Deformation of modular acetabular press-fit shells is of much interest for surgeons and manufacturers. Initial fixation is achieved through press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of modular systems and may adversely affect integrity and durability of the components and tribology of the bearing. The aim of the study was to show shell deformation as a function of bone and shell stiffness. The stiffness of the generic shells was determined using a uniaxial/ two point loading frame by applying different loads, and the change in dimension was measured by a coordinate measurement machine (CMM). Cadaver lab deformation measurements were done before and after insertion for 32 shells with 2 wall thicknesses and 11 shell sizes using the ATOS Triple Scan III (ATOS) optical system previously validated as a suitable measurement system to perform those measurements. Multiple deformation measurements per cadaver were performed by using both hip sides and stepwise increasing the reamed acetabulum by at least 1 mm, depending on sufficient residual bone stock. The under-reaming was varied between 0mm and 1mm, respectively. From the deformations, the resulting forces on the shells and bone stiffness were calculated assuming force equilibrium as well as linear-elastic material behaviour in each point at the rim of the shell.INTRODUCTION
METHODS
Deformation of modular acetabular press-fit shells is a topic of much interest for surgeons and manufacturer. Such modular components utilise a titanium shell with a liner manufactured from metal, polyethylene or ceramic. Initial fixation is achieved through a press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of inserting the bearing liner into the acetabular shell for modular systems. This may adversely affect the integrity and durability of the components and the tribology of the bearing. Most clinically relevant data to quantify and understand such shell deformation can be achieved by cadaver measurements. ATOS Triple Scan III was identified as a measurement system with the potential to perform those measurements. The study aim was to validate an ATOS Triple Scan III optical measurement system against a co-ordinate measuring machine (CMM) using in-vitro testing and to check capability/ repeatability under cadaver lab conditions.INTRODUCTION
OBJECTIVE
