Effect of cup geometry and the presence of cement on acetabular component fixation.

Two series of implanted conical, polyethylene Ring cups were studied clinically and radiographically. In one series the cups were uncemented while in the second cement was used. The results using cemented conical cups were then compared with results using a cemented cup of hemispherical design to study the effect of cup geometry. At 7-8 years a total of 3.8% of the cemented conical series and 2.9% of the uncemented were revised for aseptic loosening. At 9 years survivorship was identical. Migration of the sockets occurred in approximately 25% of both series and was directly related to cup cover of less than 80% (P < 0.001). The series of cemented hemispherical cups were reviewed after an identical period. Although the numbers revised for loosening were comparable in this and the cemented conical group, radiological migration was statistically greater in the latter (P < 0.001). Alternative methods of socket preparation and cement technique were thought to be the most likely explanation for the observed differences.