Metallurgical failure analysis of acetabular metal-backed screws

Screws are often used in total hip arthroplasty to increase the cementless acetabular metal-backed fixation stability. This study aimed at identifying metallurgical factors related to metal-backed screw fractures in two cases of premature total hip arthroplasty revision. A preliminary analysis of radiographs and retrieved parts was performed. Fractured screws were subjected to fracture analysis, energy dispersive X-ray spectroscopy (EDS) and metallographic analysis. A finite element analysis was performed to predict the stresses experienced by the screws. Two factors were identified: titanium alloy microstructure, consisting of alpha phase plates with oxygen-rich alpha case and as cast Cr–Co alloy with dendritic microstructure and unfavorably aligned shrinkage formation. Finite element analysis has showed enough level of stress to predict screw fracture in the case of unbounded metal-backed and bone interface.