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Acetabular component malposition
14%
90/666
Femoral component malposition
5%
34/666
Incompetent abductors
77%
510/666
Eccentric polyethylene wear
2%
14/666
Small femoral head
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In this case, abductor insufficiency was the indication for revision to a constrained liner.Constrained acetabular liners provide excellent stability but may limit motion and fail prematurely if placed in the wrong patient. They could be considered in the following situations: 1) cases with no identifiable cause for instability, 2) abductor deficiency, and 3) patients with neuromuscular disorders. While multiple studies have shown good short-term and long-term results, they should be considered an option of last resort due to the risks of fatigue failure and component dissociation.Bedard et al. performed a retrospective review of 148 constrained liners that were cemented into newly placed acetabular components. They found that there were no failures at the bone-implant interface, the 10-year acetabular component survival was 75%, and the 10-year survival free from dislocation was 88%. They concluded that constrained liner placement at the time of acetabular revision is a safe practice.Warschawski et al. performed a retrospective study comparing 114 cup revisions with uncemented constrained liner placement with 63 retained cups with cemented constrained liner placement. They found a 7.93% rate of cemented constrained liner failure, and an 8.77% rate of uncemented constrained liner failure at the final follow-up. They concluded that there is comparable survivorship between cemented and uncemented constrained liner placement; and that retaining the cup at the time of revision and cementing a constrained liner is a reasonable technique.Image A shows a patient with bilateral THA. On the left side, there is a metal-on-metal articulation. On the right side, there is a constrained liner.Incorrect answers: Answer 1 and 2: Malpositioned components should be revised first, before considering a constrained liner. In this case, the components appear to be reasonably positioned. Answer 4: There is no indication in this case that eccentric polyethylene wear is present. If it were, the correct surgery would be a liner exchange.Answer 5: Femoral head size is not an indication for constrained liner placement.
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