Friday, March 12, 2004
Constrained acetabular liners are highly subject to mechanical overload, but potential complications resulting from their use may be minimized by reducing prosthetic impingement, modifying liner design and avoiding technical errors, according to researchers for Poster Exhibit P043.
The increasing use of constrained acetabular liners has produced a number of unique complications. This study aimed to identify mechanisms of failure using these liners and recommended strategies to avoid them.
From a pool of 240 hips treated with constrained liners for recurrent or intraoperative instability, 27 patients (29 hips) who experienced an initial failure of the constrained acetabular construct were studied. Eight of these patients had a second recurrent failure of the constrained liners (total of 37 failures).
Clinical, implant retrieval and radiographic data were reviewed retrospectively. The time to failure ranged from 0 to 69 months.
The study indentified four key modes of failure among the 37 total failures: progressive loss of fixation to the pelvis (16 hips); dissociation of the constrained polyethylene liner from the metal shell (12 hips); biomaterial failure with polyethylene or retaining ring fracture (seven hips), and femoral head dislocation (two hips). Repetitive impingement of the femoral trunion against the elevated apex of the liner and surgical error contributed primarily to these modes of liner failure.
Based on these mechanisms of failure, researchers recommend reducing prosthetic impingement, modifying linear design and avoiding technical errors to minimize the number of complications when using constrained acetablular liners.
The research team was led by Andrew Yun, MD, and Lawrence Dorr, MD, both of Inglewood, Calif.; other team members were Douglas E. Padgett, MD, and Paul M. Pellicci, MD, both of New York, N.Y.
|Biomaterial failure: Photograph of retrieved implant demonstrating liner fracture at cup's apex.|
|Radiograph of femoral head shows dislocation despite the constrained articulation.|
|Failure of fixation: Radiograph demonstates varus rotational migration of constrained liner-reinforcement ring construct.|
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