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Good Results with Extra-Large, Press-Fit Cups for Acetabular Revision

Posted on: 11/30/1999
Sometimes, hip joint replacements come loose. When this happens, another operation may be needed. This is called a revision.

A total hip joint replacement has two parts. The top of the thighbone (femur) with the ball or head is one part. The other half is formed by the socket or cup, which fits into the hip socket, the acetabulum. When just the cup needs to be revised, the procedure is called acetabular revision. Many cup implants are held in place with cement. But during acetabular revision, the bone may be too smooth and too hard to accept cement.

In this study, an extra large cup was used without screws. The cup was pressed into the bone, which is why it's called a press-fit cup. The extra surface area gives the cup more contact area. A good fit means that no screws are needed to hold it in place. The friction between the bone and the cup helps cause bone growth. The cup becomes embedded into the bone. This can start to happen as early as two weeks after the revision.

Screws are avoided for many reasons. Screw heads may push into the cup and scrape against the ball portion of the implant. The screw holes leave spaces for tiny bits of metal to pass through. Any opening can leave the joint at risk for infection. When the screw gets loose, the cup can also move or migrate. Movement between the bone and the implant makes the joint unstable.

The authors of this study determined that extra large cups can be used with good results in cases of acetabular revision. Obtaining a good fit without needing screws avoids many problems.

Christian Obenaus, MD, et al. Extra-Large Press-Fit Cups without Screws for Acetabular Revision. In The Journal of Arthroplasty. April 2003. Vol. 18. No. 3. Pp. 271-277.

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