Macroscopic, microscopic and ultrastructural findings in experimental haemarthrosis of rhesus monkeys

The effects of a single episode of massive haemarthrosis in rhesus monkeys were studied morphologically. Autologous whole blood was injected into a femorotibial joint of 16 anaesthetized monkeys, equally divided into four groups and killed 7 days, 2, 3 and 6 months post injection (PI). Synovial membrane and articular cartilage were examined for macroscopic, microscopic and ultrastructural changes. Haemarthrosis was only evident in one monkey by 7 days PI. Slight yellow-brown discoloration of synovium and cartilage was evident in groups killed early after injection. Histologically, a hyperplastic and inflammatory reaction was present in the synovium at 7 days PI. Ultrastructural examination of synoviocytes in this group revealed numerous cytoplasmic vacuoles and prominent microplicae compatible with increased phagocytic activity. Erythrophagocytosis by synoviocytes was observed by light microscopy and confirmed by transmission EM. Results of scanning EM suggested that red cells might also pass through the synovial intima. Transmission EM also revealed mild degenerative changes in superficial chondrocytes. Rhesus monkeys reacted morphologically to haemarthrosis in the same way as dogs and rabbits, with mild morphological changes that resolved by 2 months PI.