Learning Radiology xray montage

Acetabular Protrusio
Protrusio Acetabuli

General Considerations

  • Intrapelvic displacement of the medial acetabular wall
  • Most common cause is osteoarthritis
  • Primary form – Otto pelvis
    • Marked female to male predominance
    • Usually occurs in young to middle-aged
    • Bilateral in 1/3 to 2/3 of patients
    • No underlying causative mechanism is demonstrated
  • Secondary form
    • Rheumatoid arthritis
    • Paget disease
    • Central fracture-dislocation
    • Hip implants
    • Marfan Syndrome
    • Osteomalacia

Clinical Findings

  • May be asymptomatic, or have
  • Limitation of motion
  • Joint stiffness
  • Pain

Imaging Findings

  • Bilateral axial migration of the femoral heads with or without moderate degenerative changes
  • Distance between the acetabulum and the ilioischial line should be >3 mm in males and >6 mm in females in protrusio
  • Femoral head should not project medial to a line joining the inner border of the pelvis and the lateral margin of the obturator foramen


  • Coxa vara and decreased femoral anteversion


  • Depends on age and degree of degenerative changes
  • Medial wall bone grafts
  • Joint replacement surgery may be necessary

Acetabular Protrusio

Acetabular Protrusio. There is bilateral acetabular protrusio White arrows). The femoral head should not extend medial to a line drawn from the lateral aspect of the pelvis and the lateral aspect of the obturator foramen (blue line). The distance between the acetabulum and the ilioischial line (yellow arrow) should not be > 3mm in males and >6 mm in females.
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Protrusio Acetabuli. CC Dunlop, CW Jones, and N Maffulli. Bulletin, Hospital for Joint Diseases Volume 62, Numbers 3 & 4 2005