Abstract
Aims: The purpose of this study was to assess the effect of gaps between the polyethylene liners and the metal acetabular shells used in two generations of acetabular component design. Methods: Finite element models were developed for two generations of acetabular component. The three variables assessed were: design (Mark I versus II); liner thickness (5, 8, and 11 mm); and gap size (0., 0.1, and 0.3 mm). 16 sequential quasistatic loading steps, coupled with ßexion/extension of the femoral head, were used to describe the stance phase of a patientñs gait cycle. Results: Gaps of less than 0.1 mm between the acetabular liner and the supporting metal shell will close under loading typical for gait, but only for smaller Ðsized acetabular cups. A gap of 0.1 mm seems to be at the edge of the range where rim loading, versus dome loading, occurs. Gaps of 0.1 to 0.3 mm between a polyethylene acetabular liner and the metal shell can produce ßuid pumping of approximately 100 to 250 microliters in each gait cycle. Conclusions: The changes from the 1st to the 2nd generation of this acetabular component led to important advantages. Indeed, due to an improvement of the liner conformity and the locking mechanism, backside micromotion, ßuid volume displaced, liner stresses and liner-shell contact stresses were strongly diminished.
Theses abstracts were prepared by Professor Dr. Frantz Langlais. Correspondence should be addressed to him at EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
