Advancement in the zone of calcified cartilage in osteoarthritic hands of patients detected by high definition macroradiography

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.

Cartilage degradation in osteoarthritis: A process of osteochondral remodeling resembles the endochondral ossification in growth plate?

Osteoarthritis (OA) is one of the most common degenerative disease which causes pain and disability of joint and brings heavy socioeconomic burden in the world. However, the pathogenesis of OA has not been fully understood. Articular cartilage degradation or loss was often regarded as the characteristic of osteoarthritis. But we believe that there may had a illusion that OA was simply considered to be a process of wear and tear because evidences have supported all joint tissues remodeling including cartilage, subchondral bone, synovium, ligament, fat pad, and etc, were engaged in OA, in particular the cartilage and subchondral bone. Many factors such as mechanics, inflammation and immunological abnormality could drive the joint tissues metabolic and disturb the steady state of cartilage and bone, which further devoted to a serial pathological manifestations, consisting of hypertrophy and apoptosis of articular chondrocytes, degradation of cartilage matrix, angiogenesis and calcification of hyaline cartilage, replication of tidemark, formation of osteophytes, degeneration of ligaments and, in the knee, the menisci, hypertrophy of the joint capsule and remodeling of subchondral bone along with increased permeability of the osteochondral interface. The thickening of calcified cartilage, the thinning of superficial hyaline cartilage and the remodeling of subchondral bone indicated that the cartilage degradation could be a procedure of enchondral ossification similar to the growth plate, of driven by a host of cytokines within the affected joint. Articular cartilage loses stable state from normal resting to a high turnover in the stimulation of abnormal mechanical stresses and cytokines would subsequently contributed to slowly sustained remodeling and calcification, which might be the key features of the initiation and development of OA. In this article, the development and structural comparison of articular cartilage and growth plate as well as the major pathologic features of OA will be discussed to explain that cartilage degeneration in OA might be a process of enchondral ossification similar to growth plate. This would provide a new perspective for understanding OA's pathogenesis and the treatment in the future.

Genome-wide association and functional studies identify a role for matrix Gla protein in osteoarthritis of the hand

OBJECTIVE

Osteoarthritis (OA) is the most common form of arthritis and the leading cause of disability in the elderly. Of all the joints, genetic predisposition is strongest for OA of the hand; however, only few genetic risk loci for hand OA have been identified. Our aim was to identify novel genes associated with hand OA and examine the underlying mechanism.

METHODS

We performed a genome-wide association study of a quantitative measure of hand OA in 12 784 individuals (discovery: 8743, replication: 4011). Genome-wide significant signals were followed up by analysing gene and allele-specific expression in a RNA sequencing dataset (n=96) of human articular cartilage.

RESULTS

We found two significantly associated loci in the discovery set: at chr12 (p=3.5 × 10-10) near the matrix Gla protein (MGP) gene and at chr12 (p=6.1×10-9) near the CCDC91 gene. The DNA variant near the MGP gene was validated in three additional studies, which resulted in a highly significant association between the MGP variant and hand OA (rs4764133, Betameta=0.83, Pmeta=1.8*10-15). This variant is high linkage disequilibrium with a coding variant in MGP, a vitamin K-dependent inhibitor of cartilage calcification. Using RNA sequencing data from human primary cartilage tissue (n=96), we observed that the MGP RNA expression of the hand OA risk allele was significantly lowercompared with the MGP RNA expression of the reference allele (40.7%, p<5*10-16).

CONCLUSIONS

Our results indicate that the association between the MGP variant and increased risk for hand OA is caused by a lower expression of MGP, which may increase the burden of hand OA by decreased inhibition of cartilage calcification.

Identifying Patient-Specific Pathology in Osteoarthritis Development Based on MicroCT Analysis of Subchondral Trabecular Bone

The goal of this study was to identify alternative mechanisms of osteoarthritis pathology by analyzing subchondral bone. Femoral condyle samples were collected from post-menopausal female patients with knee osteoarthritis undegoing total knee arthroplasty. In the majority of patients, subchondral trabecular bone volume doubled under a region of the medial femoral condyle with full-thickness cartilage deterioration. However, in a subset of patients the bone volume in this region remained constant. This subset also had larger areas of vascular penetration in the calcified cartilage of the lateral condyle concurrent with increased vascular endothelial growth factor expression. Subtyping by subchondral bone characteristics identified a unique population, which lacked the sclerotic bone characteristic of late-stage osteoarthritis. Identification of subtypes within the osteoarthritis population allows investigation of alternate disease pathologies.

Stereologic analysis of tibial-plateau cartilage and femoral cancellous bone in guinea pigs with spontaneous osteoarthritis

BACKGROUND

Two strains of guinea pig develop spontaneous osteoarthritis of the knee. Although the disease evolves at different rates in the two strains, it is not known whether these differences are reflected in the structure of the cartilage and cancellous bone.

QUESTIONS/PURPOSES

We determined whether the three-dimensional structure of the tibial-plateau cartilage and femoral cancellous bone differed between the two strains.

METHODS

Six Dunkin-Hartley and six GOHI/SPF guinea pigs were evaluated. The animals were sacrificed at 11 months of age. The 24 proximal tibias were used for a stereologic histomorphometric analysis of the tibial-plateau cartilage. The 24 femurs were used for a site-specific, three-dimensional quantitative analysis of the cancellous bone by micro-CT.

RESULTS

Compared to the GOHI/SPF guinea pigs, the tibial-plateau cartilage of the Dunkin-Hartley strain had a larger lesion volume (3.8% versus 1.5%) and a thicker uncalcified cartilage layer (0.042 versus 0.035 mm), but a thinner calcified cartilage zone (0.008 versus 0.01 mm) and a thinner subchondral cortical bone plate (0.035 versus 0.039 mm). The femoral cancellous bone in the Dunkin-Hartley strain had a lower bone mineral density (477 versus 509 mg/cm(3)). However, the trabeculae were thicker (3.91 versus 3.53 pixels) and farther apart (7.8 versus 5.6 pixels). The osteoarthritic changes in the cartilage were topographically mirrored in the subchondral bone. They were most severe on the medial side of the joint, particularly in the anterior region.

CONCLUSIONS

Spontaneous osteoarthritis in the guinea pig is associated with site-specific changes in the articular cartilage layer, which are topographically mirrored in the underlying subchondral bone.

CLINICAL RELEVANCE

Three-dimensional structural information not revealed by two-dimensional radiography may help characterize the stages of osteoarthritis.

Role of bone in osteoarthritis pathogenesis

Much of the attention in developing diagnostic tools and therapeutic interventions for the management of osteoarthritis (OA) has focused on the preservation or repair of articular cartilage. It is clear that all of the joint components, including the ligaments, tendons, capsule, synovial lining, and periarticular bone, undergo structural and functional alterations during the course of OA progression. This article focuses on the specific skeletal features of OA and the putative mechanisms involved in their pathogenesis.

Investigations in generalized osteoarthritis. Part 2: special histological features in generalized osteoarthritis (histological investigations in Heberden's nodes using a histological score)

OBJECTIVE

In accordance with the literature, our previous epidemiological, clinical and genetical investigations have confirmed a correlation between generalized osteoarthritis (GOA) and Heberden's nodes. Heberden's nodes can be considered as genetic markers for the existence of a generalized osteoarthritic predisposition. The present study's concern was to establish whether there are special histological features in this disease.

METHODS

Layered sections of 218 distal finger joints from 56 deceased persons were investigated using a histological-histochemical score modified by Mankin.

RESULTS

In Heberden's nodes, we found all the typical degradative sequences of the osteoarthritic process but also some specific modifications. The osteoarthritis (OA) starts with a subchondral ossification and manifests a reactive tidemark flaking. At this time, the surface of the cartilage is not yet destroyed. Later on, there is progression of general degradation. Significant differentiation from the control group is possible using a histological score.

CONCLUSIONS

In patients with Heberden's nodes, the OA starts with the subchondral ossification. Heberden's nodes are the specific manifestation of GOA in the distal finger joints. Further studies are therefore required to assess whether the same pathogenetic mechanism can be seen in OA of the large joints in GOA.

Cyclical articular joint loading leads to cartilage thinning and osteopontin production in a novel in vivo rabbit model of repetitive finger flexion

OBJECTIVE

An in vivo rabbit model of repetitive joint flexion and loading was used to characterize the morphological effects of cyclical loading on articular cartilage.

DESIGN

The forepaw digits of eight anesthetized New Zealand White adult female rabbits were repetitively flexed at 1 Hz with a mean peak digit load of 0.42 N for 2 h per day for 60 cumulative hours. Metacarpophalangeal joints were collected from loaded and contra-lateral control limbs, fixed, decalcified, embedded, and thin-sectioned. Serial sections were stained for histology or for immunohistochemistry. Morphometric data including the mean thicknesses of the uncalcified cartilage and of the calcified cartilage were collected from digital photomicrographs of safranin O-stained sections. The number of cells stained with anti-osteopontin antibody was counted.

RESULTS

We observed a decrease in uncalcified cartilage mean thickness with no significant change in calcified cartilage thickness. We also observed a significant increase in the number of cells positive for osteopontin (OPN) in the uncalcified cartilage. These changes occurred without overt cartilage surface degeneration.

CONCLUSIONS

Cyclical loading leads to changes at the tissue and cellular levels in articular cartilage. These changes are suggestive of tidemark advancement and may indicate a reactivation of cartilage mineralization steps analogous to endochondral ossification. This novel in vivo rabbit model of repetitive flexion and loading can be used to investigate the effects of cyclical loading on articular joints.

Subchondral bone changes in hand and knee osteoarthritis detected by radiography

OBJECTIVE

To describe the changes in subchondral bone that occur with the onset and progression of osteoarthritis (OA) from macroradiographic assessment of patient's hand and knee joints.

DESIGN

The high magnification and spatial resolution of macroradiography permits detailed anatomical changes to be detected in OA joints. Data on the subchondral cortical and cancellous bone, recorded from both cross-sectional and longitudinal studies of hand and knee OA, are described and discussed with reference to recent findings on the altered biomechanical properties of OA bone.

RESULTS

In OA joints, both subchondral cortical plate and subjacent horizontal trabeculae increase in thickness early, prior to joint space narrowing (JSN). With progression, cortical plate sclerosis increased in 60% of OA hands and did not change in knee OA until JSN <1.5mm in the medial diseased compartment. In knee OA, trabeculae, at sites of tibial subchondral sclerosis, increased in number and extent, changes that overlay a subarticular region that was osteoporotic. With cartilage loss, the articular surfaces in some knees appeared corrugated, and later, with bone-on-bone, the surfaces became flattened and deformed.

CONCLUSIONS

The weaker than normal bone within thickened subchondral cortical plate and trabeculae of OA joints leads, in advanced OA, to deformation of the articular surfaces and absorption of local stresses producing an effect similar to stress-shielding. This effect, it is suggested, results in the subarticular osteoporosis.

Macroradiography using conventional radiographic X-ray equipment

Macroradiography is a radiographic imaging technique used to increase the size of the image relative to that of the object. Macroradiographic images suffer degradation due mainly to geometric unsharpness (U(g)). U(g) results from the finite size of the focal spot of the X-ray tube. Specialized equipment with a small effective focal spot size (Eff FSS) is generally used to perform macroradiography. The specialized nature of the equipment means macroradiographic examinations are not commonly undertaken. Macroradiographic examinations can also be performed on conventional radiographic equipment because the Eff FSS varies in the X-ray beam along the cathode-anode axis. Calculations and measurements of FSSs at different positions along the cathode-anode direction of the X-ray beam have been made. A simple technique of angling the X-ray tube 10 degrees towards the cathode reduces the Eff FSS in one dimension while still maintaining a vertical central ray. Reduced beam coverage results from this technique and an increase in radiographic exposure is required to compensate for the anode heel effect. Macroradiographic images of line pair phantoms and a hand-wrist phantom, at various tube angles, have been obtained to compare image detail.