Histopathological findings in a representative joint in a long-term primate model of acquired hemophilia A. Left hip joint with limping in the vehicle #1 monkey (A-C) and left hip joint without limping in the ACE910 #3 monkey (D-F) are shown at original magnification ×5 (A, D), ×20 (B, E), and ×400 (C, F). Hemorrhagic changes (arrowheads) including hemosiderin deposition (arrows) and destruction of articular cartilage/underlying bone (*) are detected in the joint with limping (A-C). No hemorrhagic changes are noted in the joint without limping (D-F). Hematoxylin and eosin stain. Aca, articular cartilage of acetabulum; Hb, hip bone; Sm, synovial membrane.