Evora® chromium–cobalt dual mobility socket: Results at a minimum 10 years’ follow-up

SummaryIntroductionThe Evora chromium–cobalt alloy dual mobility socket claims to display a large articulation tribology different from that of stainless steel models, limiting the risk of intraprosthetic dislocation and wear. The present study reports a minimum of 10 years’ follow-up in a multicenter prospective series of 200 sockets previously reported on at 5 years.HypothesisThe use of chromium–cobalt in dual mobility sockets provides a low rate of failure at 10 years, especially as regards to osteolysis and intraprosthetic dislocation.Materials and methodsTwo hundred hydroxyapatite-coated molded chromium–cobalt sockets without titanium interface were implanted without cement in 194 patients with a mean age of 70 years (range, 32–91 years). Clinical results were assessed on Postel Merle d’Aubigné and Harris scores, plain radiographs and survival analysis.ResultsAt a mean 11 years’ follow-up (10–13 years), 56 patients had died and 31 were lost to follow-up. Four underwent surgical revision (3 femoral components, and 1 socket for migration at 9 years with complete disappearance of the hydroxyapatite). A total of 109 implants were analyzable in 107 patients with a mean age of 81 years (55–93 years). At follow-up, the mean Harris score was 90 (75–96) and the PMA score 16.3 (14–18). There were no cases of loosening (except for the case reoperated on at 9 years) and no acetabular radiolucency or cysts. There were 2 cases of non-evolutive femoral radiolucency and 10 of femoral granuloma, involving head size > 22 mm (P < 0.0001) and a cemented titanium stem (P = 0.004) as risk factors. There were no dislocations in the large or small articulation. Ten-year survival was 99% (95% CI: 97.3%–100%) with socket revision as censorship criterion.DiscussionThe absence of dislocation in both small and large articulations confirmed the efficacy of the dual mobility concept and suggested an advantage for chromium–cobalt sockets in reducing the rate of intraprosthetic dislocation and preventing blockage of the large articulation by a better performance in the friction couple. Granulomas were associated with wear in cemented titanium stems and with heads greater than 22 mm in diameter. Ten-year survival was 99% (censorship criterion: revision for socket failure); there was, however, one case of socket loosening with disappearance of the hydroxyapatite, indicating that surveillance should be continued in this cohort.Level of evidenceLevel IV. Retrospective study.