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Surgeons should recognize limits of large uncemented sockets in revision cases
Good circumferential acetabular exposure and rigid internal fixation are keys to good outcomes.
Large, uncemented acetabular cups can provide reliable and durable fixation for revision cases, but surgeons should be aware of the technical limitations of these components.
“In most situations, in the face of a failed acetabular component, an uncemented hemisphere is going to be your workhorse, and that’s true for cavitary defects, segmental and combined deficiencies,” Robert T. Trousdale, MD, said.
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Obtaining rigid internal fixation is a key component to achieving successful fixation in revision cases using large, uncemented sockets.
“You want sufficient contact with native bone to allow long-term biologic fixation of the uncemented hemisphere to the bone,” Trousdale said.
However, he noted that the exact amount of necessary bone contact remains an issue of debate.
“Certainly, for large cups with less than 50% host bone contact, it’s certainly sufficient if the bone contact is in key portions about the socket,” Trousdale said. “So even if you’ve got 60% to 70% bone loss, if you’ve got a good peripheral dome, a periphery and a reasonable dome and a reasonable posterior column, I think we can very reasonably go below the 50% contact rule. And certainly, how much contact you need may vary by the material that the cup is made of.” He made his comments during his presentation at the recent Current Concepts in Joint Replacement meeting.
Acetabular exposure
Having good circumferential acetabular exposure is also essential, and surgeons should remove any remaining membrane and cement at the base of the socket, Trousdale said. He uses a reamer to create a hemisphere of support bone to prevent the socket from migrating medially.
“Be careful not to ream too medially,” he said. “I usually just let the reamer work the rim, and gently ream until you get dome or medial wall contact.”
One technical error when performing revisions with uncemented cups involves failing to select adequately large sockets. Trousdale said surgeons should achieve a press fit if possible and warned against reaming the posterior wall and column.
“It’s debatable in the primary setting, but in the revision setting, I think that you want to use an uncemented hemisphere with screw holes. I like to put in as many screws as possible to maximize the secondary fixation of the socket,” he said.
Not ideal for massive defects
While surgeons can use these components for a variety of revision situations, Trousdale said the uncemented sockets are not useful for treating massive defects with limited host bone and pelvic discontinuity cases.
“An uncemented hemisphere in the face of a pelvic discontinuity is probably inadequate,” he said. “So, using uncemented hemispheres with screws distally and proximally is probably not enough fixation of the discontinuity. Our treatment of choice in those patients would be to stabilize the pelvis with plates, an uncemented hemisphere and occasionally a cage on top of that reconstruction.”
In addition, the components may not be beneficial for cases with marked pathologic bone.
“If you’ve got dead bone secondary to pelvic radiation, certainly an uncemented hemisphere alone is not going to work for that reconstruction,” Trousdale said.
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Images: Trousdale RT |
For more information:
- Robert T. Trousdale, MD, can be reached at Mayo Clinic, 200 First St. SW E14B, Rochester, MN 55905; 507-284-3663; e-mail: trousdale.robert@mayo.edu. He has no direct financial interest in any products or companies mentioned in this article.
Reference:
- Trousdale RT. The jumbo cup: The 95% solution. #97. Presented at the 8th Annual Current Concepts in Joint Replacement Spring 2007 Meeting. May 20-23, 2007. Las Vegas.