F8^em1−/− mice spontaneously develop HA. (A) Visual representation of hind legs from F8^em1−/− mouse without bleed (no bleed) and with spontaneous acute (middle) and chronic bleed (right). Arrow shows knee patella. (B-D) Histological analysis of mouse hind knee joints of F8^em1−/− mice without or with joint bleeds. Knee joints were stained with Prussian blue staining (B), showing hemosiderin deposition (indicated by arrow) and scoring. (C) Hematoxylin and eosin (H&E) staining for synovial hyperplasia and inflammation (synovium indicated by x----x) and synovitis scores; (D) Safranin O staining for cartilage (red) and degradation scoring. The scale bars represent 500 μm (Prussian blue and H&E) and 200 μm (safranin O). Data are from 5 to 9 mice per group.