of most plasticizers usually has some negative effects on the mechanical properties of the resulting composite and can sometimes make it toxic, which makes such polymers unsuitable for biomedical applications. This research focuses on the improvement of the miscibility of polymer composites using two-step mixing with a rheomixer and a mix extruder. Polylactic acid (PLA), chitin, and starch were produced after two-step mixing, using a compression molding method with decreasing composition variation (between 8% to 2%) of chitin and increasing starch content. A dynamic mechanical analysis (DMA) was used to study the mechanical behavior of the composite at various temperatures. The tensile strength, yield, elastic modulus, impact, morphology, and compatibility properties were also studied. The DMA results showed a glass transition temperature range of 50 °C to 100 °C for all samples, with a distinct peak value for the loss modulus and factor. The single distinct peak value meant the polymer blend was compatible. The storage and loss modulus increased with an increase in blending, while the loss factor decreased, indicating excellent compatibility and miscibility of the composite components. The mechanical properties of the samples improved compared to neat PLA. Small voids and immiscibility were noticed in the scanning electron microscopy images, and this was corroborated by X-ray diffraction graphs that showed an improvement in the crystalline nature of PLA with starch. Bioabsorption and toxicity tests showed compatibility with the rat system, which is similar to the human system.

Syndecan-4 is a Novel Therapeutic Target for Intervertebral Disc Degeneration via Suppressing JNK/p53 Pathway

Syndecan-4 is a member of the polysaccharide syndecan family and plays a vital role in intervertebral disc development. Several studies have demonstrated the positive relationship between syndecan-4 expression and intervertebral disc degeneration. However, the detailed molecular mechanism by which syndecan-4 affects the degeneration of nucleus pulposus cells (NPCs) remains unclear. In this study, cell viability was determined by CCK-8 assay, mRNA level was determined by qPCR, and protein expression was determined by western blot. Molecular interaction was determined by chromatin immunoprecipitation assay. A rabbit intervertebral disc degeneration model was established to test for syndecan in vivo. We found that the morphology and viability of NPCs were not affected by the expression of syndecan-4 in the long term. While the NPC function were affected, which results in the degeneration of intervertebral disc. Syndecan-4 overexpression promoted the degeneration of NPCs. Syndecan-4 also activated the JNK signaling pathway and downstream p53 pathways, and promoted degeneration. Inhibition of the JNK pathway, which down-regulated p53 expression, alleviated the degeneration. In an in vivo study, syndecan-4 siRNA injection stopped the development of rabbit disc degeneration, and even created a reverse effect, in which JNK/p53 played a role. Syndecan-4 may be a novel therapeutic target for intervertebral disc degeneration via suppressing the JNK/p53 pathway.

Application of Laparoscopic Lumbar Discectomy and Artificial Disc Replacement: At Least Two Years of Follow-Up

STUDY DESIGN

This prospective observational study included 22 patients who were diagnosed with symptomatic degenerative disc disease treated via artificial disc replacement (ADR) with a laparoscopic technique.

OBJECTIVE

The current study aimed to assess the safety and efficacy of ADR using a laparoscopic technique for lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

Symptomatic degenerative disc disease is the major cause of low back pain with lumbar segmental instability. ADR has increased in popularity as an alternative treatment for lumbar disc herniation. However, the traditional approach to spinal surgery carries the risk of catastrophic bleeding from injury to major vessels, as well as iatrogenic injury to the viscera and associated structures. Therefore, laparoscopic lumbar discectomy and ADR may represent a useful alternative.

METHODS

Twenty-two patients (8 males and 14 females) who were diagnosed with symptomatic degenerative disc disease were included in this study. Seven cases involved the L4/5 level, and 15 cases involved the L5/S1 level. All patients were ineffective after at least 6 months of conservative treatments; all patients were informed of the surgery before the operation and provided consent. Three-dimensional computed tomographic angiography (3D-CTA) of the iliac great blood vessels was completed before the surgery. All surgical procedures were performed under a laparoscope. All patients were followed up.

RESULTS

All surgeries were successfully completed. The average operation time was 120 minutes (range 110-150 min), and the average hemorrhage was 145 mL (range 80-360 mL). All cases underwent X-rays at 3 days, 3 months, 6 months, 1 year, and the final postoperative follow-up. The outcome indicated that there was no mobilization, displacement, or subsidence in all patients with the exception of one case with prosthesis migration. The follow-up time was 43.8 months (range 24-64 months). The mean visual analog scale (VAS) and Oswestry scores were decreased postoperatively. The mean improvement rate of the VAS score was 73.5%.

CONCLUSION

Lumbar ADR using a laparoscope represents a novel, minimally invasive treatment for symptomatic degenerative disc disease and severe lumbar discogenic pain.

The application of fiber-reinforced materials in disc repair

The intervertebral disc degeneration and injury are the most common spinal diseases with tremendous financial and social implications. Regenerative therapies for disc repair are promising treatments. Fiber-reinforced materials (FRMs) are a kind of composites by embedding the fibers into the matrix materials. FRMs can maintain the original properties of the matrix and enhance the mechanical properties. By now, there are still some problems for disc repair such as the unsatisfied static strength and dynamic properties for disc implants. The application of FRMs may resolve these problems to some extent. In this review, six parts such as background of FRMs in tissue repair, the comparison of mechanical properties between natural disc and some typical FRMs, the repair standard and FRMs applications in disc repair, and the possible research directions for FRMs' in the future are stated.

An injectable nucleus pulposus implant restores compressive range of motion in the ovine disc

STUDY DESIGN

Investigation of injectable nucleus pulposus (NP) implant.

OBJECTIVE

To assess the ability of a recently developed injectable hydrogel implant to restore nondegenerative disc mechanics through support of NP functional mechanics.

SUMMARY OF BACKGROUND DATA

Although surgical intervention for low back pain is effective for some patients, treated discs undergo altered biomechanics and adjacent levels are at increased risk for accelerated degeneration. One potential treatment as an alternative to surgery for degenerated disc includes the percutaneous delivery of agents to support NP functional mechanics. The implants are delivered in a minimally invasive fashion, potentially on an outpatient basis, and do not preclude later surgical options. One of the challenges in designing such implants includes the need to match key NP mechanical behavior and mimic the role of native nondegenerate NP in spinal motion.

METHODS

The oxidized hyaluronic acid gelatin implant material was prepared. In vitro mechanical testing was performed in mature ovine bone-disc-bone units in 3 stages: intact, discectomy, and implantation versus sham. Tested samples were cut axially for qualitative structural observations.

RESULTS

Discectomy increased axial range of motion (ROM) significantly compared with intact. Hydrogel implantation reduced ROM 17% (P < 0.05) compared with discectomy and returned ROM to intact levels (ROM intact 0.71 mm, discectomy 0.87 mm, postimplantation 0.72 mm). Although ROM for the hydrogel implant group was statistically unchanged compared with the intact disc, ROM for sham discs, which received a discectomy and no implant, was significantly increased compared with intact. The compression and tension stiffness were decreased with discectomy and remained unchanged for both implant and sham groups as expected because the annulus fibrosus was not repaired. Gross morphology images confirmed no ejection of NP implant.

CONCLUSION

An injectable implant that mimics nondegenerate NP has the potential to return motion segment ROM to normal subsequent to injury.

Nucleus pulposus replacement and regeneration/repair technologies: present status and future prospects

Degenerative disc disease is implicated in the pathogenesis of many painful conditions of the back, chief among which is low back pain. Acute and/or chronic low back pain (A/CLBP) afflicts a large number of people, thus making it a major healthcare issue with concomitant cost ramifications. When conservative treatments for A/CLBP, such as bed rest, anti-inflammatory medications, and physical therapy, prove to be ineffectual, surgical options are recommended. The most popular of these is discectomy followed by fusion. Although there are many reports of good to excellent outcomes with this method, there are concerns, such as long-term adverse biomechanical consequences to adjacent functional spinal unit(s). A surgical option that has been attracting much attention recently is replacement or regeneration/repair of the nucleus pulposus, an approach that holds the prospect of not compromising either mobility or function and causing no adjacent-level injury. There is a sizeable body of literature highlighting this option, comprising in vitro biomechanical studies, finite element analyses, animal-model studies, and limited clinical evaluations. This work is a review of this body of literature and is organized into four parts, with the focus being on replacement technologies, regeneration/repair technologies, and detailed expositions on 14 areas for future study. This review ends with a summary of the salient points made.

Intervertebral disk tissue engineering using biphasic silk composite scaffolds

Scaffolds composed of synthetic, natural, and hybrid materials have been investigated as options to restore intervertebral disk (IVD) tissue function. These systems fall short of the lamellar features of the native annulus fibrosus (AF) tissue or focus only on the nucleus pulposus (NP) tissue. However, successful regeneration of the entire IVD requires a combination approach to restore functions of both the AF and NP. To address this need, a biphasic biomaterial structure was generated by using silk protein for the AF and fibrin/hyaluronic acid (HA) gels for the NP. Two cell types, porcine AF cells and chondrocytes, were utilized. For the AF tissue, two types of scaffold morphologies, lamellar and porous, were studied with the porous system serving as a control. Toroidal scaffolds formed out of the lamellar, and porous silk materials were used to generate structures with an outer diameter of 8 mm, inner diameter of 3.5 mm, and a height of 3 mm (the interlamellar distance in the lamellar scaffold was 150-250 μm, and the average pore sizes in the porous scaffolds were 100-250 μm). The scaffolds were seeded with porcine AF cells to form AF tissue, whereas porcine chondrocytes were encapsulated in fibrin/HA hydrogels for the NP tissue and embedded in the center of the toroidal disk. Histology, biochemical assays, and gene expression indicated that the lamellar scaffolds supported AF-like tissue over 2 weeks. Porcine chondrocytes formed the NP phenotype within the hydrogel after 4 weeks of culture with the AF tissue that had been previously cultured for 2 weeks, for a total of 6 weeks of cultivation. This biphasic scaffold simulating in combination of both AF and NP tissues was effective in the formation of the total IVD in vitro.

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 10 days but were severely deformed, BEP discs on the other hand maintained morphology but failed to retain cell viability having only 27% viable cells after 10 days. In CEP discs, both cell viability and morphology were maintained for at least 4 weeks 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 7 days, 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.

Lumbar disc rehydration postimplantation of a posterior dynamic stabilization system

Biological attempts at disc regeneration are promising; however, disc degeneration is closely related to other predisposing factors such as alteration of disc height, intradiscal pressure, load distribution, and motion. The restoration of the physiological status of the affected spinal segment is thus necessary prior to attempts at disc regeneration. Dynamic stabilization systems now offer the potential of a mechanical approach to intervertebral disc regeneration. The authors used decompression and placement of the BioFlex dynamic stabilization device to treat a young male patient with disc degeneration. This patient underwent follow-up, and he was found to gradually improve both neurologically and radiographically. On MR imaging performed 1 year postoperatively, he had an increase in disc height and disc rehydration. This case and the concept of disc rehydration are presented in this paper.

Self-assembly of aligned tissue-engineered annulus fibrosus and intervertebral disc composite via collagen gel contraction

Many cartilaginous tissues such as intervertebral disc (IVD) display a heterogeneous collagen microstructure that results in mechanical anisotropy. These structures are responsible for mechanical function of the tissue and regulate cellular interactions and metabolic responses of cells embedded within these tissues. Using collagen gels seeded with ovine annulus fibrosus cells, constructs of varying structure and heterogeneity were created to mimic the circumferential alignment of the IVD. Alignment was induced within gels by contracting annular gels around an inner boundary using both a polyethylene center and alginate center to create a composite engineered IVD. Collagen alignment and heterogeneity were measured using second harmonic generation microscopy. Decreasing initial collagen density from 2.5 mg/mL to 1 mg/mL produced greater contraction of constructs, resulting in gels that were 55% and 6.2% of the original area after culture, respectively. As a result, more alignment occurred in annular-shaped 1 mg/mL gels compared with 2.5 mg/mL gels (p < 0.05). This alignment was also produced in a composite-engineered IVD with alginate nucleus pulposus. The resulting collagen alignment could promote further aligned collagen development necessary for the creation of a mechanically functional tissue-engineered IVD.

Effect of lumbar disc replacement on the height of the disc space and the geometry of the facet joints: a cadaver study

In a study on ten fresh human cadavers we examined the change in the height of the intervertebral disc space, the angle of lordosis and the geometry of the facet joints after insertion of intervertebral total disc replacements. SB III Charité prostheses were inserted at L3-4, L4-5, and L5-S1. The changes studied were measured using computer navigation software applied to CT scans before and after instrumentation. After disc replacement the mean lumbar disc height was doubled (p < 0.001). The mean angle of lordosis and the facet joint space increased by a statistically significant extent (p < 0.005 and p = 0.006, respectively). By contrast, the mean facet joint overlap was significantly reduced (p < 0.001). Our study indicates that the increase in the intervertebral disc height after disc replacement changes the geometry at the facet joints. This may have clinical relevance.

Features of intervertebral disc degeneration in rat's aging process

OBJECTIVE

The age-related change is important part of degenerative disc disease. However, no appropriate animal model or objective evaluation index is available. This study aimed to investigate the features of intervertebral disc degeneration in aging process of rats.

METHODS

22-month-old Sprague-Dawley (SD) rats were used as spontaneously occurring intervertebral disc degeneration models and 6-month-old rats as young controls. Expression of collagen types II and X was measured by immunohistochemistry. Degenerations of intervertebral discs were scored according to Miyamoto's method. Numbers and areas of afferent vascular buds were measured. The thicknesses of non-calcified and calcified layers were measured and statistically analyzed.

RESULTS

There were less collagen type II expression and more collagen type X expression in the calcified layer of the cartilage endplates and nucleus pulposus in the rats of the aged group than in the young control. There were fewer and smaller afferent vascular buds in the rats of the aged group than in the young control group. The ratio of the non-calcified to the calcified layers in the rats of the aged group significantly decreased, compared with that of the young control group (P<0.01).

CONCLUSION

Rats can spontaneously establish intervertebral disc age-related degeneration. The expression of collagen types II and X, numbers and areas of afferent vascular buds, the ratio of the non-calcified to the calcified layers, and water and glycosaminoglycan contents in the nucleus pulposus are sensitive indexes of intervertebral disc degeneration.

The fate of transplanted xenogeneic bone marrow-derived stem cells in rat intervertebral discs

Intervertebral disc degeneration is a major cause and a risk factor for chronic low back pain. The potential of using stem cells to treat disc degeneration has been raised. The aims of our study were to assess whether xenogeneic bone-marrow derived stem cells could survive in a rat disc degeneration model and to determine which cell types, if any, survived and differentiated into disc-like cells. Human bone-marrow derived CD34(+) (hematopoietic progenitor cells) and CD34(-) (nonhematopoietic progenitor cells, including mesenchymal stem cells) cells were isolated, fluorescent-labeled, and injected into rat coccygeal discs. The rats were sacrificed at day 1, 10, 21, and 42. Treated discs were examined by histological and immunostaining techniques and compared to control discs. The survival of transplanted cells was further confirmed with a human nuclear specific marker. Fluorescent labeled CD34(-) cells were detected until day 42 in the nucleus pulposus of the injected discs. After 3 weeks these cells had differentiated into cells expressing chondrocytic phenotype (Collagen II and Sox-9). In contrast, the fluorescent labeled CD34(+) cells could not be detected after day 21. No fluorescence-positive cells were detected in the noninjected control discs. Further, no inflammatory cells infiltrated the nucleus pulposus, even though these animals had not received immunosuppressive treatment. Our data provide evidence that transplanted human BM CD34(-) cells survived and differentiated within the relative immune privileged nucleus pulposus of intervertebral disc degeneration.

The effects of recombinant human bone morphogenetic protein-2, recombinant human bone morphogenetic protein-12, and adenoviral bone morphogenetic protein-12 on matrix synthesis in human annulus fibrosis and nucleus pulposus cells

BACKGROUND CONTEXT

Bone morphogenetic proteins (BMPs) are potential therapeutic factors for degenerative discs, and BMP-12 does not have the osteogenic potential of BMP-2, making it better suited for intradiscal injection. However, no reports have compared the actions of BMP-2 and -12 on human annulus fibrosus (AF) and nucleus pulposus (NP) cells nor evaluated adenoviral-mediated gene therapy in human AF cells.

PURPOSE

To evaluate and compare the effects of recombinant human (rh) BMP-2, rhBMP-12, and adenoviral BMP-12 (Ad-BMP-12) on nucleus pulposus and annulus fibrosis cell matrix protein synthesis.

STUDY DESIGN

In vitro study using rhBMP-2 and -12 and adenoviral BMP-12 with human intervertebral disc (IVD) cells.

METHODS

Human NP and AF IVD cells were isolated, maintained in monolayer, and incubated with BMP-2 or -12 for 2 days. AF and NP cells were transduced with Ad-BMP-12, pellets formed, and incubated for 6 days. Growth factor-treated cells were labelled with either 35-S or 3H-proline to assay matrix protein synthesis.

RESULTS

rhBMP-2 increased NP proteoglycan, collagen, and noncollagen protein synthesis to 355%, 388%, and 234% of control. RhBMP-12 increased the same NP matrix proteins' synthesis to 140%, 143%, and 160% of control. Effects on AF matrix protein synthesis were minimal. Ad-BMP-12 significantly increased matrix protein synthesis and DNA content of AF and NP cells in pellet culture. NP synthesis of all matrix proteins and AF synthesis of proteoglycans was increased when the data were normalized to pellet DNA. AF synthesis of noncollagen protein and collagen was not modulated by Ad-BMP-12 if the data are normalized to pellet DNA content.

CONCLUSIONS

Both rhBMP-2 and -12 increase human NP cell matrix protein synthesis while having minimal effects on AF cells. However, Ad-BMP-12 did increase matrix protein synthesis in both NP and AF cells, making it a potential therapy for enhancing matrix production in the IVD. These responses plus the proliferative action of Ad-BMP-12 seen in the current studies, and the lack of an osteogenic action noted in other studies justifies future studies to determine if gene therapy with BMP-12 could provide protective and/or reparative actions in degenerating discs.

Tissue-engineering approach to regenerating the intervertebral disc

In today's world there is an ever increasing incidence of low back pain, which is generally attributed to degeneration of the intervertebral disc (IVD) in those in their second or third decade of life. The most prevalent treatment modalities involve conservative methods (physical therapy and medications) or surgical fusion of the upper and lower vertebral bodies. In the last 10 years, there has been a surge of interest in applying tissue-engineering principles to treat spinal problems associated with the IVD. Tissue engineering provides many promising advantages to treating disc degeneration; it adopts a more biological and reparative approach, whereby the main goal is to restore the properties of the disc to its pre-degenerative state. This review outlines the physiology of the IVD and the etiology of disc degeneration. Much of the research carried out in the field of tissue engineering is based on three predominant constituents: cells, scaffolds, and signals. Thus, specific attention is given to these constituents and their potential use in repairing the IVD. Some of the significant challenges involved in IVD tissue engineering are also identified, and a brief discussion regarding possible future areas of research follows.

The in vivo biological effects of intradiscal recombinant human bone morphogenetic protein-2 on the injured intervertebral disc: an animal experiment

STUDY DESIGN

Prospective analysis.

OBJECTIVE

To investigate biologic influences of recombinant human bone morphogenetic protein (rhBMP)-2 on intervertebral discs after anular tears.

SUMMARY OF BACKGROUND DATA

Treatments for intervertebral disc injury or degeneration are unsatisfactory. rhBMP-2, a high-potency osteoinductive and chondroinductive substance, is approved for use in anterior lumbar interbody fusions. rhBMP-2 stimulates the proliferation of rat disc cells and the secretion of extracellular matrix in vitro. In vivo responses in the intervertebral disc after anular tears are rarely studied.

METHODS

Twenty New Zealand white rabbits received full-thickness anular tears and intradiscal injections of saline (control) and rhBMP-2 0.1 mg with and without coral grafts at L2-L3, L3-L4, and L4-L5, respectively. Three died or had infection. Therefore, 17 underwent radiography and sacrifice at 12 weeks. Spinal sections were stained with hematoxylin and eosin to examine responses to rhBMP-2.

RESULTS

Radiographs revealed degenerative changes, such as disc space narrowing and irregularity, subchondral sclerosis, osteophyte formation, and hypertrophy of vertebral endplates in all groups. Degeneration was more frequent and severe with rhBMP-2 with (P < 0.01) and without (P < 0.05) coral than with saline. Two rabbits receiving rhBMP-2 and coral achieved solid interbody bony fusion. New bone formation was noted in 2 controls, in 3 animals treated with rhBMP-2, and in 4 treated with rhBMP-2 and coral. Vascularity and fibroblast proliferation increased with rhBMP-2 (n = 14) and rhBMP-2 with coral (n = 9) compared with control (n = 3; P < 0.01 and P = 0.03, respectively). Inflammatory infiltrates increased with rhBMP-2 (n = 8) compared with control (n = 2; P = 0.03).

CONCLUSIONS

Degenerative changes were more frequent and severe in the groups treated with rhBMP-2 with or without coral in radiographic findings. In histopathologic findings, rhBMP-2 promoted hypervascularity and fibroblast proliferation of the intervertebral disc after an anular tear.

Notochord cells regulate intervertebral disc chondrocyte proteoglycan production and cell proliferation

STUDY DESIGN

Non-chondrodystrophic dog notochord cell conditioned medium was used to evaluate chondrocyte proteoglycan production and cell proliferation.

OBJECTIVES

To evaluate the responsiveness of bovine disc-derived chondrocytes to notochord-cell conditioned medium with respect to proteoglycan and cell proliferation. In addition, to examine phenotypic changes of notochord cells cultured in monolayered as compared to 3-dimensional culture.

SUMMARY OF BACKGROUND DATA

Non-chondrodystrophic dogs maintain their intervertebral disc notochord cells into adulthood and are protected from having degenerative disc disease develop. The chondrodystrophic breeds such as beagles do not preserve these cells and have disc disease develop much earlier in life. The role of the notochord cell within the disc nucleus is poorly understood.

METHODS

Canine notochord cells were cultured within alginate beads in serum-deficient conditions using Dulbecco modified Eagle medium to produce notochord cell conditioned medium (NCCM). NCCM was used to stimulate bovine disc chondrocytes from which we evaluated proteoglycan production and cell proliferation as compared to chondrocytes grown in DMEM alone. In addition, parallel cultures of notochord cells were seeded within alginate beads as well as in monolayer and cultured in order to examine for differences in phenotype between the 2 culture conditions.

RESULTS

The morphologic aspects of the intervertebral disc between the species differed markedly. A dose- dependent relationship was seen between proteoglycan production and NCCM concentration across various concentrations of NCCM in repeated experiments. Although there was a 4-fold increase in cell proliferation under all NCCM concentrations, this increase in cell proliferation was not dose dependent in the concentrations tested. Unlike chondrocytes, notochord cells do not adhere to tissue culture plate (monolayer) until at least day 4-6, do not markedly alter their phenotype, and rapidly assume masses of cells while floating within tissue culture medium.

CONCLUSIONS

The biology of the disc-derived chondrocyte is profoundly affected by NCCM in that various concentrations of NCCM activate proteoglycan production in a dose-dependent fashion. However, in the doses tested in our study, cell proliferation was increased but in a nondose-dependent fashion. Notochord cells retain their phenotype even in monolayer and through the development of floating intimately associated masses of cells suggest the development and maintenance of cell-cell interaction. These masses of cells are retained even after 6 days in culture when they do attach to the tissue plate surface. The persistence of notochord cells in non-chondrodystrophic dog species suggests that these in vitro studies may mirror the milieu of the disc in vivo, in which the notochord cell may play a key role in disc homeostasis.

Effect of the increase in the height of lumbar disc space on facet joint articulation area in sagittal plane

STUDY DESIGN

Computerized tomography (CT) of the lumbar spine cadaveric specimens was used to evaluate the effect of increasing the height of the disc space in the lumbar spine to the facet joint articulation in the sagittal plane.

OBJECTIVE

To show how the facet joint articulation is affected by increasing the height of the disc space in the lumbar spine.

SUMMARY OF BACKGROUND DATA

The Charité Artificial Disc (DePuy Spine, Inc., Raynham, MA) was successful in relieving low back pain in the majority of patients, yet there was still a significant number of patients who did not obtain pain relief, or their pain even worsened. The etiology of their pain is still not known. To our knowledge, no study has addressed the effect on the facet joints when the disc height is increased.

METHODS

CT images passing through the center of the L3-S1 facet joints (sagittal plane) were obtained from 15 cadaveric lumbar spine specimens. The articulation overlap of facet joints in sagittal plane from the L3 to S1 was measured. A 1-mm incremental increase to a total 5 mm in disc space height was performed to simulate the changes seen in disc replacement. The change in the facet joint articulation overlap in sagittal plane at normal and each displacement was then measured. There were 5 lumbar spine specimens dissected to validate the technique and standardize the measurements. Mean, percentages, and standard deviation values were calculated for all measured dimensions.

RESULTS

No significant difference was found between the measurements on CT and gross specimens (P > 0.05). In 15 specimens, the mean facet joint articulation overlap on the sagittal plane was: 16.29 +/- 1.20 mm (left) and 16.22 +/- 1.16 (right) at the L3-L4 level; 17.81 +/- 1.18 mm (left) and 17.74 +/- 1.18 mm (right) at the L4-L5 level; and 18.18 +/- 1.18 mm (left) and 18.23 +/- 1.15 mm (right) at the L5-S1 level. There is no significant difference between the measured values on left and right sides (P > 0.05). Each 1-mm incremental increase in disc space at the L3-L4 level translated to a decrease in the facet joint articulation overlap in the sagittal plane by 6%, and the mean facet joint space increased 0.4 mm. At the L4-L5 level, the articulation overlap decreased by 6%, and the facet joint space increased 0.5 mm. At the L5-S1 level, the articulation overlap decreased by 4%, and the facet joint space increased 0.7 mm.

CONCLUSIONS

There is a significant decrease of the facet joint articulation overlap in sagittal plane and an increase in the facet joint space following an increase in the lumbar disc space. The inappropriate increase of the height of disc space will result in facet joint subluxation.

Trans-Endplate Nucleotomy Increases Deformation and Creep Response in Axial Loading

Knowledge of the functional role of the nucleus pulposus is critical for the development and evaluation of disc treatment strategies to restore mechanical function. While previous motion segment studies have shown that nucleotomy alters disc mechanics, disruption of the annulus fibrosus may have influenced these experiments. The objective of this study was to determine the mechanical role of the nucleus pulposus in support of axial loads via a trans-endplate nucleotomy procedure. Sheep motion segments were randomly assigned to three groups: control, limited nucleotomy, and radical nucleotomy. Mechanical testing consisted of 20 cycles of compression-tension, a 1-h creep, and a slow constant-rate compressive ramp test. Nucleotomy led to increased axial deformations, in particular an elongated neutral zone, a greater range of motion, and altered creep behavior. In general, the elastic properties exhibited a graded response with respect to the amount of nucleus material removed. This graded effect can be attributed to swelling of the nucleus pulposus in the limited nucleotomy group, whereas little swelling was observed in the radical group. The findings of the present study indicate that functional evaluation of nucleus pulposus replacements and disc implants should include range of motion measures (including neutral zone) and viscoelastic creep experiments in addition to considering compressive stiffness.

Disc Regeneration: Why, When, and How

There is increasing acknowledgment that patients with back pain who are candidates for surgery, will benefit over the long term from less invasive procedures that facilitate dynamic stabilization, rather than fusion. Dynamic stabilization can be addressed by providing assistance using mechanical devices, or relying on biologic processes such as tissue regeneration and repair. The concept of biologic disc repair has grown in recent years because of improved understanding of the cellular and molecular events of disc aging and degeneration. This article describes approaches to cell therapy, reviews relevant studies, and discusses ways to maximize clinical efficacy. Tissue engineering approaches for disc regeneration and healing have significant clinical potential.

Cervical total disc replacement, part I: rationale, biomechanics, and implant types

Cervical total disc replacement (TDR) is an attractive alternate to arthrodesis for management of disc degeneration and herniation in the cervical spine. Theoretic advantages of TDR include preservation of normal motion and biomechanics in the cervical spine and reduction of adjacent-segment degeneration. Other potential advantages include faster return to normal activity and elimination of the need for bone graft and associated donor site morbidity. This article introduces the rationale and various implant types available for cervical TDR. Part 2 of this series reviews the results and complications of specific implant designs.

Bilateral pedicle fractures following anterior dislocation of the polyethylene inlay of a ProDisc artificial disc replacement: a case report of an unusual complication

STUDY DESIGN

An unusual complication resulting from an artificial disc replacement for lumbar degenerative disc disease and its treatment are reported

OBJECTIVE

To describe the clinical circumstance, radiologic findings, treatment, and outcome of bilateral pedicle fractures associated with dislocation of the polyethylene inlay of a ProDisc replacement at L5/S1 level.

SUMMARY OF BACKGROUND DATA

To the authors' knowledge, no published reports in the English literature have described bilateral pedicle fractures following a single level artificial lumbar total disc replacement.

METHODS

A 30-year-old male underwent a ProDisc total disc replacement at L5/S1 level for discogenic pain. Six-week postoperative assessment showed improvement in the visual analog and Oswestry scores. Assessment at 18 weeks postoperatively for acute pain revealed an anterior slip of the superior plate component, and computerized tomography showed bilateral pedicle fractures of the fifth lumbar vertebra. At surgery, the poly insert was found to have dislocated anteriorly. A salvage interbody fusion was then performed using the stand-alone anterior lumbar interbody fusion cage.

RESULTS

The most recent review confirmed radiologic evidence of fusion with improvement in the subjective evaluation scores

CONCLUSIONS

We hypothesize that the current implant design in which the contribution to lordosis angle is purely from the superior component may be responsible for the reported complication. We suggest that dividing the contribution equally between both endplates might increase the stability, and this has been discussed with the manufacturers.

Biologic strategies for the therapy of intervertebral disc degeneration

Recent advances in tissue engineering have led to promising new approaches for the biologic treatment of disc degeneration. At present, there is no effective therapy for disc degeneration, a condition which results in large healthcare and socio-economic costs. This article will examine the current approaches used in biologic therapies for disc degeneration, including cell-based tissue engineering, gene therapy and the application of mesenchymal stem cells, and discuss their therapeutic potential, as demonstrated in animal models and experimental studies to date.

Reactive endplate marrow changes: a systematic morphologic and epidemiologic evaluation

PURPOSE

To evaluate the morphology and location of vertebral endplate changes, and to analyze their association with age, gender, and body mass index (BMI).

DESIGN AND PATIENTS

At 1.5 T (T1-weighted, T2-weighted/STIR) 100 lumbar spines were evaluated separately by three observers. The readers classified the endplate bone marrow abnormalities on sagittal MR images according to the definitions of Modic et al. Findings were localized by disc segment; whether in the upper and/or lower endplate; and within each endplate divided into 15 segments. Disc space narrowing, as well as disc desiccation, was also noted at each vertebral level. In addition, endplate changes were correlated with age, gender, and BMI (weight(kg)/height(m)2).

RESULTS

A total of 15,000 data points were studied and 422 total changes recorded. A total of 99 vertebral levels were affected in 58 patients. Of these, 171 were of type I, 242 were of type II, and 9 were of type III. L4-L5 and L5-S1 vertebral levels were most commonly involved, having (142, 4.73%) and (116, 3.87%) changes respectively (P<0.0001). The upper and lower aspects of the endplate were affected similarly. Changes most frequently occurred at the anterior aspect of the endplate (P<0.0001). Endplate marrow changes were associated with increasing age (P<0.0001) and, surprisingly, male gender (P<0.0001). Endplate changes were not associated with BMI.

CONCLUSION

The fatty pattern was most common, with the sclerotic pattern being rare. Endplate marrow changes most often occurred at the anterior aspect of the endplate, particularly at L4--L5 and L5--S1 levels. Modic changes occur more frequently with aging, evidence of their degenerative etiology. They were, however, not related to body habitus, but to weight and male gender.

Lumbar disc arthroplasty

BACKGROUND CONTEXT

Painful lumbar disc degeneration is one of the most common ailments treated by spine surgeons. Currently, early disc disease and herniation are often treated with microdiscectomy. Late disc degeneration is usually treated with arthrodesis. With the advent of new technology and techniques in lumbar disc arthroplasty, interest in preserving spinal motion at degenerated motion segments has increased. The goals of lumbar disc arthroplasty are to provide long-term pain relief at the degenerated disc level, to restore disc height to protect neural elements and to preserve motion to prevent posterior facet arthropathy and adjacent segment disease.

PURPOSE

The purpose of this review is to examine the anatomy and biomechanics of the lumbar motion segment to determine the features that successful disc arthroplasty prosthesis must possess. In addition, the early clinical results of three prostheses currently being used in humans are reviewed.

STUDY DESIGN/SETTING

Review of the literature.

METHODS

A systematic review of Medline for articles related to lumbar disc arthroplasty was conducted up to and including journal articles published in August 2003. In addition, the abstracts from the annual meetings of the North American Spine Society and Scoliosis Research Society from 1998 to 2003 were searched. The literature was then reviewed and summarized.

RESULTS/CONCLUSIONS

Short-term results of lumbar disc arthroplasty as measured by pain relief and disability are good in some studies. Implants are relatively safe in the short term, and with newer designs complications are usually related to the surgical approach rather than early implant failure. Recovery times appear to be shorter than arthrodesis. Despite the relatively good early clinical results of these devices, questions remain about the long-term efficacy in pain relief and maintenance of motion, the results of randomized comparative trials with fusion and the life span of the devices. In addition, late sequelae and revision options are unknown. Current indications for lumbar disc arthroplasty are in the setting of a Food and Drug Administration trial in young, nonosteoporotic patients with one or two level symptomatic disc degeneration without severe facet arthropathy, segmental instability or neural element compression requiring a posterior decompression.

The prevalence of contraindications to total disc replacement in a cohort of lumbar surgical patients

STUDY DESIGN

This is a retrospective review of the epidemiology of contraindications to lumbar total disc replacement (TDR).

OBJECTIVE

To define the prevalence of contraindications to lumbar total disc replacement in a cohort of patients undergoing lumbar surgery in the senior author's (F.P.C.) practice.

SUMMARY OF BACKGROUND DATA

No published reports have documented the prevalence of contraindications to lumbar total disc replacement.

METHODS

We performed a retrospective review of 100 consecutive patients who had lumbar surgery by one surgeon between September and December 2002. Procedures performed and contraindications to TDR were recorded. Contraindications to TDR included central or lateral recess stenosis, facet arthrosis, spondylolysis or spondylolisthesis, herniated nucleus pulposus with radiculopathy, scoliosis, osteoporosis, and postsurgical pseudarthrosis or deficiency of posterior elements. Patients were divided into fusion and nonfusion groups. The percentage of patients without contraindications to TDR was calculated.

RESULTS

Of 100 patients, 56 had fusions and 44 had nonfusion surgery. In the fusion group, 56 of 56 patients had contraindications to TDR. In the nonfusion group, 11% (5 of 44) were candidates for TDR. Overall, 5% of patients in this series were candidates for TDR. The average number of contraindications to TDR was 2.48 (range, 0-5).

CONCLUSIONS

Predictions that TDR will replace fusion are premature. A small percentage (5%) of the patients currently indicated for lumbar surgery at our institution have no contraindications to TDR. Future growth in TDR implantation will result from the indication of patients for surgery who would not be indicated today or from the elimination of current contraindications.

In vivo growth factor treatment of degenerated intervertebral discs

STUDY DESIGN

An in vivo model was used to investigate the response of degenerated discs to various exogenous growth factors.

OBJECTIVES

To study growth factor-induced alterations of the spatial and temporal patterns of disc cellularity and matrix gene expression.

SUMMARY OF BACKGROUND DATA

Cell proliferation and proteoglycan synthesis have been stimulated by growth factors in normal disc cells, suggesting that growth factors may play a therapeutic role for degeneration. However, the response in situ in degenerated discs has not been characterized.

METHODS

Degeneration was induced in murine caudal discs by static compression. Degenerated discs were given single or multiple injections of growth and differentiation factor-5, transforming growth factor-beta, insulin-like growth factor-1, basic fibroblast growth factor, or saline as control. Comparisons of disc morphology, anular cell density, proliferating cells, disc height, and aggrecan and type II collagen gene expression were made either 1 week or 4 weeks after treatment.

RESULTS

In some growth and differentiation factor-5 and transforming growth factor-beta treated discs, expansion of inner anular fibrochondrocyte populations into the nucleus was observed. The cells actively expressed aggrecan and type II collagen mRNA. A lesser effect was observed for insulin-like growth factor-1 and little or no effect for basic fibroblast growth factor. Differences in cell density and proliferating cells were not significant between treatments but suggested a trend of increased cellularity and proliferation following growth factor treatment. A statistically significant increase in disc height 4 weeks after growth and differentiation factor-5 treatment was measured.

CONCLUSIONS

Anular fibrochondrocytes in degenerated discs are responsive to some growth factors in vivo. The results have implications in the early intervention of disc degeneration to arrest or slow the degenerative process.

Biochemical injection treatment for discogenic low back pain: a pilot study

BACKGROUND CONTEXT

Biochemical treatment options including attempts at intervertebral disc restoration are desirable for the physiologic treatment of degenerative disc disease.

PURPOSE

This was a pilot study to test the potential effectiveness of intradiscal injection therapy using agents known to induce proteoglycan synthesis in the treatment of intervertebral disc disease.

STUDY DESIGN

Prospective, within subject, experimental design was applied in the study.

PATIENT SAMPLE

Thirty patients, average age 46.5 years, with chronic intractable low back pain of 8.5 years average duration, took part in the study. All patients had lumbar discography with reproduction of pain.

OUTCOME MEASURES

Pretreatment Roland-Morris disability scores and visual analogue scores were compared with 1-year follow-up posttest values of these scores.

METHODS

Lumbar intervertebral discs were injected with a solution of glucosamine and chondroitin sulfate combined with hypertonic dextrose and dimethlysulfoxide (DMSO). Assessment of pain and disability was completed before treatment and an average of 12 months after the last treatment.

RESULTS

Posttreatment Roland-Morris scores for the entire group of 30 patients of 6.4+/-.994 were significantly (p<.001) lower than pretreatment scores of 12.0+/-.92 (mean+/-SE). The posttreatment visual analogue scores of 3.00+/-.44 were also significantly less than the pretreatment of 6.11+/-.33 (mean+/-SE). Although the results were statistically significant for the 30 patients as a whole, 17 of the 30 patients (57%) improved markedly with an average of 72% improvement in disability scores and 76% in visual analogue scores. The other 13 patients (43%) had little or no improvement. Patients who did poorly included those with failed spinal surgery, spinal stenosis and long-term disability. There were no complications or serious side effects, although postinjection pain was moderate to severe for 48 to 72 hours and required epidural steroids in five cases.

CONCLUSIONS

The results of this pilot study suggest that intradiscal injection therapy with glucosamine, chondroitin sulfate, hypertonic dextrose and DMSO warrants further evaluation with randomized controlled trials.

The molecular basis of intervertebral disk degeneration

At present, the molecular evidence involved in the degeneration of the IVD is still in its primitive stage. In general, however, intrinsic, extrinsic, and generic factors all have shown a contribution to the initiation of degeneration. These factors may stimulate cytokines and directly or indirectly generate the cellular events thus far detected and observed. Such changes discussed have been the cellularity, matrix degradation, matrix quality, and synthesis of enzymes involved in the breakdown of the matrix, including fibronectin fragments of the degraded matrix which can contribute to further degradation. The involvement of cytokines and other inflammatory mediators in the generation of vascularization and stimulation of pain receptors are still controversial but may reveal the pathway to the symptomatic conditions of IVD degeneration.

Gene therapy and tissue engineering in repair of the musculoskeletal system

Historically, surgeons have sought and used different procedures in order to augment the repair of various skeletal tissues. Now, with the completion of the Human Genome Project, many researchers have turned to gene therapy as a means to aid various ailments. In the orthopedic field, many strides have been made toward using gene therapy and tissue engineering in a clinical setting. In this review, several studies are outlined in different areas that gene therapy has or will influence orthopedic surgery. Gene therapy and tissue engineering can aid in fracture healing and spinal fusions by inducing bone formation, ligamentous repairs by increasing the production of connective tissue fibers, intervertebral disc disease by creating potential replacements, and articular cartilage repairs by providing means to improve cartilage. As we continue to see great contributions, such as the few mentioned here, this field will continue to mature and develop.