Acute hemarthrosis model. (A) Difference between the knee diameter 72 hours after the injury and before the injury in F8^−/−Pros1^+/+, F8^−/−Pros1^+/−, F8^−/−Pros1^−/−, and F8^+/+Pros1^+/+ mice. (B) Microscopic evaluation (Masson’s trichrome stain and immunostaining for insoluble fibrin) of the knee intra-articular space of a representative, uninjured leg and injured leg after 72 hours in F8^+/+Pros1^+/+, F8^−/−Pros1^+/+, and F8^−/−Pros1^−/− mice. (C) In vivo mPS silencing using specific siRNA: evaluation of the joint diameter 72 hours after injury in F8^−/−Pros1^+/− and F8^−/−Pros1^+/+ mice treated with a single intraperitoneal infusion of mPS siRNA or control siRNA. (D) Microscopic evaluation (Masson’s trichrome stain) of the knee intra-articular space of a representative injured leg after 72 hours in F8^−/−Pros1^+/+ mice previously treated with mPS siRNA or control siRNA. Arrowheads on Masson’s trichrome staining indicate red blood cell extravasation, whereas in the immunohistochemistry, they indicate the deposit of insoluble fibrin. Measurements are presented as means ± SEMs. *P < .05; **P < .005; ****P < .0001. ctrl, control; n.s., not significant. Scale bars: 200 μm.