Veterinary Science - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemInvestigation of the osteochondral response to injury in racing Thoroughbreds( 2013)For prevention and appropriate treatment of subchondral bone (SCB) injuries a thorough understanding of the prevalence, pathogenesis and repair mechanisms of the condition are mandatory. Palmar/plantar osteochondral disease (POD) is a SCB fatigue injury in racehorses that occurs with a high prevalence. There is limited quantitative data on the role of microfractures, osteocyte death, modelling, remodelling, loading intensity and unloading on SCB injury (SCBI) and repair. The association between articular cartilage and SCB injuries in this condition is not well understood. Qualitative associations have been established between SCBI, modelling and remodelling and it has been speculated that modelling and remodelling may contribute to injury by creating brittle and/or porotic bone or stiffness gradients within bone. To better understand the pathogenesis of SCBI and its association with loading intensity, the injury and bone response to injury (resorption and formation) were quantified and their associations with recent and life-time exercise intensity were investigated in a cross-sectional study. It was also intended to study if resting from training had an effect on removal of microdamage from SCB. It was hypothesized that SCBI occurs prior to cartilage damage, is consistent with bone fatigue and therefore is associated with the history of exercise duration and intensity. According to second hypothesis the response of bone to injury could contribute to the pathogenesis of SCBI. Fore- and hind limbs from two separate groups of Thoroughbred racehorse cadavers were collected at post-mortem and severity of POD was graded 0-3. Forelimbs from 38 horses were examined using high-resolution peripheral quantitative CT, back scattered electron microscopy and histomorphometry. Also, hind limbs from 46 horses were collected for histomorphometry using cryosections, 1 µm thick resin embedded sections and transmission electron microscopy. Of the forelimb cohort 65.8% of horses had some degree of POD and 30.7% of horses had at least one Grade 2-3 lesion. In hind limbs 57.8% had at least one POD lesion of any severity and 24.4% had grade 2-3 lesions. The majority of horses had some degree of SCB microfracture or osteocyte loss. SCB microfractures were present in all grades of the disease whereas significant cartilage changes were limited to grade 3 lesions. SCB lesions were characterised by accumulations of microfractures, osteocyte loss in the affected area, sclerosis of the surrounding trabecular bone, focal resorption of superficial SCB, and in grade 3 lesions, articular surface attrition (collapse). Short term rest was associated with greater focal bone resorption which in some cases was concentrated in the immediate SCB leading to loss of support of the overlying cartilage and subchondral plate. The severity of macroscopic and microscopic lesions correlated with age and indicators of the accumulation of training distance. In conclusion, SCB appears to respond to fatigue injury in a similar manner to cortical bone i.e. sclerosis in the surrounding bone accompanies localised resorption at the site of damage. It is unclear whether focal resorption at the site of fatigue injury contributes to further bone fatigue however, bone resorption accelerates when horses are rested from training and this appears to contribute to collapse of the articular cartilage into the SCB. SCB was the primary site of the injury and articular cartilage changes were only associated with severe injuries where SCB attrition had occurred. A better understanding of the effects of training and rest on bone turnover rate is required to reduce the accumulation of SCB fatigue damage that occurs throughout the careers of equine athletes.