Veterinary Science Collected Works - Theses
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ItemResponse of subchondral bone and articular cartilage to joint surface incongruity: an equine osteochondral defect model( 2019)Many diseases and injuries of synovial joints result in a focal loss of articular surface congruity. These conditions are known to lead to degenerative changes within the affected joint and subsequent osteoarthritis (OA). Incongruity due to loss of articular cartilage is also a feature of OA itself. However there is little work specifically investigating how the tissues of a synovial joint respond to loss of congruity. The aim of this study was to observe how articular cartilage and subchondral bone (SCB) respond to a focal loss of surface congruity using an equine model. It was hypothesised that the degree of remodelling and bone volume of SCB is dependent on local loading of the overlying joint surface and that intact cartilage would respond to changes in local surface pressure in a way that attempts to restore congruity. An osteochondral defect was created in one surface of the midcarpal joint of six adult horses. Two weeks post-operatively the animals began an eight-week treadmill training program. Following this, osteochondral samples were collected from the site of the defect and immediately adjacent to it in the radial carpal bone (Cr), and from the unloaded site directly opposing the defect and a loaded site immediately adjacent to this in the third carpal bone (C3). Control samples were collected from equivalent sites in the sham-operated contralateral limb and from un-operated, untrained control animals. Undemineralised samples were imaged with microCT and backscattered scanning electron microscopy (BSEM) and stained with Masson’s Goldner trichrome to measure cartilage thickness and osteoid. Decalcified cryosections were stained for TRAP to identify osteoclasts. Cartilage was examined with routine histology and differential interference contrast microscopy. In SCB immediately below the Cr lesion in treated joints bone volume fraction (BV/TV) was 32% lower and bone formation and erosion were markedly increased, whereas in the deeper bone formation was increased, erosion activity became less prominent and BV/TV did not change. In the unloaded region of C3 opposing the defect in treated joints the hyaline cartilage (HC) was 50% thicker, while SCB displayed a mild increase in remodelling activity with a net decrease in BV/TV of 5.3%. In the loaded region adjacent to the lesion in Cr HC was 30% thinner in treated joints while there was no change in SCB parameters. At the loaded site of C3 the HC thickness was unchanged while the calcified cartilage in treated joints was 40% thicker than in controls. In the underlying SCB in treated joints there was a mild reduction in remodelling activity and unchanged BV/TV. In this equine osteochondral defect model the articular cartilage and SCB of adult synovial joints responded in a focal manner to changes in joint surface congruity. Local unloading due to a loss of surface contact resulted in thickened HC and, in the underlying SCB, increased remodelling activity and loss of bone volume. Focally increased loading resulted in thickened calcified cartilage and decreased SCB bone remodelling activity. These focal responses may play a role in normal joint homeostasis and in the pathogenesis of OA.