Intervertebral disc degeneration adjacent to a lumbar fusion. An experimental rabbit model

Immuno-Modulatory Effects of Intervertebral Disc Cells

Low back pain is a highly prevalent, chronic, and costly medical condition predominantly triggered by intervertebral disc degeneration (IDD). IDD is often caused by structural and biochemical changes in intervertebral discs (IVD) that prompt a pathologic shift from an anabolic to catabolic state, affecting extracellular matrix (ECM) production, enzyme generation, cytokine and chemokine production, neurotrophic and angiogenic factor production. The IVD is an immune-privileged organ. However, during degeneration immune cells and inflammatory factors can infiltrate through defects in the cartilage endplate and annulus fibrosus fissures, further accelerating the catabolic environment. Remarkably, though, catabolic ECM disruption also occurs in the absence of immune cell infiltration, largely due to native disc cell production of catabolic enzymes and cytokines. An unbalanced metabolism could be induced by many different factors, including a harsh microenvironment, biomechanical cues, genetics, and infection. The complex, multifactorial nature of IDD brings the challenge of identifying key factors which initiate the degenerative cascade, eventually leading to back pain. These factors are often investigated through methods including animal models, 3D cell culture, bioreactors, and computational models. However, the crosstalk between the IVD, immune system, and shifted metabolism is frequently misconstrued, often with the assumption that the presence of cytokines and chemokines is synonymous to inflammation or an immune response, which is not true for the intact disc. Therefore, this review will tackle immunomodulatory and IVD cell roles in IDD, clarifying the differences between cellular involvements and implications for therapeutic development and assessing models used to explore inflammatory or catabolic IVD environments.

ISSLS Prize in Bioengineering Science 2022: low rate cyclic loading as a therapeutic strategy for intervertebral disc regeneration

BACKGROUND

The intervertebral disc degenerates with age and has a poor propensity for regeneration. Small molecule transport plays a key role in long-term degradation and repair. Convection (bulk flow), induced by low rate cyclic loading of the intervertebral disc, has been shown to increase transport of small molecules. However, the potential therapeutic benefit of low rate cyclic loading on degenerated discs has not been described. The purpose of this study was to determine if a sustained (daily) low rate cyclic loading regimen could slow, arrest, or reverse intervertebral disc degeneration in the rabbit lumbar spine.

METHODS

Fifty-six New Zealand white rabbits (>12 months old) were designated as either Control (no disc puncture), 8D (disc puncture followed by 8 weeks of degeneration), 16D (disc puncture followed by 16 weeks of degeneration), or Therapy (disc puncture followed by 8 weeks of degeneration and then 8 weeks of daily low rate cyclic loading). Specimens were evaluated by T2 mapping, Pfirrmann scale grading, nucleus volume, disc height index, disc morphology and structure, and proteoglycan content.

RESULTS

In every metric, mean values for the Therapy group fell between Controls and 8D animals. These results suggest that sustained low rate cyclic loading had a therapeutic effect on the already degenerated disc and the regimen promoted signs of regeneration. If these results translate clinically, this approach could fulfil a significant clinical need by providing a means of non-invasively treating intervertebral disc degeneration.

Intervertebral Disc Degeneration Is Associated With Aberrant Endplate Remodeling and Reduced Small Molecule Transport

The intervertebral disc is the largest avascular structure in the body, and cells within the disc rely on diffusive transport via vasculature located within the vertebral endplate to receive nutrients, eliminate waste products, and maintain disc health. However, the mechanisms by which small molecule transport into the disc occurs in vivo and how these parameters change with disc degeneration remain understudied. Here, we utilize an in vivo rabbit puncture disc degeneration model to study these interactions and provide evidence that remodeling of the endplate adjacent to the disc occurs concomitant with degeneration. Our results identify significant increases in endplate bone volume fraction, increases in microscale stiffness of the soft tissue interfaces between the disc and vertebral bone, and reductions in endplate vascularity and small molecule transport into the disc as a function of degenerative state. A neural network model identified changes in diffusion into the disc as the most significant predictor of disc degeneration. These findings support the critical role of trans-endplate transport in disease progression and will improve patient selection to direct appropriate surgical intervention and inform new therapeutic approaches to improve disc health. © 2020 American Society for Bone and Mineral Research. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

The effects of simulated +Gz and microgravity on intervertebral disc degeneration in rabbits

The overall objective of this study was to test the hypothesis that +Gz (hypergravity/positive acceleration) and microgravity can both aggravate intervertebral disc degeneration (IVDD). Due to +Gz and microgravity, many pilots develop IVDD. However, the lack of animal models of IVDD under conditions of simulated +Gz and microgravity has hampered research on the onset and prevention of IVDD. Rabbits were randomly allotted to a control group, microgravity group, +Gz group, or mixed (+Gz + microgravity) group. A tail-suspension model was utilized to simulate a microgravity environment and an animal centrifuge to mimic +Gz conditions. After exposure to the above conditions for 4, 8, and 24 weeks, the body weights (BW) of animals in the control group gradually increased over time, while those of animals in the microgravity and mixed groups both decreased (p < 0.001). As compared with the control group, the proteoglycan content of animals in the other three groups was significantly reduced (F = 192.83, p < 0.001). The imageological, histopathological, and immunohistochemical changes to the L6-S1 intervertebral disc samples suggests that the effects of +Gz and microgravity can aggravate IVDD over time. The mixed effects of +Gz and microgravity had the greatest effect on degeneration and +Gz had a particularly greater effect than microgravity.

Bicortical Screw Purchase at Upper Instrumented Vertebra (UIV) Can Cause UIV Fracture After Adult Spinal Deformity Surgery: A Finite Element Analysis Study

OBJECTIVE

To examine the biomechanical stress distribution at the upper instrumented vertebra (UIV) according to unicortical- and bicortical purchase model by finite element analysis (FEA).

METHODS

A T8 to Sacrum with implant finite element model was developed and validated. The pedicle screws were unicortically or bicortically inserted from T10 to L5, and each model was compared and the von Mises (VM) yield stress of T10 was calculated. According to the motion (flexion, extension, lateral bending, and axial rotation) of spine, boundary condition values were set as 15°, 15°, 10°, 4°.

RESULTS

Although the 2 stress values did not show a significant difference between the unicortical- and bicortical purchase models in the flexion and extension, bicortical purchase model showed a larger stress distribution. However, the asymmetric behavior was significantly greater in the case of lateral bending (0.802 MPa vs. 0.489 MPa) and the rotation (5.545 MPa vs. 4.905 MPa). The greater stress was observed on the spinal body surface abutting the implanted screw. Although the maximum stress was observed around the implanted screw in the bicortical purchase model under axial loading, the VM stress of both models was not significantly different.

CONCLUSION

Bicortical purchase model showed a larger stress distribution than the unicortical model, especially in the case of lateral bending and the rotation behavior. Our biomechanical simulation by FEA indicates that bicortical fixation at UIV can be a risk factor for early UIV compression fracture after adult spinal deformity surgery.

Berberine prevents human nucleus pulposus cells from IL‑1β‑induced extracellular matrix degradation and apoptosis by inhibiting the NF‑κB pathway

Intervertebral disc degeneration (IDD) is widely considered to be one of the main causes of lower back pain, which is a chronic progressive disease closely related to inflammation, nucleus pulposus (NP) cell apoptosis and extracellular matrix (ECM) degradation. Berberine (BBR) is an alkaloid compound with an anti-inflammatory effect and has been reported to exert therapeutic action in several inflammatory diseases, including osteoarthritis. Therefore, it was hypothesized that BBR may have a therapeutic effect on IDD through inhibition of the inflammatory response. The aim of the present study was to evaluate the influence of BBR on IDD in interleukin (IL)-1β-treated human NP cells in vitro. The results showed that BBR attenuated the upregulation of ECM-catabolic factors [matrix metalloproteinase (MMP)-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motif (ADAMTS)-4 and ADAMTS-5], and the downregulation of ECM-anabolic factors (type II collagen and aggrecan) following stimulation of the human NP cells with IL-1β. Treatment with BBR also protected human NP cells from IL-1β-induced apoptosis, as determined by western blotting and flow cytometry. Mechanistically, the IL-1β-stimulated degradation of IκBα, and the phosphorylation and translocation of nuclear factor (NF)-κB p65 were found to be attenuated by BBR, indicating that NF-κB pathway activation was suppressed by BBR in the IL-1β-treated human NP cells. The results of the experiments revealed a therapeutic potential of BBR for the prevention or treatment of IDD.

A novel in vivo large animal model of lumbar spinal joint degeneration

BACKGROUND CONTEXT

Degenerative disc disease (DDD) is a common, widespread socioeconomic problem. Appropriate large animal models of DDD are required for improved understanding and to serve as preclinical test beds for therapeutic strategies.

PURPOSE

To evaluate the effects of short and medium duration immobilization on the sheep lumbar intervertebral disc (IVD) and facet joints (FJs), and to establish a large animal model for DDD research.

STUDY DESIGN

An in vivo sheep model evaluating the effect of short- and medium-term immobilization on disc degeneration.

METHODS

Eighteen sheep were equally randomized into three groups: short-term (6-week) immobilization (n=6), medium-term (26-week) immobilization (n=6), and control (no surgery) (n=6). Immobilization of L3-L4 was achieved with pedicle screw and rod implantation, the IVD was kept intact, and the annulus and end plates were not disrupted. The IVD and FJs were assessed with planar radiography, computerized tomography (CT), magnetic resonance imaging (MRI), pure moment biomechanical testing, and histologic analysis.

RESULTS

Disc height was reduced for 6- and 26-week immobilization groups. The MRI and histologic analysis demonstrated significant disc degeneration for both immobilized groups compared with control, but no statistical difference was detected between short- and medium-term duration. Progressive degenerative changes in FJs were observed with micro-CT and histologic end points. Immobilization significantly reduced lateral bending and flexion-extension range of motion.

CONCLUSIONS

The mechanical environment set up by immobilization alone is capable of inducing lumbar disc degeneration at both 6 and 26 weeks in sheep. Longer duration immobilization did not advance disc degeneration process beyond of that found with short duration. The present model produces a degenerative disc with intact annulus and without acute injury, more closely representing the scenario common in human disc degeneration. This provides a suitable large animal in vivo model for the evaluation of the new therapies for disc degeneration. Further studies would do well to examine the effect of remobilization after immobilization in this model.

In vitro investigation of two connector types for continuous rod construct to extend lumbar spinal instrumentation

PURPOSE

Instrumentation of the lumbar spine is a common procedure for treating pathologic conditions. Studies have revealed the risks of pathologies in the adjacent segments, with the incidence rate being up to 36.1%. Revision procedures are often required, including extension of the instrumentation by the use of connectors to adjacent levels. The aim of this study was to determine the stiffness of side-to-side and end-to-end connectors for comparison with the use of continuous rods.

METHODS

Ten human lumbar spine specimens (L1-S1) were tested about the three axes under pure moment loading of ± 7.5 Nm. Nine conditions were used to investigate the functions of the extensions for different instrumentation lengths (L3-S1 and L2-S1) and different connector levels (L3/4 and L2/3). The intersegmental range of motion (iROM) and intersegmental neutral zone as well as total range of motion (tROM) and total neutral zone (tNZ) were analyzed.

RESULTS

The application of the spinal system significantly decreased the tROMs (- 44 to - 83%) and iROMs in levels L2/3 (- 56 to - 94%) and L3/4 (- 68 to - 99%) in all the tested directions, and the tNZ under flexion/extension (- 63 to - 71%) and axial rotation (- 34 to - 72%). These decreases were independent of the employed configuration (p < 0.05). The only significant changes in the iROM were observed under lateral bending between the continuous rod and the side-to-side connector at level L3/4 (p = 0.006).

CONCLUSION

From a biomechanical viewpoint, the tested connectors are comparable to continuous rods in terms of ROM and NZ. These slides can be retrieved under Electronic Supplementary Material.

Evidence-Based Analysis of Adjacent Segment Degeneration and Disease After LIF: A Narrative Review

STUDY DESIGN

Narrative review.

OBJECTIVES

The etiology of adjacent segment degeneration (ASDeg) and adjacent segment disease (ASDz) after lumbar interbody fusion (LIF) remains controversial. The aim of this narrative review was to provide an evidence-based analysis of the peer-reviewed literature on clinical studies of ASDeg and ASDz after LIF.

METHODS

A review was performed utilizing Medline, Embase, and Cochrane databases. Two reviewers independently extracted relevant data from each included study. Statistical comparisons were made when appropriate.

RESULTS

Nine articles that matched the inclusion and exclusion criteria were included. All the studies were Level III and retrospective. MINORS scores ranged from 9.5 to 13. Clinical outcomes were assessed in all 9 studies, but only 6 studies used validated outcomes measures. Only 6 studies reported values for both ASDeg and ASDz. ASDeg alone was reported in 3 studies. Due to the variability in the criteria for designation as ASDz (different radiographic modalities) and ASDeg (different outcomes measures), we were unable to calculate frequency-weighted mean values or compare the various surgical techniques.

CONCLUSIONS

This review highlights the various limitations of the current literature on ASDeg and ASDz after lumbar fusion, specifically the absence of a rigorous definition and classification system and an extraordinary heterogeneity in methodology. There needs to be a fundamental shift in the current ASDeg and ASDz research landscape, toward a consensus, so that the high-level clinical research that is essential for treatment of spinal pathology may become available.

Functional compressive mechanics and tissue biocompatibility of an injectable SF/PU hydrogel for nucleus pulposus replacement

In spinal degenerative disease, an injectable liquid hydrogel can fill in defect entirely, lessen the danger of implant relocation and following loss of disc height, minimizing the operative trauma. Here, we propose an injectable in-situ chemically cross-linked hydrogel by a two-component reaction of liquid silk fibroin with liquid polyurethane at physiological temperature conditions. Confined compression tests and fatigue tests were reported to assess physical properties of the hydrogel. Impact of different diameter on the biomechanical behaviours was tested to evaluate the clinical potentiality of the hydrogel for replacing nucleus pulposus. Degradation behaviours in different solutions and animal experiments were also investigated to examine the tissue biocompatibility of the hydrogel. The hydrogel modulus was affected by the hydrogel geometrical (diameter) parameters. SF/PU composite hydrogel can survive a million cycles, unconstrained fatigue resistance. More importantly, in vivo biocompatibility using New Zealand white rabbits, showed good biocompatibility over a three-month period in culture. Particularly, they showed the significant clinical merit of providing stronger axial compressive stiffness on confined compression test. Based on the outcomes of the present research, the SF/PU composite hydrogel may provide significant advantages for use in future clinical application in replacing nucleus pulposus field.

Association between bicortical screw fixation at upper instrumented vertebra and risk for upper instrumented vertebra fracture

OBJECTIVE

The aim of this study was to investigate the risk of upper instrumented vertebra (UIV) fractures associated with UIV screw fixation (unicortical vs bicortical) and polymethylmethacrylate (PMMA) augmentation after adult spinal deformity surgery.

METHODS

A single-center, single-surgeon consecutive series of adult patients who underwent lumbar fusion for ≥ 4 levels (that is, the lower instrumented vertebra at the sacrum or pelvis and the UIV of the thoracolumbar spine [T9–L2]) were retrospectively reviewed. Age, sex, follow-up duration, sagittal UIV angle immediately postoperatively including several balance-related parameters (lumbar lordosis [LL], pelvic incidence, and sagittal vertical axis), bone mineral density, UIV screw fixation type, UIV PMMA augmentation, and UIV fracture were evaluated. Patients were divided into 3 groups: Group U, 15 patients with unicortical screw fixation at the UIV; Group P, 16 with bicortical screw fixation and PMMA augmentation at the UIV; and Group B, 21 with bicortical screw fixation without PMMA augmentation at the UIV.

RESULTS

The mean number of levels fused was 6.5 ± 2.5, 7.5 ± 2.5, and 6.5 ± 2.5; the median age was 50 ± 29, 72 ± 6, and 59 ± 24 years; and the mean follow-up was 31.5 ± 23.5, 13 ± 6, and 24 ± 17.5 months in Groups U, P, and B, respectively (p > 0.05). There were no significant differences in balance-related parameters (LL, sagittal vertical axis, pelvic incidence–LL, and so on) among the groups. UIV fracture rates in Groups U (0%), P (31.3%), and B (42.9%) increased in sequence by group (p = 0.006). UIV bicortical screw fixation increased the risk for UIV fracture (OR 5.39; p = 0.02).

CONCLUSIONS

Bicortical screw fixation at the UIV is a major risk factor for early UIV compression fracture, regardless of whether a thoracolumbosacral orthosis is used. To reduce the proximal junctional failure, unicortical screw fixation at the UIV is essential in adult spinal deformity correction surgery.

A Review of Animal Models of Intervertebral Disc Degeneration: Pathophysiology, Regeneration, and Translation to the Clinic

Lower back pain is the leading cause of disability worldwide. Discogenic pain secondary to intervertebral disc degeneration is a significant cause of low back pain. Disc degeneration is a complex multifactorial process. Animal models are essential to furthering understanding of the degenerative process and testing potential therapies. The adult human lumbar intervertebral disc is characterized by the loss of notochordal cells, relatively large size, essentially avascular nature, and exposure to biomechanical stresses influenced by bipedalism. Animal models are compared with regard to the above characteristics. Numerous methods of inducing disc degeneration are reported. Broadly these can be considered under the categories of spontaneous degeneration, mechanical and structural models. The purpose of such animal models is to further our understanding and, ultimately, improve treatment of disc degeneration. The role of animal models of disc degeneration in translational research leading to clinical trials of novel cellular therapies is explored.

Longitudinal Comparison of Enzyme- and Laser-Treated Intervertebral Disc by MRI, X-Ray, and Histological Analyses Reveals Discrepancies in the Progression of Disc Degeneration: A Rabbit Study

Regenerative medicine is considered an attractive prospect for the treatment of intervertebral disc (IVD) degeneration. To assess the efficacy of the regenerative approach, animal models of IVD degeneration are needed. Among these animal models, chemonucleolysis based on the enzymatic degradation of the Nucleus Pulposus (NP) is often used, but this technique remains far from the natural physiopathological process of IVD degeneration. Recently, we developed an innovative animal model of IVD degeneration based on the use of a laser beam. In the present study, this laser model was compared with the chemonucleolysis model in a longitudinal study in rabbits. The effects of the treatments were studied by MRI (T2-weighted signal intensity (T2wsi)), radiography (IVD height index), and histology (NP area and Boos' scoring). The results showed that both treatments induced a degeneration of the IVD with a decrease in IVD height and T2wsi as well as NP area and an increase in Boos' scoring. The enzyme treatment leads to a rapid and acute process of IVD degeneration. Conversely, laser radiation induced more progressive and less pronounced degeneration. It can be concluded that laser treatment provides an instrumental in vivo model of slowly evolving IVD degenerative disease that can be of preclinical relevance for assessing new prophylactic biological treatments of disc degeneration.

Protective effect of calcitonin on lumbar fusion-induced adjacent-segment disc degeneration in ovariectomized rat

Background

Intervertebral disc (IVD) degeneration and pathological changes in the spinal cord are major causes of back pain. In addition to its well-established anti-resorptive effect on bone, calcitonin (CT) potentially exerts protective effects on IVD degeneration in ovariectomized rats. However, possible therapeutic effects of CT on lumbar fusion-induced adjacent-segment disc degeneration (ASDD) have not been investigated yet. In this study, we examined the effects of CT on IVD degeneration adjacent to a lumbar fusion in ovariectomized rats.

Methods

Posterolateral lumbar fusion (PLF) at L4–5 was performed 4 weeks after ovariectomy (OVX) or sham surgery in female Sprague–Dawley rats. Following PLF + OVX, rats received either salmon CT (OVX + PLF + sCT, 16 IU/Kg/2d) or vehicle (OVX + PLF + V) treatment for 12 weeks; the remaining rats were divided into Sham + V, OVX + V, and PLF + V groups. Fusion status was analyzed by manual palpation and radiography. Adjacent segment disc was assessed by histological, histomorphometric, immunohistochemical analysis. L6 vertebrae microstructures were evaluated by micro-computed tomography.

Results

Histological analysis showed more severe ASDD occurred in OVX + PLF + V rats compared with the OVX + V or PLF + V groups. CT treatment suppressed the score for ASDD, increased disc height, and decreased the area of endplate calcification. Immunohistochemical staining demonstrated that CT decreased the expression of collagen type-I, matrix metalloproteinase-13, and a disintegrin and metalloproteinase with thrombospondin motifs-4, whereas it increased the expression of collagen type-II and aggrecan in the disc. Micro-computed tomography indicated that CT increased bone mass and improved the microstructure of the L6 vertebrae.

Conclusions

These results suggest that CT can prevent ASDD, induce beneficial changes in IVD metabolism, and inhibit deterioration of the trabecular microarchitecture of vertebrae in osteoporotic rats with lumbar fusion.

Alendronate Prevents Intervertebral Disc Degeneration Adjacent to a Lumbar Fusion in Ovariectomized Rats

STUDY DESIGN

A model of disc degeneration adjacent to a lumbar fusion in osteoporotic rats.

OBJECTIVE

We determined the effect of alendronate (ALN) on the disc degeneration adjacent to a lumbar fusion in ovariectomized rats.

SUMMARY OF BACKGROUND DATA

Adjacent-segment disc degeneration (ASDD) is one of the negative sequelae of spinal fusion. Previous studies have shown that ALN can alleviate disc degeneration. However, no data have been documented regarding the effect of ALN on ASDD after posterolateral lumbar fusion (PLF) in osteoporosis.

METHODS

50 female Sprague-Dawley rats underwent either a sham operation (sham) (n = 20) or bilateral ovariectomy (OVX) (n = 30). 4 weeks later, all but 10 rats from each group underwent PLF consisting of an intertransverse process spinal fusion using autologous-iliac-bone grafts with spinous-process wire fixation at the L4-L5 segment. Animals were subcutaneously administered vehicle (V) or ALN (70 μg/kg/wk) for 12 weeks post-PLF as follows: Sham+V, OVX+V, PLF+V, OVX+PLF+V, and OVX+PLF+ALN. Fusion status was analyzed by manual palpation and radiography. Adjacent-segment disc was assessed by histological, histomorphometric, immunohistochemical, and mRNA analysis. L6 vertebrae microstructures were evaluated by microcomputed tomography.

RESULTS

The fused segments showed clear evidence of fusion based on manual palpation and radiographs. The OVX+PLF+V group showed more severe degenerative alterations and higher histological scores in the disc than the Sham+V, OVX+V, and PLF+V groups (P < 0.05). Compared with the OVX+PLF+V group, the OVX+PLF+ALN group exhibited significantly improved bone mass and vertebrae microstructures (P < 0.05), an increased disc height, and a decreased endplate calcification area (P < 0.05). ALN also significantly decreased Col-I, MMP-13, and ADAMTS-4 expression and increased Col-II and Aggrecan expression in the disc matrix (P < 0.05).

CONCLUSION

ALN effectively alleviated ASDD post-PLF in ovariectomized rats. These data indicate that ALN can be used as a potential therapeutic agent to attenuate ASDD progression in osteoporosis.

Pathomechanisms of discogenic low back pain in humans and animal models

BACKGROUND CONTEXT

Although explored in humans and animal models, the pathomechanisms of discogenic low back pain (LBP) remain unknown.

PURPOSE

The aim of this study was to review the literature about the pathomechanisms of discogenic LBP.

METHODS

Animal models of discogenic pain and specimens from degenerated human intervertebral discs (IVDs) have provided clues about the pathomechanisms of discogenic LBP. Painful discs are characterized by a confluence of innervation, inflammation, and mechanical hypermobility. These three possible mechanisms are discussed in this review.

RESULTS

Animal models and specimens from humans have revealed sensory innervation of lumbar IVDs and sensory nerve ingrowth into the inner layer of IVDs. Cytokines such as tumor necrosis factor-α and interleukins induce this ingrowth. Nerve growth factor has also been recently identified as an inducer of ingrowth. Finally, disc degeneration induces several collagenases; their action results in hypermobility and pain.

CONCLUSIONS

To treat discogenic LBP, it is important to prevent sensitization of sensory nerve fibers innervating the IVD, to suppress pathogenic increases of cytokines, and to decrease disc hypermobility.

MiR-34a promotes Fas-mediated cartilage endplate chondrocyte apoptosis by targeting Bcl-2

Apoptosis of cartilage endplate (CEP) chondrocytes is associated with the pathogenesis of intervertebral disk degeneration (IDD). Recent studies have shown that miR-34a is crucially involved in chondrocyte apoptosis during osteoarthritic cartilage. Here, we investigated the involvement of miR-34a in CEP chondrocyte apoptosis in IDD. In human degenerated CEP chondrocytes, miRNA (miR)-34a was markedly elevated in association with increased apoptosis. Bioinformatics target prediction identified Bcl-2 as a putative target of miR-34a. Furthermore, miR-34a inhibited Bcl-2 expression by directly targeting their 3'-untranslated regions, and this inhibition was abolished by mutation of the miR-34a binding sites. In vitro, knockdown of miR-34a in human endplate chondrocytes resulted in overexpression of Bcl-2, whereas upregulation of miR-34a led to repression of Bcl-2. Fas-mediated apoptosis was decreased when antagonizing miR-34a with locked nucleotide analog-miR-34a in human endplate chondrocytes. Taken together, our results demonstrate that upregulated miR-34a potentiates Fas-mediated endplate chondrocyte apoptosis, which is associated with IDD.

Effects of hypoxia on differentiation from human placenta-derived mesenchymal stem cells to nucleus pulposus-like cells

BACKGROUND CONTEXT

Low back pain is a frequently occurring disease caused by intervertebral disc degeneration. Mesenchymal stem cells (MSCs) are a possible treatment modality. Studies have shown MSCs can be transformed into nucleus pulposus-like cells under normoxic conditions. However, this is not a true representation of the hypoxic environment nucleus pulposus cells experience during in vivo growth and differentiation.

PURPOSE

To determine the effects of a hypoxic environment on the differentiation of human placenta-derived mesenchymal stem cells (PMSCs) to nucleus pulposus-like cells.

STUDY DESIGN

An experimental study.

METHODS

Placenta-derived mesenchymal stem cells were cultured and the mesenchymal lineage was confirmed by flow cytometry. Two groups of PMSCs were then cultured under different oxygen concentrations creating a hypoxic group and normoxic group. The proliferation of cells in each group was compared by cell counting kit-8 on Day 1, 3, 5, and 7. Real-time polymerase chain reaction on Days 3 and 7 compared the expressions of Sox-9, Type II collagen, aggrecan, and hypoxia inducible factor-1α (HIF-1α) between the two groups. Immunofluorescence was used to compare the expression of Type II collagen between the two groups after 14 days.

RESULTS

Placenta-derived mesenchymal stem cells were successfully isolated and cultured. Mesenchymal markers were positive. On Days 3 and 5, the hypoxic group had a significantly higher proliferation rate than the normoxic group (p<.05). The expression of Sox-9 and HIF-1α was significantly higher (p<.05) in the hypoxic group at Days 3 and 7. Type II collagen and aggrecan expressions were significantly higher (p<.05) in the hypoxic group at Day 7. The hypoxic group stained more positive for Type II collagen at Day 14.

CONCLUSIONS

Hypoxic conditions lead to an increased differentiation and proliferation of nucleus pulposus-like cells. Placenta-derived mesenchymal stem cells cultured in nucleus pulposus inducing media and a hypoxic environment show enhanced expression of the nucleus pulposus-like cell markers, Sox-9, Type II collagen, aggrecan, and HIF-1α.

Evaluation of intervertebral disc regeneration with implantation of bone marrow mesenchymal stem cells (BMSCs) using quantitative T2 mapping: a study in rabbits

PURPOSE

The aim of the study was to investigate the curative effects of transplantation of bone marrow mesenchymal stem cells (BMSCs) on intervertebral disc regeneration and to investigate the feasibility of the quantitative T2 mapping method for evaluating repair of the nucleus pulposus after implantation of BMSCs.

METHODS

Forty-eight New Zealand white rabbits were used to establish the lumber disc degenerative model by stabbing the annulus fibrosus and then randomly divided into four groups, i.e. two weeks afterwards, BMSCs or phosphate-buffered saline (PBS) were transplanted into degenerative discs (BMSCs group and PBS group), while the operated rabbits without implantation of BMSCs or PBS served as the sham group and the rabbits without operation were used as the control group. At weeks two, six and ten after operation, the T2 values and disc height indices (DHI) were calculated by magnetic resonance imaging (MRI 3.0 T), and the gene expressions of type II collagen (COL2) and aggrecan (ACAN) in degenerative discs were evaluated by real-time reverse transcription polymerase chain reaction (RT-PCR). T2 values for the nucleus pulposus were correlated with ACAN or COL2 expression by regression analysis.

RESULTS

Cell clusters, disorganised fibres, interlamellar glycosaminoglycan (GAG) matrix and vascularisation were observed in lumber degenerative discs. BMSCs could be found to survive in intervertebral discs and differentiate into nucleus pulposus-like cells expressing COL2 and ACAN. The gene expression of COL2 and ACAN increased during ten weeks after transplantation as well as the T2 signal intensity and T2 value. The DHI in the BMSCs group decreased more slowly than that in PBS and sham groups. The T2 value correlated significantly with the gene expression of ACAN and COL2 in the nucleus pulposus.

CONCLUSIONS

Transplantation of BMSCs was able to promote the regeneration of degenerative discs. Quantitative and non-invasive T2 mapping could be used to evaluate the regeneration of the nucleus pulposus with good sensitivity.

Adjacent segment disease

EDUCATIONAL OBJECTIVES As a result of reading this article, physicians should be able to: 1. Understand the forces that predispose adjacent cervical segments to degeneration. 2. Understand the challenges of radiographic evaluation in the diagnosis of cervical and lumbar adjacent segment disease. 3. Describe the changes in biomechanical forces applied to adjacent segments of lumbar vertebrae with fusion. 4. Know the risk factors for adjacent segment disease in spinal fusion. Adjacent segment disease (ASD) is a broad term encompassing many complications of spinal fusion, including listhesis, instability, herniated nucleus pulposus, stenosis, hypertrophic facet arthritis, scoliosis, and vertebral compression fracture. The area of the cervical spine where most fusions occur (C3-C7) is adjacent to a highly mobile upper cervical region, and this contributes to the biomechanical stress put on the adjacent cervical segments postfusion. Studies have shown that after fusion surgery, there is increased load on adjacent segments. Definitive treatment of ASD is a topic of continuing research, but in general, treatment choices are dictated by patient age and degree of debilitation. Investigators have also studied the risk factors associated with spinal fusion that may predispose certain patients to ASD postfusion, and these data are invaluable for properly counseling patients considering spinal fusion surgery. Biomechanical studies have confirmed the added stress on adjacent segments in the cervical and lumbar spine. The diagnosis of cervical ASD is complicated given the imprecise correlation of radiographic and clinical findings. Although radiological and clinical diagnoses do not always correlate, radiographs and clinical examination dictate how a patient with prolonged pain is treated. Options for both cervical and lumbar spine ASD include fusion and/or decompression. Current studies are encouraging regarding the adoption of arthroplasty in spinal surgery, but more long-term data are required for full adoption of arthroplasty as the standard of care for prevention of ASD.

Lumbar clinical adjacent segment pathology: predilection for proximal levels

STUDY DESIGN

Retrospective case series.

OBJECTIVE

To evaluate reoperations for lumbar adjacent segment pathology (ASP) during a 10-year period.

SUMMARY OF BACKGROUND DATA

ASP after lumbar arthrodesis is an important clinical problem. There remains controversy, however, on the distribution of the most commonly affected levels.

METHODS

Thirty-one patients undergoing revision operation for ASP in the lumbar spine were included in this study. Patients' charts were evaluated for demographic data including age at index and revision operations, time to revision operation, and index and revision levels fused.

RESULTS

L4-L5 was the most commonly instrumented level in both single-level (n = 12), and multilevel (n = 13) index fusions. The mean length of time from the index operation to revision surgery was 81 months (range, 11-570 mo). Kaplan-Meier analysis predicted a disease-free survival rate of 32.3% at 5 years and of 12.9% at 10 years after the index operation. L3-L4 was the most commonly affected level by ASP with 75% (16/20) requiring reoperation. L2-L3 was the next most commonly affected level at 52% (14/27). The L5-S1 disk was relatively protected from ASP, with only 4/17 (24%) disks at risk developing ASP. A subgroup analysis of patients undergoing revision after a single-level L4-L5 arthrodesis revealed ASP at L3-L4 in 83% (10/12) of patients, compared with only 3/12 (25%) at L5-S1 (P < 0.05). Of all cases of ASP, the proximal segments were involved 90% of the time.

CONCLUSION

ASP most commonly affects proximal levels in the lumbar spine. In this cohort of patients undergoing revision fusion for ASP, 90% of affected levels were rostral to the index level(s). In patients undergoing L4-L5 single-level arthrodesis, L3-L4 is at high risk, whereas L5-S1 is somewhat protected. Surgeons should pay particular attention to proximal levels when planning a lumbar arthrodesis, however, motion segments distal to fusion may not be as protected as previously thought.

LEVEL OF EVIDENCE

4.

Injectable laminin-functionalized hydrogel for nucleus pulposus regeneration

Cell delivery to the pathological intervertebral disc (IVD) has significant therapeutic potential for enhancing IVD regeneration. The development of injectable biomaterials that retain delivered cells, promote cell survival, and maintain or promote an NP cell phenotype in vivo remains a significant challenge. Previous studies have demonstrated NP cell - laminin interactions in the nucleus pulposus (NP) region of the IVD that promote cell attachment and biosynthesis. These findings suggest that incorporating laminin ligands into carriers for cell delivery may be beneficial for promoting NP cell survival and phenotype. Here, an injectable, laminin-111 functionalized poly(ethylene glycol) (PEG-LM111) hydrogel was developed as a biomaterial carrier for cell delivery to the IVD. We evaluated the mechanical properties of the PEG-LM111 hydrogel, and its ability to retain delivered cells in the IVD space. Gelation occurred in approximately 20 min without an initiator, with dynamic shear moduli in the range of 0.9-1.4 kPa. Primary NP cell retention in cultured IVD explants was significantly higher over 14 days when cells were delivered within a PEG-LM111 carrier, as compared to cells in liquid suspension. Together, these results suggest this injectable laminin-functionalized biomaterial may be an easy to use carrier for delivering cells to the IVD.

Upper instrumented vertebral fractures in long lumbar fusions: what are the associated risk factors?

STUDY DESIGN

A retrospective comparative study.

OBJECTIVE

To investigate the risk factors associated with upper instrumented vertebral (UIV) fractures in adult lumbar deformity.

SUMMARY OF BACKGROUND DATA

Long segment lumbar fusions may lead to junctional failures. The purpose of this study was to determine factors associated with junctional failures.

METHODS

Twenty-seven consecutive patients from 2001 to 2008 with minimum 4 levels fused, lower instrumented vertebra (LIV) of L5 or S1, upper instrumented vertebra of T10 or distal, and no previous surgery proximal to the instrumentation were retrospectively reviewed. We describe the UIV angle, the sagittal angle of the upper instrumented vertebra with the horizontal. Patients were divided into 3 groups: group 1, 7 patients with UIV fractures; group 2, 6 patients with other proximal failures; and group 3, 14 patients with no proximal complications.

RESULTS

The mean number of levels fused was 5.7 (4-7), 5.2 (4-8), and 6.2 (4-8); mean age was 64.1, 61.8, and 64.1, and mean body mass index was 33.5, 30.0, and 31.6 for groups 1, 2, and 3, respectively (P > 0.05). Osteotomies were performed in 5 of 7 in group 1, 1 of 6 in group 2, and 5 of 14 in group 3. Mean follow-up was 26.3 months. The average intraoperative UIV angle (UIV0) and immediate postoperative UIV angle (UIV1) were 18.6°/15.4° for group 1, 5.7°/5.3° for group 2, and 10.3°/7.1° for group 3 (P < 0.05). Surgical revision rates were higher in group 1 (71%) compared with groups 2 (50%) and 3 (43%). Eight of 11 (73%) patients with upper instrumented vertebra of L1 or L2 had either UIV fracture or other proximal failure compared with 5 of 16 (31%) in patients with upper instrumented vertebra of T10, T11, or T12.

CONCLUSION

Our series of long lumbar fusions had a high long-term complication and revision rate. A high UIV angle on intraoperative lateral radiograph was strongly associated with UIV fractures. UIVs of L1 or L2 had a higher rate of adjacent segment or UIV failure.

Síndrome adyacente

OBJETIVO: Estudiamos la incidencia de SDA quirúrgico de localización lumbar y los factores relacionados con el mismo. MÉTODO: Estudio retrospectivo de corte transversal. RESULTADOS: Encontramos 50 casos operados por SDA en 1662 cirugías realizadas, 530 en columna lumbar; incidencia 9,4%. Edad promedio 62 años. Síntoma principal: claudicación radicular (80%). Las Rx previas a la primera cirugía del nivel que sufrirá SDA: UCLA 1 (45%) y 2 (27%); lordosis prerrevisión: 36° promedio y pos 44°. Prerrevisión: IP55°, VP26°, PS29° y posoperatoria IP56°, VP22° y PS34°. Desequilibrio sagital prerrevisión 60% y posoperatorio 27%, equilibrio coronal recuperado en los 2 casos. IRM previa a la primera intervención mostró 83% con Pfirmann IV. Tipos de SDA: estenosis lumbar monosegmentaria agravada por antelistesis en 20 y por retrolistesis en 14; estenosis multisegmentaria 4, hernia discal 4, fractura por aplastamiento 4, estenosis sin listesis 4. Período entre las 2 cirugías: 6 años promedio. CONCLUSIÓN: Una incidencia de 9,4% de reintervenciones a causa de un Síndrome Adyacente, hace de esta patología un importante problema a largo plazo, lo que obligaría al cirujano a tomar las medidas que sean posibles para evitarlo. Con los resultados de este estudio retrospectivo solo podríamos decir que tendrían más posibilidades de desarrollar un SDA los segmentos con Pfirmann IV en la IRM y que se debería tener en cuenta las relaciones VP (20%) y PS (80%) pre y pos operatorias para devolver las condiciones mecánicas ideales al raquis. Se necesitarían estudios clínicos prospectivos para tener conclusiones más firmes.

Quantitative MRI analysis of the surface area, signal intensity and MRI index of the central bright area for the evaluation of early adjacent disc degeneration after lumbar fusion

PURPOSE

The aim of this study was to evaluate early ASD at short-term follow-up in fused and unoperated patients with degenerative disc disease, using quantitative magnetic resonance imaging (MRI) analysis of the area, signal intensity and their product, i.e., MRI index of the central bright area of the disc as well as measures of intervertebral disc height and Pfirrmann grading scale. The further purpose was to determine whether fusion accelerates ASD compared with non-surgical treatment in short-term follow-up.

METHODS

One hundred and eight chronic low back patients diagnosed as L4/L5 degeneration undertook either one-level instrumented posterior lumbar interbody fusion or conservative treatment. They were followed up for about 1 year. Finally 46 fused and 45 conservatively treated patients with MRI follow-up were included. Pre- and post-treatment MRIs were compared to determine the progression of disc degeneration at the two cranial adjacent segments.

RESULTS

The area, signal intensity and MRI index of the central bright area of the adjacent discs decreased in the operated and unoperated groups from pre-treatment to follow-up, except for an insignificant decrease of signal intensity at the second adjacent segment in the unoperated group. The changes in these parameters were statistically greater at the first than the second adjacent segment in the fused group, but not in the unoperated group. And the changes in the fused group were more pronounced than those at both neighbouring levels in the unoperated group. However, the Pfirrmann grading scale and intervertebral disc height did not detect any changes at adjacent discs in either group.

CONCLUSIONS

Decrease in the parameters of quantitative MRI analysis indicated early degeneration at discs adjacent to lumbar spinal fusion. Fusion had an independent effect on the natural history of ASD during short-term follow-up. Continued longitudinal follow-up is required to determine whether these MRI changes lead to pathologic changes.

Injectable silk fibroin/polyurethane composite hydrogel for nucleus pulposus replacement

In degenerative disc disease, an injectable hydrogel can fill a degenerate area completely, reduce the risk of implant migration and subsequent loss of height of the intervertebral disc, and minimise surgical defects. Here, we propose a method of preparing an injectable silk fibroin/polyurethane (SF/PU) composite hydrogel by chemical cross-linking under physiological conditions. Mechanical testing was used to determine the mechanical strength of the hydrogel. The impact of hydrogel height on the biomechanical properties was discussed to estimate the working capacity of the hydrogel for further clinical application. Rheological properties were also examined to assess the practical ability of the hydrogel for clinical application. Hydrogel injection and cell assessment is also of interest for clinical application. An SF/PU composite hydrogel can be injected through a small incision. A cell proliferation assay using bone marrow stromal cells showed positive cell viability and increased proliferation over a seven-day period in culture. Importantly, the hydrogel can be monitored in real-time using X-ray fluoroscopy during and after surgery according to the results of X-ray fluoroscopy examination, and shows good visibility based on X-ray assays. In particular, the hydrogel offers the clinically important advantage of visibility in CT and T2-weighted magnetic resonance imaging. Based on the results of the current study, the SF/AU composite hydrogel may offer several advantages for future application in nucleus pulposus replacement.

Good functional outcome and adjacent segment disc quality 10 years after single-level anterior lumbar interbody fusion with posterior fixation

We reviewed the records of a prospective consecutive cohort to evaluate the clinical performance of anterior lumbar interbody fusion with a titanium box cage and posterior fixation, with emphasis on long-term functional outcome. Thirty-two patients with chronic low back pain underwent anterior lumbar interbody fusion and posterior fixation. Radiological and functional results (visual analogue scale [VAS] and Oswestry score) were evaluated. Adjacent segment degeneration (ASD) was evaluated radiologically and by magnetic resonance imaging (MRI). Twenty-five patients (78%) were available for follow-up. Functional scores showed significant improvement in pain and function up to the 2-year follow-up observation. At 4 years, there was some deterioration of the clinical results. At 10-year follow-up, results remained stable compared with 4-year results. MRI showed ASD in 3/25 (12%) above and 2/10 (20%) below index level (compared with absent preoperatively). ASD could not be related to clinical outcome in this study. Anterior lumbar interbody fusion and posterior fixation is safe and effective. Initial improvement in VAS and Oswestry scores is partly lost at the 4-year follow-up. Good clinical results are maintained at 10-year follow-up and are not related to adjacent segment degeneration.

Biomechanical effect of different interspinous devices on lumbar spinal range of motion under preload conditions

INTRODUCTION

Interspinous devices are used as an alternative to the current gold standard treatment, decompressive surgery with or without fusion, for lumbar spinal stenosis. They are supposed to limit extension and expand the spinal canal and foramen at the symptomatic level, but still allow lateral bending and axial rotation in the motion segment. The aim of the present study is the biomechanical evaluation of the change in the range of motion of the affected and adjacent segments following implantation of different interspinous devices under load in all directions of motion.

METHOD

Eight fresh frozen human cadaver lumbar spines (L2-L5) were tested in a spinal testing device with a moment of 7.5 nm in flexion/extension, lateral bending and rotation with and without a preload (follower load of 400 N). The ROM was measured after implantation of Aperius (Kyphon, Mannheim), In-Space (Synthes, Umkirch), X-Stop (Tikom, Fürth) and Coflex (Paradigm Spine, Wurmlingen) into the segment L3/L4.

RESULTS

All interspinous devices caused a significant reduction in extension of the instrumented segment without significantly affecting the other directions of motion. The flexion was reduced by all implants only when the follower load was applied. All devices caused a higher ROM of the whole spine during lateral bending and rotation.

CONCLUSION

The actual evaluated interspinous devices led to a significant reduction in ROM during flexion-extension, but to a significant increase in ROM for the whole specimen (L2-L5) during lateral bending and rotation, which could increase the risk of adjacent segment degeneration.

How does lumbar degenerative disc disease affect the disc deformation at the cephalic levels in vivo?

STUDY DESIGN

Case-control study.

OBJECTIVE

To evaluate the effect of lumbar degenerative disc disease (DDD) on the disc deformation at the adjacent level and at the level one above the adjacent level during end ranges of lumbar motion.

SUMMARY OF BACKGROUND DATA

It has been reported that in patients with DDD, the intervertebral discs adjacent to the diseased levels have a greater tendency to degenerate. Although altered biomechanics have been suggested to be the causative factors, few data have been reported on the deformation characteristics of the adjacent discs in patients with DDD.

METHODS

Ten symptomatic patients with discogenic low back pain between L4 and S1 and with healthy discs at the cephalic segments were involved. Eight healthy subjects recruited in our previous studies were used as a reference comparison. The In Vivo kinematics of L3-L4 (the cephalic adjacent level to the degenerated discs) and L2-L3 (the level one above the adjacent level) lumbar discs of both groups were obtained using a combined magnetic resonance imaging and dual fluoroscopic imaging technique at functional postures. Deformation characteristics, in terms of areas of minimal deformation (defined as less than 5%), deformations at the center of the discs, and maximum tensile and shear deformations, were compared between the two groups at the two disc levels.

RESULTS

In the patients with DDD, there were significantly smaller areas of minimal disc deformation at L3-L4 and L2-L3 than the healthy subjects (18% compared with 45% of the total disc area, on average). Both L2-L3 and L3-L4 discs underwent larger tensile and shear deformations in all postures than the healthy subjects. The maximum tensile deformations were higher by up to 23% (of the local disc height in standing) and the maximum shear deformations were higher by approximately 25% to 40% (of the local disc height in standing) compared with those of the healthy subjects.

CONCLUSION

Both the discs of the adjacent level and the level one above experienced higher tensile and shear deformations during end ranges of lumbar motion in the patients with DDD before surgical treatments when compared with the healthy subjects. The larger disc deformations at the cephalic segments were otherwise not detectable using conventional magnetic resonance imaging techniques. Future studies should investigate the effect of surgical treatments, such as fusion or disc replacement, on the biomechanics of the adjacent segments during end ranges of lumbar motion.

Do the adjacent level intervertebral discs degenerate after a lumbar spinal fusion? An experimental study using a rabbit model

STUDY DESIGN

A rabbit model of disc degeneration adjacent to a lumbar spinal fusion.

OBJECTIVE

To use a rabbit model to determine the long-term changes in the intervertebral discs at the levels above (cephalad) and below (caudad) 2 fused lumbar levels.

SUMMARY OF BACKGROUND DATA

Lumbar spinal fusion is generally carried out to eliminate motion at a specific lumbar level. However, it is commonly thought that by eliminating motion at a level, one increases the motion at the adjacent levels cephalad and caudad the fused levels. There have been studies that have reported on degeneration occurring at the cephalad and caudad levels adjacent to the fused levels.

METHODS

A total of 9 New Zealand white, female rabbits: 4 rabbits in the control group and 5 rabbits in the experimental group. The 5 rabbits in the experimental group underwent a posterolateral 2-level lumbar spinal fusion from L3 to L5. The changes in the lumbar discs were assessed using radiographs, magnetic resonance (MR) images, and histology at 6 months and 12 months.

RESULTS

The results at 6 months are less clear than those at 12 months. The results at 12 months for the experimental group are (1) the intervertebral disc height decreased at the caudad adjacent level and to a lesser extent at the cephalad adjacent level; (2) the MRI scores for the discs at the caudad and cephalad adjacent levels showed severe loss of signal intensity as compared to the discs at the same levels in the control group. This loss was more pronounced at the caudad level where the loss of signal intensity was similar to that seen at the fused levels; (3) the histologic analysis showed severe degenerative changes with a lack of live cells in the nucleus pulposus and in the endplate at the caudad adjacent level. At the cephalad level, live cells were apparent (albeit few) in the nucleus pulposus, and there was a more normal looking endplate with live cells.

CONCLUSION

The intervertebral discs at both the cephalad and the caudad levels adjacent to the 2 fused lumbar levels in this rabbit-model experiment carried out over 12 months after surgery showed degenerative changes asassessed using disc-height measurements, MR images, and histology, and the effect was more severe at the caudad adjacent level.

New progress in adjacent segment degeneration/disease

Adjacent segment degeneration/disease (ASD) has been generally accepted as a long-term complication after spinal surgery. Although the incidence of ASD is not very high, it is gradually recognized to be a very important factor in evaluation of the long-term effect of spinal fusion. There are many views concerning pathogenic factors and ways of prevention and treatment. The authors review and discuss the current research and this article will describe recent advances in ASD.

Proximal junctional vertebral fracture in adults after spinal deformity surgery using pedicle screw constructs: analysis of morphological features

STUDY DESIGN

A retrospective comparative study.

OBJECTIVE

To investigate the morphologic features of proximal vertebral fractures in adults following spinal deformity surgery using segmental pedicle screw instrumentation.

SUMMARY OF BACKGROUND DATA

Fractures above pedicle screw constructs are a clinical problem that warrants further investigation for prevention and treatment.

METHODS

Ten adult patients (6 lumbar scoliosis, 4 degenerative sagittal imbalance) who underwent segmental spinal instrumented fusion were analyzed. Patients were divided into 2 groups according to the features of vertebral fracture: upper instrumented vertebral collapse + adjacent vertebral subluxation (SUB group: n = 5), and adjacent vertebral fracture (Fracture group: n = 5).

RESULTS

Both groups demonstrated a high frequency of osteopenia and all patients in the SUB group had comorbidities before surgery. The SUB group demonstrated a shorter interval between initial surgery and the fracture (subluxation: 3 +/- 1.9 months; fracture: 33 +/- 25.3 months, P < 0.05), and hypokyphosis (T5-T12) in the thoracic region before surgery (SUB: 13 degrees +/- 6.4 degrees; fracture: 33 degrees +/- 15.6 degrees). Both groups demonstrated severe global sagittal imbalance (SUB: 151 +/- 62.8 mm; fracture: 94 +/- 102.2 mm), and hypolordosis (T12-S1) in the lumbar spine (SUB: -19 degrees +/- 24.4 degrees ; fracture: -33 degrees +/- 22.7 degrees) before surgery. Global sagittal imbalance in the SUB group was corrected to 8 +/- 17.4 mm immediately postoperative (P < 0.05), but increased to 64 +/- 19.9 mm after the junctional fractures (P < 0.05). The SUB group demonstrated a significantly higher wedging rate (SUB: 65% +/- 12.4%; fracture: 36% +/- 16.0%, P < 0.05) and greater local kyphosis (SUB: 42 degrees +/- 11.1 degrees; fracture: 17 degrees +/- 4.1 degrees, P < 0.05) after the fracture. Two of 5 patients in the SUB group demonstrated severe neurologic deficit from E to B after the fractures by a modified Frankel classification.

CONCLUSION

Old age, osteopenia, preoperative comorbidities, and severe global sagittal imbalance were found to be frequent in patients with proximal junctional fracture. In addition, marked correction of sagittal malalignment might be considered as a risk factor of upper instrumented vertebra collapse followed by adjacent vertebral subluxation, which occurred in the first 6 months after corrective surgery with the potential for causing severe neurologic deficit because of the severe local kyphotic deformity.

Resect or not to resect: the role of posterior longitudinal ligament in lumbar total disc replacement

With regard to the literature, several factors are considered to have an impact on postoperative mobility after lumbar total disc replacement (TDR). As TDR results in a distraction of the ligamentous structures, theoretically the postoperatively disc height and ligamentous integrity have also an influence on biomechanics of a treated segment. The purpose of the study was to evaluate the influence of posterior longitudinal ligament (PLL) resection and segmental distraction on range of motion (ROM). Six human, lumbar spines (L2-L3) were tested with pure moments of ±7.5 Nm in a spine loading apparatus. The ROM was determined in all three motion planes. Testing sequences included: (1) intact state, (2) 10 mm prosthesis (PLL intact), (3) 10 mm prosthesis (PLL resected), (4) 12 mm prosthesis (PLL resected). The prosthesis used was a prototype with a constrained design using the ball-and-socket principle. The implantation of the 10 mm prosthesis already increased the disc height significantly (intact: 9.9 mm; 10 mm prosthesis: 10.6 mm; 12 mm prosthesis: 12.7 mm). Compared to the intact status, the implantation of the 10 mm prosthesis resulted in an increase of ROM for flexion/extension (8.6° vs 10.8°; P = 0.245) and axial rotation (2.9° vs 4.5°; P = 0.028), whereas lateral bending decreased (9.0° vs 7.6°; P = 0.445). The resection of the PLL for the 10 mm prosthesis resulted in an increase of ROM in all motion planes compared to the 10 mm prosthesis with intact PLL (flexion/extension: 11.4°, P = 0.046; axial rotation: 5.1°, P = 0.046; lateral bending: 8.6°, P = 0.028). The subsequent implantation of a 12 mm prosthesis, with resected PLL, resulted in a significant decrease of ROM in all motion planes compared to the 10 mm prosthesis with intact PLL (flexion/extension: 8.4°, P = 0.028; axial rotation: 3.3°, P = 0.028; lateral bending: 5.1°, P = 0.028). Compared to the intact status, the 12 mm prosthesis with resected PLL only decreased lateral bending significantly while the 10 mm prosthesis with intact PLL increased axial rotation significantly. The resection of the PLL during TDR results in a significant increase of ROM in all three principle motion planes. But it still remains unclear if this increase which is in median not more than 1° may alter the clinical results. Moreover, the destabilizing effect of PLL resection can be reversed using a higher implant. The prosthesis height seems more crucial than PLL preservation to maintain the primary stability after TDR.

Junction kinematics between proximal mobile and distal fused lumbar segments: biomechanical analysis of pedicle and hook constructs

BACKGROUND CONTEXT

Biomechanical studies have demonstrated increased motion in motion segments adjacent to instrumentation or arthrodesis. The effects of different configurations of hook and pedicle screw instrumentation on the biomechanical behaviors of adjacent segments have not been well documented.

PURPOSE

To compare the effect of three different fusion constructs on adjacent segment motion proximal to lumbar arthrodesis.

METHODS

Seven human cadaver lumbar spines were tested in the following conditions: 1) intact; 2) L4-L5-simulated circumferential fusion (CF); 3) L4-L5-simulated fusion extended to L3 with pedicle screws; and 4) L4-L5-simulated fusion extended to L3 with sublaminar hooks. Rotation data at L2-L3, L3-L4, and L4-L5 were analyzed using both load limit control (+/-7.5N.m) and displacement limit control (truncated to the greatest common angular motion of the segments for each specimen).

RESULTS

Both the L3-L4 and L2-L3 motion segments above the L4-L5-simulated CF had significantly increased motion in all loading planes compared with the intact spine, but no significant differences were found between L3-L4 and L2-L3 motion. When the L3-L4 segment was stabilized with pedicle screws, its motion was significantly smaller in flexion, lateral bending, and axial rotation than when stabilized with sublaminar hooks. At the same time, L2-L3 motion was significantly larger in flexion, lateral bending, and axial rotation in the pedicle screw model compared with the sublaminar hook construct.

CONCLUSIONS

The use of sublaminar hooks to stabilize the motion segment above a circumferential lumbar fusion reduced motion at the next cephalad segment compared with a similar construct using pedicle screws. The semiconstrained hook enhancement may be considered if a patient is at a risk of adjacent segment disorders.

A prospective randomised study on the long-term effect of lumbar fusion on adjacent disc degeneration

The existence and importance of an accelerated adjacent segment disc degeneration (ASD) after lumbar fusion have previously not been demonstrated by RCTs. The objectives of this study were, to determine whether lumbar fusion in the long term accelerates degenerative changes in the adjacent disc and whether this affects the outcome, by using a prospective randomised design. A total of 111 patients, aged 18-55, with isthmic spondylolisthesis were randomised to exercise (EX, n = 34) or posterolateral fusion (PLF, n = 77), with (n = 37) or without pedicle screw instrumentation (n = 40). The minimum 10 years FU rate was 72%, with a mean FU time of 12.6 years (range 10-17 years). Three radiographic methods of ASD quantification were used, i.e. two digital radiographic measurement methods and the semi quantitative UCLA grading scale. One digital measurement method showed a mean disc height reduction by 2% in the EX group and by 15% in the PLF group (p = 0.0016), and the other showed 0.5 mm more disc height reduction in the PLF compared to the Ex group (ns). The UCLA grading scale showed normal discs in 100% of patients in the EX group, compared to 62% in the PLF group (p = 0.026). There were no significant differences between instrumented and non-instrumented patients. In patients with laminectomy we found a significantly higher incidence of ASD compared to non laminectomised patients (22/47 vs. 2/16 respectively, p = 0.015). In the longitudinal analysis, the posterior and anterior disc heights were significantly reduced in the PLF group, whereas in the EX group only the posterior disc height was significantly reduced. Except for global outcome, which was significantly better for patients without ASD, the clinical outcome was not statistically different in patients with and without ASD. In conclusion, the long-term RCT shows that fusion accelerates degenerative changes at the adjacent level compared with natural history. The study suggests that not only fusion, but also laminectomy may be of pathogenetic importance. The clinical importance of ASD seems limited, with only the more severe forms affecting the outcome.

Sublaminar wiring stabilization to prevent adjacent segment degeneration after lumbar spinal fusion

INTRODUCTION

Adjacent segment degeneration (ASD) is a complication of lumbar spinal fusion. There are some reports on the cause of this degeneration but none concerning its prevention. We performed sublaminar wiring stabilization to prevent ASD after posterolateral lumbar spinal fusion with instrumentation. The purpose of this study was to prospectively evaluate the efficacy of this procedure.

PATIENTS AND METHODS

Between 2003 and 2004, 54 consecutive patients with lumbar spinal canal stenosis and multilevel instability of the lumbar spine underwent posterior decompression and posterolateral fusion with instrumentation. The mean age at the time of surgery was 66.7 +/- 1.3 years, and the mean follow-up period was 40.0 +/- 1.1 months, with a minimum of 29 months. Twenty-seven of the patients underwent conventional sublaminar wiring stabilization at the cephalad segment adjacent to the site of fusion to prevent ASD (group A), and the other 27 patients did not (group B). Some items were assessed, including clinical outcome using Japanese Orthopaedic Association (JOA) score, sagittal global lumbar alignment, and segmental motion in flexion-extension radiographs of the cephalad vertebral body adjacent to the site of fusion.

RESULTS

There were no significant differences in JOA scores between two groups, but 2 patients in group B underwent subsequent surgery due to ASD. Sagittal lumbar alignment did not change in group A but was significantly decreased in group B. With respect to segmental motion in flexion-extension radiographs, group A showed a significant decrease from 6.9 degrees before surgery to 3.4 degrees after surgery, on the other hand group B showed a significant increase from 5.6 degrees before surgery to 8.4 degrees after surgery.

CONCLUSIONS

In this study, it was suggested that sublaminar wiring stabilization significantly reduces the range of motion of the adjacent segment and preserves sagittal lumbar alignment, which lead to prevention of ASD. The clinical outcome of the subsequent surgeries is relatively poor, so it is important to prevent ASD by any prevention such as sublaminar wiring stabilization.

Adjacent segment mobility after rigid and semirigid instrumentation of the lumbar spine

STUDY DESIGN

Retrospective radiographic analysis of lumbar spine range of motion (ROM) after monosegmental fusion and posterior dynamic stabilization at the level L4-L5.

OBJECTIVE

Comparison of segmental ROM at the index level and the cranial and caudal adjacent levels and of global lumbar spine ROM after monosegmental fusion and posterior dynamic stabilization.

SUMMARY OF BACKGROUND DATA

The postulated advantage of nonfusion technology compared with fusion is based on the assumption that preservation of motion at the treated segment reduces the incidence of adjacent segment effects. Therefore, it is imperative to provide evidence that dynamic stabilization devices avoid hypermobility at the adjacent segments because this might substantiate a protective effect on the adjacent segments.

METHODS

Twenty-six patients with low back pain and claudication due to degenerative instability at the level L4-L5 with concomitant spinal stenosis were treated either with decompression and Dynesys (n = 11) or with decompression and fusion (n = 15). All patients underwent flexion/extension radiographs before surgery and at latest follow-up. ROM was assessed at the index level (L4-L5), the cranial/caudal adjacent levels (L3-L4/L5-S1), and at the lumbar spine from L2 to S1.

RESULTS

There was a significant reduction of the global ROM of the lumbar spine (L2-S1) and the segmental ROM at the index level (L4-L5) in the fusion group, whereas adjacent level ROM did not change significantly. In the Dynesys group, no significant changes of global lumbar spine ROM (L2-S1) and segmental ROM (index level and cranial/caudal adjacent levels) were seen.

CONCLUSION

This study shows that neither monosegmental instrumented fusion nor monosegmental posterior dynamic stabilization with Dynesys alter the ROM of the cranial and caudal adjacent levels. Consequently, monosegmental posterior dynamic stabilization with Dynesys has no effect with regard to adjacent segment mobility compared with monosegmental fusion.

Nerve injury to the posterior rami medial branch during the insertion of pedicle screws: comparison of mini-open versus percutaneous pedicle screw insertion techniques

STUDY DESIGN

The risk for transection of the medial branch nerve (MBN) after minimally invasive insertion of pedicle screws was evaluated in a human cadaver model.

OBJECTIVE

The purpose of this study is to compare the risk of MBN transection after pedicle screw insertion using mini-open versus percutaneous minimally invasive techniques.

SUMMARY OF BACKGROUND DATA

The multifidus muscle is innervated by the MBN that originates from the posterior rami. Since the anatomic course of the MBN passes near the mamillary process it is vulnerable to injury during pedicle screw insertion, even if minimally invasive spine techniques are implemented.

METHODS

Five cadaveric specimens were used for the study. Pedicle screws were inserted into the lumbar spine using either percutaneous or mini-open techniques. The integrity of the MBN was examined directly through anatomic dissection of the posterior spine.

RESULTS

The soft tissue damage area around the screw insertion site was significantly greater in the mini-open compared with the percutaneous technique. MBN transection was observed in 84% (21/25) of the pedicles when using the mini-open technique and in 20% (5/25) when the percutaneous insertion technique was used (P < 0.01%).

CONCLUSION

Using a percutaneous technique for pedicle screw insertion significantly reduces the risk of injury to the MBN. We therefore recommend using this technique especially at the most cephalic levels to minimize the risk of denervating the multifidus muscle fascicles that originate from the adjacent mobile level.

Future perspectives of cell-based therapy for intervertebral disc disease

Intervertebral disc degeneration is a primary cause of low back pain and has a high societal cost. Research on cell-based therapies for intervertebral disc disease is emerging, along with the interest in biological therapy to treat disc disease without reducing the mobility of the spinal motion segment. Results from animal models have shown promising results under limited conditions; however, future studies are needed to optimise efficacy, methodology, and safety. To advance research on cell-based therapy for intervertebral disc disease, a better understanding of the phenotype and differentiation of disc cells and of their microenvironment is essential. This article reviews current concepts in cell-based therapy for intervertebral disc disease, with updates on potential cell sources tested primarily using animal models, and discusses the hurdles to clinical application. Future perspectives for cell-based therapies for intervertebral disc disease are also discussed.

A porcine model of intervertebral disc degeneration induced by annular injury characterized with magnetic resonance imaging and histopathological findings. Laboratory investigation

OBJECT

Appropriate animal models of disc degeneration are critical for the study of proposed interventions as well as to further delineate the degenerative process. The purpose of this study was to characterize a porcine model for disc degeneration confirmed on magnetic resonance (MR) imaging studies and histological analysis.

METHODS

Twelve miniature pigs were used (weight 48-65 kg) to study degeneration in the lumbar spine. Under fluoroscopic guidance, the disc was percutaneously punctured with a 3.2-mm-diameter trephine to a 5-mm depth into the annulus fibrosus. Control and experimental levels were randomized among 6 levels in the lumbar spine. The unlesioned spinal levels were used as controls and were compared with lesioned levels. Magnetic resonance imaging grading and disc height were serially recorded preoperatively, and at 5, 8, 19, 32, and 39 weeks postoperatively. The animals were killed in groups of 3 at 7, 18, 32, and 41 weeks postinjury, and the discs were examined histopathologically.

RESULTS

Consistent, sequential, and progressive degeneration of the annular injury was observed on MR imaging and histopathological studies from the time of injury to the final time point. The disc height and the disc height index also sequentially decreased from the time of the injury in a consistent manner. The uninjured control levels did not show any progressive degeneration and maintained their normal state.

CONCLUSIONS

Based on MR imaging and histopathological findings, the authors demonstrated and characterized a reliable model of sequential disc degeneration in miniature pigs with percutaneous injury to the annulus fibrosus. In the early stages, as soon as 5 weeks after injury, significant disc degeneration was seen on MR imaging grading with decreases in disc height. This degeneration did not improve by the final time point of 39 weeks.

Evaluation of quantitative magnetic resonance imaging, biochemical and mechanical properties of trypsin-treated intervertebral discs under physiological compression loading

PURPOSE

To investigate the influence of targeted trypsin digestion and 16 hours compression loading on MR parameters and the mechanical and biochemical properties of bovine disc segments.

MATERIALS AND METHODS

Twenty-two 3-disc bovine coccygeal segments underwent compression loading for 16 hours after the nucleus pulposus (NP) of each disc was injected with a solution of trypsin or buffer. The properties of the NP and annulus fibrosus (AF) tissues of each disc were analyzed by quantitative MRI, biochemical tests, and confined compression tests.

RESULTS

Loading had a significant effect on the MR properties (T(1), T(2), T(1rho), MTR, ADC) of both the NP and AF tissues. Loading had a greater effect on the MR parameters and biochemical composition of the NP than trypsin. In contrast, trypsin had a larger effect on the mechanical properties. Our data also indicated that localized trypsin injection predominantly affected the NP. T(1rho) was sensitive to loading and correlated with the water content of the NP and AF but not with their proteoglycan content.

CONCLUSION

Our studies indicate that physiological loading is an important parameter to consider and that T(1rho) contributes new information in efforts to develop quantitative MRI as a noninvasive diagnostic tool to detect changes in early disc degeneration.

Adjacent segment degeneration: observations in a goat spinal fusion study

STUDY DESIGN

The adjacent discs of 13 goats, originally used in a lumbar spinal fusion model study, were analyzed for symptoms of intervertebral disc degeneration by means of magnetic resonance imaging (MRI), macroscopy, and histology. These goats were followed for 6 months and the results were compared with 6 control goats.

OBJECTIVE

To evaluate the development of adjacent segment disc degeneration in vivo in a goat lumbar spinal fusion model.

SUMMARY OF BACKGROUND DATA

There is ongoing debate on whether adjacent segment degeneration (ASD) develops through increased biomechanical load on discs adjacent to fusion sites, or by the natural process of pre-existing degenerative disease. Animal models offer an opportunity to separate these factors by evaluating the development of ASD in nondegenerated animal spines.

METHODS

In a spinal fusion model study 2 segments (L3-L4 and L1-L2) were fixated and followed for 3 months (n = 6) and 6 months (n = 7) in 13 skeletally mature goats. Two adjacent discs (T13-L1 and L4-L5), 1 interjacent disc (L2-L3) and a control disc (L5-L6) were analyzed by means of magnetic resonance imaging, macroscopy, and histology. These results were compared with the discs of 6, nonoperated "normal" goats.

RESULTS

No differences were observed in the adjacent and interjacent intervertebral discs after both follow-up periods. However, severe degenerative changes were observed in the L5-L6 level, originally included as controls.

CONCLUSION

Large animal fusion models offer an excellent opportunity to study ASD in vivo, as pre-existing degenerative disc disease is not present and biomechanical effects of the fusion can be studied more isolated. Our results suggest that adjacent disc degeneration does not develop in our spinal goat fusion model. There is, however, an increased risk of disc degeneration in the L5-L6 level through an unclear mechanism.

Simulated radioscapholunate fusion alters carpal kinematics while preserving dart-thrower's motion

PURPOSE

Midcarpal degeneration is well documented after radioscapholunate fusion. This study tested the hypothesis that radioscapholunate fusion alters the kinematic behavior of the remaining lunotriquetral and midcarpal joints, with specific focus on the dart-thrower's motion.

METHODS

Simulated radioscapholunate fusions were performed on 6 cadaveric wrists in an anatomically neutral posture. Two 0.060-in. carbon fiber pins were placed from proximal to distal across the radiolunate and radioscaphoid joints, respectively. The wrists were passively positioned in a custom jig toward a full range of motion along the orthogonal axes as well as oblique motions, with additional intermediate positions along the dart-thrower's path. Using a computed tomography-based markerless bone registration technique, each carpal bone's three-dimensional rotation was defined as a function of wrist flexion/extension from the pinned neutral position. Kinematic data was analyzed against data collected on the same wrist prior to fixation using hierarchical linear regression analysis and paired Student's t-tests.

RESULTS

After simulated fusion, wrist motion was restricted to an average flexion-extension arc of 48 degrees , reduced from 77 degrees , and radial-ulnar deviation arc of 19 degrees , reduced from 33 degrees . The remaining motion was maximally preserved along the dart-thrower's path from radial-extension toward ulnar-flexion. The simulated fusion significantly increased rotation through the scaphotrapezial joint, scaphocapitate joint, triquetrohamate joint, and lunotriquetral joint. For example, in the pinned wrist, the rotation of the hamate relative to the triquetrum increased 85%. Therefore, during every 10 degrees of total wrist motion, the hamate rotated an average of nearly 8 degrees relative to the triquetrum after pinning versus 4 degrees in the normal state.

CONCLUSIONS

Simulated radioscapholunate fusion altered midcarpal and lunotriquetral kinematics. The increased rotations across these remaining joints provide one potential explanation for midcarpal degeneration after radioscapholunate fusion. Additionally, this fusion model confirms the dart-thrower's hypothesis, as wrist motion after simulated radioscapholunate fusion was primarily preserved from radial-extension toward ulnar-flexion.