RESUMO
A slowly progressive osteoarthritis model in the skeletally immature canine knee joint is described. Forty-four young female beagle dogs were chosen as experimental animals. In 15 dogs, a 30 degrees valgus angulation of the right tibia was created by operation. Fourteen dogs underwent sham operation. Fifteen dogs served as control subjects. Alterations in the knee joints were evaluated macroscopically and histologically 7 and 18 months after operation. Seven months after surgery, two of seven beagles that had valgus osteotomy had a lesion with discoloration of cartilage in the medial condyle of the femur. Eighteen months after operation, five of the eight dogs that had valgus osteotomy showed fibrillation of the femoral and tibial cartilages. Mankin's scoring of the knee joint cartilages indicated statistically significant changes as compared with control subjects 7 and 18 months after surgery. Biomechanical analysis revealed shift of the mechanical axis toward the lateral compartment of the knee by the valgus osteotomy, patellofemoral malalignment, and inclination of the tibiofemoral joint line. These biomechanical alterations brought about the most severe cartilage lesions to the medial condyle of the femur and the patellofemoral joint. Cartilage fibrillation took more than 7 months to develop. Thus, this model offers a slowly progressive, well standardized, and reproducible method for the study of early changes of osteoarthritis in young beagle dogs.