Comparison of the initial stability of hemispherical and elliptical acetabular cups

摘要

Porous coated cups have been used clinically to obtain biological fixation by promoting ingrowth of fibrous tissue and bone into the components' porous surfaces. Conducive bone ingrowth conditions are typically achieved by using hemispherical components that are oversized relative to the reamed acetabulum so as to maximize stability by minimizing relative motion at the bone-cup interface and maximizing initial bone-cup interfacial contact. However, gaps have been shown to exist at the bone-implant surface immediately after cup insertion, which may increase the periprosthetic joint space and lead to progressive radiolucency. An alternative to oversized hemispherical cups is to use differently shaped cups. For example, the elliptical cup design, which has a greater equatorial rim radius than polar dome radius, is motivated by the measured ellipsoidal topography of the reamed acetabulum and the 'flattening' of the acetabulum during insertion. In this study, we used a detailed three-dimensional finite element model of the acetabulum and surrounding pelvis to compare the conditions affecting the initial stability of oversized hemispherical and elliptical cups during surgical insertion and after subsequent joint loading.