Osteoporosis: a paradox in ankylosing spondylitis

Intermittent administration of PTH for the treatment of inflammatory bone loss does not enhance entheseal pathological new bone formation

OBJECTIVE

To investigate the effect of intermittent parathyroid hormone (iPTH) administration on pathological new bone formation during treatment of ankylosing spondylitis-related osteoporosis.

METHODS

Animal models with pathological bone formation caused by hypothetical AS pathogenesis received treatment with iPTH. We determined the effects of iPTH on bone loss and the formation of pathological new bone with micro-computed tomography (micro-CT) and histological examination. In addition, the tamoxifen-inducible conditional knockout mice (CAGGCre-ERTM; PTHflox/flox, PTH-/-) was established to delete PTH and investigate the effect of endogenous PTH on pathological new bone formation.

RESULTS

iPTH treatment significantly improved trabecular bone mass in the modified collagen-induced arthritis (m-CIA) model and unbalanced mechanical loading models. Meanwhile, iPTH treatment did not enhance pathological new bone formation in all types of animal models. Endogenous PTH deficiency had no effects on pathological new bone formation in unbalanced mechanical loading models.

CONCLUSION

Experimental animal models of AS treated with iPTH show improvement in trabecular bone density, but not entheseal pathological bone formation，indicating it may be a potential treatment for inflammatory bone loss does in AS.

Investigation of the Shared Biomarkers in Heterotopic Ossification Between Ossification of the Ligamentum Flavum and Ankylosing Spondylitis

STUDY DESIGN

Bioinformatics analysis of Gene Expression Omnibus (GEO).

OBJECTIVE

Ossification of the ligamentum flavum (OLF) and ankylosing spondylitis (AS) represent intricate conditions marked by the gradual progression of endochondral ossification. This investigation endeavors to unveil common biomarkers associated with heterotopic ossification and explore the potential molecular regulatory mechanisms.

METHODS

Microarray and RNA-sequencing datasets retrieved from the Gene Expression Omnibus (GEO) repository were harnessed to discern differentially expressed genes (DEGs) within the OLF and AS datasets. Subsequently, Weighted Gene Co-expression Network Analysis (WGCNA) was implemented to pinpoint co-expression modules linked to OLF and AS. Common genes were further subjected to an examination of functional pathway enrichment. Moreover, hub intersection genes were identified using the Least Absolute Shrinkage and Selection Operator (LASSO) regression, followed by an evaluation of diagnostic performance in external OLF and AS cohorts. Lastly, an analysis of immune cell infiltration was conducted to scrutinize the correlation of immune cell presence with shared biomarkers in OLF and AS.

RESULTS

A total of 1353 and 91 Differentially Expressed Genes (DEGs) were identified in OLF and AS, respectively. Using the Weighted Gene Co-expression Network Analysis (WGCNA), 2 modules were found to be notably significant for OLF and AS. The integrative bioinformatic analysis revealed 3 hub genes (MAB21L2, MEGF10, ISLR) as shared risk biomarkers, with MAB21L2 being the central focus. Receiver Operating Characteristic (ROC) analysis exhibited a strong diagnostic potential for these hub genes. Gene Ontology (GO) analysis indicated their involvement in the positive regulation of myoblast proliferation. Notably, MAB21L2 was singled out as the optimal common biomarker for OLF and AS. Furthermore, an analysis of immune infiltration demonstrated a correlation between MAB21L2 expression and changes in immune cells. Activated CD8 T cells were identified as shared differential immune infiltrating cells significantly linked to MAB21L2 in both OLF and AS.

CONCLUSION

This study represents the first instance of identifying MAB21L2 as a prospective diagnostic marker for patients contending with OLF associated with AS. The research results indicate that the ECM-receptor interaction and the cell-cell adhesion may play a role in both disease processes. This newfound knowledge not only enhances our understanding of the pathogenesis behind spinal ligament ossification but also uncovers potential targets for therapeutic interventions.

CD_99 G1 neutrophils modulate osteogenic differentiation of mesenchymal stem cells in the pathological process of ankylosing spondylitis

OBJECTIVES

This study aimed to identify the types and heterogeneity of cells within the spinal enthesis and investigate the underlying mechanisms of osteogenesis.

METHODS

Single-cell RNA sequencing was used to identify cell populations and their gene signatures in the spinal enthesis of five patients with ankylosing spondylitis (AS) and three healthy individuals. The transcriptomes of 40 065 single cells were profiled and divided into 7 clusters: neutrophils, monocytic cells, granulomonocytic progenitor_erythroblasts, T cells, B cells, plasma cells and stromal cells. Real-time quantitative PCR, immunofluorescence, flow cytometry, osteogenesis induction, alizarin red staining, immunohistochemistry, short hairpin RNA and H&E staining were applied to validate the bioinformatics analysis.

RESULTS

Pseudo-time analysis showed two differentiation directions of stromal cells from the mesenchymal stem cell subpopulation MSC-C2 to two Cxcl12-abundant-reticular (CAR) cell subsets, Osteo-CAR and Adipo-CAR, within which three transcription factors, C-JUN, C-FOS and CAVIN1, were highly expressed in AS and regulated the osteogenesis of mesenchymal stem cells. A novel subcluster of early-stage neutrophils, CD99_G1, was elevated in AS. The proinflammatory characteristics of monocyte dendritic cell progenitor-recombinant adiponectin receptor 2 monocytic cells were explored. Interactions between Adipo-CAR cells, CD99_G1 neutrophils and other cell types were mapped by identifying ligand-receptor pairs, revealing the recruitment characteristics of CD99_G1 neutrophils by Adipo-CAR cells and the pathogenesis of osteogenesis induced in AS.

CONCLUSIONS

Our results revealed the dynamics of cell subpopulations, gene expression and intercellular interactions during AS pathogenesis. These findings provide new insights into the cellular and molecular mechanisms of osteogenesis and will benefit the development of novel therapeutic strategies.

Bone density and fracture risk factors in ankylosing spondylitis: a meta-analysis

We included 39 studies in our meta-analysis, finding that patients with ankylosing spondylitis (AS) exhibit decreased bone mineral density (BMD) and an elevated risk of fractures. Additionally, we analyzed the risk factors associated with fractures in these patients.

INTRODUCTION

AS is a chronic inflammatory disease primarily affecting the spine and sacroiliac joints, with reduced BMD, osteoporosis, and fractures being common complications. This study aims to systematically consolidate and conduct a meta-analysis of existing research to comprehensively understand decreased bone mineral density, osteoporosis, and fracture risks at various anatomical sites in AS patients. The objective is to provide reliable information for the management of AS patients and to inform clinical decision making.

METHODS

We conducted a thorough search in various databases including Embase, PubMed, Cochrane Library, and Web of Science. These studies focused on the risk of and risk factors for decreased BMD, osteopenia, osteoporosis, and fractures at different sites among AS patients such as the lumbar spine and femoral neck. The quality of eligible studies was evaluated. Sensitivity analysis was performed to assess the reliability of our analysis results and understand the effects of individual studies on the heterogeneity across studies.

RESULTS

A total of 39 studies were included. Our meta-analysis results revealed significant differences between AS patients and healthy controls. AS patients had significantly lower BMDs at the femoral neck, hip, lumbar vertebra 2 (L2), lumbar vertebra 3 (L3), and lumbar vertebra 4 (L4), but higher BMDs at 1/3 distal radius and ultra distal radius. Risk factors for fractures among AS patients included old age, long course of disease, and low BMD at the lumbar spine. In contrast, factors such as erythrocyte sedimentation rate (ESR), the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score, gender, and body mass index (BMI) were not risk factors for fractures in AS patients.

CONCLUSION

Our study highlights that BMD at the femoral neck is more effective for evaluating AS patients compared with the BMD at the lumbar spine. Additionally, the risk of osteoporosis and fractures in AS patients is higher in younger patients and those at the early stage of this disease.

Evaluation of cortical and trabecular bone structure of the mandible in patients with ankylosing spondylitis

This study aimed to examine the difference between the fractal dimension (FD) values of the mandibular trabecular bone and the panoramic mandibular index (PMI), mandibular cortical index (MCI) and mandibular cortical thickness (MCW) of patients with ankylosing spondylitis (AS) and healthy control group. A total of 184 individuals (92 cases, 92 controls), were examined in our study. PMI, MCI, and MCW values were calculated on panoramic images of all individuals. For FD values, the region of interest (ROI) was selected with the size of 100 × 100 pixels from the right-left gonial and interdental regions and 50 × 50 pixels from the condylar region. Degenerative changes in the temporomandibular joint (TMJ) region were recorded. PMI, MCI, and MCW values showed statistically significant differences between the groups (p = 0.000, p < 0.001). The radiological signs of mandibular cortical resorption were more severe in the case group than in the control group. PMI and MCW values were found to be lower in the case group than in the control group. It was determined that the number of C3 and C2 values, among the MCI values, was higher in the case group. Only the FD values of the ROI selected from the condyle region were found to be statistically significant and were lower in the case group (p = 0.026, p < 0.05). Degenerative changes in the TMJ region were significantly more frequent in the case groups (p = 0.000, p < 0.001). The fact that the mandibular cortex shows more resorptive features in individuals with AS may require further evaluation in terms of osteoporosis. Because of the low FD values of the condylar regions of these patients and the more frequent degenerative changes, the TMJ region should be followed carefully. Detailed examination of the mandibular cortex and condylar region is beneficial in patients with AS for screening and following osteoporotic changes in these individuals, which is essential for the patient's life quality.

Association Between SPARC Polymorphisms and Ankylosing Spondylitis and Its mRNA and Protein Expression in a Chinese Han Population: A Case-Control Study

Objective

We explore the association of polymorphisms in Secreted protein acidic and rich in cysteine (SPARC) with ankylosing spondylitis (AS) and detect SPARC mRNA and protein expression in a Chinese Han population.

Methods

Nine single-nucleotide polymorphisms (SNPs) of SPARC were genotyped in 768 AS patients and 768 controls by TaqMan genotyping assay. mRNA expression of SPARC was detected by real-time polymerase chain reaction (RT-PCR), and serum level of SPARC protein was detected by ELISA.

Results

The frequency of A allele of rs171121187 was significantly higher in AS patients than in controls (Pc=0.003, odds ratio [OR]=1.45, 95% confidence interval [95% CI] = 1.18-1.77), the AA and AC genotypes increased the risk of AS when compared with CC genotype (Pc=0.003, OR=3.96, 95% CI=1.80-8.75, and Pc=0.003, OR=1.27, 95% CI=1.01-1.61, respectively). The frequency of G allele of rs4958487 was significantly lower in AS than in controls (Pc=0.001, OR=0.60, 95% CI=0.47-0.68), the GG and GA genotypes reduced the risk of AS when compared with AA genotype (Pc=0.005, OR=0.46, 95% CI 0.18-1.14, and Pc=0.005, OR=0.60, 95% CI=0.45-0.79, respectively). The haplotype AA of rs17112187/rs4958487 significantly increased the risk of AS (P=2.31E-5, OR=1.60, 95% CI=1.28-1.98), while haplotype CG decreased the risk of AS (P=5.42E-5, OR=0.55, 95% CI=0.41-0.74). Expression levels of SPARC mRNA were significantly lower in both Peripheral blood mononuclear cells (PBMC) and granulocytes in AS patients than in controls (P=0.008 and P=0.005, respectively). SPARC protein levels were also reduced in AS patients versus the controls (P=0.002).

Conclusion

This study indicates that polymorphisms in SPARC are associated with AS susceptibility, and both mRNA and protein levels of SPARC are decreased in AS patients in a Chinese Han population.

Computational Drug Discovery in Ankylosing Spondylitis-Induced Osteoporosis Based on Data Mining and Bioinformatics Analysis

BACKGROUND

Ankylosing spondylitis (AS) and osteoporosis (OP) are both prevalent illnesses in spine surgery, with OP being a possible consequence of AS. However, the mechanism of AS-induced OP (AS-OP) remains unknown, limiting etiologic research and therapy of the illness. To mine targetable medicine for the prevention and treatment of AS-OP, this study analyzes public data sets using bioinformatics to identify genes and biological pathways relevant to AS-OP.

METHODS

First, text mining was used to identify common genes associated with AS and OP, after which functional analysis was carried out. The STRING database and Cytoscape software were used to create protein-protein interaction networks. Hub genes and potential drugs were discovered using drug-gene interaction analysis and transcription factors-gene interaction analysis.

RESULTS

The results of text mining showed 241 genes common to AS and OP, from which 115 key symbols were sorted out by functional analysis. As options for treating AS-OP, protein-protein interaction analysis yielded 20 genes, which may be targeted by 13 medications.

CONCLUSIONS

Carlumab, bermekimab, rilonacept, rilotumumab, and ficlatuzumab were first identified as the potential drugs for the treatment of AS-OP, proving the value of text mining and pathway analysis in drug discovery.

Spine Surgery and Ankylosing Spondylitis: Optimizing Perioperative Management

Ankylosing spondylitis (AS) is a common form of axial spondyloarthritis, characterized by inflammatory back pain, radiographic sacroiliitis, excess spinal bone formation, and a high prevalence of HLA-B27. Commonly, AS patients require spinal surgery for kyphotic deformities, spinal trauma, and spinal infections. For preoperative management, proper interruption considering each specific half-lives of disease-modifying antirheumatic drugs are necessary to avoid complications, such as infections. When feasible, bone quality assessment before surgery is mandatory. For intraoperative measurements, airway management should be carefully evaluated, especially in patients with severe cervical deformities. Cardiac, renal, and pulmonary assessment should be made considering specific pathologic characteristics involved in AS patients, such as pulmonary restrictive disease and chronic anti-inflammatory drugs use. Multimodal neurophysiological intraoperative monitoring is recommended once these patients had a high risk for neurological deterioration. At the postoperative period, early oral intake, early mobilization, and aggressive pain control may decrease complications and enhance recovery. AS presents several unique challenges that require specific attention around spine surgery. This includes handling preoperative and postoperative pharmacotherapeutics, intraoperative airway management, and the mitigation of postoperative complications. In this paper, we provide a literature review of optimal strategies for the perioperative management for patients with AS.

Evaluation of temporomandibular joint components and mandibular bone structure in ankylosing spondylitis patients

OBJECTIVES

The study aimed to investigate the mandible and temporomandibular joint (TMJ) in patients with ankylosing spondylitis (AS) who had no signs or symptoms of TMJ-related disease and compare them with a control group.

STUDY DESIGN

In total, 128 panoramic radiographs (63 patients with AS, 65 controls) were evaluated. Fractal analysis was conducted on the mandibular condyle (ROI1), angle of the mandible (ROI2), and the area adjacent to the mental foramen (ROI3). Articular eminence inclination (AEI) values were measured. Klemetti index (KI) evaluation of the mandibular cortex was also performed.

RESULTS

Fractal dimension (FD) values were significantly lower in the patients with AS than the controls in ROI1 and ROI2 (P = .001), but there were no significant differences between groups for FD in ROI3, AEI, or KI (P ≥ .09). No significant differences were found in any parameters between patients with AS with different disease durations (P ≥ .06).

CONCLUSIONS

Patients with AS displayed significantly lower FD values in condyles and the angle of the mandible and slightly lower AEI values; therefore, they should be examined routinely for TMJ disorders. Clinicians should be aware of the possibility of secondary osteoporosis in patients with AS and consider its probable effects on the mandible.

Results of in situ fixation of Andersson lesion by posterior approach in 35 cases

STUDY OBJECTIVE

Due to the rarity of the Andersson lesion (AL), the literature is ambiguous regarding the type of surgical fixation, need for debridement and deformity correction. The purpose of this retrospective study is to evaluate the efficacy, feasibility and functional outcome of posterior fixation in AL.

MATERIALS AND METHODS

This study included 35 patients having thoracolumbar AL operated for in situ fixation and fusion with minimum of 24-month follow-up. VAS (Visual Analogue Score) back pain, ODI (Oswestry Disability Index), Frankel's grade were compared and analyzed. Union status was noted with complications.

RESULTS

The mean age of 35 patients was 56.34(± 11.3) years with average follow-up of 51.49 months. Two patients had AL at two levels. 27/37 AL were at discal level. Average estimated blood loss (EBL) was 276.43 ml and duration of surgery was 130.43 min. On an average, operated segments needed 7.77 screws. There were ten minor complications without long-term sequel. Neurological improvement was noted in 30 patients. Average preoperative VAS score improved from 8.69 to 3.14, ODI score improved from 68.76 to 18.77 at final follow-up which were significant (p < 0.05). There was significant improvement in Frankel's grading (Z = - 4.354, P = 0.00).

CONCLUSIONS

Surgical management of AL by posterior approach and posterior stabilization can give satisfactory results without the need of extensive anterior reconstruction, bone grafting or deformity correction procedures without added morbidity and complications.

The usefulness of trabecular bone score in patients with ankylosing spondylitis

BACKGROUNDS/AIMS

This study was performed to reveal the usefulness of the trabecular bone score (TBS) in assessing bone strength in patients with ankylosing spondylitis (AS) in comparison with dual-energy X-ray absorptiometry (DXA) methods.

METHODS

A total of 215 AS patients (75.8% male) were enrolled from a single university hospital in Korea. Demographic and clinical information were assessed. Patients completed X-rays of the cervical and lumbar spine (L-spine), and spinal ankyloses were quantified using the modified Stoke AS Spine Score (mSASSS). Hip, anteroposterior and lateral L-spine bone mineral density (BMD) and TBS were assessed by DXA methods. Clinical characteristics and bone strength measurement results were compared between male and female AS patients. The accuracy of each bone strength evaluation method in predicting Fracture Risk Assessment Tool (FRAX) scores indicating moderate or higher fracture risk was compared by receiver operating characteristic curves in patients aged ≥ 40 years. Correlations between each bone strength measurement method and mSASSS were examined.

RESULTS

Male patients showed higher mSASSS and less prevalent peripheral joint involvement compared to female patients (p < 0.05). TBS, hip BMD, and L-spine lateral BMD showed comparably high areas under the curve (AUCs) for predicting FRAX-major osteoporotic fractures (MOF) ≥ 10% (AUC ranged 0.72 to 0.76). TBS negatively correlated with mSASSS in both male and female patients (p < 0.01).

CONCLUSION

TBS could predict the risk of MOF and is not influenced by spinal osteoproliferation in AS patients, even in those with advanced spinal changes.

Juvenile Spondyloarthritis: What More Do We Know About HLA-B27, Enthesitis, and New Bone Formation?

Juvenile spondyloarthritis (JSpA) refers to a diverse spectrum of immune-mediated inflammatory arthritides whose onset occurs in late childhood and adolescence. Like its adult counterpart, JSpA is typified by a strong association with human leukocyte antigen-B27 (HLA-B27) and potential axial involvement, while lacking rheumatoid factor (RF) and distinguishing autoantibodies. A characteristic manifestation of JSpA is enthesitis (inflammation of insertion sites of tendons, ligaments, joint capsules or fascia to bone), which is commonly accompanied by bone resorption and new bone formation at affected sites. In this Review, advances in the role of HLA-B27, enthesitis and its associated osteoproliferation in JSpA pathophysiology and treatment options will be discussed. A deeper appreciation of how these elements contribute to the JSpA disease mechanism will better inform diagnosis, prognosis and therapy, which in turn translates to an improved quality of life for patients.

A Contemporary View of the Diagnosis of Osteoporosis in Patients With Axial Spondyloarthritis

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that primarily affects the axial joints. Altered bone metabolism associated with chronic inflammation leads to both new bone formation in the spine and increased bone loss. It is known that patients with axSpA have a high prevalence of osteoporosis and fractures. However, there is no consensus on which imaging modality is the most appropriate for diagnosing osteoporosis in axSpA. Bone mineral density measurement using dual-energy X-ray absorptiometry is the primary diagnostic method for osteoporosis, but it has notable limitations in patients with axSpA. This method may lead to the overestimation of bone density in patients with axSpA because they often exhibit abnormal calcification of spinal ligaments or syndesmophytes. Therefore, the method may not provide adequate information about bone microarchitecture. These limitations result in the underdiagnosis of osteoporosis. Recently, new imaging techniques, such as high-resolution peripheral quantitative computed tomography, and trabecular bone score have been introduced for the evaluation of osteoporosis risk in patients with axSpA. In this review, we summarize the current knowledge regarding imaging techniques for diagnosing osteoporosis in patients with axSpA.

No relationship between bone mineral density and syndesmophyte formation at the same level in the lumbar spine of patients with radiographic axial Spondyloarthritis

Objective

To investigate if in radiographic axial Spondyloarthritis (r-axSpA) low vertebral bone mineral density (BMD) is associated with development of new syndesmophytes at the same vertebral level.

Methods

In a post-hoc analysis from the ASSERT trial (infliximab vs placebo), dual-energy X-ray absorptiometry was used to measure baseline BMD (g/cm²) of the lumbar spine L1 to L4. Syndesmophyte formation was assessed in the same vertebrae on conventional radiographs defined as an increase in modified Stoke Ankylosing Spondylitis Spine Score from 0 or 1 to 2 or 3 after 2 years. Radiographs were scored by two readers. Generalised estimating equations (GEE) adjusted for within-patient correlation across multiple vertebrae, taking potential confounders into account.

Results

We analysed 599 vertebrae in 165 r-axSpA patients (78% male, mean (SD) age 38 (10) years, 67% with at least one syndesmophyte anywhere in the spine). In total, 24 to 74 new syndesmophytes developed in 9 (5%) to 30 (18%) patients and 13 (2%) to 39 (7%) vertebrae, if either a syndesmophyte was seen by both or only one of the readers (ie, specific and sensitive definitions) respectively. In multivariable analyses, no association was found between baseline local vertebral BMD and new syndesmophyte formation after 2 years: adjOR (95% CI): 0.56 (0.01, 44.45) (specific definition) and 0.26 (0.03, 2.63) (sensitive definition).

Conclusion

In patients with active and established r-axSpA, with an observed low incidence of lumbar spine syndesmophyte formation over 2 years, no relationship was found between baseline BMD and new radiographic syndesmophyte formation at the same vertebra.

The contribution of pre-existing spinal pseudarthrosis to the surgical correction for thoracolumbar kyphosis secondary to ankylosing spondylitis

The correction of global kyphosis (GK) for ankylosing spondylitis (AS) patients with pre-existing pseudarthrosis were frequently over 45°. Mismatch between kyphosis correction of GK and pedicle subtraction osteotomy (PSO) may be ascribed to contribution of pseudarthrosis. The aim of the present study was to evaluate surgical outcomes of PSO away from the level of pseudarthrosis and to elucidate the contribution of pre-existing spinal pseudarthrosis in surgical correction of thoracolumbar kyphosis caused by AS. Eighteen AS patients with pre-existing pseudarthrosis were included. PSO outside the level of pseudarthrosis were performed for all the patients. The average follow-up period were 29 months. Radiographs were analyzed for correction and complications. Significant improvement in all sagittal parameters were found postoperatively without obvious correction loss at the final follow-up. Local kyphosis (LK) improved from 23.88° preoperatively to 12.67° postoperatively with a mean correction of 11.47°. Average correction of per PSO segment, GK and sum of disc wedging within fused region (SDW) were 33.53°, 49.27° and 4.00°, respectively. PSO away from the level of pseudarthrosis, but with posterior instrumentation crossing it was a feasible method and was able to maintain sustained surgical outcomes. Regarding GK correction, PSO accounted for 68.1% while pre-existing pseudarthrosis provided 23.3%, which resulted from anterior column opening postoperatively. Thus, extra kyphosis correction attributed to pre-existing pseudarthrosis should be considered for surgical-decision making to prevent overcorrection.

Performance of bone mineral density and trabecular bone score in assessment of bone quality in Egyptian male patients with ankylosing spondylitis

Background

Osteoporosis is a common complication of ankylosing spondylitis (AS) even in the early stages of disease; however, previously published studies have demonstrated large discrepancies in the reported incidence of osteoporosis, based on measurement of bone mineral density (BMD). The aim of the present study was to compare bone quality using trabecular bone score (TBS) between AS patients and healthy controls and to evaluate factors associated with TBS in patients with AS.

Results

Ankylosing spondylitis patients had significantly lower BMD and T score at the neck of femur and lower total hip BMD than controls (BMD p = 0.010 and 0.032 respectively), (T score p = 0.006 and p = 0.025 respectively). The mean TBS was significantly lower in AS patients than in controls (p < 0.001). Lumbar spine TBS was directly correlated with BMI (p = 0.029) and BMD at the neck of femur (p = 0.016) and BMD of total hip (p = 0.007) while inversely correlated with the Bath AS Metrology Index (BASMI) (p = 0.026), the modified Stoke AS Spinal Score (mSASS) (p = 0.029), ESR (p = 0.031), and CRP (p = 0.033).

Conclusion

TBS evaluation detected lower bone quality in the lumbar spine in patients with AS when compared with matched controls, while lumbar BMD failed to identify it. These findings encourage the use of TBS as a beneficial tool to recognize the risk of axial osteoporosis as early as possible in AS patients. Also, we recommend its use for regular follow up of drug treatment for those patients.

Bone phenotypes in rheumatology - there is more to bone than just bone

Osteoarthritis, rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis, all have one clear common denominator; an altered turnover of bone. However, this may be more complex than a simple change in bone matrix and mineral turnover. While these diseases share a common tissue axis, their manifestations in the area of pathology are highly diverse, ranging from sclerosis to erosion of bone in different regions. The management of these diseases will benefit from a deeper understanding of the local versus systemic effects, the relation to the equilibrium of the bone balance (i.e., bone formation versus bone resorption), and the physiological and pathophysiological phenotypes of the cells involved (e.g., osteoblasts, osteoclasts, osteocytes and chondrocytes). For example, the process of endochondral bone formation in chondrocytes occurs exists during skeletal development and healthy conditions, but also in pathological conditions. This review focuses on the complex molecular and cellular taxonomy of bone in the context of rheumatological diseases that alter bone matrix composition and maintenance, giving rise to different bone turnover phenotypes, and how biomarkers (biochemical markers) can be applied to potentially describe specific bone phenotypic tissue profiles.

Association of Regional Bone Synthetic Activities of Vertebral Corners and Vertebral Bodies Quantified Using 18F-Fluoride Positron Emission Tomography with Bone Mineral Density on Dual Energy X-ray Absorptiometry in Patients with Ankylosing Spondylitis

We investigated whether the bone-synthetic activities of vertebral bodies or vertebral corners quantified using ¹⁸F-fluoride positron emission tomography (PET) was associated with bone mineral density (BMD) at the corresponding lumbar vertebrae in ankylosing spondylitis (AS) at each vertebra level. We analyzed 48 lumbar vertebrae in 12 AS patients who underwent ¹⁸F-fluoride PET and dual energy X-ray absorptiometry (DXA). The mean standardized uptake values (SUVmean) of the vertebral body and corners from L1 to L4 were measured using the spatially separated region of interest (ROI). The L1–L4 BMDs were calculated based on the DXA (“conventional BMD”). The BMD of the internal vertebral bodies was measured by manually drawing ROIs to represent the trabecular BMD (“alternative BMD”). After adjusting the within-patient correlation, the ¹⁸F-fluoride SUVmean of the vertebral corners but not that of vertebral bodies was significantly related with the conventional BMD of the vertebra. Otherwise, the ¹⁸F-fluoride uptake of both the vertebral and vertebral bodies was significantly related with the alternative BMD. The bone-synthetic activities of the vertebral corners may be more closely related with BMD than those of the vertebral bodies, suggesting that the effects of regional bone metabolism at the vertebral corners and bodies on BMD differ in AS.

Measuring bone density in axial spondyloarthropathy: Time to turn things on their side?

AIM

Osteoporosis in axial spondyloarthropathy (axSpA) is difficult to accurately diagnose due to osteoproliferation of the spine interfering with conventional (anteroposterior, AP) dual-energy X-ray absorptiometry (DXA). This study compares AP and lateral projections of DXA when assessing bone mineral density (BMD) of the spine and investigates the impact of osteoproliferation on AP DXA.

METHOD

In this cross-sectional study, structured standardized assessments collected demographic, clinical, laboratory and radiographic data. DXA assessed BMD of the spine using PA and lateral projections. Hip BMD was assessed in the usual manner. World Health Organization (WHO) criteria assessed prevalence of low BMD. Incorporating lateral DXA in the bone health assessment of axSpA was investigated. SPSS was used for statistical analysis.

RESULTS

A total of 100 patients had paired AP and lateral DXA studies: 78% were male, mean (SD) age 52 (12) years. BMD of the spine measured by AP projection was significantly higher than BMD measured by lateral projection (mean difference 0.34 g/cm² , 95% CI 0.30-0.37). More patients had low BMD with lateral compared to AP projection (47% vs 16%, P = .01). At the hip, 34% of patients had low BMD. Disease duration, body mass index and radiographic severity independently predicted a difference between AP and lateral measurements of the spine.

CONCLUSION

Lateral DXA of the spine is unaffected by osteoproliferation of the spine in axSpA and detects significantly more cases of low BMD than conventional AP DXA. Lateral DXA should be included in BMD assessment of patients with axSpA.

Low bone mineral density of vertebral lateral projections can predict spinal radiographic damage in patients with ankylosing spondylitis

OBJECTIVES

To investigate the association between bone mineral status and spinal radiographic damage in patients with ankylosing spondylitis (AS) and determine whether bone mineral status can predict further spinal radiographic damage after 2 years.

METHODS

Bone mineral density (BMD) of the lumbar spine (anteroposterior and lateral projections), femoral neck, and total hip and trabecular bone score (TBS) of the lumbar spine were measured in AS patients (n = 54) who fulfilled the modified New York criteria. Spinal radiographic damage was scored on cervical and lumbar spine radiographs using modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) at baseline and after 2 years. Simple and multiple linear regression analyses were performed to examine predictors of spinal radiographic damage.

RESULTS

Patients with advanced AS exhibited low BMD on lumbar spine lateral projections, femoral neck, and total hip and low TBS. Low vertebral bone mass at baseline, assessed by BMD of the lateral projections or TBS, was independently associated with baseline mSASSS. After 2 years, mSASSS change from baseline was significantly associated with high baseline mSASSS, high baseline erythrocyte sedimentation rate and C-reactive protein (CRP) levels, and low baseline BMD of the lumbar spine lateral projections. The best predictive model for spinal radiographic progression consisted of baseline mSASSS, baseline CRP, and low BMD of lateral lumbar spine (area under curve = 0.826).

CONCLUSIONS

BMD at vertebral lateral projections and TBS were inversely associated with baseline mSASSS in AS patients. Low BMD at vertebral lateral projections, as well as baseline mSASSS and inflammatory markers, might predict spinal radiographic damage in AS.Key Points• Vertebral bone mineral density of lateral projections and trabecular bone score are inversely associated with baseline mSASSS in patients with ankylosing spondylitis.• Baseline mSASSS, inflammatory markers, and low vertebral bone mineral density might predict spinal radiographic progression in patients with ankylosing spondylitis.

Assessing bone impairment in ankylosing spondylitis (AS) using the trabecular bone score (TBS) and high-resolution peripheral quantitative computed tomography (HR-pQCT)

OBJECTIVES

To compare bone quality using the trabecular bone score (TBS) and bone microarchitecture in the distal tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT) in ankylosing spondylitis (AS) patients and healthy controls (HC).

METHODS

Areal bone mineral density (aBMD) and TBS (TBS iNsight software) were evaluated using DXA (Hologic, QDR 4500); while volumetric bone mineral density (vBMD) and bone microarchitecture were analyzed in the distal tibia using HR-pQCT (Scanco) in 73 male patients with AS and 52 age-matched HC.

RESULTS

AS patients were a mean 41.6 ± 7.9 years old and had a mean disease duration of 16.4 ± 8.6 y, with a mean mSASSS 25.6 ± 16.4. No difference was observed in lumbar spine aBMD in AS patients and HC (p = 0.112), but total hip BMD (p = 0.011) and TBS (p < 0.001) were lower in AS patients. In the distal tibia, reduced trabecular volumetric density [Tb.vBMD (p < 0.006)] and structural alterations - trabecular thickness (Tb.Th), p = 0.044 and trabecular separation (Tb.Sp), p = 0.039 - were observed in AS patients relative to controls. Further analysis comparing TBS < 1.310 and TBS ≥ 1.310 in AS patients revealed a higher mean body mass index [BMI] (p = 0.010), lower tibia cortical vBMD [Ct.vBMD] (p = 0.007), lower tibia cortical thickness [Ct.Th]: (p = 0.048) in the former group. On logistic regression analysis, BMI (OR = 1.27; 95%IC = 1.08-1.50, p = 0.005), (VF 4.65; 1.13-19.1, p = 0.033) and tibial Ct.vBMD (0.98; 0.97-1.00, p = 0.007) were associated with a lower TBS (<1.310).

CONCLUSIONS

The present study demonstrates that TBS and HR-pQCT imaging are important technologies evaluating bone impairment in AS patients. Moreover, in these patients vertebral fractures were associated with lower TBS.

Association of Genetic Variants of RANK, RANKL, and OPG with Ankylosing Spondylitis Clinical Features in Taiwanese

Ankylosing spondylitis (AS) is a chronic inflammatory disease that leads to spinal ankylosis. The receptor activator of the nuclear factor-kappa (RANK), RANK ligand, and osteoprotegerin (OPG) (RANK/RANKL/OPG) pathway plays critical roles in bone metabolism and the immune system. The current study was aimed at investigating whether six single-nucleotide polymorphisms (SNPs) within the RANK, RANKL, and OPG genes essential for bone homeostasis are associated with AS. Genotype distributions, allele and haplotype frequencies, were compared between 1120 AS patients and 1435 healthy controls and among AS patients with stratification by syndesmophyte formation, onset age, and HLA-B27 positivity. We found that RANKL SNPs were associated with AS syndesmophyte formation. Notably, the RANKL SNP haplotype rs7984870C/rs9533155G/rs9525641C was negatively associated with AS susceptibility and appeared to protect against syndesmophyte formation in AS. Functionally, RANKL promoter SNPs (rs9525641 C/T and rs9533155 G/C) affected DNA-protein complex formation and promoter activity in promoter reporter analyses. The OPG SNP haplotype rs2073618G/rs3102735T was significantly associated with HLA-B27 negativity in AS patients. Furthermore, AS patients with syndesmophyte formation had significantly lower levels of soluble RANKL levels than those without syndesmophyte formation. Our data suggested a role for RANKL in AS susceptibility and severity.

Advances in understanding the pathophysiology of spondyloarthritis

Progressive understanding of the underlying pathophysiology of axial spondyloarthritis has successfully translated into innovative therapeutic strategies and successful management of patients in the clinic. This review summarizes the key roles of the pro-inflammatory cytokines tumor necrosis factor and interleukin-17 in the onset and progression of disease and how these cytokines are instrumental in shaping the concept that enthesitis is a key feature of axial spondyloarthritis. Advances in immunological technologies have led to the important insight that different cell populations, part of both the innate and adaptive immune system, play a key role in axial spondyloarthritis. In addition to inflammation, structural damage to the axial skeleton, in particular progressive ankylosis of the sacroiliac joints and the spine, is key to the outcome of patients. Novel data integrate the role of pro-inflammatory cytokines and enthesitis in this context.

Monocytes from male patients with ankylosing spondylitis display decreased osteoclastogenesis and decreased RANKL/OPG ratio

The present study investigates the osteoclastogenic capacity of peripheral blood mononuclear cells (PBMCs) in male patients with ankylosing spondylitis (AS). We demonstrated that monocytes from these patients display a lower capacity to generate osteoclasts compared to cells from healthy controls, and osteoclastogenesis was negatively correlated with disease duration.

INTRODUCTION

Ankylosing spondylitis (AS) is a disease characterized by new bone growth that leads to syndesmophyte formation but AS patients frequently present with low bone mineral density/fractures. Osteoclastogenesis in AS patients is poorly studied and controversial. The aim of this study is to determine if the osteoclastogenic capacity of PBMCs is different in AS patients compared to controls and the relationship between osteoclastogenesis and clinical/laboratory parameters.

METHODS

PBMCs from 85 male AS patients and 59 controls were tested for CD16+ cells and induced to differentiate into osteoclasts over 3 weeks in vitro. Serum levels of RANKL, osteoprotegerin (OPG), C-terminal telopeptide of type I collagen (CTX), and amino-terminal pro-peptide of type I collagen (P1NP) were also evaluated.

RESULTS

PBMCs from AS patients had fewer CD16+ cells and produced fewer osteoclasts compared to controls. Apoptosis occurred less frequently in osteoclasts obtained from AS patients than in osteoclasts from the controls. A lower RANKL/OPG and CTX/P1NP were observed in AS patients compared to controls. AS patients taking NSAIDs presented no difference regarding the number of OCs produced and the percentage of CD16+ cells compared to controls. However, patients taking TNF inhibitors (TNFi) presented lower OC numbers than controls. A negative correlation was demonstrated between the number of osteoclasts generated from PBMCs of AS patients and disease duration.

CONCLUSION

Monocytes from male AS patients display a lower capacity to generate osteoclasts in vitro compared to cells from controls. Osteoclastogenesis was negatively correlated with disease duration. This finding supports the idea that osteoclasts play a role in the physiopathology of bone disease in AS patients.

The Relationship between the Occipitocervical Junction and Thoracic Kyphosis in Ankylosing Spondylitis: A Retrospective Cohort Study of 86 Cervical Fractures in Surgically Treated Patients

Study Design

Retrospective analysis of prospectively collected data.

Purpose

To describe the radiological characteristics of the occipitocervical area in patients with ankylosing spondylitis (AS) using the novel measure X-angle and to describe the correlation between the ankylosed occipitoatlantoaxial (OAA) joint and thoracic kyphosis (TK).

Overview of Literature

AS affects the axial skeleton, leading to progressive ankylosis of all vertebral segments. The effect of ankylosis on the upper cervical area of these patients is not well documented.

Methods

All patients with complete ankylosis of the spinal column between C3 and T1, treated for cervical spinal fracture between 2007 and 2014, were eligible for inclusion in this study. The level of cervical fracture was identified. The T1–12 and T5–12 angles were measured using preoperative lateral radiography. The progressive degeneration of the C0-C1-C2 joints was evaluated via the new indicator X-angle, through the measurement of the angle of the C0-C1-C2 articulations in the coronal plane using computed tomography.

Results

We included 86 consecutive patients with AS (67 males) aged 69±12 years. The patients were divided into two groups according to the degenerative change in the C0–C1 joint (62 patients with a mobile joint and 24 patients with an ankylosed joint). There was no significant difference between the two groups in terms of age (p =0.094) and level of fracture (p =0.949). The most commonly affected level was C6. There was no requirement for revision due to non-union in any of the patients. There was a statistically significant difference observed in the T1–12, T5–12, and X-angles (p =0.004, 0.001, and <0.001, respectively). TK was greater in the ankylosed joint group than in the mobile joint group. The X-angle was also greater in the ankylosed joint group because of the vertical destruction of the OAA joint.

Conclusions

Thoracic hyperkyphosis resulted in degenerative changes in the C0-C1-C2 joint in patients with AS. The X-angle is a reliable method for measuring the integrity of the C0-C1-C2 joint in such patients.

Low bone mineral density predicts the formation of new syndesmophytes in patients with axial spondyloarthritis

Background

This study aimed to investigate whether the presence of low bone mineral density (BMD) in patients with axial spondyloarthritis (axSpA) predicts formation of new syndesmophytes over 2 years.

Methods

One hundred and nineteen patients fulfilling the imaging arm of the Assessment of SpondyloArthritis International Society axSpA criteria were enrolled. All patients were under 50 years of age. The modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) was assessed by two trained readers blinded to the patients’ data. BMD (lumbar spine, femoral neck or total hip) at baseline was assessed using dual-energy absorptiometry. Low BMD was defined as Z score ≤ − 2.0. Spinal radiographic progression was defined as worsening of the mSASSS by ≥ 2 points over 2 years. Logistic regression analyses were performed to identify predictors associated with development of new syndesmophytes and spinal radiographic progression.

Results

At baseline, 19 (16%) patients had low BMD. New syndesmophytes had developed in 22 (21%) patients at 2-year follow-up. New syndesmophyte formation after 2 years occurred more in patients with low BMD than in those with normal BMD (p = 0.047). In the multivariable analysis, current smoking, existing syndesmophytes and low BMD at baseline were associated with spinal radiographic progression (OR (95% CI) 3.0 (1.1, 7.7), 4.6 (1.8, 11.8) and 3.6 (1.2, 11.2), respectively). The presence of syndesmophytes at baseline and low BMD were predictors of new syndesmophytes over the following 2 years (OR (95% CI) 5.5 (2.0, 15.2) and 3.6 (1.1, 11.8), respectively).

Conclusions

Low BMD and existing syndesmophytes at baseline were independently associated with the development of new syndesmophytes in young axSpA patients.

Vitamin D levels in patients with ankylosing spondylitis: Is it related to disease activity?

Objective:

Ankylosing Spondylitis (AS) is an inflammatory rheumatic disease that mainly affects the axial spine. Osteopenia and osteoporosis are the main complications of AS. Vitamin D has functions on the immune system. In this study, we aimed to compare vitamin D levels and Bone Mineral Density (BMD) values between AS patients and controls.

Methods:

A total of 68 patients with axial AS and 34 healthy controls were enrolled in this study conducted between March 2018 and May 2018. Vitamin D concentrations, BMD values, disease activity, back mobility, functionality and radiologic damage were evaluated.

Results:

Vitamin D concentrations, the total BMD-femur and BMD-femur neck values were significantly lower in AS patients (p = 0.001, p = 0.011 and p = 0.003). No significant correlations were detected between vitamin D levels and BMD-femur total, BMD-femur neck values, disease activity, back mobility, functionality and radiologic damage scores (p > 0.05). Disease activity parameters were significantly and negatively correlated with total BMD-femur and BMD-femur neck values (p < 0.05).

Conclusion:

Our study demonstrates that AS patients have lower vitamin D levels, total BMD-femur and BMD-femur neck values. Higher disease activity increases bone loss in AS. Regular measurement of BMD and vitamin D should be kept in mind when planning a treatment in AS.

Bone Disease in Axial Spondyloarthritis

Axial spondyloarthritis is a chronic inflammatory skeletal disorder with an important burden of disease, affecting the spine and sacroiliac joints and typically presenting in young adults. Ankylosing spondylitis, diagnosed by the presence of structural changes to the skeleton, is the prototype of this disease group. Bone disease in axial spondyloarthritis is a complex phenomenon with the coexistence of bone loss and new bone formation, both contributing to the morbidity of the disease, in addition to pain caused by inflammation. The skeletal structural changes respectively lead to increased fracture risk and to permanent disability caused by ankylosis of the sacroiliac joints and the spine. The mechanism of this new bone formation leading to ankylosis is insufficiently known. The process appears to originate from entheses, specialized structures that provide a transition zone in which tendon and ligaments insert into the underlying bone. Growth factor signaling pathways such as bone morphogenetic proteins, Wnts, and Hedgehogs have been identified as molecular drivers of new bone formation, but the relationship between inflammation and activation of these pathways remains debated. Long-standing control of inflammation appears necessary to avoid ankylosis. Recent evidence and concepts suggest an important role for biomechanical factors in both the onset and progression of the disease. With regard to new bone formation, these processes can be understood as ectopic repair responses secondary to inflammation-induced bone loss and instability. In this review, we discuss the clinical implications of the skeletal changes as well as the underlying molecular mechanisms, the relation between inflammation and new bone formation, and the potential role of biomechanical stress.

Do biological disease-modifying antirheumatic drugs reduce the spinal fracture risk related to ankylosing spondylitis? A longitudinal multiregistry matched cohort study

OBJECTIVES

Ankylosing spondylitis (AS) is associated with an increased spinal fracture risk due to the loss of elasticity in spinal motion segments. With the introduction of biological disease-modifying antirheumatic drug (bDMARD) treatment for AS, the individual course of the disease has been ameliorated. This study aims to examine the association of bDMARD treatment and risk of spinal fracture.

DESIGN

Longitudinal population-based multiregistry observational matched cohort study.

SETTING

Swedish Patient Registry 1987-2014 and Swedish Prescribed Drugs Registry 2005-2014.

PARTICIPANTS

Included were patients ≥18 years of age receiving treatment at a healthcare facility for the primary diagnosis of AS. About 1352 patients received more than one prescription of bDMARD from 2005 to 2014. An untreated control group was created by propensity score matching for age, sex, comorbidity, antirheumatic prescriptions and years with AS (n=1352).

MAIN OUTCOME MEASURES

Spinal fracture-free survival.

RESULTS

No bDMARD treatment-related effect on spinal fracture-free survival was observed in the matched cohorts. Male gender (HR=2.54, 95% CI 1.48 to 4.36) and Charlson Comorbidity Index score (HR=3.02, 95% CI 1.59 to 5.75) contributed significantly to spinal fracture risk.

CONCLUSION

bDMARD had no medium-term effect on the spinal fracture-free survival in patients with AS.

TRIAL REGISTRATION NUMBER

NCT02840695; Post-results.

Osteoblast Role in Rheumatic Diseases

Alterations in osteoblast growth, differentiation and activity play a role in the pathogenesis of several rheumatic diseases, such as rheumatoid arthritis, spondyloarthritides, osteoarthritis, and osteoporosis. In fact, in these rheumatic diseases, abnormal activity of Wnt signaling, receptor activator of nuclear factor-κB (RANK)-RANK ligand (RANKL)-osteoprotegerin (OPG) signaling, bone morphogenetic proteins (BMPs) pathway and other mechanisms have been described in osteoblasts. This review article is focused on current knowledge on the role of osteoblast dysregulation occurring in rheumatic diseases.

Circumferential Fusion through All-Posterior Approach in Andersson Lesion

Study Design

Retrospective case series.

Purpose

To assess safety and efficacy of single stage, posterior stabilisation and anterior cage reconstruction through the transforaminal or lateral extra-cavitary route for Andersson lesions.

Overview of Literature

Pseudoarthrosis in ankylosing spondylitis (Andersson lesion, AL) can cause progressive kyphosis and neurological deficit. Management involves early recognition and surgical stabilisation in patients with instability. However, the need and safety of anterior reconstruction of the vertebral body defect remains unclear.

Methods

Twenty consecutive patients with AL whom presented with instability back pain and or neurological deficit were managed by single stage posterior approach with long segment pedicle screw fixation and anterior vertebral reconstruction. Radiological evaluation included- the regional kyphotic angle, measurement of anterior defect in computed tomography (CT) scan and the spinal cord status in magnetic resonance imaging. Radiological outcomes were assessed for fusion and kyphosis correction. Functional outcomes were assessed with visual analogue scale (VAS), ankylosing spondylitis quality of life (ASQoL) and Oswestry disability index (ODI).

Results

The mean age of the patients was 50.1 years (male, 18; female, 2). The levels affected include thoracolumbar (n=12), lower thoracic (n=5) and lumbar (n=3) regions. The mean level of fixation was 6.2±2.4 vertebrae. The mean anterior column defect was 1.6±0.6 cm. The mean surgical duration, blood loss and hospital stay were 112 minutes, 452 mL and 6.2 days, respectively. The mean followup was 2.1 years. At final follow up, VAS for back pain improved from 8.2 to 2.4 while ODI improved from 62.7 to 18.5 (p <0.05) and ASQoL improved from 14.3±2.08 to 7.90±1.48 (p <0.05). All patients had achieved radiological union at a mean 7.2±4.6 months. The mean regional kyphotic angle was 27° preoperatively, 16.7° postoperatively and 18.1° at the final follow-up.

Conclusions

Posterior stabilisation and anterior reconstruction with cage through an all-posterior approach is safe and can achieve good results in Andersson lesions.

Simultaneous Quantification of Bone Edema/Adiposity and Structure in Inflamed Bone Using Chemical Shift-Encoded MRI in Spondyloarthritis

Purpose

To evaluate proton density fat fraction (PDFF) and R2* as markers of bone marrow composition and structure in inflamed bone in patients with spondyloarthritis.

Methods

Phantoms containing fat, water, and trabecular bone were constructed with proton density fat fraction (PDFF) and bone mineral density (BMD) values matching those expected in healthy bone marrow and disease states, and scanned using chemical shift‐encoded MRI (CSE‐MRI) at 3T. Measured PDFF and R2* values in phantoms were compared with reference FF and BMD values. Eight spondyloarthritis patients and 10 controls underwent CSE‐MRI of the sacroiliac joints. PDFF and R2* in areas of inflamed bone and fat metaplasia in patients were compared with normal bone marrow in controls.

Results

In phantoms, PDFF measurements were accurate over the full range of PDFF and BMD values. R2* measurements were positively associated with BMD but also were influenced by variations in PDFF. In patients, PDFF was reduced in areas of inflammation and increased in fat metaplasia compared to normal marrow. R2* measurements were significantly reduced in areas of fat metaplasia.

Conclusion

PDFF measurements reflect changes in marrow composition in areas of active inflammation and structural damage and could be used for disease monitoring in spondyloarthritis. R2* measurements may provide additional information bone mineral density but also are influenced by fat content. Magn Reson Med 79:1031–1042, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Microtrauma: no longer to be ignored in spondyloarthritis?

PURPOSE OF REVIEW

Novel clinical and animal model data support that biomechanical factors play a role in the onset and progression of spondyloarthritis. Bringing together these insights with the progress made in our understanding of the immunopathogenesis and genetic susceptibility of spondyloarthritis may provide new opportunities for better management.

RECENT FINDINGS

Tail suspension prevents arthritis in a tumor necrosis factor overexpression model. A similar approach also reduces new bone formation after acute arthritis in mice. Physical labor is associated with disease severity, including structural disease progression. Sentinel immune cells in the enthesis provide a link between local damage and the development of inflammation. Loss of stability likely triggers tissue remodeling, including the formation of syndesmophytes. Improving muscle strength and control while avoiding excessive strain or overuse should be considered in the approach toward patients. New regulators of tissue turnover and remodeling are emerging including microRNAs.

SUMMARY

Local damage may provide a trigger for spondyloarthritis. For structural disease progression loss of stability may be an important factor. Control of inflammation will prevent stability issues and improve the long-term prognosis of disease. Physical therapy will continue to provide benefit for patients in the short and in long-term management of disease.

C5aR inhibition in the early inflammatory phase does not affect bone regeneration in a model of uneventful fracture healing

Background

Recent studies were able to demonstrate involvement of the complement cascade in bone biology. Further studies analyzed the role of complement in traumatic injuries and demonstrated negative effects after excessive systemic activation of the inflammatory response with early abrogation of complement activation after application of a C5aR-antagonist exerting beneficial effects upon bone regeneration. In contrast, own fracture healing experiments with complement-deficient animals implied a crucial role of the complement cascade for sufficient fracture healing.

Methods

To analyze the effect of a short abrogation of the complement system in the local process of fracture healing, a fracture healing experiment with wild-type mice (C57BL6), femoral osteotomy, consecutive external fixation for 21 days and blockade of the early complement activation (C5aRA) directly after trauma and after 12 h was performed. Control animals received a peptide without any biological effects. After 1–3 days, the inflammatory response was monitored with IL-6 immunostaining, serum analyses of C5a and after 3 days with histological evaluation of PMN. Fracture healing was examined with biomechanical, radiological and histological methods after 21 days.

Results

While a decrease of the early inflammatory response was seen on day 1 of the C5aRA-treated group regarding immunostaining for IL-6 and after 3 days in the histological evaluation of PMN, no significant differences were demonstrated between both experimental groups after 21 days in the biomechanical, radiological and histological evaluation.

Conclusions

The present results demonstrate that the short-term inhibition of complement activation immediately after fracture does not significantly affect bone regeneration in an experimental model of regular fracture healing. Whereas other studies demonstrated that the early posttraumatic blockade of the C5aR improves fracture healing in a scenario of combined trauma, the present findings implicate that the same treatment has no effect in uneventful bone healing.

Imbalance Between Bone Morphogenetic Protein 2 and Noggin Induces Abnormal Osteogenic Differentiation of Mesenchymal Stem Cells in Ankylosing Spondylitis

OBJECTIVE

To study the osteogenic differentiation capacity of bone marrow-derived mesenchymal stem cells (BM-MSCs) from patients with ankylosing spondylitis (AS) and to investigate the mechanisms of abnormal osteogenic differentiation of BM-MSCs in AS.

METHODS

BM-MSCs from healthy donors (HD-MSCs) and patients with AS (AS-MSCs) were cultured in osteogenic differentiation medium for 0-21 days, after which their osteogenic differentiation capacity was determined using alizarin red S and alkaline phosphatase assays. Gene expression levels of osteoblastic markers and related cytokines were detected by high-throughput quantitative reverse transcription-polymerase chain reaction. Enzyme-linked immunosorbent assay was performed to detect protein levels of bone morphogenetic protein 2 (BMP-2) and Noggin in the cell culture supernatant. The activation of Smad1/5/8 and MAPK signaling pathways was measured by Western blotting. The balance between BMP-2 and Noggin expression was regulated using lentiviruses encoding short hairpin RNA and exogenous Noggin, respectively, which enabled evaluation of how this balance affected osteogenic differentiation of AS-MSCs.

RESULTS

AS-MSCs outperformed HD-MSCs in osteogenic differentiation capacity. During osteogenic differentiation, AS-MSCs secreted more BMP-2 but less Noggin, accompanied by an overactivation of Smad1/5/8 and ERK-1/2. When the Noggin concentration was increased or BMP-2 expression was inhibited, the abnormal osteogenic differentiation of AS-MSCs was rectified. In addition, the balance between BMP-2 and Noggin secretion was restored.

CONCLUSION

The results of this study demonstrate that an imbalance between BMP-2 and Noggin secretion induces abnormal osteogenic differentiation of AS-MSCs. These findings reveal a mechanism of pathologic osteogenesis in AS and provide a new perspective on inhibiting pathologic osteogenesis by regulating the balance between BMP-2 and Noggin.

Selection of Lowest Instrumented Vertebra for Thoracolumbar Kyphosis in Ankylosing Spondylitis

STUDY DESIGN

Retrospective study.

OBJECTIVE

To determine the optimal osteotomized vertebra (OV) and lowest instrumented vertebra (LIV) in ankylosing spondylitis (AS) kyphosis.

SUMMARY OF BACKGROUND DATA

Although most of AS kyphosis cases are treated by pedicle subtraction osteotomy (PSO), few studies have focused on the selection of the LIV relative to distal OV.

METHODS

We reviewed all AS kyphosis cases surgically treated at our institution between 2010 and 2013. Patients were divided into groups based on the relative position of LIV and distal OV: group OV+2, the LIV was the second vertebra below OV; group OV+3, the LIV was the third vertebra below OV; group OV+4, the LIV was the fourth vertebra below OV. The preoperative and 2-year postoperative radiographic parameters and clinical data of the former two groups were compared. In addition, if the LIV was S1, patients were included in group S1, and those remaining were included in group non-S1 (the LIV was L5 or above).

RESULTS

None of the patients presented fixation failure. Groups OV+2 and OV+3 had similar magnitudes of kyphosis (P > 0.05) and sagittal vertical axis corrections (P > 0.05) at the last follow-up. There was no difference in the incidence of proximal junctional kyphosis (PJK) between groups (P > 0.05). Between groups S1 and non-S1, the incidence of PJK and the magnitudes of kyphosis and sagittal vertical axis corrections were not significantly different (P > 0.05). The lumbosacral visual analogue scale and the incidence of pressure sores in group S1 were higher than in group non-S1 (P < 0.05).

CONCLUSION

When PSO is performed at the level of L2 or L3, the instrumentation can be limited to the two caudal vertebra that follow. Extending the fixation to more vertebra or to the sacrum does not appear to improve the stability of the instrumentation and the fusion rate, and it is not suitable to carry out PSO at L4.

LEVEL OF EVIDENCE

4.

Utility of DXA scanning and risk factors for osteoporosis in ankylosing spondylitis-A prospective study

BACKGROUND

Conventional DXA imaging of spine and hip to measure bone mineral density (BMD) has limitations in patients with ankylosing spondylitis (AS). We investigated the correlation of hip and spine BMD measurements in patients with AS to determine if hip DXA will prove clinically useful while avoiding the confounding effect of spinal disease. Also, we studied risk factors for osteoporosis (OP) and osteopenia in AS.

METHODS

We randomly identified patients from our validated AS registry ≥18 years of age who met the Modified New York Classification criteria for AS. BMD was measured and interpreted using ISCD 2007 guidelines and diagnosis of OP was based on WHO criteria. ESR, CRP, urinary N-telopeptide, and 25-hydroxy vitamin D were also measured. Correlation between the BMD (total hip and/or femoral neck) and lumbar spine was calculated. Statistical comparisons between the 2 sites, lumbar spine (AP) and hip (total hip and or femoral neck) were made using Bowker's test for symmetry and kappa statistics. Chi-square and odds ratio using logistic regression were used to assess the association of the purported risk factors for OP in these patients.

RESULTS

Frequency of OP among AS patients ≥50 years of age was 23%, and that of osteopenia was 41%. Among patients <50 years of age, the frequency of low bone mass for expected age (Z-score ≤-2.0) was 14.7%. There was moderate correlation (ρ = 0.59) and a fair agreement (κ = 0.26; 95% CI: 0.10-0.42) between the lowest T-values of hip and lumbar spine (AP view). OP was significantly associated with elevated CRP level [OR = 4.2 (95% CI: 1.13-15.9), p < 0.03] and African American race [OR = 7.2 (95% CI: 1.18-44.99), p < 0.03].

CONCLUSION

Our results demonstrated a moderate correlation and fair agreement between the T-scores of hip and the lumbar spine (AP view) in patients with AS, suggesting that DXA of the hip and the lumbar spine (AP view) may both be useful for OP and osteopenia screening in patients with AS without fused spines. We confirm the previous reports of an association of elevated CRP level with an increased risk of OP in patients with AS, but this is the first study to demonstrate that African American patients with AS may be at a higher risk of developing OP compared to Caucasians.

Bone morphogenetic proteins in inflammation, glucose homeostasis and adipose tissue energy metabolism

Bore morphogenetic proteins (BMPs) are members of the transforming growth factor (TGF)-β superfamily, a group of secreted proteins that regulate embryonic development. This review summarizes the effects of BMPs on physiological processes not exclusively linked to the musculoskeletal system. Specifically, we focus on the involvement of BMPs in inflammatory disorders, e.g. fibrosis, inflammatory bowel disease, anchylosing spondylitis, rheumatoid arthritis. Moreover, we discuss the role of BMPs in the context of vascular disorders, and explore the role of these signalling proteins in iron homeostasis (anaemia, hemochromatosis) and oxidative damage. The second and third parts of this review focus on BMPs in the development of metabolic pathologies such as type-2 diabetes mellitus and obesity. The pancreatic beta cells are the sole source of the hormone insulin and BMPs have recently been implicated in pancreas development as well as control of adult glucose homeostasis. Lastly, we review the recently recognized role of BMPs in brown adipose tissue formation and their consequences for energy expenditure and adiposity. In summary, BMPs play a pivotal role in metabolism beyond their role in skeletal homeostasis. However, increased understanding of these pleiotropic functions also highlights the necessity of tissue-specific strategies when harnessing BMP action as a therapeutic target.

Surgical Stabilization Improves Survival of Spinal Fractures Related to Ankylosing Spondylitis

STUDY DESIGN

National registry cohort study.

OBJECTIVE

The aim of this study was to investigate the effect of surgical stabilization on survival of spinal fractures related to ankylosing spondylitis (AS).

SUMMARY OF BACKGROUND DATA

Spinal fractures related to AS are associated with considerable morbidity and mortality. Multiple studies suggest a beneficial effect of surgical stabilization in these patients.

METHODS

In the Swedish patient registry, all patients treated in an inpatient facility are registered with diagnosis and treatment codes. The Swedish mortality registry collects date and cause of death for all fatalities. Registry extracts of all patients with AS and spinal fractures including date of death and treatment were prepared and analyzed for epidemiological purposes.

RESULTS

Seventeen thousand two hundred ninety-seven individual patients with AS were admitted to treatment facilities in Sweden between 1987 and 2011. Nine hundred ninety patients with AS (age 66 ± 14 years) had 1131 spinal fractures, of which 534 affected cervical, 352 thoracic, and 245 lumbar vertebrae. Thirteen percent had multiple levels of injuries during the observed period. Surgically treated patients had a greater survival than those treated nonsurgically [hazard ratio (HR) 0.79, P = 0.029]. Spinal cord injury was the major factor contributing to mortality in this cohort (HR 1.55, P < 0.001). The proportion of surgically treated spinal fractures increased linearly during the last decades (r = 0.92, P < 0.001) and was 64% throughout the observed years.

CONCLUSIONS

Spinal cord injury threatened the survival of patients with spinal fractures related to AS. Even though surgical treatment is associated with a considerable complication rate, it improved the survival of spinal fractures related to AS.

LEVEL OF EVIDENCE

3.

Is allopurinol use associated with an excess risk of osteoporotic fracture? A National Prescription Registry study

Using a Danish Register cohort of 86,039 adult new allopurinol users and propensity score matched controls, we found that gout requiring allopurinol prescription was associated with an increased fracture risk.

PURPOSE

Gout, an acute inflammatory arthritis, is common and associated with elevated serum urate, obesity and high alcohol consumption. The mainstay of therapy is the urate-lowering agent, allopurinol. Here, we report the relationship between allopurinol prescription and fracture in a large registry population.

METHODS

We established a Danish Register cohort of 86,039 adult cases (new allopurinol users) and 86,039 age, sex and propensity score matched controls (not exposed to allopurinol or with a gout diagnosis), with no diagnosis of malignancy in the year prior.

RESULTS

We found a modest adjusted effect of allopurinol prescription on major osteoporotic fractures (hazard ratio (HR) 1.09, 95 % confidence interval (CI) 1.05-1.14, p = 0.04) and on hip fractures (HR 1.07, 95 % CI 1.11-1.14, p < 0.001), robust to adjustment for confounding factors (age, sex, comorbidity, medication use). Associations were stronger in men than women, and among incident allopurinol users whose gout diagnosis had been confirmed by at least one hospital contact. Prespecified subanalyses by filled dose of allopurinol (mg/day in first year of prescription) showed increased hip and major fracture risk in women in the highest allopurinol dose grouping only, while a less strong dose effect was evident for fracture rates in men.

CONCLUSION

Gouty arthritis requiring allopurinol is associated with an excess risk of major or hip fracture, with an allopurinol dose effect evident in women such that women taking the highest doses of allopurinol--suggestive of more severe disease--were at increased risk relative to women taking lower doses.

Complications and survival after long posterior instrumentation of cervical and cervicothoracic fractures related to ankylosing spondylitis or diffuse idiopathic skeletal hyperostosis

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

This study investigates the results of long posterior instrumentation with regard to complications and survival.

SUMMARY OF BACKGROUND DATA

Fractures of the cervical spine and the cervicothoracic junction related to ankylosing spinal disease (ASD) endanger both sagittal profile and spinal cord. Both anterior and posterior stabilization methods are well established, and clear treatment guidelines are missing.

METHODS

Forty-one consecutive patients with fractures of the cervicothoracic junction related to ASD were treated by posterior instrumentation. All patients were followed prospectively for 2 years using a standardized protocol.

RESULTS

Five patients experienced postoperative infections, 3 patients experienced postoperative pneumonia, 2 patients required postoperative tracheostomy, and 1 patient had postoperative cerebrospinal fluid leakage due to accidental durotomy. No patient required reoperation due to implant failure or nonunion. Mean survival was 52 months (95% confidence interval: 42-62 mo). Survival was affected by patient age, sex, smoking, and spinal cord injury.

CONCLUSION

Patients with ASD experiencing a fracture of the cervicothoracic region are at high risk of developing complications. The posterior instrumentation of cervical spinal fractures related to ASD is recommended due to biomechanical superiority.

LEVEL OF EVIDENCE

4.

Complement C3 and C5 deficiency affects fracture healing

There is increasing evidence that complement may play a role in bone development. Our previous studies demonstrated that the key complement receptor C5aR was strongly expressed in the fracture callus not only by immune cells but also by bone cells and chondroblasts, indicating a function in bone repair. To further elucidate the role of complement in bone healing, this study investigated fracture healing in mice in the absence of the key complement molecules C3 and C5. C3^-/- and C5^-/- as well as the corresponding wildtype mice received a standardized femur osteotomy, which was stabilized using an external fixator. Fracture healing was investigated after 7 and 21 days using histological, micro-computed tomography and biomechanical measurements. In the early phase of fracture healing, reduced callus area (C3^-/-: -25%, p=0.02; C5^-/-: -20% p=0.052) and newly formed bone (C3^-/-: -38%, p=0.01; C5^-/-: -52%, p=0.009) was found in both C3- and C5-deficient mice. After 21 days, healing was successful in the absence of C3, whereas in C5-deficient mice fracture repair was significantly reduced, which was confirmed by a reduced bending stiffness (-45%; p=0.029) and a smaller callus volume (-17%; p=0.039). We further demonstrated that C5a was activated in C3^-/- mice, suggesting cleavage via extrinsic pathways. Our results suggest that the activation of the terminal complement cascade in particular may be crucial for successful fracture healing.

Increased occurrence of spinal fractures related to ankylosing spondylitis: a prospective 22-year cohort study in 17,764 patients from a national registry in Sweden

BACKGROUND

Ankylosing spondylitis (AS) is a rheumatoid disease leading to progressive ossification of the spinal column. Patients suffering from AS are highly susceptible to unstable vertebral fractures and often require surgical stabilisation due to long lever arms. Medical treatment of these patients improved during the last decades, but until now it is unknown whether the annual number of spinal fractures changed during the last years. Since the annual count of fracture is an effective measure for efficacy of injury prevention and patient safety in AS patients, the current recommendations of activity have to be revised accordingly.

METHODS

Data for all patients with AS treated as inpatients between 01/01/1987 and 31/12/2008 were extracted from the Swedish National Hospital Discharge Registry (SNHDR). The data in the registry are collected prospectively, recording all inpatient admissions throughout Sweden. The SNHDR uses the codes for diagnoses at discharge according to the Swedish versions of the International Classification of Diseases (ICD-9 and ICD-10).

RESULTS

During the years from 1987 to 2008 17,764 patients with AS were treated as inpatients; of these 724 patients were treated due to spinal fractures. The annual number of cervical, thoracic and lumbar fractures in the registry increased until 2008 (r = 0.94).

CONCLUSIONS

Despite the improved treatment of AS the annual number of vertebral fractures requiring inpatient care increased during the last two decades. Possible explanations are population growth, greater awareness of fractures, improved diagnostics, improved emergency care reducing fatalities, and a higher activity level of patients receiving modern medical therapy. Obviously the improvement of medical treatment did not reduce the susceptibility of these patients to unstable fractures. Thus the restrictive injury prevention recommendations for patients with AS cannot be defused, but must be critically revised to improve patient safety.