Subchondral Trabecular Bone Research Articles

Research Progress in Promotion of Tissue Regeneration and Reconstruction with Exosomes Derived from Mesenchymal Stem Cells

In regenerative medicine, stem cell therapy is an effective strategy for tissue regeneration and has a positive therapeutic effect on the regeneration and repair of defective tissues. In recent years, a series of studies have shown that the positive effects of stem cell therapy are mediated by exosomes released by the paracrine action of mesenchymal stem cells. Researchers have thus proposed a novel treatment strategy to use stem-cell-derived exosomes alone for tissue regeneration and repair, and affirmed through studies that the effects achieved were comparable to those of stem-cell-based therapies. Therefore, as a promising treatment strategy, exosome-based tissue regeneration treatment measures have been extensively studied. In this review, we discussed the latest knowledge of exosomes and the research progress in the regeneration and repair of related connective tissues, including the regeneration of bones, cartilage, skin, spinal cord and tendons, and briefly discussed the corresponding mechanisms. In addition, the challenges and prospects of tissue regeneration and repair based on mesenchymal stem cell exosomes were discussed.

Greater heterogeneity of the bone mineralisation density distribution and low bone matrix mineralisation characterise tibial subchondral bone marrow lesions in knee osteoarthritis patients.

Tibial subchondral bone marrow lesions (BMLs) identified by MRI have been recognised as potential disease predictors in knee osteoarthritis (KOA), and may associate with abnormal bone matrix mineralisation and reduced bone quality. However, these tissue-level changes of BMLs have not been extensively investigated. Thus, the aim of this study was to quantify the degree of subchondral bone matrix mineralisation (both plate and trabeculae) in relation to histomorphometric parameters of bone remodelling and osteocyte lacunae (OL) characteristics in the tibial plateau (TP) of KOA patients with and without BMLs (OA-BML and OA No-BML, respectively) in comparison to nonOA cadaveric controls (CTL). Osteochondral (cartilage-bone) tissue was sampled from the BML signal region within the medial compartment for each OA-BML TP, and from a corresponding medial region for OA No-BML and CTL TPs. The tissue samples were embedded in resin, and sections stained with Von-Kossa Haematoxylin and Eosin (H&E) for quantitation of static indices of bone remodelling. Resin blocks were then further polished, and carbon-coated for quantitative backscattered electron imaging (qBEI) to determine the bone mineralisation density distribution (BMDD), as well as OL characteristics. It was found that OA-BML contained higher osteoid volume per tissue volume (OV/TV; %) and per bone volume (OV/BV; %) in both subchondral plate and trabecular bone compared to OA No-BML and CTL. The BMDD of OA-BML in both subchondral plate and trabecular bone was shifted toward a lower degree of mineralisation. Typically, an increase in both the heterogeneity of mineralisation density (Ca Width; wt%Ca) and the percentage of lower calcium (Ca Low; % B.Ar) in trabecular bone with OA-BML versus CTL was observed. Further, unmineralised OL density (#/mm2) in subchondral plate was distinctly higher in OA-BML samples compared to CTL. The KOA patients with and without BMLs had significantly decreased density of mineralised OL (#/mm2) in trabecular bone compared to CTL. Taken together, these findings indicate that tibial BMLs in advanced KOA patients are characterised by significantly hypo-mineralised subchondral bone compared with CTL. These differences associated with evidence of increased bone remodelling in OA-BML, and may influence the mechanical properties of the subchondral bone, with implications for the overlying cartilage.

Differentiated activities of decorin and biglycan in the progression of post-traumatic osteoarthritis

To delineate the activities of decorin and biglycan in the progression of post-traumatic osteoarthritis (PTOA). Three-month-old inducible biglycan (BgniKO) and decorin/biglycan compound (Dcn/BgniKO) knockout mice were subjected to the destabilization of the medial meniscus (DMM) surgery to induce PTOA. The OA phenotype was evaluated by assessing joint structure and sulfated glycosaminoglycan (sGAG) staining via histology, surface collagen fibril nanostructure and calcium content via scanning electron microscopy, tissue modulus via atomic force microscopy-nanoindentation, as well as subchondral bone structure and meniscus ossification via micro-computed tomography. Outcomes were compared with previous findings in the inducible decorin (DcniKO) knockout mice. In the DMM model, BgniKO mice developed similar degree of OA as the control (0.44 [-0.18 1.05] difference in modified Mankin score), different from the more severe OA phenotype observed in DcniKO mice (1.38 [0.91 1.85] difference). Dcn/BgniKO mice exhibited similar histological OA phenotype as DcniKO mice (1.51 [0.97 2.04] difference vs control), including aggravated loss of sGAGs, salient surface fibrillation and formation of osteophyte. Meanwhile, Dcn/BgniKO mice showed further cartilage thinning than DcniKO mice, resulting in the exposure of underlying calcified tissues and aberrantly high surface modulus. BgniKO and Dcn/BgniKO mice developed altered subchondral trabecular bone structure in both Sham and DMM groups, while DcniKO and control mice did not. In PTOA, decorin plays a more crucial role than biglycan in regulating cartilage degeneration, while biglycan is more important in regulating subchondral bone structure. The two have distinct activities and modest synergy in the pathogenesis of PTOA.

Differential proteomic analysis of tibial subchondral bone from male and female guinea pigs with spontaneous osteoarthritis.

A proteomic study on the tibial subchondral bone in guinea pigs with spontaneous osteoarthritis was performed to investigate the molecular alterations that occur in early osteoarthritis. A total of 132 healthy Hartley guinea pigs (aged 1 month; 66 female and 66 male) were randomly divided into 11 groups of six. Changes in articular cartilage and tibial subchondral bone were assessed using macroscopic examinations and micro-computed tomography. iTRAQ-integrated liquid chromatography-tandem mass spectrometry was used to identify differentially altered proteins in the tibial subchondral bone between 1- and 3-month-old guinea pigs, which were then validated using western blotting. A gradual progression of cartilage degeneration was observed in the knee joints of the subject animals from 5-11 months. With aging, the tibial subchondral trabecular bone acquired more plate-like and less anisotropic properties, with increased bone mineral density, bone volume, trabecular thickness and numbers. The proteomic study identified 138 and 113 proteins significantly differentially expressed between 3- and 1-month old guinea pigs in both the male and female animals, respectively. Western blotting confirmed the increased expression of osteoblast-associated protein S100 calcium-binding protein A8 (S100A8) and the deregulated expression of osteoclast-associated proteins coronin 1A (CORO1A) and T-cell immune regulator 1 (TCIRG1) in the 3-month old guinea pigs in comparison to the 1-month old guinea pigs. Spontaneous cartilage degeneration in the knee joints of male Hartley guinea pigs tended to be more serious compared with the females during the development of osteoarthritis. Together, the results suggest that osteoblast-associated protein S100A8 and osteoclast-associated proteins CORO1A and TCIRG1 are potentially key regulators of early osteoarthritic development in tibial subchondral bone.

Microstructural changes at the osteochondral junction in naturally occurring osteoarthritis of the equine medial femorotibial joint

Purpose: Osteoarthritis (OA) is a progressive degenerative disease of the joint organ and affects all species. The medial femorotibial (MFT) joint is the knee compartment most commonly affected with OA in humans, dogs, and horses. We hypothesized that microCT (μCT) assessment of specimens with naturally occurring equine MFT-OA will provide new insight into the pathophysiology of OA in this joint. The aim of this study was to compare healthy and MFT-OA joint microarchitectural changes in both 2 and 3D μCT images. Methods: Equine medial femoral condyles (MFC; n = 24) and tibial plateaus (MTP; n = 24) were available in a tissue bank. Regions of interest (cranial and caudal) were scored for lesions. Articular surfaces were macroscopically scored for OA (cartilage fibrillation and erosion) and categorized into 2 groups (healthy and OA) for comparative purposes. MFCs and MTPs were scanned with μCT (Xtek HMXST 225, Nexus Metrology, Canada) and 2D and 3D images were assessed. Hyaline articular cartilage (HAC) was scored for fibrillation (0-3) and high density mineralized protrusions (HDMP) (0-3). The calcified cartilage/subchondral bone plate (ACC/SCP) was also assessed for radiolucencies and the subchondral trabecular bone (SCB) for sclerosis. Results: Seventeen healthy MFTs and 7 OA MFTs were studied. HAC fibrillation was more prevalent in the MFC OA group (100%) compared with the healthy MFC group (71%) and the scores (s) were also more severe: OA MFCs (s2- 29%, s3- 71%); healthy MFCs (s1- 29%, s2- 24%, s3- 18%). Although HAC fibrillation was almost equally observed in the MTP OA group (100%) and the healthy MTP group (94%), the scores were worse in the MTP OA group (s2- 29%, s3- 71%) compared with MTP healthy group (s1- 12%, s2- 43%, s3- 43%). HDMPs were observed frequently in both groups: in 57% OA MFCs and in 47% healthy MFCs. However, the HDMP scores were more severe in MFC OA (s1- 14%, s3- 43%) compared with healthy MFCs (s1- 12%, s2- 12%, s3- 23%). They were located almost exclusively in the cranial MFC (100% OA, 87% healthy) (Figure 1). Although HDMPs were more prevalent in the MTP OA group (43%) compared with the healthy MTP group (18%), the severity of the lesions was similar in both groups: OA MTPs (s1- 29%, s3- 14%); healthy MTPs (s1- 6%, s3- 12%). ACC/SCP radiolucency was never observed in either healthy or OA MFCs. However, ACC/SCP radiolucency was observed in the MTP: MTP OA (86%) and healthy (65%) and almost all were located in the caudal part of the plateau in both healthy (91%) and OA (100%) MTPs. SCB sclerosis had a similar prevalence in both healthy (82%) and OA (86%) MFCs but the distribution pattern was different. In the healthy MFCs, sclerosis was more frequent caudally (71%) whereas in OA MFCs, it was distributed equally in both regions (57%). At the tibial plateau, sclerosis was most frequently observed in MTP OA specimens (86%) and predominantly at the caudal site (86%). In healthy MTPs it was identified in 65% with a more balanced distribution between cranial (41%) and caudal (59%) sites. Conclusions: High density mineralized protrusions (HDMP) were observed protruding into macroscopically normal appearing cartilage and OA cartilage. However, they were more severe in OA joints. This confirms our previous identification of HDMP in equine post traumatic osteoarthritis (PTOA) of the carpal bones and extends them to the equine MFT where racing-induced PTOA is not a characteristic feature and suggests that HDMP is feature all forms of OA. ACC/SCP radiolucency was never observed in the MFCs but occurred in the caudal MTP of both groups, but more frequently in OA.

Trabecular subchondral bone analysis of the distal radius at ultra-high field (7t) MRI: comparison with 3T MRI and radiography

Purpose: Bone fractal signature analysis (FSA) is a tool assessing structural changes that may relate to clinical outcomes and function. Bone structural changes play a role in onset and progression of several musculoskeletal diseases, and FSA has been applied to different anatomic body regions. However, its applicability in a routine clinical environment has not been extensively explored. Our aim was to evaluate and compare bone texture analysis of the distal radius in patients and controls using radiography, 3 Tesla (T) and 7T magnetic resonance imaging (MRI).

Subchondral bone microarchitecture and mineral density in human osteoarthritis and osteoporosis: A regional and compartmental analysis.

Osteoarthritis (OA) and osteoporosis (OP) are historically considered to be inversely correlated but there may be an overlap between the pathophysiology of the two diseases. This study aimed to investigate the subchondral bone microarchitecture and matrix mineralization, and the association between them in OA and OP in relation to the degree of cartilage degeneration. Fifty-six osteochondral plugs were collected from 16 OA femoral heads. They were graded on a regional basis according to the stages of cartilage degeneration, as evaluated by a new macroscopic and a modified microscopic grading system. Twenty-one plugs were collected from seven femoral heads with OP. Plugs were scanned by microcomputed tomography and the microarchitectural and mineral properties were obtained for both subchondral plate and trabecular bone. Microarchitecture and material and apparent densities of subchondral bone in OP were similar to regions with early cartilage degeneration but different from regions with advanced cartilage degradation in OA femoral heads. Subchondral trabecular bone was more mineralized than subchondral plate in both OP and OA, and this compartmental difference varied by severity of cartilage degradation. Furthermore, the relationship among trabecular bone volume fraction, tissue mineral density, and apparent bone density was similar in OP and different stages of OA. Subchondral bone microarchitecture and mineral properties in OP are different from OA in a regionalized manner in relation to stages of cartilage degeneration. Both regional and compartmental differences at structural, material, and cellular levels need to be studied to understand the transition of OA subchondral bone from being osteoporotic to sclerotic.

Necrosis of the femoral head, X-ray microtomography (microCT) and histology of retrieved human femoral heads

Aseptic osteonecrosis of the hip (AON) is a rare, but well-known pathology in rheumatology and orthopedic surgery that is a necrosis of the articular cartilage secondary to a necrosis of the subchondral bone. The microscopic aspect is well known, but the microCT aspect has never been reported or correlated with histopathological findings. The objective of this study was to improve the knowledge of the pathophysiology of AON using histochemistry and microCT. One hundred and sixty femoral heads with stage 3 or 4 AON were analyzed: one half of the head was sent for microCT analysis after impregnation with phosphotungstic acid (PTA) and the other half was used for histological analysis without decalcification. The microCT analysis provides relevant information on the cracked articular cartilage and the relationship with the necrotic subchondral trabecular bone well illustrated on three videos. In histology, Goldner's trichrome showed that the articular cartilage remains well preserved for a long time. In addition, toluidine blue staining reveals a modeling process, i.e. the apposition of new bone without prior resorption by osteoclasts. Rhodamine B staining (fluorescence analysis) reveals that the osteonecrotic trabeculae and subchondral bone were devoid of osteocytes. Areas of peri-necrotic osteosclerosis are due to direct bone formation on the surface of pre-existing necrotic trabeculae.

Subchondral Trabecular Microstructure and Articular Cartilage Damage Variations Between Osteoarthritis and Osteoporotic Osteoarthritis: A Cross-sectional Cohort Study.

Osteoporotic osteoarthritis (OP-OA) is a specific type of OA. In this study, we aimed to assess the subchondral plate and rod microstructural differences between OA and OP-OA patients by using an individual trabeculae segmentation (ITS) system and to analyze the relationships between subchondral microstructures and cartilage damage in OA and OP-OA patients. Overall, 31 femoral heads were included in this study, which included 11 samples with OA and 13 samples with OP-OA; the normal control (NC) group contained 7 healthy femoral heads. ITS was performed to segment the subchondral trabecular bone into plate and rod trabeculae based on microcomputed tomography (micro-CT) images. We compared the plate and rod trabeculae of the subchondral trabecular bone between OA and OP-OA patients. The Osteoarthritis Research Society International (OARSI) score was employed to evaluate cartilage damage based on histological observations. Pearson's correlation coefficient and linear regression analysis were applied to analyze the relationships between subchondral microstructures and articular cartilage damage. Results showed that several microstructural parameters, including bone volume fraction (BV/TV), plate bone volume fraction (pBV/TV), rod bone volume fraction (rBV/TV), plate trabecular number (pTb.N), rod trabecular number (rTb.N), junction density between rod and plate (R-P Junc.D), and junction density between plate and plate (P-P Junc.D), were significantly decreased in patients with OP-OA compared with those in patients with OA (p < 0.05). Histological observations indicated that cartilage damage was more serious in patients with OP-OA than that in patients with OA (p < 0.05). Moreover, BV/TV, pBV/TV, pTb.N, and pTb.Th were significantly related to the OARSI score in both OA and OP-OA patients. These results indicated that there were differences in the subchondral rod and plate trabeculae between OA and OP-OA patients. Subchondral decreased plate trabeculae (pBV/TV, pTb.N, and pTb.Th) might account for cartilage damage in the progression of OP-OA. This study provided new insights to research OA when it is combined with OP.

Metabolic Syndrome Predisposes to Osteoarthritis: Lessons from Model System.

The present study aims to assess for temporal changes in tibial subchondral bone and cartilage in WNIN/Gr-Ob rats (portraying obesity, insulin resistance, dyslipidemia, impaired glucose tolerance, hypertension) in comparison with Wistar controls (WNIN) using anthropometry, micro-computed tomography (micro-CT), scanning electron microscopy (SEM), histopathology, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence. Body weight, abdominal circumference, body mass index (BMI), lean/fat mass, serum tumor necrosis factor (TNF)-α levels were measured (ELISA), followed by ultrastructural analysis of tibial subchondral bone (micro-CT) and cartilage architecture (histopathology and SEM) in WNIN/Gr-Ob and WNIN rats with age (3, 6 and 9 months). Additionally, primary cultures of articular chondrocytes isolated from 6-month-old WNIN/Gr-Ob and WNIN rats were assessed for matrix metalloproteinase (MMP)-13 and Collagen type II (COL2A1) by immunofluorescence. WNIN/Gr-Ob rats exhibited frank obesity with increased BMI, lean and fat mass vis-à-vis significantly higher levels of serum TNF-α (6>9>3 months) as compared with the controls. With an increase in BMI, WNIN/Gr-Ob rats presented with tibial cartilage fibrillation, erosion, osteophyte formation (6 months) and subchondral bone cyst (9 months) confirmed by histology and SEM. An increase in subchondral trabecular bone volume (sclerosis with decreased plate porosity) was observed in all ages in WNIN/Gr-Ob rats compared to their Control. Gaining insights, primary cultures of articular chondrocytes complemented with altered cellular expressions of COL2A1 and MMP-13 from WNIN/Gr-Ob rats, indicating osteoarthritis (OA) progression. Multiple metabolic perturbations featured in WNIN/Gr-Ob rats were effective to induce spontaneous OA-like degenerative changes affecting knee joints akin to human OA.

Tibial cartilage, subchondral bone plate and trabecular bone microarchitecture in varus-and valgus-osteoarthritis versus controls.

This preliminary study quantified tibia cartilage thickness (Cart.Th), subchondral bone plate thickness (SBPl.Th)and subchondral trabecular bone (STB) microarchitecture in subjects with varus- or valgus- malaligned knees diagnosed with end-stage knee osteoarthritis (OA) and compared them to controls (non-OA). Tibial plateaus from 25 subjects with knee-OA (undergoing knee arthroplasty) and 15 cadavers (controls) were micro-CT scanned (17 µm/voxel). Joint alignment was classified radiographically for OA subjects (varus-aligned n = 18, valgus-aligned n = 7). Cart.Th, SBPl.Th, STB bone volume fraction (BV/TV) and their medial-to-lateral ratios were analyzed in anteromedial, anterolateral, posteromedial and posterolateral subregions. Varus-OA and valgus-OA were compared to controls. Compared to controls (1.19-1.54 mm), Cart.Th in varus-OA was significantly lower anteromedially (0.58 mm, -59%) and higher laterally (2.19-2.47 mm,+60-63%); in valgus-OA, Cart.Th was significantly higher posteromedially (1.86 mm,+56%). Control medial-to-lateral Cart.Th ratios were around unity (0.8-1.1), in varus-OA significantly below (0.2-0.6) and in valgus-OA slightly above (1.0-1.3) controls. SBPl.Th and BV/TV were significantly higher medially in varus-OA (0.58-0.72 mm and 37-44%, respectively) and laterally in valgus-OA (0.60-0.61 mm and 32-37%), compared to controls (0.26-0.47 mm and 18-37%). In varus-OA, the medial-to-lateral SBPl.Th and BV/TV ratios were above unity (1.4-2.4) and controls (0.8-2.1); in valgus-OA they were closer to unity (0.8-1.1) and below controls. Varus- and valgus-OA tibia differ significantly from controls in Cart.Th, SBPl.Thand STB microarchitecture depending on joint alignment, suggesting structural changes in OA may reflect differences in medial-to-lateral load distribution upon the tibial plateau. Here we identified an inverse relationship between cartilage thickness and underlying subchondral bone, suggesting a whole-joint response in OA to daily stimuli.

Traumatic joint injury induces acute catabolic bone turnover concurrent with articular cartilage damage in a rat model of posttraumatic osteoarthritis.

Assess acute alterations in bone turnover, microstructure, and histomorphometry following noninvasive anterior cruciate ligament rupture (ACLR). Twelve female Lewis rats were randomized to receive noninvasive ACLR or Sham loading (n = 6/group). In vivo μCT was performed at 3, 7, 10, and 14 days postinjury to quantify compartment-dependent subchondral (SCB) and epiphyseal trabecular bone remodeling. Near-infrared (NIR) molecular imaging was used to measure in vivo bone anabolism (800 CW BoneTag) and catabolism (Cat K 680 FAST). Metaphyseal bone remodeling and articular cartilage morphology was quantified using ex vivo μCT and contrast-enhanced µCT, respectively. Calcein-based dynamic histomorphometry was used to quantify bone formation. OARSI scoring was used to assess joint degeneration, and osteoclast number was quantified on TRAP stained-sections. ACLR induced acute catabolic bone remodeling in subchondral, epiphyseal, and metaphyseal compartments. Thinning of medial femoral condyle (MFC) SCB was observed as early as 7 days postinjury, while lateral femoral condyles (LFCs) exhibited SCB gains. Trabecular thinning was observed in MFC epiphyseal bone, with minimal changes to LFC. NIR imaging demonstrated immediate and sustained reduction of bone anabolism (~15%-20%), and a ~32% increase in bone catabolism at 14 days, compared to contralateral limbs. These findings were corroborated by reduced bone formation rate and increased osteoclast numbers, observed histologically. ACLR-injured femora had significantly elevated OARSI score, cartilage thickness, and cartilage surface deviation. ACL rupture induces immediate and sustained reduction of bone anabolism and overactivation of bone catabolism, with mild-to-moderate articular cartilage damage at 14 days postinjury.

Degradation of subchondral bone collagen in the weight-bearing area of femoral head is associated with osteoarthritis and osteonecrosis

BackgroundThe aim of the study was to evaluate the change of subchondral bone collagen and trabecular bone in the weight-bearing area of femoral head from patients with osteoarthritis (OA) or osteonecrosis of femoral head (ONFH), and discuss the effect of collagen degradation on OA and ONFH.MethodsFemoral heads from patients with femoral neck fracture (FNF) were collected as control group. All collected samples were divided into OA group (N = 10), ONFH group (N = 10), and FNF group (N = 10). Differences of subchondral bone collagen were compared through scanning electron microscope (SEM) observation, immunohistochemistry staining, and Masson’s trichrome staining. Alteration of subchondral bone was displayed through hematoxylin and eosin (H&E) staining and gross morphology.ResultsSEM results showed that collagen fibers in OA and ONFH group appeared to be thinner, rougher, sparser, and more wizened. Immunohistochemistry and Masson’s trichrome staining results demonstrated that the content of collagen fibers in the OA and ONFH group was obviously less than the FNF group. H&E staining results showed that trabecular bone in OA and ONFH group appeared to be thinner and ruptured. Gross morphology results showed that the degeneration and destruction of cartilage and subchondral bone in OA and ONFH group were severer than FNF group. The characteristics mentioned above in ONFH group were more apparent than OA group.ConclusionsThis study revealed that degradation of collagen fibers from subchondral bone in the weight-bearing area of femoral head was associated with OA and ONFH, which may help to find new therapeutic strategies of the diseases.

No Effect of Long-Term Risedronate Use on Cartilage and Subchondral Bone in an Experimental Rabbit Model of Osteoarthritis.

Osteoarthritis (OA) is the most prevalent degenerative joint disease in animals and humans. It is characterized by pain, articular cartilage damage and joint stiffness. It has been suggested that the status of the subchondral bone compartment plays an important role in the initiation and progression of OA. Bisphosphonates have been proposed as a potential disease-modifying treatment for OA, however their effectiveness is not yet clear. Twenty-four male adult New Zealand rabbits were used to evaluate the effects of risedronate on the subchondral bone quality and cartilage degradation in a long-term model of experimentally induced OA. Animals underwent an anterior cruciate ligament transection and partial medial meniscectomy or sham operation in only one knee, which was randomly chosen, using the contralateral as healthy control. Animals were divided into three groups (n = 8): untreated control group and sham surgery control group; both groups received only vehicle; and risedronate group, treated with 2.5 mg orally weekly for 24 weeks. Stifle joints were harvested and scanned using a high-resolution micro-CT to evaluate the subchondral plate and trabecular bone changes. The macroscopic evaluation and histological analysis were determined using an adapted Osteoarthritis Research Society International scoring scheme to assess the cartilage degeneration. The lateral and medial femoral condyle and tibial plateau were evaluated. Additionally, the histological synovial membrane assessment was carried out. Sample analysis showed that the experimental model induced osteoarthritic changes in the operated joints, whereas in sham-operated rabbits, almost no histological changes were observed on articular cartilage surfaces. In terms of macroscopic and histological analyses, risedronate-treated animals did not show improved cartilage health compared with untreated operated rabbits, but a slightly anti-inflammatory activity was observed in the synovial membrane. Risedronate administration showed a slight tendency to increase subchondral bone plate thickness in lateral compartments but, it did not show conservation of periarticular bone and was not be able to suppress the osteophyte formation. In conclusion, long-term risedronate use did not demonstrate a positive effect on reducing the cartilage damage, and failed to prevent the subchondral bone changes and osteophytogenesis in an experimental rabbit model of OA.

Association between knee alignment, osteoarthritis disease severity, and subchondral trabecular bone microarchitecture in patients with knee osteoarthritis: a cross-sectional study

BackgroundKnee osteoarthritis (OA) is a common disabling disease involving the entire joint tissue, and its onset and progression are affected by many factors. However, the current number of studies investigating the relationship between subchondral trabecular bone (STB), knee alignment, and OA severity is limited. We aimed to investigate the variation in tibial plateau STB microarchitecture in end-stage knee OA patients and their association with knee alignment (hip-knee-ankle, HKA, angle) and OA severity.MethodsSeventy-one knee OA patients scheduled for total knee arthroplasty (TKA) underwent preoperative radiography to measure the HKA angle and Kellgren-Lawrence grade. Tibial plateaus collected from TKA were scanned using micro-computed tomography to analyze the STB microarchitecture. Histological sections were used to assess cartilage degeneration (OARSI score). Correlations between the HKA angle, OA severity (OARSI score, Kellgren-Lawrence grade), and STB microarchitecture were evaluated. Differences in STB microstructural parameters between varus and valgus alignment groups based on the HKA angle were examined.ResultsThe HKA angle was significantly correlated with all STB microarchitecture parameters (p < 0.01). The HKA angle was more correlated with the medial-to-lateral ratios of the microarchitecture parameters than with the medial or lateral tibia plateaus. The HKA angle and all STB microarchitecture parameters are significantly correlated with both the OARSI score and Kellgren-Lawrence grade (p < 0.01).ConclusionsThe STB microarchitecture is associated with the HKA angle and OA severity. With the increase of the knee alignment deviation and OA severity, the STB of the affected side tibial plateau increased in bone volume, trabecular number, and trabecular thickness and decreased in trabecular separation.

Age-related changes of micro-morphological subchondral bone properties in the healthy femoral head

Alterations in the subchondral bone (SCB) are likely to play a decisive role in the development of osteoarthritis (OA). Since aging represents a major risk factor for OA, the aim of the current study was to assess the microstructural changes of the subchondral bone in the femoral head during aging. Femoral heads and matched iliac crest biopsies of 80 individuals (age 21-99 years) were collected post-mortem. The bone microstructure of the subchondral trabecular bone as well as the cartilage thickness (Cg.Th) and subchondral bone plate thickness (SCB.Th) were quantified using histomorphometry. The different subregions of the SCB were also imaged by quantitative backscattered electron imaging (qBEI) in 31 aged cases to assess the bone mineral density distribution (BMDD). The detected linear decline of bone volume per tissue volume (BV/TV) in the femoral head with aging (Slope, 95% CI:-0.208 to-0.109 %/yr.) was primarily due to a decrease in trabecular thickness (Tb.Th, Slope, 95% CI:-0.774 to-0.343μm/yr). While SCB.Th declined with aging (Slope, 95% CI:-1.941 to-0.034μm/yr), no changes in Cg.Th were detected (Slope, 95% CI:-0.001 to 0.005mm/yr). The matrix mineralization of the subchondral bone was lower compared to the trabecular bone and also decreased with aging. Regular changes of the SCB during aging primarily involve a reduction of Tb.Th, SCB.Th and matrix mineralization. Our findings facilitate future interpretations of early and late OA specimens to decipher the role of the SCB in OA pathogenesis.

Irisin inhibits osteocyte apoptosis by activating the Erk signaling pathway in vitro and attenuates ALCT-induced osteoarthritis in mice

Moderate exercise can alleviate symptoms of osteoarthritis (OA) such as pain, stiffness, and joint deformities that are associated with progressive cartilaginous degeneration, osteophyte formation, subchondral bone changes, and synovial inflammation. Irisin is an exercise-related myokine that reportedly plays a crucial role in bone remodeling. However, its role in OA remains unknown. This study aimed to determine whether irisin can attenuate OA progression and the mechanism of its therapeutic effect. Three-month-old male C57BL/6J mice were randomized to groups that underwent sham operation, and anterior cruciate ligament transection (ACLT) intraperitoneally injected with vehicle or irisin in vivo. Apoptosis was induced by stretching murine osteocyte-like MLO-Y4 cells in vitro. Irisin reduced wear, maintained the proportion of hyaline cartilage, a more complete cartilage structure, and lower Osteoarthritis Research Society International (OARSI) scores at 4weeks after ACLT. Irisin reduced the expression of matrix metalloproteinase (MMP)-13 in cartilage and caspase 3 in the subchondral bone. Irisin exerted rescue effects in microstructural parameters of subchondral trabecular bone including bone volume fraction (BV/TV), trabecular number (Tb.N), connection density (Conn. D), and the structure model index (SMI) compared with ACLT-vehicle group. Bone histomorphometry showed that irisin increased subchondral bone remodeling. The decreasing ratio (%) of the eroded surface (ES/BS) was reversed by irisin in the ACLT+vehicle group. Staining with tartrate-resistant acid phosphatase showed a decreased number of osteoclasts. Irisin significantly increased the proliferation of osteocytes, protected them from apoptosis, and maintained cellular activity by regulating the expression of Bax, Bcl-2, and osteoprotegerin/receptor activator of nuclear factor (NF)-kB-ligand (OPG/Rankl). Irisin activated serine/threonine-selective protein kinases (Erk) and p38 signaling, and its anti-apoptosis function depended on the Erk signaling pathway. Irisin attenuated OA progression by decreasing osteocyte apoptosis and improving the microarchitecture of subchondral bone. Activation of the Erk pathway by irisin plays an important role in reducing osteocyte apoptosis in vitro.

Estimating tissue-level properties of porcine talar subchondral bone

Tissue-level properties of bone play an important role when characterising apparent-level bone biomechanical behaviour and yet little is known about its effect at this hierarchical level. In combination with trabecular morphological data these properties can be used to predict bone strength, which becomes an invaluable tool for clinicians in patient treatment planning.This study developed specimen-specific micro-finite element (μFE) models using validated continuum-level models, containing grayscale-derived material properties, to indirectly establish tissue-level properties of porcine talar subchondral bone.Specimen-specific continuum finite element (hFE) models of subchondral trabecular bone were setup using μCT data of ten cylindrical specimens extracted from juvenile porcine tali. The models were validated using quasi-static uniaxial compression testing. Validated hFE models were used to calibrate the tissue modulus of corresponding μFE models by minimising the difference between the μFE and hFE stiffness values. Key trabecular morphological indices (BV/TV, DA, Conn.D, Tb.Th, EF) were evaluated.Good agreement was observed between hFE models and experiment (CCC = 0.66). Calibrated Etiss was 504 ± 37.65 MPa. Average BV/TV and DA for μFE specimens were 0.37 ± 0.05 and 0.68 ± 0.11, respectively. BV/TV (r2 = 0.667) correlated highly with μFE stiffness.The small intra-specimen variation to tissue-level properties suggests that variations to apparent-level stiffness originate from variations to microarchitecture rather than tissue mechanical properties.

Active Preservation of Osteochondral Graft under Cyclic Hydrostatic Pressure for Maintaining Cartilage Integrity and Subchondral Bone Quality

Objectives:Osteochondral allografts (OCA) are currently stored at 4˚C for an average of 24 days after procurement. However, chondrocyte viability, the major determinant of graft performance in-vivo, decreases and matrix integrity deteriorates with time under such conditions; for instance, chondrocyte viability falls below the acceptable level of 70% by 28 days. Hydrostatic pressure (HP) is a significant component in the mechanical loading environment and its application in vitro (0.5 - 15 MPa) elicited favorable effects on cartilage and bone. The purpose of this study was to investigate the effects of HP during osteochondral storage.Methods:Osteochondral (OC) explants (6x8 mm) were harvested from bovine humeral heads purchased from a local slaughterhouse (Fig. 1). OCs were randomly assigned to one of 4 groups: freshly harvested; stored at 4°C and atmospheric pressure (4˚C AP); stored at 37°C and AP (37˚C AP); and stored at 37°C with cyclic HP at 0-0.5 MPa, 0.5 Hz (37˚C HP). The explants were stored for 7, 14, 21, or 28 days in Dulbecco’s modified eagle medium/Ham’s nutrient mixture F12 (1:1), with antibiotics and with or without fetal bovine serum (FBS). Chondrocyte viability and density were assessed using LIVE/DEAD® staining in the entire tissue section and in the superficial, middle, and deep zones using the Image J program. In addition, we stained OC explants with safranin-O fast green; hematoxylin and eosin, sudan IV and antibodies against proliferating cell nuclear antigen (PCNA), keratan sulfate (KS). Furthermore, the microstructure and material composition of subchondral bone in the explants was quantified using micro-computed tomography (micro-CT, Scanco uCT 35) at a 12 micron nominal resolution.Results:Cartilage thickness was maintained at 37°C HP, significantly increased at 37°C AP and significantly decreased at 4°C AP (P < 0.05) with/without FBS at 28 days. Full-thickness chondrocyte viability was significantly higher at 21 and 28 days in the 37˚C HP group compared to 4°C or 37°C AP regardless of FBS (P<0.05). Specifically, chondrocyte viability in the superficial zone was maintained with 37˚C HP (Fig. 3) versus not in the other culture conditions. Cartilage matrices were similar between the conditions by 14 days (Fig. 4). However, surface fibrillation and degeneration were demonstrated in the 37 °C AP. KS seemed to be maintained in the superficial zone with HP by 28 days but decreased under other conditions (Fig. 5). More proliferating cells with 37°C HP were observed in the superficial zone compared to other conditions at 28 days. Utilization of FBS further increased the number of proliferating cells in each condition. The fatty granules were observed and distributed evenly throughout the subchondral bone and trabecular bone under all conditions at 28 days (Fig. 6). However, in the 4°C and 37°C AP groups, fewer fatty granules were observed in the subchondral bone and more fat in the trabecular bone (Fig. 6). Micro-CT evaluation revealed that the conditions produced similar tissue mineral density (Fig. 7). However, the trabecular number was significantly lower with 37°C AP compared to the other conditions (P<0.05).Conclusion:Osteochondral explants stored with 37°C HP maintained chondrocyte viability, histologically determined cartilage integrity, and subchondral bone quality.Figure 1.

Differences in subchondral trabecular bone microstructure and finite element analysis-based biomechanical properties between osteoporosis and osteoarthritis.

SummaryBackground/ObjectiveThe microstructure of the subchondral trabecular bone, including the composition and distribution of plates and rods, has an important influence on the disease progression and mechanical properties of osteoarthritis (OA) and osteoporosis (OP). We aimed to determine whether differences in plates and rods influence the variations in the quantities and qualities of the subchondral trabecular bone between OA and OP.Materials and methodsThirty-eight femoral head samples [OA, n = 13; OP, n = 17; normal control (NC), n = 8] were collected from male patients undergoing total hip arthroplasty. They were scanned using microcomputed tomography, and subchondral trabecular structures were analysed using individual trabecular segmentation. Micro-finite element analysis (μFEA) was applied to assess the mechanical property of the trabecular bone. Cartilage changes were evaluated by using histological assessment. Analysis of variance was used to compare intergroup differences in structural and mechanical properties and cartilage degradation. Pearson analysis was used to evaluate the relationship between the trabecula microstructure and biomechanical properties.ResultsCompared with the OP and NC group, there was serious cartilage damage in the OA group. With respect to the microstructure results, the OA group had the highest plate and rod trabecular microstructures including number and junction density among the three groups. For the mechanical properties detected via μFEA, the OA group had higher stiffness and failure load than did the OP group. Pearson analysis revealed that compared with OP, OA had a higher number of microstructure parameters (e.g., rod bone volume fraction and rod trabecular number) that were positively correlated with its mechanical property.ConclusionsCompared with OP, the OA subchondral bone has both increased plate and rod microarchitecture and has more microstructures positively related with its mechanical property. These differences may help explain the variation in mechanical properties between these bone diseases.The translational potential of this articleOur findings suggested that changes in the plates and rods of the subchondral trabecular bone play a critical role in OA and OP progression and that the improvement of the subchondral trabecular bone may be a promising treatment approach.