Abstract
Good short-term results with Mt Blanc uncemented acetabular cups have been previously reported. However, in the medium term, we have observed acetabular loosening related to large granulomatous lytic lesions. To determine the cause of the polyethylene load causing the granulomatous lytic lesions, we subjected six explanted Mt Blanc acetabular cups to retrieval analysis. We also reviewed the literature on polyethylene locking mechanisms in uncemented metal-backed cups and on the deformability of metal-backed cups.
We subjected the retrieved cups to stereo-photographic analysis and to dye penetration and surface scanning electron microscopy techniques. We demonstrated severe polyethylene wear and particle generation on the back surface of the polyethylene insert. This was due both to two-body sliding wear, as characterised by surface deformation and delamination of the polyethylene, and to three-body abrasive wear, as characterised by surface roughness and embedded titanium particles. The literature confirmed that the locking mechanism of the Mt Blanc cup was particularly poor and the deformability greater than in other cups tested. This confirmed the wear patterns on the back-surface of the polyethylene liner.
We caution against the use of uncemented cups that have poor locking mechanisms for the polyethylene liners and those that deform excessively. The combination of poor locking mechanisms and titanium shells is especially dangerous.
Secretary: Dr H.J.S. Colyn, Editor: Professor M.B.E. Sweet. Correspondence should be addressed to SAOA, Box 47363, Parklands, Johannesburg, 2121, South Africa.
