Polyethylene liner dissociation in a DePuy pinnacle cup with a manufacturer analysis of the failed component

A 74-year-old patient presented to the emergency department with acute atraumatic hip pain 9 years after her primary left total hip arthroplasty (THA). Plain radiographic imaging demonstrated lateralisation of the femoral head within the acetabular shell—indicating an issue with the polyethylene liner. The patient required revision of the acetabular component and the femoral head, as well as a new polyethylene liner. A detailed analysis of the components removed was performed by DePuy Synthes Engineering. Between 2009 and 2020, 8 publications have documented 52 cases of liner dissociation with the Pinnacle acetabular component and Marathon polyethylene liner. Various theories have been proposed in the literature as all of these components appear to fail in the same way, with shearing of the locking tabs in the polyethylene liner. In spite of a manufacturer analysis of the components, no root cause was identified as to why the polyethylene liner failed.

Influence of outer geometry on primary stability for uncemented acetabular shells in developmental dysplasia of the hip

Excellent primary stability of uncemented acetabular shells is essential to obtain successful clinical outcomes. However, in the case of developmental dysplasia of the hip (DDH), aseptic loosening may be induced by instability due to a decrease of the contact area between the acetabular shell and host bone. The aim of this study was to assess the primary stability of two commercially-available acetabular shells, hemispherical and hemielliptical, in normal and DDH models. Synthetic bone was reamed using appropriate surgical reamers for each reaming condition (normal acetabular model). The normal acetabular model was also cut diagonally at 40° to create a dysplasia model. Stability of the acetabular components was evaluated by the lever-out test. In the normal acetabular model conditions, the maximum primary stabilities of hemispherical and hemielliptical shells were observed in the 1-mm under- and 1-mm over-reamed conditions, respectively, and the resulting stabilities were comparable. The lateral defect in the dysplasia model had an adverse effect on the primary stabilities of the two designs. The lever-out moment of the hemielliptical acetabular shell was 1.4 times greater than that of the hemispherical acetabular shell in the dysplasia model. The hemispherical shell is useful for the normal acetabular condition, and the hemielliptical shell for the severe dysplasia condition, in the context of primary stability.