Microarchitectural adaptations in aging and osteoarthrotic subchondral bone issues

Long-Term Natural Hydroxyapatite and Synthetic Collagen Hydroxyapatite Enhance Bone Regeneration and Implant Fixation Similar to Allograft in a Sheep Model of Implant Integration

There is an increasing demand for a suitable bone substitute to replace current clinical gold standard autografts or allografts. Majority of previous studies have focused on the early effects of substitutes on bone formation, while information on their long-term efficacies remains limited. This study investigated the efficacies of natural hydroxyapatite (nHA) derived from oyster shells and synthetic hydroxyapatite mixed with collagen (COL/HA) or chitosan (CS/HA) on bone regeneration and implant fixation in sheep. Titanium implants were inserted into critical-size defects in distal femur condyles bilaterally, and circumferential gaps around implants were filled with substitute materials or allografts (as control). 14 or 24 weeks post-operatively, the implant-bone blocks were harvested and evaluated using microarchitectural, histomorphometric, and mechanical methods. The nHA and COL/HA groups showed significant bone formation at both 14 and 24 weeks. There was a pronounced increase in bone tissue volume and ingrowth into titanium implant's porous surfaces, significantly enhancing mechanical fixation strength at 24 weeks. CS/HA had a limited ability to induce bone formation and implant fixation. We conclude that nHA and COL/HA revealed long-term effects on enhancing bone formation and implant fixation that were at least as good as allograft after 24 weeks, and both nHA and COL/HA appear to be good alternative materials to bone allograft.

Cardamonin inhibits osteogenic differentiation by downregulating Wnt/beta-catenin signaling and alleviates subchondral osteosclerosis in osteoarthritic mice

Osteoarthritis (OA) is a common degenerative joint disease, and subchondral osteosclerosis is an important pathological change that occurs in its late stages. Cardamonin (CD) is a natural flavonoid isolated from Alpinia katsumadai that has anti-inflammatory activity. The objectives of this study were to investigate the therapeutic effects and potential mechanism of CD in regulating OA subchondral osteosclerosis at in vivo and in vitro settings. Eight-week-old male C57BL/6J mice were randomly divided into four groups: sham operation, anterior cruciate ligament transection (ACLT)-induced OA model, low-dose and high-dose CD treated ACLT-OA model groups. Histological assessment and immunohistochemical examinations for chondrocyte metabolism-related markers metalloproteinase-13, ADAMTS-4, Col II, and Sox-9 were performed. Microcomputed tomography was used to assess the sclerosis indicators in subchondral bone. Further, MC3T3-E1 (a mouse calvarial preosteoblast cell line) cells were treated with various concentrations of CD to reveal the influence and potential molecular pathways of CD in osteogenic differentiations. Animal studies suggested that CD alleviated the pathological changes in OA mice such as maintaining integrity and increasing the thickness of hyaline cartilage, decreasing the thickness of calcified cartilage, decreasing the Osteoarthritis Research Society International score, regulating articular cartilage metabolism, and inhibiting subchondral osteosclerosis. In vitro investigation indicated that CD inhibited alkaline phosphatase expression and production of calcium nodules during osteogenic differentiation of MC3T3-E1 cells. In addition, CD inhibited the expression of osteogenic differentiation-related indicators and Wnt/β-catenin pathway-related proteins. In conclusion, CD inhibits osteogenic differentiation by downregulating Wnt/β-catenin signaling and alleviating subchondral osteosclerosis in a mouse model of OA.

Changes in subchondral bone morphology with osteoarthritis in the ankle

Significant alterations to subchondral trabecular bone microarchitecture are observed in late-stage osteoarthritis (OA). However, detailed investigation of these changes to bone in the ankle are under-reported. This study aimed to fully characterise the trabecular morphology in OA ankle bone specimens compared to non-diseased (ND) controls using both standard and individual-trabecular segmentation-based (ITS) analyses. Ten ND tibial bone specimens were extracted from three cadaveric ankles, as well as five OA bone specimens from patients undergoing total ankle arthroplasty surgery. Each specimen was scanned using microcomputed tomography from which a 4 mm cuboidal volume was extracted for analysis. Morphological parameters for the subchondral trabecular bone were measured using BoneJ (NIH ImageJ) and 3D ITS for whole volumes and at each depth level in 1 mm increments. The results show an overall increase in bone volume fraction (p<0.01) and trabecular thickness (p<0.001) with OA, with a decrease in anisotropy (p<0.05). ITS analysis showed OA bone was composed of more rod-like trabeculae and plate-like trabeculae compared to ND bone. Numerous properties were depth dependent, but the results demonstrated that towards the subchondral bone plate, both rod- and plate-like trabeculae were thicker, rods were longer and plates had increased surface area. Overall, this study has verified key microstructural alterations to ankle subchondral bone that are found in other OA lower-limb joints. Depth-based analysis has highlighted differences of interest for further evaluation into the remodelling mechanisms that occur with OA, which is critical to understanding the role of subchondral bone microarchitecture in the progression of the disease.

Fluid-solid coupling numerical simulation of the effects of different doses of verapamil on cancellous bone in type 2 diabetic rats

BACKGROUND

The purpose of this study was to investigate the effects of four different doses of verapamil on the mechanical behaviors of solid and the characteristics of fluid flow in cancellous bone of distal femur of type 2 diabetes rats under dynamic external load.

METHODS

Based on the micro-CT images, the finite element models of cancellous bones and fluids at distal femurs of rats in control group, diabetes group, treatment groups VER 4, VER 12, VER 24, and VER 48 (verapamil doses of 4, 12, 24, and 48 mg/kg/day, respectively) were constructed. A sinusoidal time-varying displacement load with an amplitude of 0.8 μm and a period of 1s was applied to the upper surface of the solid region. Then, fluid-solid coupling numerical simulation method was used to analyze the magnitudes and distributions of von Mises stress, flow velocity, and fluid shear stress of cancellous bone models in each group.

RESULTS

The results for mean values of von Mises stress, flow velocity and FSS (t = 0.25s) were as follows: their values in control group were lower than those in diabetes group; the three parameters varied with the dose of verapamil; in the four treatment groups, the values of VER 48 group were the lowest, they were the closest to control group, and they were smaller than diabetes group. Among the four treatment groups, VER 48 group had the highest proportion of the nodes with FSS = 1-3 Pa on the surface of cancellous bone, and more areas in VER 48 group were subjected to fluid shear stress of 1-3 Pa for more than half of the time.

CONCLUSION

It could be seen that among the four treatment groups, osteoblasts on the cancellous bone surface in the highest dose group (VER 48 group) were more easily activated by mechanical loading, and the treatment effect was the best. This study might help in understanding the mechanism of verapamil's effect on the bone of type 2 diabetes mellitus, and provide theoretical guidance for the selection of verapamil dose in the clinical treatment of type 2 diabetes mellitus.

Dihydrotanshinone I protects human chondrocytes and alleviates damage from spontaneous osteoarthritis in a guinea pig model

Osteoarthritis (OA) is the most common degenerative joint disease. Currently, no satisfactory pharmacological treatment exists for OA. The potential anti-inflammatory properties of Dihydrotanshinone I (DHT) have been reported, but its effects on OA are unclear. In this study, we assess the impact of DHT on the viability of human chondrocytes in vitro. We then use a guinea pig model to investigate the effects of DHT on knee osteoarthritis progression. Twelve-week-old Dunkin Hartley guinea pigs spontaneously developing OA were intraperitoneally injected with different doses of DHT for eight weeks. Micro-CT analysis was performed on the subchondral bone in the knee, and histological assessment of the knee joint was done using stained sections, the ratio of hyaline to calcified cartilage, and Mankin scores. DHT successfully restored IL-1β-induced decreases in cell viability in human primary chondrocytes. In the guinea pig model, intraperitoneal injections of DHT ameliorated age-induced OA, effectively reduced the expression level of two cartilage metabolism-related genes (ADAMTS4 and MMP13) and decreased the inflammatory biomarker IL-6 in the serum of guinea pigs developing spontaneous osteoarthritis. These findings demonstrate DHT's protective effects on chondrocytes and suggest that it alleviates cartilage degradation and proteoglycan loss in OA.

Bone marrow lesions in osteoarthritis: From basic science to clinical implications

Osteoarthritis (OA) is the most prevalent musculoskeletal disease characterized by multiple joint structure damages, including articular cartilage, subchondral bone and synovium, resulting in disability and economic burden. Bone marrow lesions (BMLs) are common and important magnetic resonance imaging (MRI) features in OA patients. Basic and clinical research on subchondral BMLs in the pathogenesis of OA has been a hotspot. New evidence shows that subchondral bone degeneration, including BML and angiogenesis, occurs not only at or after cartilage degeneration, but even earlier than cartilage degeneration. Although BMLs are recognized as important biomarkers for OA, their exact roles in the pathogenesis of OA are still unclear, and disputes about the clinical impact and treatment of BMLs remain. This review summarizes the current basic and clinical research progress of BMLs. We particularly focus on molecular pathways, cellular abnormalities and microenvironmental changes of subchondral bone that contributed to the formation of BMLs, and emphasize the crosstalk between subchondral bone and cartilage in OA development. Finally, potential therapeutic strategies targeting BMLs in OA are discussed, which provides novel strategies for OA treatment.

Association between radiographic hand osteoarthritis and bone microarchitecture in a population-based sample

Background

Subchondral bone plays an important role in the pathogenesis of radiographic osteoarthritis (OA). However, the bony changes that occur in hand OA (HOA) are much less understood. This study aimed to describe the association between radiographic HOA and high-resolution peripheral quantitative computed tomography (HRpQCT) measures of the hand and radius in a population-based sample.

Methods

A total of 201 participants (mean age 72, 46% female) from the Tasmanian Older Adult Cohort (TASOAC) study underwent HRpQCT assessment of the 2nd distal and proximal interphalangeal (DIP, PIP), 1st carpometacarpal (CMC) joint, and distal radius. Radiographic HOA was assessed at the 2nd DIP, PIP joints, and the 1st CMC joint using the OARSI atlas.

Results

Proximal osteophyte and joint space narrowing (JSN) scores were consistently more strongly associated with HRpQCT measures compared to the distal site with positive associations for indices of bone size (total and trabecular bone area and cortical perimeter but inconsistent for cortical area) and negative associations for volumetric bone mineral density (vBMD). There was a decrease in trabecular number and bone volume fraction with increasing osteophyte and JSN score as well as an increase in trabecular separation and inhomogeneity. Osteophyte and JSN scores in the hand were not associated with HRpQCT measures at the distal radius.

Conclusions

This hypothesis generating data suggests that bone size and trabecular disorganization increase with both osteophyte formation and JSN (proximal more than distal), while local vBMD decreases. This process appears to be primarily at the site of pathology rather than nearby unaffected bone.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02907-6.

Ontogenetic Patterning of Human Subchondral Bone Microarchitecture in the Proximal Tibia

High-resolution computed tomography images were acquired for 31 proximal human tibiae, age 8 to 37.5 years, from Norris Farms #36 cemetery site (A.D. 1300). Morphometric analysis of subchondral cortical and trabecular bone architecture was performed between and within the tibial condyles. Kruskal−Wallis and Wilcoxon signed-rank tests were used to examine the association between region, age, body mass, and each morphometric parameter. The findings indicate that age-related changes in mechanical loading have varied effects on subchondral bone morphology. With age, trabecular microstructure increased in bone volume fraction (p = 0.033) and degree of anisotropy (p = 0.012), and decreased in connectivity density (p = 0.001). In the subchondral cortical plate, there was an increase in thickness (p < 0.001). When comparing condylar regions, only degree of anisotropy differed (p = 0.004) between the medial and lateral condyles. Trabeculae in the medial condyle were more anisotropic than in the lateral region. This research represents an innovative approach to quantifying both cortical and trabecular subchondral bone microarchitecture in archaeological remains.

Metformin alleviates osteoarthritis in mice by inhibiting chondrocyte ferroptosis and improving subchondral osteosclerosis and angiogenesis

BACKGROUND

Osteoarthritis (OA) is the most common musculoskeletal disease, and it has a complex pathology and unknown pathogenesis. Chondrocyte ferroptosis is closely associated with the development of OA. As a common drug administered for the treatment of type 2 diabetes, metformin (Met) is known to inhibit the development of ferroptosis. However, its therapeutic effect in OA remains unknown. The present study aimed to explore the effects of Met on cartilage and subchondral bone in a mouse OA model and to explore the potential underlying mechanisms.

METHODS

A mouse OA model was induced using destabilization of the medial meniscus (DMM) surgery, chondrocyte ferroptosis was induced using an intra-articular injection of Erastin, and Met (200 mg/kg/day) was intragastrically administered for 8 weeks after surgery. H&E and Safranin O‑fast green staining were used to evaluate cartilage degeneration, and μ‑computed tomography was used to evaluate changes in subchondral bone microarchitecture. Moreover, immunohistochemical staining was performed to detect mechanistic metalloproteinases 13, type II collagen, glutathione peroxidase 4, acyl-CoA synthetase long-chain family member 4, solute carrier family 7 member 11 and p53. Runt-associated transcription factor 2 and CD31 were detected using immunofluorescent staining.

RESULTS

Met protected articular cartilage and reversed the abnormal expression of ferroptosis-related proteins in the chondrocytes of DMM mice. Moreover, intra-articular injection of Erastin induced ferroptosis in mouse chondrocytes, and Met eliminated the ferroptosis effects induced by Erastin and protected articular cartilage. In addition, the results of the present study demonstrated that Met alleviated the microstructural changes of subchondral osteosclerosis and reduced heterotypic angiogenesis in DMM mice.

CONCLUSION

Met alleviates the pathological changes of OA by inhibiting ferroptosis in OA chondrocytes, alleviating subchondral sclerosis and reducing abnormal angiogenesis in subchondral bone in advanced OA.

Subchondral versus intra-articular orthobiologic injections for the treatment of knee osteoarthritis: a review

Recent perspectives suggest that osteoarthritis (OA) is a disease involving not only the articular cartilage but also the osteochondral unit, including the synovium, supportive cartilage and subchondral bone. Current conservative treatments for OA are symptomatic and do not prevent progression or reverse the disease process. Compelling data show that intra-articular orthobiologic injections, such as platelet-rich plasma and mesenchymal stromal cells, are effective in providing relief of OA symptoms. However, recent data suggest that injections of orthobiologics into the subchondral bone may be superior to intra-articular injections for the management of OA. This review highlights the rationale and current evidence for intra-articular and subchondral bone injections of orthobiologics for the treatment of OA.

Efficacy of bioreactor-activated bone substitute with bone marrow nuclear cells on fusion rate and fusion mass microarchitecture in sheep

Bioreactors have been used for bone graft engineering in pre-clinical investigations over the past 15 years. The ability of bioreactor-incubated bone marrow nuclear cells (BMNCs) to enhance bone-forming potential varies significantly, and the three-dimensional (3D) distribution of BMNCs within the scaffold is largely unknown. The aims of this study were (1) to investigate the efficacy of a carbonated hydroxyapatite (CHA) with/without BMNCs on spine fusion rate and fusion mass microarchitecture using a highly challenging two-level posterolateral spine fusion without instrumentation; and (2) to evaluate 3D distribution of BMNCs within scaffolds characterized by immunohistochemistry. Fusion rate and fusion mass were quantified by micro-CT, microarchitectural analysis, and histology. While the homogenous 3D distribution of BMNCs was not observed, BMNCs were found to migrate towards a substitute core. In the autograft group, the healing rate was 83.3%, irrespective of the presence of BMNCs. In the CHA group, also 83.3% was fused in the presence of BMNCs, and 66.7% fused without BMNCs. A significant decrease in the fusion mass porosity (p = .001) of the CHA group suggested the deposition of mineralized bone. The autograft group revealed more bone, thicker trabeculae, and better trabecular orientation but less connection compared to the CHA group. Immunohistochemistry confirmed the ability of bioreactors to incubate a large-sized substitute coated with viable BMNCs with the potential for proliferation and differentiation. These findings suggested that a bioreactor-activated substitute is comparable to autograft on spine fusion and that new functional bone regeneration could be achieved by a combination of BMNCs, biomaterials, and bioreactors.

Degenerations in Global Morphometry of Cancellous Bone in Rheumatoid Arthritis, Osteoarthritis and Osteoporosis of Femoral Heads are Similar but More Severe than in Ageing Controls

We have recently revealed significant differences in microarchitectural properties (i.e. global and local morphometries) and mechanical properties between rheumatoid arthritis (RA), osteoarthritis (OA) and osteoporosis (OP) in cancellous bones. This study compared these properties with those of ageing controls by matching bone volume fraction (BV/TV), the most important determinant for bones' mechanical properties, to investigate whether these bones have similar properties and degenerative potentials. RA, OA and OP femoral heads were harvested from patients undergoing total hip replacement surgery. The selected patients were matched by similar cancellous bone BV/TV, with seven patients in each group. Four samples were prepared from each femoral head and scanned with micro-CT to quantify microarchitectural properties and compression tested to determine mechanical properties. In terms of global morphometry, no significant differences were observed between these diseased bones. In terms of local morphometry, the number of plates in the RA group was significantly greater than that of the OP and control groups. Plate volume density in the RA group was significantly greater than in the control group. Interestingly, the ultimate stresses in the three diseased groups were 77% to 195% lower than in the control group (p < 0.001). Degenerations of global morphometry of cancellous bones in these diseased femoral heads are similar but more severe than in ageing controls matched by BV/TV, as evidenced by pronounced reduction in bone strength. This phenomenon suggests that some local morphometric parameters, along with other factors, such as abnormal collagen, mineralisation, erosion and microdamage, may contribute to further compromising mechanical properties.

Suppressing phosphoinositide-specific phospholipases Cγ1 promotes mineralization of osteoarthritic subchondral bone osteoblasts via increasing autophagy, thereby ameliorating articular cartilage degeneration

INTRODUCTION

Phosphoinositide-specific phospholipases C-γ1 (PLC-γ1) signaling has been shown to modulate osteoarthritis (OA) chondrocyte metabolism. However, the role of PLC-γ1 in OA osteoblasts remains unclear. Herein, whether and how PLC-γ1 was involved in mineralization in OA subchondral bone osteoblasts were investigated.

METHODS

Primary non-OA and OA osteoblasts of human and rat isolated from the subchondral bone or the calvaria were cultured in vitro, as well as mouse pre-osteoblastic cell line MC3T3-E1 cells. Rat knee OA model was induced by anterior cruciate ligament transection (ACLT), in which bone canal was carried out from the surface of lateral epicondyle of femur using micro-electric drill. Morphological characteristics of subchondral bone structure and articular cartilage were assessed using CT, micro-CT, and Safranin O/Fast green staining, respectively. Mineralization was measured by alizarin red staining. The expression and production of genes involved in osteoblastic phenotype and mineralization were evaluated by qPCR, western blotting, and immunohistochemistry assays, respectively. The inhibitions were performed using inhibitors and ShRNAs.

RESULTS

The decreased relative bone density and thickness in the early stage of OA and the increased one in the late stage of OA were observed in subchondral bone of ACLT-rat model. Decreased ALP and OCN levels and absorbance values of ARS content were observed in in vitro osteoblasts isolated from 2 w post-ACLT rat model, as well as IL-1β-treated (for maintaining and mimicking inflammatory status) human OA and rat osteoblasts. Decreased Atg7 level and LC3BII/I ratio in combination with an increase in the P62 level, was concomitant with decreased ALP and OCN mRNA levels and absorbance values of ARS content in OA or IL-1β-treated osteoblasts. Specific inhibition of PLC-γ1 by ShRNAs or inhibitor (U73122) elevated ALP and OCN mRNA levels and absorbance values of ARS content accompanied with increased Atg7 level and LC3BII/I ratio in combination with a decrease in the P62 level in OA osteoblasts. Furthermore, the promoting effect of PLC-γ1 inhibition on ALP and OCN mRNA levels and absorbance values of ARS content was reversed by endoplasmic reticulum (ER) stress activator HA15, as well as autophagic inhibitors CQ and 3MA. Injection with PLC-γ1 inhibitor U73122 from the surface of lateral epicondyle of femur reduced aberrant subchondral bone formation and attenuated articular cartilage degeneration in ACLT-rat.

CONCLUSION

Aberrant changes of OA subchondral bone structure were concomitant with altered osteoblastic phenotype and mineralization. Impaired autophagy contributed to decreased osteoblastic mineralization in the early stage of OA. PLC-γ1 inhibition promoted osteoblastic mineralization through increasing autophagy in OA osteoblasts, which was partially attributed to suppression of ER stress. Targeting PLC-γ1 in subchondral bone osteoblasts could be more efficacious for OA therapy through treating the bone and cartilage at the same time. In summary, we hypothesize that suppressing PLCγ1 promotes mineralization of osteoarthritic subchondral bone osteoblasts via increasing autophagy, thereby ameliorating articular cartilage degeneration.

Intermittent Hypoxic Therapy Inhibits Allogenic Bone-Graft Resorption by Inhibition of Osteoclastogenesis in a Mouse Model

Systemic Intermittent Hypoxic Therapy (IHT) relies on the adaptive response to hypoxic stress. We investigated allogenic bone-graft resorption in the lumbar spine in 48 mice. The mice were exposed to IHT for 1 week before surgery or 1 week after surgery and compared with controls after 1 and 4 weeks. Complete graft resorption was observed in 33-36% of the animals in the control group, but none in the preoperative IHT group. Increased bone-graft volume was demonstrated by micro-computed tomography in the preoperative IHT group after 1 week (p = 0.03) while a non-significant difference was observed after 4 weeks (p = 0.12). There were no significant differences in the postoperative IHT group. Increased concentration of immune cells was localized in the graft area, and more positive tartrate-resistant acid phosphatase (TRAP) staining was found in controls compared with IHT allogenic bone grafts. Systemic IHT resulted in a significant increase of the major osteoclast inhibitor osteoprotegerin as well as osteogenic and angiogenic regulators Tgfbr3, Fst3l, Wisp1, and Vegfd. Inflammatory cytokines and receptor activator of nuclear factor kappa-B ligand (RANKL) stimulators IL-6, IL-17a, IL-17f, and IL-23r increased after 1 and 4 weeks, and serum RANKL expression remained constant while Ccl3 and Ccl5 decreased. We conclude that the adaptive response to IHT activates numerous pathways leading to inhibition of osteoclastic activity and inhibition of allogenic bone-graft resorption.

Early Alterations of Subchondral Bone in the Rat Anterior Cruciate Ligament Transection Model of Osteoarthritis

OBJECTIVE

Advances in research have shown that the subchondral bone plays an important role in the propagation of cartilage loss and progression of osteoarthritis (OA), but whether the subchondral bone changes precede or lead to articular cartilage loss remains debatable. In order to elucidate the subchondral bone and cartilage changes that occur in early OA, an experiment using anterior cruciate ligament transection (ACLT) induced posttraumatic OA model of the rat knee was conducted.

DESIGN

Forty-two Sprague Dawley rats were divided into 2 groups: the ACLT group and the nonoperated control group. Surgery was conducted on the ACLT group, and subsequently rats from both groups were sacrificed at 1, 2, and 3 weeks postsurgery. Subchondral bone was evaluated using a high-resolution peripheral quantitative computed tomography scanner, while cartilage was histologically evaluated and scored.

RESULTS

A significant reduction in the subchondral trabecular bone thickness and spacing was found as early as 1 week postsurgery in ACLT rats compared with the nonoperated control. This was subsequently followed by a reduction in bone mineral density and bone fractional volume at week 2, and finally a decrease in the trabecular number at week 3. These changes occurred together with cartilage degeneration as reflected by an increasing Mankin score over all 3 weeks.

CONCLUSIONS

Significant changes in subchondral bone occur very early in OA concurrent with surface articular cartilage degenerative change suggest that factors affecting bone remodeling and resorption together with cartilage matrix degradation occur very early in the disease.

3-D microarchitectural properties and rod- and plate-like trabecular morphometric properties of femur head cancellous bones in patients with rheumatoid arthritis, osteoarthritis, and osteoporosis

Objectives

We quantify 3-D microarchitectural properties of femoral head cancellous bones from patients with rheumatoid arthritis (RA, n ​= ​12), osteoarthritis (OA, n ​= ​15), osteoporosis (OP, n ​= ​24), or donor controls (CNT, n ​= ​8); and investigate their rod- and plate-like trabecular morphometric properties of trabecular bone tissues and compare these properties between them.

Methods

Femoral heads were harvested during total hip replacement surgeries or collected from donors. Four cubic cancellous bone samples produced from each femoral head were micro-CT scanned to quantify their microarchitectural and rod- and plate-like trabecular properties. The samples were then tested in compression to determine mechanical properties.

Results

The microarchitectural properties of femoral head cancellous bone revealed significant differences among the 4 groups, but not between RA and OA. Bone volume fraction was significantly greater in the RA and the OA than in the OP and the CNT. Structure model index was significantly lower in the RA and the OA than in the OP. Number of rods in the RA was significantly greater than in the other 3 groups. Number of plates and plate volume density in the RA and the OA were significantly greater than in the OP and the CNT. Mechanical properties were significantly greater in the RA and the OA than in the OP. The single best determinant for mechanical properties was bone volume fraction.

Conclusions

This study demonstrates significant differences in 3-D microarchitectural properties and rod- and plate-like trabecular morphometric properties among patients with RA, OA, or OP. The RA and OA cancellous bones displayed similar patterns of microarchitectural degeneration and pronounced different microarchitectures from the OP. The OP group revealed the weakest cancellous bone strength, while the RA and OA groups exhibited a compensatory effect that maintains bone tissues, and hence mechanical properties.

The translational potential of this article

The study enhances the understanding of microarchitectural degeneration of diseased cancellous bone. The OP group had the weakest cancellous bone strength, while the RA and OA groups exhibited a compensatory effect that maintains bone tissues, and hence mechanical properties. These results are particularly important for design and survival of joint prosthesis.

Parathyroid hormone ameliorates temporomandibular joint osteoarthritic-like changes related to age

OBJECTIVES

Ageing could be a contributing factor to the progression of temporomandibular joint osteoarthritis (TMJ OA), whereas its pathogenesis and potential therapeutic strategy have not been comprehensively investigated.

MATERIALS AND METHODS

We generated ageing mouse models (45-week and 60-week; 12-week mice as control) and intermittently injected 45-week mice with parathyroid hormone (PTH(1-34)) or vehicle for 4 weeks. Cartilage and subchondral bone of TMJ were analysed by microCT, histological and immunostaining. Western blot, qRT-PCR, ChIP, ELISA and immunohistochemical analysis were utilized to examination the mechanism of PTH(1-34)'s function.

RESULTS

We showed apparent OA-like phenotypes in ageing mice. PTH treatment could ameliorate the degenerative changes and improve bone microarchitecture in the subchondral bone by activating bone remodelling. Moreover, PTH inhibited phosphorylation level of Smad3, which can combine with p16^ink4a gene promoter region, resulting in reduced senescent cells accumulation and increased cellular proliferation of marrow mesenchymal stem cells (MSCs). ELISA also showed relieved levels of specific senescent-associated secretory phenotype (SASP) in ageing mice after PTH treatment.

CONCLUSIONS

In summary, PTH may reduce the accumulation of senescent cells in subchondral bone by inhibiting p16^ink4a and improve bone marrow microenvironment to active bone remodelling process, indicating PTH administration could be a potential preventative and therapeutic treatment for age-related TMJ OA.

Age-related histological changes in calcified cartilage and subchondral bone in femoral heads from healthy humans

OBJECTIVE

Age is the most important risk factor for osteoarthritis (OA). It is suggested that changes in subchondral bone and calcified cartilage may occur in early OA. Therefore, the aim was to investigate age-related changes in the femoral head composition. We hypothesise that the thickness of the subchondral bone plate decreases with age, while the thickness of the calcified cartilage increases with age as seen in early-stage OA.

METHODS

Femoral heads from 29 women (20-74 years) and 32 men (23-78 years), who had died suddenly and unexpectedly, were obtained at autopsy. Individuals with bone or joint diseases or macroscopic abnormal cartilage were excluded. Using design-based stereology, femoral head volume as well as thickness and volume of the calcified cartilage and subchondral bone plate were estimated and correlated to sex and age.

RESULTS

The thickness and volume of the subchondral bone plate were not correlated with age. Calcified cartilage thickness and volume correlated positively with age in women, while the femoral head volume was correlated positively with age in men.

CONCLUSION

In human femoral heads obtained from a cross-sectional population without macroscopic OA changes, the thickness of the subchondral bone plate did not change with age, which differs from the thinning seen in early OA. Surprisingly, the age-related changes of the volume and thickness of the calcified cartilage and of the volume of the femoral head were different for women and men. This indicate that cartilage and bone metabolism is sex-specific, which may influence ageing of the hip joint.

Bone marrow lesions in knee osteoarthritis: regional differences in tibial subchondral bone microstructure and their association with cartilage degeneration

OBJECTIVE

The aim of this study was to investigate how bone microstructure within bone marrow lesions (BMLs) relates to the bone and cartilage across the whole human tibial plateau.

DESIGN

Thirty-two tibial plateaus from patients with osteoarthritis (OA) at total knee arthroplasty and eleven age-matched non-OA controls, were scanned ex vivo by MRI to identify BMLs and by micro CT to quantitate the subchondral (plate and trabecular) bone microstructure. For cartilage evaluation, specimens were processed histologically.

RESULTS

BMLs were detected in 75% of the OA samples (OA-BML), located predominantly in the anterior-medial (AM) region. In contrast to non-OA control and OA-no BML, in OA-BML differences in microstructure were significantly more evident between subregions. In OA-BML, the AM region contained the most prominent structural alterations. Between-group comparisons showed that the AM region of the OA-BML group had significantly higher histological degeneration (OARSI grade) (P < .0001, P < .05), thicker subchondral plate (P < .05, P < .05), trabeculae that are more anisotropic (P < .0001, P < .05), well connected (P < .05, P = n.s), and more plate-like (P < 0.05, P < 0.05), compared to controls and OA-no BML at this site. Compared to controls, OA-no BML had significantly higher OARSI grade (P < .0001), and lower trabecular number (P < .05).

CONCLUSION

In established knee OA, both the extent of cartilage damage and microstructural degeneration of the subchondral bone were dependent on the presence of a BML. In OA-no BML, bone microstructural alterations are consistent with a bone attrition phase of the disease. Thus, the use of BMLs as MRI image-based biomarkers appear to inform on the degenerative state within the osteochondral unit.

Quantifying Subresolution 3D Morphology of Bone with Clinical Computed Tomography

The aim of this study was to quantify sub-resolution trabecular bone morphometrics, which are also related to osteoarthritis (OA), from clinical resolution cone beam computed tomography (CBCT). Samples (n = 53) were harvested from human tibiae (N = 4) and femora (N = 7). Grey-level co-occurrence matrix (GLCM) texture and histogram-based parameters were calculated from CBCT imaged trabecular bone data, and compared with the morphometric parameters quantified from micro-computed tomography. As a reference for OA severity, histological sections were subjected to OARSI histopathological grading. GLCM and histogram parameters were correlated to bone morphometrics and OARSI individually. Furthermore, a statistical model of combined GLCM/histogram parameters was generated to estimate the bone morphometrics. Several individual histogram and GLCM parameters had strong associations with various bone morphometrics (|r| > 0.7). The most prominent correlation was observed between the histogram mean and bone volume fraction (r = 0.907). The statistical model combining GLCM and histogram-parameters resulted in even better association with bone volume fraction determined from CBCT data (adjusted R² change = 0.047). Histopathology showed mainly moderate associations with bone morphometrics (|r| > 0.4). In conclusion, we demonstrated that GLCM- and histogram-based parameters from CBCT imaged trabecular bone (ex vivo) are associated with sub-resolution morphometrics. Our results suggest that sub-resolution morphometrics can be estimated from clinical CBCT images, associations becoming even stronger when combining histogram and GLCM-based parameters.

Methods for evaluating effects of unloader knee braces on joint health: a review

The paper aims to provide a state-of-the-art review of methods for evaluating the effectiveness and effect of unloader knee braces on the knee joint and discuss their limitations and future directions. Unloader braces are prescribed as a non-pharmacological conservative treatment option for patients with medial knee osteoarthritis to provide relief in terms of pain reduction, returning to regular physical activities, and enhancing the quality of life. Methods used to evaluate and monitor the effectiveness of these devices on patients' health are categorized into three broad categories (perception-, biochemical-, and morphology-based), depending upon the process and tools used. The main focus of these methods is on the short-term clinical outcome (pain or unloading efficiency). There is a significant technical, research, and clinical literature gap in understanding the short- and long-term consequences of these braces on the tissues in the knee joint, including the cartilage and ligaments. Future research directions may complement existing methods with advanced quantitative imaging (morphological, biochemical, and molecular) and numerical simulation are discussed as they offer potential in assessing long-term and post-bracing effects on the knee joint.

Aberrant activation of latent transforming growth factor-β initiates the onset of temporomandibular joint osteoarthritis

There is currently no effective medical treatment for temporomandibular joint osteoarthritis (TMJ-OA) due to a limited understanding of its pathogenesis. This study was undertaken to investigate the key role of transforming growth factor-β (TGF-β) signalling in the cartilage and subchondral bone of the TMJ using a temporomandibular joint disorder (TMD) rat model, an ageing mouse model and a Camurati–Engelmann disease (CED) mouse model. In the three animal models, the subchondral bone phenotypes in the mandibular condyles were evaluated by µCT, and changes in TMJ condyles were examined by TRAP staining and immunohistochemical analysis of Osterix and p-Smad2/3. Condyle degradation was confirmed by Safranin O staining, the Mankin and OARSI scoring systems and type X collagen (Col X), p-Smad2/3a and Osterix immunohistochemical analyses. We found apparent histological phenotypes of TMJ-OA in the TMD, ageing and CED animal models, with abnormal activation of TGF-β signalling in the condylar cartilage and subchondral bone. Moreover, inhibition of TGF-β receptor I attenuated TMJ-OA progression in the TMD models. Therefore, aberrant activation of TGF-β signalling could be a key player in TMJ-OA development.

Blocking the activity of a critical growth factor could help treat degenerative disease of the jaw joint, according to experiments in three rodent models. Xuedong Zhou from Sichuan University in Chengdu, China, examined the cartilage and adjoining layer of bone found at the ends of the jawbone in a rat model of temporomandibular joint disorder and in two related mouse models. In all three, the researchers observed tissue abnormalities consistent with what’s seen in humans with osteoarthritis of the jaw joint, a condition with no effective therapeutic options. They showed that transforming growth factor-β, a master regulatory protein, displayed aberrant signalling patterns in these tissues and that blocking this protein’s receptor with a drug attenuated the disease process. The findings help explain what drives jaw joint osteoarthritis — and point to a strategy for treating it.

Morphological, biochemical and mechanical properties of articular cartilage and subchondral bone in rat tibial plateau are age related

The purpose of this study was to investigate age-related changes in the morphological, biochemical and mechanical properties of articular cartilage (AC) and subchondral bone in the rat tibial plateau. Female Wistar rats were grouped according to age (1, 3, 5, 7, 9, 11, 13, 15, 16 and 17 months, with 10 rats in each group). The ultrastructures, surface topographies, and biochemical and mechanical properties of the AC and subchondral bone in the knee joints of the rats were determined through X-ray micro-tomography, histology, immunohistochemistry, scanning electron microscopy (SEM), atomic force microscopy and nanoindentation. We found that cartilage thickness decreased with age. This decrease was accompanied by functional condensation of the underlying subchondral bone. Increased thickness and bone mineral density and decreased porosity were observed in the subchondral plate (SP). Growth decreased collagen II expression in the tibial cartilage. The arrangement of trabeculae in the subchondral trabecular bone became disordered. The thickness and strength of the fibers decreased with age, as detected by SEM. The SP and trabeculae in the tibial plateau increased in roughness in the first phase (1-9 months of age), and then were constant in the second phase (11-17 months of age). Meanwhile, the roughness of the AC changed significantly in the first phase (1-9 months of age), but the changes were independent of age thereafter. This study gives a comprehensive insight into the growth-related structural, biochemical and mechanical changes in the AC and subchondral bone. The results presented herein may contribute to a new understanding of the pathogenesis of age-related bone diseases.

Three-dimensional morphometric properties of rod- and plate-like trabeculae in adolescent cancellous bone

Background/Objective

Despite many researches have been carried out on the three-dimensional microarchitecture of cancellous bone, the morphometric properties of rod and plate trabeculae in adolescent cancellous bone have not yet been investigated. This study aimed to investigate three-dimensional morphometric properties of rod- and plate-like trabeculae in normal adolescent cancellous bone, and to compare them with adult cancellous bones to reveal morphometric changes from adolescence to adult life to obtain more insight into the subchondral bone adaptations during development and growth.

Methods

This study included 23 normal human proximal tibiae. These tibiae were divided into three groups: adolescents (9–17 years, n = 6), young adults (18–24 years, n = 9), and adults (25–30 years, n = 8). From each tibia, six cubic cancellous bone samples (dimensions 8 × 8 × 8 mm³) were sawed from each medial and lateral condyle, yielding a total of 276 samples. These samples were scanned using micro computed tomography leading to three-dimensional cubic voxel sizes of 10.5 × 10.5 × 10.5 μm³. The morphometric parameters of individual rod- and plate-like trabeculae were calculated and compared among three age groups.

Results

Significant differences in some morphometric parameters were revealed. The mean longitudinal length of rods was significantly greater in the adolescents than in the young adults. Plate volume density showed an increasing trend with age, although not significant. Trabeculae were more plate-like in adolescents in the medial condyle of adolescents than in the lateral condyle, and changed towards more plate-like trabeculae in the adults. The single best predictor for the mechanical properties was apparent density. Apparent density alone explained 59% variations in Young’s modulus, 77% in ultimate stress and 34% in failure energy, respectively (all p < 0.01). Morphometric parameters might improve this prediction.

Conclusion

In conclusion, this study has reported for the first time the morphometric parameters of rod- and plate-like trabeculae in adolescent proximal tibial cancellous bone, which will improve our understanding of morphometric changes in individual trabeculae during development and growth. Furthermore, separate analysis of individual rods and plates may also help reveal disease-related morphometric changes beyond bone mineral density.

The translational potential of this article

A thorough quantification of individual trabeculae during development and growth may help understand disease-related 3-D morphometric changes beyond bone mineral density.

Osteoarthritis alters the patellar bones subchondral trabecular architecture

Following the principles of "morphology reveals biomechanics," the cartilage-osseous interface and the trabecular network show defined adaptation in response to physiological loading. In the case of a compromised relationship, the ability to support the load diminishes and the onset of osteoarthritis (OA) may arise. To describe and quantify the changes within the subchondral bone plate (SBP) and trabecular architecture, 10 human OA patellae were investigated by CT and micro-CT. The results are presented in comparison to a previously published dataset of 10 non-OA patellae which were evaluated in the same manner. The analyzed OA samples showed no distinctive mineralization pattern in regards to the physiological biomechanics, but a highly irregular disseminated distribution. In addition, no regularity in bone distribution and architecture across the trabecular network was found. We observed a decrease of material as the bone volume and trabecular thickness/number were significantly reduced. In comparison to non-OA samples, greatest differences for all parameters were found within the first mm of trabecular bone. The differences decreased toward the fifth mm in a logarithmic manner. The interpretation of the logarithmic relation leads to the conclusion that the main impact of OA on bony structures is located beneath the SBP and lessens with depth. In addition to the clear difference in material with approximately 12% less bone volume in the first mm in OA patellae, the architectural arrangement is more rod-like and isotropic, accounting for an architectural decrease in stability and support. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1982-1989, 2017.

The Src family kinase inhibitor dasatinib delays pain-related behaviour and conserves bone in a rat model of cancer-induced bone pain

Pain is a severe and debilitating complication of metastatic bone cancer. Current analgesics do not provide sufficient pain relief for all patients, creating a great need for new treatment options. The Src kinase, a non-receptor protein tyrosine kinase, is implicated in processes involved in cancer-induced bone pain, including cancer growth, osteoclastic bone degradation and nociceptive signalling. Here we investigate the role of dasatinib, an oral Src kinase family and Bcr-Abl tyrosine kinase inhibitor, in an animal model of cancer-induced bone pain. Daily administration of dasatinib (15 mg/kg, p.o.) from day 7 after inoculation of MRMT-1 mammary carcinoma cells significantly attenuated movement-evoked and non-evoked pain behaviour in cancer-bearing rats. Radiographic - and microcomputed tomographic analyses showed significantly higher relative bone density and considerably preserved bone micro-architecture in the dasatinib treated groups, suggesting a bone-preserving effect. This was supported by a significant reduction of serum TRACP 5b levels in cancer-bearing rats treated with 15 mg/kg dasatinib. Furthermore, immunoblotting of lumbar spinal segments showed an increased activation of Src but not the NMDA receptor subunit 2B. These findings support a role of dasatinib as a disease modifying drug in pain pathologies characterized by increased osteoclast activity, such as bone metastases.

Attenuation of subchondral bone abnormal changes in osteoarthritis by inhibition of SDF-1 signaling

BACKGROUND

Current conservative treatments for osteoarthritis (OA) are largely symptoms control therapies. Further understanding on the pathological mechanisms of OA is crucial for new pharmacological intervention.

OBJECTIVE

In this study, we investigated the role of Stromal cell-derived factor-1(SDF-1) in regulating subchondral bone changes during the progression of OA.

METHODS

Clinical samples of different stages of OA severity were analyzed by histology staining, micro-CT, enzyme-linked immunosorbent assay (ELISA) and western blotting, to compare SDF-1 level in subchondral bone. The effects of SDF-1 on human mesenchymal stem cells (MSCs) osteogenic differentiation were evaluated. In vivo assessment was performed in an anterior cruciate ligament transaction plus medial meniscus resection in the SD rats. The OA rats received continuous infusion of AMD3100 (SDF-1 receptor blocker) in osmotic mini-pump implanted subcutaneously for 6 weeks. These rats were then terminated and subjected to the same in vitro assessments as human OA samples.

RESULTS

SDF-1 level was significantly elevated in the subchondral bone of human OA samples. In the cell studies, the results showed SDF-1 plays an important role in osteogenic differentiation of MSCs. In the OA animal studies, there were less cartilage damage in the AMD3100-treated group; microCT results showed that the subchondral bone formation was significantly reduced and so did the number of positive Nestin or Osterix cells in the subchondral bone region.

CONCLUSIONS

Higher level of SDF-1 may induce the subchondral bone abnormal changes in OA and inhibition of SDF-1 signaling could be a potential therapeutic approach for OA.

Comparison of Bone Tissue Elements Between Normal and Osteoarthritic Pelvic Bones in Dogs

Physiochemical analysis of bones affected with osteoarthritis (OA) can be used to better understand the etiology of this disease. We investigated the percentage of chemical elements in canine pelvic bone affected with varying degrees of OA using a handheld X-ray fluorescence (XRF) analyzer that discriminates magnesium (Mg(12)) through bismuth (Bi(83)). A total of 45 pelvic bones, including both ilium and subchondral acetabular bone plates, were categorized as normal (n = 20), mild grade OA (n = 5), moderate grade OA (n = 15), and severe grade OA (n = 5). In normal pelvic, seven elements (P, Ca, Mn, Ag, Cd, Sn, and Sb) differed (p < 0.005) in percentage between ilium and acetabulum. Comparisons among the four OA groups found Mn and Fe to be highest in severe grades (p < 0.05) in both ilium and acetabulum. Three heavy metals (Ag, Sn, and Sb) were detected in high percentages (p < 0.05) in the severe OA group in the acetabulum, but in ilium only Sn was high (p < 0.05) in severe OA. In conclusion, the percentages of several elements differed between pelvic types in dogs, and also with increasing severity of OA. The finding of high Mn and Fe in severe grade OA bone suggests these two elements may be useful in future studies of the etiology and pathophysiology of OA.

Cancellous and Cortical Bone Microarchitectures of Femoral Neck in Rheumatoid Arthritis and Osteoarthritis Compared with Donor Controls

This study investigated the 3D microarchitecture of cancellous and cortical bones of the femoral neck in rheumatoid arthritis (RA), osteoarthritis (OA) and donor controls. 26 femoral necks (including heads) were harvested during total hip replacement surgeries in 11 patients with RA (mean age 66.7 ± 12.8 years) and 15 patients with OA (67.3 ± 8.4 years). Femoral heads/necks were also harvested from 8 donors (74.9 ± 10.2 years). Bone samples of 10 mm thickness were prepared from each femoral neck and scanned with micro-CT to evaluate microarchitectural parameters. The RA and OA samples showed no significant differences in microarchitectural parameters in cancellous or cortical bone. Compared with the donor controls, bone volume fraction in RA and OA cancellous bone was significantly greater, the structure model index in OA was significantly lower, and the surface density in RA was significantly greater. The RA bone tissues showed erosion and marked osteophyte formation. This study demonstrated that RA and OA have similar trends of overall microarchitectural degeneration in the femoral neck, despite marked erosion in RA bone and osteophyte formation in OA bone. However, we could not eliminate the possibility of local differences between RA and OA bone. The age-related bone loss in RA and OA was less severe than those of normal ageing and osteoporosis, suggesting a compensatory effect of the diseases to increase bone density.

Effects of P-15 Peptide Coated Hydroxyapatite on Tibial Defect Repair In Vivo in Normal and Osteoporotic Rats

This study assessed the efficacy of anorganic bone mineral coated with P-15 peptide (ABM/P-15) on tibia defect repair longitudinally in both normal and osteoporotic rats in vivo. A paired design was used. 24 Norwegian brown rats were divided into normal and osteoporotic groups. 48 cylindrical defects were created in proximal tibias bilaterally. Defects were filled with ABM/P-15 or left empty. Osteoporotic status was assessed by microarchitectural analysis. Microarchitectural properties of proximal tibial defects were evaluated at 4 time points. 21 days after surgery, tibias were harvested for histology and histomorphometry. Significantly increased bone volume fraction, surface density, and connectivity were seen in all groups at days 14 and 21 compared with day 0. Moreover, the structure type of ABM/P-15 group was changed toward typical plate-like structure. Microarchitectural properties of ABM/P-15 treated newly formed bones at 21 days were similar in normal and osteoporotic rats. Histologically, significant bone formation was seen in all groups. Interestingly, significantly increased bone formation was seen in osteoporotic rats treated with ABM/P-15 indicating optimized healing potential. Empty defects showed lower healing potential in osteoporotic bone. In conclusion, ABM/P-15 accelerated bone regeneration in osteoporotic rats but did not enhance bone regeneration in normal rats.

Osteochondral repair by a novel interconnecting collagen-hydroxyapatite substitute: a large-animal study

A novel three-dimensional bicomponent substitute made of collagen type I and hydroxyapatite was tested for the repair of osteochondral lesions in a swine model. This scaffold was assembled by a newly developed method that guarantees the strict integration between the organic and the inorganic parts, mimicking the biological tissue between the chondral and the osseous phase. Thirty-six osteochondral lesions were created in the trochlea of six pigs; in each pig, two lesions were treated with scaffolds seeded with autologous chondrocytes (cell+group), two lesions were treated with unseeded scaffolds (cell- group), and the two remaining lesions were left untreated (untreated group). After 3 months, the animals were sacrificed and the newly formed tissue was analyzed to evaluate the degree of maturation. The International Cartilage Repair Society (ICRS) macroscopic assessment showed significantly higher scores in the cell- and untreated groups when compared with the cell+ group. Histological evaluation showed the presence of repaired tissue, with fibroblast-like and hyaline-like areas in all groups; however, with respect to the other groups, the cell- group showed significantly higher values in the ICRS II histological scores for "cell morphology" and for the "surface/superficial assessment." While the scaffold seeded with autologous chondrocytes promoted the formation of a reparative tissue with high cellularity but low glycosaminoglycans (GAG) production, on the contrary, the reparative tissue observed with the unseeded scaffold presented lower cellularity but higher and uniform GAG distribution. Finally, in the lesions treated with scaffolds, the immunohistochemical analysis showed the presence of collagen type II in the peripheral part of the defect, indicating tissue maturation due to the migration of local cells from the surroundings. This study showed that the novel osteochondral scaffold was easy to handle for surgical implantation and was stable within the site of lesion; at the end of the experimental time, all implants were well integrated with the surrounding tissue and no signs of synovitis were observed. The quality of the reparative tissue seemed to be superior for the lesions treated with the unseeded scaffolds, indicating the promising potential of this novel biomaterial for use in a one-stage procedure for osteochondral repair.

Subchondral bone in osteoarthritis: insight into risk factors and microstructural changes

Osteoarthritis (OA) is a major cause of disability in the adult population. As a progressive degenerative joint disorder, OA is characterized by cartilage damage, changes in the subchondral bone, osteophyte formation, muscle weakness, and inflammation of the synovium tissue and tendon. Although OA has long been viewed as a primary disorder of articular cartilage, subchondral bone is attracting increasing attention. It is commonly reported to play a vital role in the pathogenesis of OA. Subchondral bone sclerosis, together with progressive cartilage degradation, is widely considered as a hallmark of OA. Despite the increase in bone volume fraction, subchondral bone is hypomineralized, due to abnormal bone remodeling. Some histopathological changes in the subchondral bone have also been detected, including microdamage, bone marrow edema-like lesions and bone cysts. This review summarizes basic features of the osteochondral junction, which comprises subchondral bone and articular cartilage. Importantly, we discuss risk factors influencing subchondral bone integrity. We also focus on the microarchitectural and histopathological changes of subchondral bone in OA, and provide an overview of their potential contribution to the progression of OA. A hypothetical model for the pathogenesis of OA is proposed.

Subchondral bone trabecular integrity predicts and changes concurrently with radiographic and magnetic resonance imaging-determined knee osteoarthritis progression

OBJECTIVE

To evaluate subchondral bone trabecular integrity (BTI) on radiographs as a predictor of knee osteoarthritis (OA) progression.

METHODS

Longitudinal (baseline, 12-month, and 24-month) knee radiographs were available for 60 female subjects with knee OA. OA progression was defined by 12- and 24-month changes in radiographic medial compartment minimal joint space width (JSW) and medial joint space area (JSA), and by medial tibial and femoral cartilage volume on magnetic resonance imaging. BTI of the medial tibial plateau was analyzed by fractal signature analysis using commercially available software. Receiver operating characteristic (ROC) curves for BTI were used to predict a 5% change in OA progression parameters.

RESULTS

Individual terms (linear and quadratic) of baseline BTI of vertical trabeculae predicted knee OA progression based on 12- and 24-month changes in JSA (P < 0.01 for 24 months), 24-month change in tibial (P < 0.05), but not femoral, cartilage volume, and 24-month change in JSW (P = 0.05). ROC curves using both terms of baseline BTI predicted a 5% change in the following OA progression parameters over 24 months with high accuracy, as reflected by the area under the curve measures: JSW 81%, JSA 85%, tibial cartilage volume 75%, and femoral cartilage volume 85%. Change in BTI was also significantly associated (P < 0.05) with concurrent change in JSA over 12 and 24 months and with change in tibial cartilage volume over 24 months.

CONCLUSION

BTI predicts structural OA progression as determined by radiographic and MRI outcomes. BTI may therefore be worthy of study as an outcome measure for OA studies and clinical trials.

Steering the osteoclast through the demineralization-collagenolysis balance

There is a lot of interest for how and how much osteoclasts resorb bone. However, little is known about the mechanism which controls the orientation and the duration of a resorptive event, thereby determining the specific geometry of a cavitation. Here we show that the relative rate of collagenolysis vs. demineralization plays a critical role in this process. First we observed that when culturing osteoclasts on bone slices, excavations appeared either as round pits containing demineralized collagen, or as elongated trenches without demineralized collagen. This suggests that round pits are generated when collagen degradation is slower than demineralization, and trenches when collagen degradation is as fast as demineralization. Next we treated the osteoclasts with a low dose of a carbonic anhydrase inhibitor to slightly decrease the rate of demineralization, thereby allowing collagen degradation to proceed as fast as demineralization. This resulted in about a two-fold increase of the proportion of trenches, thus supporting our hypothesis. The same result was obtained if facilitating collagen degradation by pre-treating the bone slices with NaOCl. In contrast, when decreasing the rate of collagenolysis vs. demineralization by the addition of a cathepsin K specific inhibitor, the proportion of trenches fell close to 0%, and furthermore the round pits became almost half as deep. These observations lead to a model where the osteoclast resorption route starts perpendicularly to the bone surface, forming a pit, and continues parallel to the bone surface, forming a trench. Importantly, we show that the progress of the osteoclast along this route depends on the balance between the rate of collagenolysis and demineralization. We propose that the osteocytes and bone lining cells surrounding the osteoclast may act on this balance to steer the osteoclast resorptive activity in order to give the excavations a specific shape.

Quality of root fillings performed with two root filling techniques. An in vitro study using micro-CT

Objective.

The aim of this study was to compare the presence of voids in root fillings performed in oval and ribbon-shaped canals with two root filling techniques, lateral compaction technique (LCT) or hybrid technique (HT), a combination of a gutta-percha masterpoint and thermoplastic gutta-percha. Furthermore, the obturation time for the two techniques was evaluated.

Materials and methods.

Sixty-seven roots with oval and ribbon-shaped canals were prepared using Profile Ni-Ti rotary files. After preparation, the roots were randomly allocated to two groups according to root filling technique. All roots were filled with AH plus and gutta-percha. Group 1 was filled using LCT (n = 34) and group 2 was filled using HT (n = 33). The obturation time was measured in 30 cases evenly distributed between the two techniques. Voids in relation to the root canal fillings were assessed using cross-section images from Micro-computed Tomography scans.

Results.

All root canal fillings had voids. Permutation test showed no statistically significant difference between the two root filling techniques in relation to presence of voids (p = 0.092). A statistically significant difference in obturation time between the two techniques was found (p < 0.001).

Conclusion.

The present study found no statistically significant difference in percentage of voids between two root filling techniques. A 40% reduction in obturation time was found for the HT compared to the LCT.

Hormonal modulation of connective tissue homeostasis and sex differences in risk for osteoarthritis of the knee

Young female athletes experience a higher incidence of ligament injuries than their male counterparts, females experience a higher incidence of joint hypermobility syndrome (a risk factor for osteoarthritis development), and post-menopausal females experience a higher prevalence of osteoarthritis than age-matched males. These observations indicate that fluctuating sex hormone levels in young females and loss of ovarian sex hormone production due to menopause likely contribute to observed sex differences in knee joint function and risk for loss of function. In studies of osteoarthritis, however, there is a general lack of appreciation for the heterogeneity of hormonal control in both women and men. Progress in this field is limited by the relatively few preclinical osteoarthritis models, and that most of the work with established models uses only male animals. To elucidate sex differences in osteoarthritis, it is important to examine sex hormone mechanisms in cells from knee tissues and the sexual dimorphism in the role of inflammation at the cell, tissue, and organ levels. There is a need to determine if the risk for loss of knee function and integrity in females is restricted to only the knee or if sex-specific changes in other tissues play a role. This paper discusses these gaps in knowledge and suggests remedies.

Three-dimensional microarchitecture of adolescent cancellous bone

This study investigated microarchitectural, mechanical, collagen and mineral properties of normal adolescent cancellous bone, and compared them with adult and aging cancellous bone, to obtain more insight into the subchondral bone adaptations during development and growth. Twenty-three human proximal tibiae were harvested and divided into 3 groups according to their ages: adolescence (9 to 17 years, n=6), young adult (18 to 24 years, n=9), and adult (25 to 30 years, n=8). Twelve cubic cancellous bone samples with dimensions of 8×8×8 mm(3) were produced from each tibia, 6 from each medial and lateral condyle. These samples were micro-CT scanned (vivaCT 40, Scanco Medical AG, Switzerland) resulting in cubic voxel sizes of 10.5*10.5*10.5 μm(3). Microarchitectural properties were calculated. The samples were then tested in compression followed by collagen and mineral determination. Interestingly, the adolescent cancellous bone had similar bone volume fraction (BV/TV), structure type (plate, rod or mixtures), and connectivity (3-D trabecular networks) as the adult cancellous bone. The adolescent cancellous bone had significantly lower bone surface density (bone surface per total volume of specimen) but higher collagen concentration (collagen weight per dry weight of specimen) than the adult cancellous bone; and significant greater trabecular separation (mean distance between trabeculae), significant lower trabecular number (number of trabeculae per volume), tissue density (dry weight per volume of bone matrix excluding marrow space) and mineral concentration (ash weight per dry weight of specimen) than the young adult and adult cancellous bones. Despite these differences, ultimate stress and failure energy were not significantly different among the three groups, only the Young's modulus in anterior-posterior direction was significantly lower in adolescence. Apparent density appears to be the single best predictor of mechanical properties. In conclusion, adolescent cancellous bone has similar bone volume fraction, structure type, and connectivity as the young adult and adult cancellous bones, and significant lower tissue density, bone surface density and mineral concentration but higher collagen concentration than in the young adult and adult bone. Despite these differences, the mechanical properties did not show significant difference among the three groups except less stiffness in anterior-posterior direction in the adolescents.

Chronic administration of the selective P2X3, P2X2/3 receptor antagonist, A-317491, transiently attenuates cancer-induced bone pain in mice

The purinergic P2X3 and P2X2/3 receptors are in the peripheral nervous system almost exclusively confined to afferent sensory neurons, where they are found both at peripheral and central synapses. The P2X3 receptor is implicated in both neuropathic and inflammatory pain. However, the role of the P2X3 receptor in chronic cancer-induced bone pain is less known. Here we investigated the effect of systemic acute and chronic administration of the selective P2X3, P2X2/3 receptor antagonist (5-[[[(3-Phenoxyphenyl)methyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]carbonyl]-1,2,4-benzenetricarboxylic acid sodium salt hydrate) (A-317491) in a murine model of cancer-induced bone pain. Chronic administration of A-317491 (30 μmol/kgs.c., b.i.d.) resulted in a transient attenuation of pain related behaviours in the early stage of the bone cancer model, but had no effect in the late and more progressed stage of bone cancer. Also, acute administration of A-317491 (100 μmol/kgs.c.) had no effect in the progressed stage of the bone cancer pain model. Thus, systemically administered A-317491 did not demonstrate a robust effect in the present mouse model of cancer-induced bone pain.

P2X7 receptor-deficient mice are susceptible to bone cancer pain

The purinergic P2X7 receptor is implicated in both neuropathic and inflammatory pain, and has been suggested as a possible target in pain treatment. However, the specific role of the P2X7 receptor in bone cancer pain is unknown. We demonstrated that BALB/cJ P2X7 receptor knockout (P2X7R KO) mice were susceptible to bone cancer pain and moreover had an earlier onset of pain-related behaviours compared with cancer-bearing, wild-type mice. Furthermore, acute treatment with the selective P2X7 receptor antagonist, A-438079, failed to alleviate pain-related behaviours in models of bone cancer pain with and without astrocyte activation (BALB/cJ or C3H mice inoculated with 4T1 mammary cancer cells or NCTC 2472 osteosarcoma cells, respectively), suggesting that astrocytic P2X7 receptors play a negligible role in bone cancer pain. The results support the hypothesis that bone cancer pain is a separate pain state compared with those of neuropathic and inflammatory pain. However, the recent discovery of a P2X7 receptor splice variant expressed in the knockout mice used for this study complicates the interpretation of the results. The P2X7 splice variant receptor was detected in the spinal cord but not in osteoclasts of the P2X7R KO mouse. Further experiments are needed to elucidate the exact role of the P2X7 receptors in bone cancer pain.