Protrusio acetabuli

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Protrusio acetabuli is an uncommon defect of the acetabulum. The acetabulum is the socket that receives the femoral head to make the hip joint. It is composed of three bones, the ilium, the ischium and the pubis. The socket is too deep and may protrude into the pelvis.

Right sided Protrusio acetabuli


Protrusio acetabuli is divided into two types, primary and secondary.

Primary protrusio acetabuli

  • Characterized by progressive protrusio in middle aged women
  • May be associated with OA
  • May be familial

Secondary protrusio acetabuli

Causes include:

may be present bilaterally in paget's, marfan's, RA, AS, & osteomalacia;

Signs and Symptoms

  • May be asymptomatic
  • Limitation of joint range of movement is the earliest sign
  • Pain

Natural course

The protrusio may progress until the femoral neck impinges against the pelvis.


Diagnosis is made on the basis of an anteroposterior radiograph of the pelvis that demonstrates a center-edge angle greater than 40 degrees and medialisation of the medial wall of the acetabulum past the ilioischial line.


Joint replacement surgery is indicated for severe pain or substantial joint restriction


J Am Acad Orthop Surg, Vol 9, No 2, March/April 2001, 79-88.

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