The radiograph taken in the emergency department (A) showed the femoral head to be eccentric in the acetabulum, although a previous radiograph (B) had shown it in a stable position.

AAOS Now

Published 12/1/2011

What’s your diagnosis?

In this feature, AAOS Now publishes a series of images, challenging readers to diagnose the condition depicted. The images for this month’s challenge were submitted by Stuart J. Fischer, MD, who provided the following information:

The patient is a 63-year-old man, who had a total hip arthroplasty 18 years ago. He was seen in the emergency department after experiencing a sudden snap in his hip, inability to bear weight, and a feeling that his hip was giving way. Prior to the episode he reported having mild pain but no mechanical symptoms and was able to walk without difficulty.

A radiograph taken in the emergency department showed the femoral head to be eccentric in the acetabulum. A previous radiograph had shown the femoral head in a stable position. What’s your diagnosis?

Do you have a challenging case you’d like to submit for publication? Email a short case description and any accompanying images to aaoscomm@aaos.org

The radiograph taken in the emergency department (A) showed the femoral head to be eccentric in the acetabulum, although a previous radiograph (B) had shown it in a stable position.
Although not common, a fracture of the polyethylene liner can result from progressive long term wear, most often at the superior edge of the acetabulum.

Find the answer to this month’s challenge below

Open larger version of images (PDF)

Answer
According to Stuart J. Fischer, MD, who submitted the case, the patient was diagnosed with a fracture of the polyethylene liner. Dr. Fischer reports that polyethylene fractures are unusual but can result from progressive, long-term wear. They most often occur at the superior edge of the acetabulum. Mechanical factors believed to contribute include the following: vertical cup position placing increased stress on the superior edge; femoral neck impingement; failure of the locking mechanism causing the polyethylene to loosen in the metal shell; and liner design with thin polyethylene at the rim.

Do you have a challenging case you’d like to submit for publication? Email a short case description and any accompanying images to aaoscomm@aaos.org