New Concepts for Improved Durability of MOM Total Hip Endoprostheses. A Review

Analyzing some hip prostheses retrieved by revision, the appearance of some forms of polishing of the femoral head were observed, as well as significant plastic deformations followed by local hardening. At the same time, obvious traces of wearing through fretting of the acetabular cup of UHMWPE, which in some studies are confounded or assimilated with the adhesive wear. Starting with the well-known fact that the rolling movement always has a lower friction compared to sliding friction, the authors have conceived and realized a pivoting movement joint on a “layer of balls” with “compensation space”, placed between the acetabular cup and the femoral head. This technical MOM solution allows free self-directed migration of the balls, depending on the resistance opposed, with successive occupation of the “compensation space”. As a concept, the proposed technical solution excludes the existence of a cage for maintaining the spheres relative positions.