The mechanical effects of cup inclination and anteversion angle on the bearing surface

Finite Element Analysis of Stress Distribution in Flat and Elevated-Rim Polyethylene Acetabular Liners

Backgroud

No study has compared flat and elevated-rim polyethylene liners in terms of stress distribution on the bearing surface. The purpose of this study was to investigate the difference in stress distribution between flat and elevated-rim polyethylene liners.

Methods

A stress analysis was performed by using the 3-dimensional finite element method. The cup was placed at an open angle of 20°, the flat liner and the liner with a 10° elevation was placed at inclination angles of 80°, 70°, and 60°.

Results

Compared with the 60° flat liner, the 80° and 70° flat liners showed higher stress at the liner edge. In the elevated-rim liner, the stress was high at the liner edge along the cup edge. When the von Mises equivalent stress was applied to each element of the liner, the high stress area (volume) was the largest for the 80° flat liner, second largest for the 80° elevated-rim liner, and third largest for the 70° flat liner. The average contact pressure also followed the same order.

Conclusions

Elevated-rim liners affect the stress distribution by increasing the area of contact. However, since elevated-rim liners exhibit high stress at the cup edge, they are likely to result in new problems including liner failure. These findings could aid surgeons in the selection of liners and determination of revision methods such as isolated liner exchange vs. acetabular cup revision for a well-fixed metal cup with a higher inclination angle in revision total hip arthroplasty.