Retrieval analysis of three generations of Biolox® femoral heads: spectroscopic and SEM characterisation

Wear and osteolysis continue to be the major reasons for revision surgery in Total Hip Arthroplasty. The introduction of the ceramic-on-ceramic bearings eliminates the problem of polyethylene wear debris. During the last 40 years, three generations of Biolox® ceramics were developed (Biolox®, Biolox® forte, and Biolox® delta), each better than the previous from the density, grain size and purity point of view. We conducted a retrieval study on 15 Biolox® femoral heads (Biolox®, Biolox® forte, and Biolox® delta) articulating against liners of the same type. Surface properties and residual stress were assessed using SEM, fluorescence and Raman spectroscopy. At SEM examination, the Biolox® delta retrievals showed a lower wear than the previous generations. The fluorescence measurements suggested different wear mechanisms in the three sets of retrievals. Micro-cracking was predominant in Biolox®, while in Biolox® forte and Biolox® delta a wider range of residual stress values was observed upon wear. Surface polishing was observed only in Biolox® and Biolox® forte. Raman spectroscopy of Biolox® delta femoral heads showed a progressive improvement in material composition. Wear induced a tetragonal to monoclinic transformation. The Raman results on the retrievals, here reported for the first time, allowed to validate the in vitro ageing protocols proposed in the literature to simulate the effects of the in vivo wear.