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Saturday, March 13, 2004

Impingement contributes to wear, metallosis

By Carolyn Rogers

Impingement in a modular acetabular cup is associated with increased backside polyethylene wear and screw-metallic shell fretting, report investigators for Poster Exhibit P038

This association could be due to increased micromotion between the polyethylene liner and the screw-metallic shell interface during impingement. As the contact area moves closer to the rim of the component, increased polyethylene stresses on the side of the component opposite the impingement could also be a factor, the researchers say.

Modular acetabular components with screw fixation are associated with polyethylene liner wear and metallosis. Impingement between acetabular and femoral components produces abnormal loads on the edge of the implant resulting in wear debris and may increase the motion between polyethylene liner and metal shell. With this study, the researchers sought to evaluate the effect of impingement on backside polyethylene wear and screw-metallic shell corrosion and fretting.

The investigators subjectively evaluated 86 modular acetabular components via visual and stereomicroscopic examination. Impingement, backside polyethylene damage, corrosion and fretting at the screw-metallic shell interface were assessed on the basis of the location and the severity using a subjective scoring system. Demographic data and revision diagnosis were obtained from each patient's medical records; component position was determined from radiographs.

Impingement was found in 62 cups (75 percent). Inner and backside polyethylene wear and screw-metallic shell corrosion and fretting were significantly correlated (p=<0.001) with impingement. Polyethylene creep was significantly correlated to backside wear and tended to be higher for the cups that had impingement (p=0.06). No correlation was found between backside polyethylene wear and implant design or cup position.

Led by Douglas E. Padgett, MD, of New York City,, the research team also included Mordechai Kligman, MD, of Queens, N.Y.; Bridgette D. Furman, Res. Eng., of New York City, and Timothy M. Wright, PhD, of Stamford, Conn.

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