Bone and Soft-Tissue Disorders
= X-linked deficiency / functional abnormality of coagulation factor VIII (= hemophilia A) in >80% / factor IX (= hemophilia B = Christmas disease)
Prevalence: 1÷10,000 males
Hemophilic Arthropathy (most common) 
Cause: repeated bleeding into synovial joint
Path: pannus formation erodes cartilage with loss of sub-chondral bone plate and formation of subarticular cysts
Histo: synovial hyperplasia, chronic inflammatory changes, fibrosis, siderosis of synovial membrane
Age: 1st and 2nd decade
- tense red warm joint with decreased range of motion ← muscle spasm; fever, elevated WBC (DDx: septic arthritis)
Location: knee >ankle >elbow >shoulder; commonly bilateral although bleeding episodes tend to recur within same joint
- joint effusion (= hemarthrosis)
- enlargement of epiphysis ← synovial inflammation with hyperemia)
- juxtaarticular osteoporosis ← synovial inflammation with hyperemia
- joint space narrowing (particularly patella) ← cartilaginous denudation
- erosion of articular surface with multiple subchondral cysts
- sclerosis + osteophytosis ← superimposed degenerative joint disease
- Knee
- “squared” patella
- widening of intercondylar notch
- flattening of condylar surface
- medial “slanting” of tibiotalar joint
MR:
- low SI of hypertrophied synovial membrane on all pulse sequences ← magnetic susceptibility effect of hemosiderin
- varying intensity of subarticular defects (depending on substrate: fluid / soft tissue / hemosiderin)
= posthemorrhagic cystic swelling within muscle + bone characterized by pressure necrosis + destruction
- juvenile form = usually multiple intramedullary expansile lesions without soft-tissue mass in small bones of hand / feet (before epiphyseal closure)
- adult form = usually single intramedullary expansile lesion with large soft-tissue mass in ilium / femur
- soft-tissue involvement of retroperitoneum (psoas muscle), bowel wall, renal collecting system
- mixed cystic expansile lesion
- bone erosion + pathologic fracture
CT:
- sometimes encapsulated mass containing areas of low attenuation + calcifications
MR:
- hemorrhage of varying age
Cx: joint contracture (after repeated bleeding into muscle)
N.B.: Needle aspiration / biopsy / excision may cause fistulae / infection / uncontrolled bleeding!
Rx: palliative radiation therapy (destroys vessels prone to bleed) + transfusion of procoagulation factor concentrate