Blood-induced synovitis as a murine model of human HS. Factor VIII-deficient mice were subjected to a controlled blunt trauma to the right knee joint to induce 2 (days 0 and 7) or 3 (days 0, 7, and 14) episodes of hemarthrosis one week apart. Sham injury was performed on the left knee at each time point. (A) Normal appearance of a right knee joint from a mouse killed on day 0, not having had hemarthosis. (B) Abnormal appearance of a right knee joint from a mouse killed on day 14 following 2 episodes of hemarthrosis. (C) Normal appearance of the left knee of a mouse killed on day 14 after sham injury. (D) A mouse killed on day 21 after 3 episodes of hemarthrosis. Hematoxylin and eosin-stained sections of murine knee joints. More than 20 mice have been evaluated in 4 different experiments with similar results. Images were acquired using a CK2 microscope (Olympus, Melville, NY), objective lenses 4×, 0.10 (A-B) or 10×, 0.25 (C-D), and a DP12 microscope digital camera system with DP-Soft acquisition software (Olympus).