Long-term periarticular bone adaptation in a feline knee injury model for post-traumatic experimental osteoarthritis

A role for subchondral bone changes in the process of osteoarthritis; a micro-CT study of two canine models

BACKGROUND

This study evaluates changes in peri-articular bone in two canine models for osteoarthritis: the groove model and the anterior cruciate ligament transection (ACLT) model.

METHODS

Evaluation was performed at 10 and 20 weeks post-surgery and in addition a 3-weeks time point was studied for the groove model. Cartilage was analysed, and architecture of the subchondral plate and trabecular bone of epiphyses was quantified using micro-CT.

RESULTS

At 10 and 20 weeks cartilage histology and biochemistry demonstrated characteristic features of osteoarthritis in both models (very mild changes at 3 weeks). The groove model presented osteophytes only at 20 weeks, whereas the ACLT model showed osteophytes already at 10 weeks. Trabecular bone changes in the groove model were small and not consistent. This contrasts the ACLT model in which bone volume fraction was clearly reduced at 10 and 20 weeks (15-20%). However, changes in metaphyseal bone indicate unloading in the ACLT model, not in the groove model. For both models the subchondral plate thickness was strongly reduced (25-40%) and plate porosity was strongly increased (25-85%) at all time points studied.

CONCLUSION

These findings show differential regulation of subchondral trabecular bone in the groove and ACLT model, with mild changes in the groove model and more severe changes in the ACLT model. In the ACLT model, part of these changes may be explained by unloading of the treated leg. In contrast, subchondral plate thinning and increased porosity were very consistent in both models, independent of loading conditions, indicating that this thinning is an early response in the osteoarthritis process.

Microstructural adaptation in trapezial bone due to subluxation of the thumb

Although the thumb saddle is one of the most common sites of degenerative osteoarthritis in the hand, little is known about the altered microstructure in osteoarthritic trapezial bones. External forces resulting from subluxation of the carpometacarpal joint of the thumb (CMC I) should provoke microstructural changes in the trapezium. The purpose of this study was to compare the regional differences of the microstructure between osteoarthritic and healthy trapezial bones. Fifteen trapezia harvested from female patients with radiologically and clinically diagnosed saddle joint osteoarthritis (OA) were compared with 15 unaffected controls. Microstructural parameters, such as bone volume ratio (BV/TV), three-dimensional connectivity (Conn.D), trabecular number (Tb.N), and trabecular thickness (Tb.Th) were studied using a microcomputed tomography (microCT) system. While the trapezial height in OA was 22% less, the sclerotic subchondral bone layer thickness was 50% higher in OA compared with the control group (p < 0.001). In the OA group there was a 42% higher bone volume ratio (p <or= 0.001), an 18% increase in Tb.Th (p = 0.006), and a 10% greater Tb.N (p = 0.034) compared with the control group. Although in both groups BV/TV was significantly lower in the radial region, the radial column showed the highest relative increase in bone volume and structure compared with the control group (+67% BV/TV, +20% Tb.Th, +23% Tb.N). The reinforcement of the bony microstructure in CMC I OA, especially at the radial side, is a sign for bone adaptation reacting to radially shifted joint forces. This has to be considered during the development of new prosthetic alternatives.

Diagnostic value of micro-CT in comparison with histology in the qualitative assessment of historical human postcranial bone pathologies

Micro-computed tomography (muCT) is of great interest for palaeopathological examination because it is less invasive than histology. This study evaluates the diagnostic value of muCT for postcranial macerated bones. We investigated five specimens (osteomyelitis, tuberculosis, trauma, osteosarcoma and hypertrophic osteoarthropathy) of a pathology reference series by muCT and polarised light microscopy. The 3D muCT images allow an easy orientation within the specimen. Surface structures, thickness, continuity of the cortex and number, thickness and orientation of the trabeculae can be evaluated. The high number of muCT slices helps to choose the most interesting areas for further investigations. Grey value images display the degree of mineralisation. Yet, the differentiation between woven and lamellar bone is only possible using polarised light microscopy. muCT is a tool of high value for the examination of postcranial bone disorders. It cannot replace histological examinations completely because it cannot assess the bone quality (woven or lamellar). For the choice of the optimal location where slices for the microscopic investigation are later cut in heterogeneous samples, muCT is very useful. Therefore, we suggest performing the muCT examination first, followed by histology if necessary.

Forced mobilization accelerates pathogenesis: characterization of a preclinical surgical model of osteoarthritis

Preclinical osteoarthritis (OA) models are often employed in studies investigating disease-modifying OA drugs (DMOADs). In this study we present a comprehensive, longitudinal evaluation of OA pathogenesis in a rat model of OA, including histologic and biochemical analyses of articular cartilage degradation and assessment of subchondral bone sclerosis. Male Sprague-Dawley rats underwent joint destabilization surgery by anterior cruciate ligament transection and partial medial meniscectomy. The contralateral joint was evaluated as a secondary treatment, and sham surgery was performed in a separate group of animals (controls). Furthermore, the effects of walking on a rotating cylinder (to force mobilization of the joint) on OA pathogenesis were assessed. Destabilization-induced OA was investigated at several time points up to 20 weeks after surgery using Osteoarthritis Research Society International histopathology scores, in vivo micro-computed tomography (CT) volumetric bone mineral density analysis, and biochemical analysis of type II collagen breakdown using the CTX II biomarker. Expression of hypertrophic chondrocyte markers was also assessed in articular cartilage. Cartilage degradation, subchondral changes, and subchondral bone loss were observed as early as 2 weeks after surgery, with considerable correlation to that seen in human OA. We found excellent correlation between histologic changes and micro-CT analysis of underlying bone, which reflected properties of human OA, and identified additional molecular changes that enhance our understanding of OA pathogenesis. Interestingly, forced mobilization exercise accelerated OA progression. Minor OA activity was also observed in the contralateral joint, including proteoglycan loss. Finally, we observed increased chondrocyte hypertrophy during pathogenesis. We conclude that forced mobilization accelerates OA damage in the destabilized joint. This surgical model of OA with forced mobilization is suitable for longitudinal preclinical studies, and it is well adapted for investigation of both early and late stages of OA. The time course of OA progression can be modulated through the use of forced mobilization.

Animal models of osteoarthritis: lessons learned while seeking the "Holy Grail"

PURPOSE OF REVIEW

Difficulties in studying osteoarthritis in humans that stem from both the low sensitivity of diagnostic tools and the low availability of diseased tissues explain why research on animal models remains highly dynamic. This review will summarize the recent advances in this field.

RECENT FINDINGS

With regard to the etiology of osteoarthritis, synovial macrophages mediate osteophyte formation, whereas increased ligament laxity could be responsible for spontaneous osteoarthritis in guinea pigs. The concomitant changes in subchondral bone and cartilage reported in several models, and the structure-modifying effects of some bone inhibitors have confirmed the importance of bone in osteoarthritis. With regard to cartilage pathobiology, ADAMTS-5 is the major aggrecanase responsible for cartilage destruction, whereas inadequate control of oxidative stress and decreased expression of transforming growth factor-beta receptors could predispose to osteoarthritis. New models include a postmenopausal rat model, the groove model and a joint-specific bone morphogenetic receptor-deficient mouse. The iodoacetate model was also validated as the first pain model of osteoarthritis.

SUMMARY

In view of the multiple animal models available, there is a need to reach a consensus on one or several gold standard animal model(s). New studies indicate that important differences in therapeutic response exist between young and old animals, and between spontaneous and surgical models, suggesting that not all models are adequate models of osteoarthritis.

Considerations on Joint and Articular Cartilage Mechanics

When studying joint degeneration leading to osteoarthritis (OA), it seems imperative that local joint tissue loading is known during normal everyday movement and that the adaptive/degenerative effects of this loading are quantified systematically. Philosophically, we believe the best way to approach this problem is by studying joint degeneration and osteoarthritis in long-term experimental models and by representing diarthrodial joints and the associated tissues with accurate, geometric and structural, theoretical models. Here, we present selected examples of our work representing this approach. Experimentally, we demonstrate that the local loading of joints changes continuously in experimental models of OA, not only because of the changing external and internal loading, but also because of the continuous alterations in joint contact geometry and tissue mechanical properties. Furthermore, we show that single bouts of joint loading affect gene expression, and that gene expression, as well as subsequent joint degeneration is site-specific. In fact, opposing articular surfaces that are exposed to the same loading may degenerate at completely different rates. Finally, we propose a series of theoretical models of articular cartilage and contact mechanics, demonstrating that many of the anisotropic and inhomogeneous properties can be explained by structural elements and their orientation and volumetric concentration across the tissue.

Changes in Bone Microarchitecture and Bone Mineral Density following Experimental Osteonecrosis of the Hip in Rabbits

BACKGROUND

Osteonecrosis of the femoral head is a common disorder which can lead to hip joint destruction usually necessitating total hip replacement.

METHODS

Quantitative micro-computed tomography, digital radiography and histology were used to characterize changes in bone microarchitecture and bone mineral density during the repair of the osteonecrotic femoral head as well as during the development of secondary osteoarthritis in the ipsilateral acetabulum. Osteonecrosis was induced surgically in 17 adult, male rabbits and the contralateral side was used as control.

RESULTS

At 4 weeks no changes in microarchitecture in the femoral head nor in the acetabulum were found. At 6 months the repair process led to an increase in bone mass in the trabecular region of the femoral head. However, a decrease in volumetric bone mineral density and an increase in apparent porosity were seen in the compact subchondral and cortical region of the osteonecrotic femoral head. At 6 months the subchondral bone of the osteoarthritic ipsilateral acetabulum was thicker, but had a lower volumetric bone mineral density and a higher apparent porosity.

CONCLUSION

Resorption of necrotic compact bone may weaken the structural properties of the femoral head. Moreover, remodeling and resorption of subchondral bone may play a critical role in the disease process of osteoarthritis.