Do thin acetabular shells increase the disassociation risk of ceramic liners?

This study suggests that contemporary modular acetabular shell designs employing ceramic liners deform during implantation where acetabular bed under-reaming is employed. The liner retention strength did not degrade by comparison to non-deformed shells using ASTM static push-out methods. A larger question, however, is the influence of this deformation on liner retention strength over time when both bone remodeling and cyclic activity occur. The idealization of component seating in the laboratory where surface contaminants, component position, and loading are controlled does not typify the operating room environment where liner seating is often an issue. Nevertheless, in this optimal situation, shell deformation was consistently observed as was striping on outer ceramic liner surfaces. Factors influencing the failure to seat components, as has been reported, need to be further documented. This study evaluates both metal banded and non-banded ceramic liners of like ceramic composition where a taper lock is utilized to achieve fixation. A further consideration, in this regard, may be the mismatch of shell-band stiffness where both CoCrMo and Ti-6Al-4V are employed. It is more likely that a CoCrMo band will diminish the possibility of any ceramic liner deformation because of its increased stiffness. Any amount of ceramic liner deformation can impact ceramic couple function particular to clearance and sphericity, which in turn may adversely affect fluid-film lubrication and wear. Elimination of a regional clearance around the joint space opening could account for observed ceramic surface alterations and suggests a potential causality of striping and the squeaking phenomenon. The shell deformation measured in this study could be an initiating factor of these processes. If this is a manifest cause, a logical operative alternative would be the advocation of stiffer shells or line-to-line reaming and augmentation with fixation screws. These ongoing studies are an attempt to identify factors which influence ceramic couple performance, a topic of contemporary clinical interest.