gms | German Medical Science

Objective: Wolff’s law states that bone remodeling is driven by external loads on bone. When loads increase, bone mass will increase accordingly, making it stronger, while bone mass will decrease when loading forces are lower. This may cause problems when bone is stress shielded by rigid metal implants, particularly in the acetabular region. Therefore, low-stiffness acetabular cups have been proposed to avoid stress shielding.

The aim of this study was to compare load transfer across a cemented polyethylene cup, a rigid cementless cup and an elastic cementless press-fit cup. Our secondary goal was to analyse the effect of increasing cup elasticity on socket micromotions.

Methods: A Finite Element Analysis (FEA) model was developed of the human pelvis, in which the three acetabular sockets were introduced. The models were loaded simulating a cycle of normal walking, during which we calculated the strain energy density distribution in subchondral bone and socket micro-motion levels.

Results and conclusions: The FEA results show that the elastic press-fit cup avoids acetabular stress shielding. The interfacial micro-motions of the elastic press-fit cup were highest compared to the other sockets.

These results support our view that elastic acetabular components protect acetabular bone from stress shielding and lead to the retainment of pelvic bone stock according to Wolff´s law. Due to its elasticity, the elastic press fit cup showed the highest local interfacial micro-motions levels.

The clinical relevance of these micro-motion levels should be evaluated using RSA measurements in future in vivo studies.