Home | Hip Research | Knee Research
Comparison of In Vivo Wear Between Polyethylene Liners Articulating With Ceramic and Cobalt-Chrome
Christi J. Sychterz, MS, C. Anderson Engh, Jr., MD, Anthony M. Young, BS, Robert H. Hopper, PhD, Charles A. Engh, MD
At a mean of seven years, this study found no difference between the radiographic wear performance of alumina ceramic femoral heads and a well-matched group of cobalt-chrome heads.
Purpose: This study radiographically compared the wear performance between 81 alumina ceramic femoral heads and a well-matched group of 43 cobalt-chrome (CoCr) femoral heads.
Methods: The ceramic group consisted of 81 hips followed for mean 7.0 years; the CoCr group consisted of 43 hips followed for mean 6.8 years. The two groups were matched on acetabular component, femoral component, head size and manufacturer, and polyethylene sterilization. No statistical difference existed in patient age, weight, or gender between the groups. A computer-assisted measurement system was used to assess two-dimensional head penetration into the polyethylene liner at annual intervals. Linear regression analysis of temporal head penetration data was used to calculate true polyethylene wear rates for these groups.
Results: At a mean of 7 years, the true polyethylene wear rate of the ceramic group was greater (0.09 ± 0.07 mm/year) than that of the cobalt-chrome group (0.07 ± 0.04 mm/year).
Conclusions: Although ceramic heads typically out-perform CoCr heads during in vitro testing, the in vivo wear performance of both heads was surprisingly similar in this study. One possible explanation could lie in the multifactorial nature of the polyethylene wear process in vivo. Numerous confounding factors acting together in vivo may essentially neutralize the advantages of the ceramic surface, rendering its in vivo performance similar to that of CoCr. We conclude that, for the particular components studied, a ceramic femoral head offers little advantage over a CoCr head in decreasing in vivo polyethylene wear.