Subchondral Bone Plate Changes More Rapidly than Trabecular Bone in Osteoarthritis

Pathological progression of osteoarthritis: a perspective on subchondral bone

Osteoarthritis (OA) is a degenerative bone disease associated with aging. The rising global aging population has led to a surge in OA cases, thereby imposing a significant socioeconomic burden. Researchers have been keenly investigating the mechanisms underlying OA. Previous studies have suggested that the disease starts with synovial inflammation and hyperplasia, advancing toward cartilage degradation. Ultimately, subchondral-bone collapse, sclerosis, and osteophyte formation occur. This progression is deemed as "top to bottom." However, recent research is challenging this perspective by indicating that initial changes occur in subchondral bone, precipitating cartilage breakdown. In this review, we elucidate the epidemiology of OA and present an in-depth overview of the subchondral bone's physiological state, functions, and the varied pathological shifts during OA progression. We also introduce the role of multifunctional signal pathways (including osteoprotegerin (OPG)/receptor activator of nuclear factor-kappa B ligand (RANKL)/receptor activator of nuclear factor-kappa B (RANK), and chemokine (CXC motif) ligand 12 (CXCL12)/CXC motif chemokine receptor 4 (CXCR4)) in the pathology of subchondral bone and their role in the "bottom-up" progression of OA. Using vivid pattern maps and clinical images, this review highlights the crucial role of subchondral bone in driving OA progression, illuminating its interplay with the condition.

Early Degenerative Changes in a Spontaneous Osteoarthritis Model Assessed by Nanoindentation

Understanding early mechanical changes in articular cartilage (AC) and subchondral bone (SB) is crucial for improved treatment of osteoarthritis (OA). The aim of this study was to develop a method for nanoindentation of fresh, unfixed osteochondral tissue to assess the early changes in the mechanical properties of AC and SB. Nanoindentation was performed throughout the depth of AC and SB in the proximal tibia of Dunkin Hartley guinea pigs at 2 months, 3 months, and 2 years of age. The contralateral tibias were either histologically graded for OA or analyzed using immunohistochemistry. The results showed an increase in the reduced modulus (Er) in the deep zone of AC during early-stage OA (6.0 ± 1.75 MPa) compared to values at 2 months (4.04 ± 1.25 MPa) (*** p < 0.001). In severe OA (2-year) specimens, there was a significant reduction in Er throughout the superficial and middle AC zones, which correlated to increased ADAMTS 4 and 5 staining, and proteoglycan loss in these regions. In the subchondral bone, a 35.0% reduction in stiffness was observed between 2-month and 3-month specimens (*** p < 0.001). The severe OA age group had significantly increased SB stiffness of 36.2% and 109.6% compared to 2-month and 3-month-old specimens respectively (*** p < 0.001). In conclusion, this study provides useful information about the changes in the mechanical properties of both AC and SB during both early- and late-stage OA and indicates that an initial reduction in stiffness of the SB and an increase in stiffness in the deep zone of AC may precede early-stage cartilage degeneration.

Injectable Double Positively Charged Hydrogel Microspheres for Targeting-Penetration-Phagocytosis

The localization and accumulation of drugs in the body determine their therapeutic effects; however, the specific microstructure of damaged tissues hinders drug delivery. Currently, there is a shortage of effective drug carriers to breach these barriers and achieve efficient tissue and cellular delivery of drugs. In this study, an injectable double positively charged functional hydrogel microsphere with "targeting cartilage extracellular matrix", "cartilage penetration", and "cellular phagocytosis" is designed for matching the structural characteristics of joints, addressing the difficulties of drug delivery in joints. The microspheres could be adsorbed on the negatively charged cartilage surface because of their positively charged poly-lysine surface. Furthermore, the internally loaded positively charged polyamidoamine contained kartogenin, which helped further the penetration of the cartilage under the guidance of electrical charge. The microspheres could release kartogenin for more than 21 days. In in vivo experiments, the microspheres effectively improve the efficiency of drug delivery, inhibit the degradation of cartilage matrix and subchondral bone, and delay the development of osteoarthritis. As a double positively charged drug delivery system, the versatile microsphere has great potential for treating osteoarthritis and other diseases.

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.

Naturally Occurring Osteoarthritis Features and Treatments: Systematic Review on the Aged Guinea Pig Model

To date, several in vivo models have been used to reproduce the onset and monitor the progression of osteoarthritis (OA), and guinea pigs represent a standard model for studying naturally occurring, age-related OA. This systematic review aims to characterize the guinea pig for its employment in in vivo, naturally occurring OA studies and for the evaluation of specific disease-modifying agents. The search was performed in PubMed, Scopus, and Web of Knowledge in the last 10 years. Of the 233 records screened, 49 studies were included. Results showed that within a relatively short period of time, this model develops specific OA aspects, including cartilage degeneration, marginal osteophytes formation, and subchondral bone alterations. Disease severity increases with age, beginning at 3 months with mild OA and reaching moderate–severe OA at 18 months. Among the different strains, Dunkin Hartley develops OA at a relatively early age. Thus, disease-modifying agents have mainly been evaluated for this strain. As summarized herein, spontaneous development of OA in guinea pigs represents an excellent model for studying disease pathogenesis and for evaluating therapeutic interventions. In an ongoing effort at standardization, a detailed characterization of specific OA models is necessary, even considering the main purpose of these models, i.e., translatability to human OA.

Biochemical and Morphological Abnormalities of Subchondral Bone and Their Association with Cartilage Degeneration in Spontaneous Osteoarthritis

This study aims to investigate how biochemical composition in subchondral bone (SB) relates to the sulfated glycosaminoglycan (sGAG) content of articular cartilage (AC) in the knee joint of guinea pigs from the early to moderate osteoarthritis (OA). Male Dunkin Hartley strain guinea pigs were grouped according to age (1, 3, 6, and 9 months, with 10 guinea pigs in each group). The biochemical properties of the AC and SB in the tibial plateau of the guinea pigs were determined through histology and Raman spectroscopy, respectively. Furthermore, the microstructures of the SB were investigated using micro-computed tomography (micro-CT) and histology. Increased thickness and bone mineral density (BMD) and decreased porosity were observed in the subchondral plate (SP) with the progression of spontaneous OA, accompanied by a decreasing trend in sGAG integrated optical density (IOD) of AC. Compared with the changes in the microstructure of subchondral bone, the content of sGAG was more correlated to the changes in the mineral/matrix ratio of subchondral bone. The mineralization of the matrix was significantly correlated to the content of sGAG compared with crystallinity/maturity and Type B carbonate substitution. PO₄^3- ν1/Amide III was more correlated to the content of sGAG than PO₄^3- ν1/Amide I, PO₄^3- ν1/CH₂ wag during the progression of spontaneous osteoarthritis. This study demonstrated that the mineralization of subchondral bone plays a crucial role in the pathogenesis of OA. Future studies may access to the mineralization of subchondral bone in addition to its microstructure in the study for pathogenesis and early diagnosis of osteoarthritis.

Macro, Micro, and Molecular. Changes of the Osteochondral Interface in Osteoarthritis Development

Osteoarthritis (OA) is a long-term condition that causes joint pain and reduced movement. Notably, the same pathways governing cell growth, death, and differentiation during the growth and development of the body are also common drivers of OA. The osteochondral interface is a vital structure located between hyaline cartilage and subchondral bone. It plays a critical role in maintaining the physical and biological function, conveying joint mechanical stress, maintaining chondral microenvironment, as well as crosstalk and substance exchange through the osteochondral unit. In this review, we summarized the progress in research concerning the area of osteochondral junction, including its pathophysiological changes, molecular interactions, and signaling pathways that are related to the ultrastructure change. Multiple potential treatment options were also discussed in this review. A thorough understanding of these biological changes and molecular mechanisms in the pathologic process will advance our understanding of OA progression, and inform the development of effective therapeutics targeting OA.

Multipotential stromal cells in the talus and distal tibia in ankle osteoarthritis - Presence, potency and relationships to subchondral bone changes

A large proportion of ankle osteoarthritis (OA) has an early onset and is post‐traumatic. Surgical interventions have low patient satisfaction and relatively poor clinical outcome, whereas joint‐preserving treatments, which rely on endogenous multipotential stromal cells (MSCs), result in suboptimal repair. This study investigates MSC presence and potency in OA‐affected talocrural osteochondral tissue. Bone volume fraction (BV/TV) changes for the loading region trabecular volume and subchondral bone plate (SBP) thickness in OA compared with healthy tissue were investigated using microcomputed tomography. CD271‐positive MSC topography was related to bone and cartilage damage in OA tissue, and in vitro MSC potency was compared with control healthy iliac crest (IC) MSCs. A 1.3‐ to 2.5‐fold SBP thickening was found in both OA talus and tibia, whereas BV/TV changes were depth‐dependent. MSCs were abundant in OA talus and tibia, with similar colony characteristics. Tibial and talar MSCs were tripotential, but talar MSCs had 10‐fold lower adipogenesis and twofold higher chondrogenesis than IC MSCs (P = .01 for both). Cartilage damage in both OA tibia and talus correlated with SBP thickening and CD271+ MSCs was 1.4‐ to twofold more concentrated near the SBP. This work shows multipotential MSCs are present in OA talocrural subchondral bone, with their topography suggesting ongoing involvement in SBP thickening. Potentially, biomechanical stimulation could augment the chondrogenic differentiation of MSCs for joint‐preserving treatments.

Initiating factors for the onset of OA: A systematic review of animal bone and cartilage pathology in OA

There is controversy over whether bone or cartilage is primarily involved in osteoarthritis (OA) pathogenesis; this is important for targeting early interventions. We explored evidence from animal models of knee OA by preforming a systematic review of PubMed, Scopus, and Web of Science for original articles reporting subchondral bone and cartilage pathology in animal models with epiphyseal closure. Extracted data included: method of induction; animal model; cartilage and bone assessment and method; meniscal assessment; skeletal maturity; controls; and time points assessed. Quality scoring was performed. The best evidence was synthesized from high-quality skeletally mature models, without direct trauma to tissues of interest and with multiple time points. Altogether, 2849 abstracts were reviewed. Forty-seven papers were included reporting eight different methods of inducing OA, six different species, six different methods of assessing cartilage, five different bone structural parameters, and four assessed meniscus as a potential initiator. Overall, the simultaneous onset of OA in cartilage and bone was reported in 82% of datasets, 16% reported bone onset, and 2% reported cartilage onset. No dataset containing meniscal data reported meniscal onset. However, using the best evidence synthesis (n = 8), five reported simultaneous onset when OA was induced, while three reported bone onset when OA occurred spontaneously; none reported cartilage onset. In summary, there is a paucity of well-designed studies in this area which makes the conclusions drawn conjectures rather than proven certainties. However, within the limitation of data quality, this review suggests that in animal models, the structural onset of knee OA occurs either in bone prior to cartilage pathology or simultaneously.

The role of indoleamine 2,3 dioxygenase 1 in the osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease and a leading cause of disability. It involves articular cartilage destruction and a whole joint inflammation. In spite of OA pathogenesis is still unclear, new studies on the OA pathophysiological aetiology and immunomodulation therapy continuously achieve significant advances with new concepts. Here, we focus on the indoleamine-2,3-dioxygenase1 (IDO1) activity in the osteoarthritis (OA), which is one of the noticeable enzymes in the synovial fluid of arthritis patients. It was recognized as an essential mediator of autoreactive B and T cell responses in rheumatoid arthritis (RA) and an interesting therapeutic target against RA. However, the role IDO1 plays in the OA pathogenesis hasn't been discussed. The new OA experimental analysis evidenced IDO1 overexpression in the synovial fluid of OA patients, and recent studies reported that IDO1 metabolites were found higher in the OA synovial fluid than RA and spondyloarthropathies (SpA) patients. Moreover, the positive relation of IDO1 metabolites with OA pain and joint stiffness has been confirmed. Thus, the IDO1 plays a pivotal role in the pathogenesis of OA. In this review, the role IDO1 plays in the OA pathogenesis has been deeply discussed. It could be a promising target in the immunotherapy of OA disease.

Specific inhibition of FAK signaling attenuates subchondral bone deterioration and articular cartilage degeneration during osteoarthritis pathogenesis

Osteoarthritis (OA), a disease of the entire joint, is characterized by abnormal bone remodeling and coalescent degradation of articular cartilage. We have previously found that elevated levels of H-type vessels in subchondral bone correlate with OA and that focal adhesion kinase (FAK) is critical for H-type vessel formation in osteoporosis. However, the potential role of FAK in OA remains unexplored. Here, we demonstrate that the p-FAK level was dramatically elevated in subchondral bone following anterior cruciate ligament transection (ACLT) in rats. Specific inhibition of FAK signaling with Y15 in subchondral bone resulted in the suppression of subchondral bone deterioration and this effect was mediated by H-type vessel-induced ectopic bone formation. Further, articular cartilage degeneration was also alleviated after Y15 treatment. In vitro, the p-FAK level was significantly elevated in mesenchymal stem cells (MSCs) from vehicle-treated ACLT rats as compared to that in MSCs from sham controls and Y15-treated ACLT rats. Elevated p-FAK level in MSCs promoted vascular endothelial growth factor (VEGF) expression, as demonstrated from the high VEGF level in the blood, subchondral bone, and conditioned medium (CM) of MSCs from vehicle-treated ACLT rats. The CM of MSCs from vehicle-treated ACLT rats might promote the angiogenesis of endothelial cells and the catabolic response of chondrocytes through the FAK-growth factor receptor-bound protein 2-mitogen-activated protein kinase-mediated expression of VEGF. The effect of the CM from MSCs of Y15-treated ACLT rats or that treated with a VEGF-neutralizing antibody on vessel formation and the catabolic response was lowered. Thus, the specific inhibition of FAK signaling may be a promising avenue for the prevention or early treatment of OA.

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.

Subchondral Trabecular Rod Loss and Plate Thickening in the Development of Osteoarthritis

Developing effective treatment for osteoarthritis (OA), a prevalent and disabling disease, has remained a challenge, primarily because of limited understanding of its pathogenesis and late diagnosis. In the subchondral bone, rapid bone loss after traumatic injuries and bone sclerosis at the advanced stage of OA are well-recognized hallmarks of the disease. Recent studies have further demonstrated the crucial contribution of subchondral bone in the development of OA. However, the microstructural basis of these bone changes has not been examined thoroughly, and the paradox of how abnormal resorption can eventually lead to bone sclerosis remains unanswered. By applying a novel microstructural analysis technique, individual trabecula segmentation (ITS), to micro-computed tomography (μCT) images of human OA knees, we have identified a drastic loss of rod-like trabeculae and thickening of plate-like trabeculae that persisted in all regions of the tibial plateau, underneath both severely damaged and still intact cartilage. The simultaneous reduction in trabecular rods and thickening of trabecular plates provide important insights to the dynamic and paradoxical subchondral bone changes observed in OA. Furthermore, using an established guinea pig model of spontaneous OA, we discovered similar trabecular rod loss and plate thickening that preceded cartilage degradation. Thus, our study suggests that rod-and-plate microstructural changes in the subchondral trabecular bone may play an important role in the development of OA and that advanced microstructural analysis techniques such as ITS are necessary in detecting these early but subtle changes. With emerging high-resolution skeletal imaging modalities such as the high-resolution peripheral quantitative computed tomography (HR-pQCT), trabecular rod loss identified by ITS could potentially be used as a marker in assessing the progression of OA in future longitudinal studies or clinical diagnosis. © 2017 American Society for Bone and Mineral Research.