Answer
The pathologic-anatomic appearance progresses from joint hemorrhage to joint effusion; synovial hyperplasia; hemosiderin deposition in the synovium, cartilage, and bone; osteoporosis; erosion of subchondral bone; bone cysts; articular cartilage destruction; overgrowth of the epiphysis; joint contracture; and degenerative arthritis.
The disease tends to be asymmetric in its involvement. Approximately 50% of patients with hemophilia develop permanent changes in the joint. These chronic changes include thick synovial deposition, richly laden with hemosiderin. The synovial masses erode the juxta-articular cartilage and the subchondral bone (see the first image below). Invasion into the bone substance produces intraosseous cyst formation. Bleeding into the bone may rarely produce large, vacuolated spaces that are referred to as intraosseous pseudotumors. Similar blood masses may occur in the cortex and the soft tissues (see the second image below).

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Knee radiograph in a 37-year-old man with moderate factor IX hemophilia. This image shows bony excrescence on the lateral side of the femur is a hemophilic pseudotumor.
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Radiograph of the lower extremity of the 3-year-old daughter of the patient in the previous image. This image shows talar tilt. The girl not only inherited 1 diseased X chromosome with mild factor IX hemophilia from her father, but she also has Turner (XO) syndrome. The child's only X chromosome had the hemophilia gene.
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Magnetic resonance image from a patient with hemophilia. This image shows dark, synovial masses that erode the cartilage and produce subchondral cysts (arrows).
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Anteroposterior radiograph from a patient with hemophilia. This image demonstrates hemarthrosis with hemosiderin deposition. Note the irregularity of the articular surfaces and the presence of subchondral sclerosis with cysts. Image courtesy of Javier Beltran, MD.
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Lateral radiograph from the same patient as in the previous image. This image shows a large hemarthrosis that is distending the suprapatellar recess. Image courtesy of Javier Beltran, MD.
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Axial gradient-echo magnetic resonance image from a patient with hemophilia. This image demonstrates hemosiderin deposition in the synovium as hypointense material that outlines the joint capsule. Image courtesy of Javier Beltran, MD.
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Radiograph in a patient with hemophilia. This image depicts a pseudotumor that is deforming the cortex of the femur (arrow). Other ossified masses in the soft tissues (arrowheads) are probably soft-tissue pseudotumors.
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Sagittal magnetic resonance image of the ankle joint in a patient with hemophilia. This image shows extension of abnormal joint fluid from the ankle joint into the subtalar joint. Note the dark hemosiderin posterior to the subtalar fluid (arrow).
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Computed tomography scan of the pelvis in a patient with hemophilia. This image demonstrates a giant pseudotumor (a large expansile lytic lesion that involves the right iliac bone and extends into the sacrum, with inhomogeneous internal attenuation). Image courtesy of Javier Beltran, MD.
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Axial T2-weighted magnetic resonance image of the pelvis. This image demonstrates a large pseudotumor of the pelvis with sacral extension. Image courtesy of Javier Beltran, MD.
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Lateral elbow radiograph in a patient with hemophilia. This image shows an opaque joint effusion due to the presence of iron in the synovium (arrows).
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Radiograph of the ankle in a 20-year-old patient with hemophilia. This image shows the development of osteonecrosis (arrow) in the talar dome.
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Sagittal T2-weighted magnetic resonance image of the lower extremity in a patient with hemophilia. This image demonstrates hemosiderin-laden synovium with low signal intensity that outlines the capsule of the tibiotalar joint. Image courtesy of Javier Beltran, MD.
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Radiograph of the shoulder of a 35-year-old man with hemophilia. This image shows advanced degenerative joint disease. The infiltrate in the lung is due to a fungal infection as a complication of the patient's positive human immunodeficiency virus (HIV) status.
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Radiograph of the leg in a patient with hemophilia. This image depicts stage III joint disease, as determined by the Arnold-Hilgartner classification.
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Radiograph of the leg in a patient with hemophilia. This image depicts stage IV joint disease, as determined by the Arnold-Hilgartner classification.
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Coronal T2-weighted magnetic resonance image of the knee in a patient with hemophilia. This image demonstrates pseudotumor of the knee, a lytic lesion in the lateral femoral condyle, as well as the characteristic manifestations of hemosiderin deposition in the knee joint and the subchondral cystic changes in the medial femoral condyle. Image courtesy of Javier Beltran, MD.