Abstract
The Authors analysed two cases of catastrophic failures of Total Hip Prostheses due to the disruption of the PE inlay and the Ti-alloy metal back of the acetabular components. In the cases reported the PE inlay (4 mm in thickness) was coupled with a 32 mm in diameter Alumina ball heads. At time of revision the alumina ball heads showed many black marks due to the contacts with the Ti-alloy metal back. The sockets showed severe damages, concentrated in the superolateral zone. The PE inlays were disrupted. Almost a third of the metal back is missing. A large metallosis was also visible in the membrane at the interface between implant and bone. Histologic sections showed a large amount of metallic debris in a pseudovillous membrane. At higher magnification oligonuclear cells in a rich in vessels stroma were in contact with metal particles. PE debris with the characteristic birifrangent aspect to the polarised light microscope was contained into polynuclear giant cells. SEM showed that the size of 25% of particles was less than 1 μm, while the size of 53% of wear debris is in the range from 1 to 5 mm. EDAX confirmed that these particles consisted of Ti alloy. The Authors analysed the possible roles of different factors in the etiology of this cup failures and concluded that in both the cases analysed the initiator of the failure was the size selection of the prosthesis, and in particular the PE thickness, followed by the positioning of the acetabular component. The deformation of the PE inlay leads to rupture of the inlay itself, followed by the direct contact between the Alumina ball head and the titanium alloy cup, causing the disruption of the Ti-alloy metal back, with massive release of wear debris in the surrounding tissues.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
