AbstractObjectiveCartilage of young but skeletally mature dogs is more susceptible to blood‐induced damage than that of old dogs. The aim of the present study was to investigate whether cartilage of skeletally immature individuals is even more adversely affected by exposure to blood than that of mature individuals, as suggested by clinical practice experience with humans.MethodsRight knees of 3 groups of 6 beagle dogs (skeletally immature, young mature, and old animals) were injected with autologous blood on days 0 and 2. On day 4, cartilage matrix proteoglycan turnover (content, synthesis, and release), synovial inflammation, and cartilage‐destructive properties of the synovial tissue were determined and compared with those of the left uninjected control knees.ResultsSubsequent to intraarticular bleeding, cartilage proteoglycan content decreased in an age‐dependent manner, with the largest decrease occurring in cartilage of immature animals. Proteoglycan synthesis per cell also decreased in an age‐dependent manner, with the largest decrease occurring in the immature animals. Cartilage proteoglycan release increased in all 3 groups, but the decrease was not age dependent. Interestingly, immature animals showed a large increase in cartilage DNA content upon exposure to blood, whereas mature animals did not. Histologic analysis showed a mild synovitis in animals of all ages, but catabolic inflammatory activity was found only in immature animals.ConclusionJoints of skeletally immature dogs appeared to be more susceptible than joints of mature dogs to the adverse effects of a joint hemorrhage. These data suggest that for humans, specifically young children are at risk for joint damage after a joint hemorrhage.