August 21, 2009

Importance of Visualization of Normal Acetabular Landmarks

Author: Aasis Unnanantana, M.D.

Figure 1: Pelvic radiograph (AP) shows a displaced left femoral neck fracture (arrow) in an old woman who fell.

Do you see anything else?

What normal bony structures do you expect to see in the acetabulum?
  • Iliopectineal line
  • Ilioischial line (Kohler's line)
  • Acetabular roof (dome) or sourcil
  • Radiographic teardrop
  • Anterior wall
  • Posterior wall

In this case, there is bowel gas overlying the left hemipelvis - making it difficult to assess. However, normal anatomic landmarks of the left acetabulum and pelvis are not visualized.

Same figure, with an outline of "non-visualized" acetabulum and left hemipelvis due to involvement of lytic metastasis. The patient also has a history of known renal cell carcinoma. Findings were confirmed on a CT scan.

Take Home Messages
  • When normal radiographic features of acetabulum are not visualized on conventional radiographs, further imaging should be considered (e.g. additional radiographic views such as obliques, or CT) to assess the particular structures.
  • Be aware of "satisfaction of search".
Barrack RL, Booth Jr RE, Lonner JH, et al (eds). Orthopedic Knowledge Update: Hip and Knee Reconstruction 3. 2006
Line art: Rathachai Kaewlai, MD

About Guest Author: Dr. Aasis Unnanantana, MD, is a clinical fellow in orthopedics (Metabolic Bone Diseases Service) at the Hospital for Special Surgery, Cornell University, New York, NY. He is a member of orthopedic instructor at Siriraj Hospital, Mahidol University, Bangkok, Thailand.

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