| Osteoarthritis and subchondral cystic lesions in the equine medial femorotibial joint, lead to lameness and wastage. It is unknown whether a single trauma can initiate these alterations. Our goal was to characterize cartilage injury threshold in the equine medial femoral condyle and to determine if a focal, contusive injury would progress to osteoarthritis.; Threshold values for cartilage degeneration were determined using ex vivo osteochondral explants. Impact injuries were created and chondrocyte viability was assessed daily using live/dead staining methods.; Ten horses received impact injuries. Short-term horses (n=5) were followed for 84 days, long-term horses (n=5) for 180 days. Synovial fluid was collected on days 14, 28, 42, 56, 84, 112, 140, 168 and 180. Synovial fluid and cartilage sulphated glycosaminoglycan concentrations were measured. Radiographic and lameness evaluations were completed. Cartilage damage was scored macroscopically and histologically. TdT-mediated dUTP nick end-labeling (TUNEL) and type II collagen immunohistochemical staining was performed.; Explants demonstrated superficial chondrocyte injury between 15-30 MPa similar to controls. At 50-60 MPa there was significant chondrocyte injury in the superficial and radial zones, as well as adjacent to fissures. Chondrocytes did not recover (3 day culture).; Horses had mild lameness but no radiographic abnormalities. Mean synovial fluid sulphated glycosaminoglycan concentration demonstrated a significant decrease on days 14, 28, 42 and 56. Cartilage sulphated glycosaminoglycan concentration was significantly decreased at the impact site. Macroscopic and histologic examination revealed focal, severe cartilage loss (approximately 5 mm), with centrifugal progression of abnormalities. Subchondral cystic lesions were not observed. All horses showed increased TUNEL and type II collagen immunohistochemical staining.; Our model reproduces many features of post-traumatic osteoarthritis reported in other species, though threshold values for cartilage injury are higher. Lesions appear similar to those in naturally-occurring disease, supporting the hypothesis that a single, focal traumatic injury can lead to initiation and progression of osteoarthritis in the equine medial femorotibial joint. Decreased synovial fluid sulphated glycosaminoglycan concentration revealed that markers of cartilage degeneration can identify early cases of osteoarthritis. Analysis of more specific biomarkers is warranted. This model may be useful for assessment of diagnostic, preventive and therapeutic strategies in posttraumatic osteoarthritis. |
