Introduction: The dual-mobility cup (DMC) was introduced in 1979. Due to lack of referenced publications, this interesting and innovating concept was ignored during close to 20 years. However, 180 studies (level III or IV) have now been published. Evidence-based medicine is based on level I studies. Over the past three decades, the role of national registries developed with the intention of surveying orthopaedic implants. In 2012, we developed, registered, and implemented a specific database for contemporary DMC.
Material and methods: Data are collected with an electronic case-report form, and this evaluation is limited to a single product line . From May 2012 to December 2016, 2090 cases of Quattro cup implantation have been registered; results of the first 636 primary cases with a minimum follow-up of three years were previously reported (series 1). Of the 1454 remaining cases, dislocation rate only was monitored (series 2) and results are reported here.
Results: In series1 comprising 553 degenerative diseases and 83 proximal femoral fractures (PFF), one dislocation (1.2%) occurred in PFF and none in degenerative disease. Survivorship (infection excluded) at three years was 99.8%. In series 2 (1315 degenerative diseases; 139 PFFs), dislocation rate was 0.27% (four cases). In neither series did we observe any intraprosthetic dislocation.
Discussion: Results of this private regional register confirm the high efficiency of DMC to decrease dislocation rate (0.23%). Few outcomes of DMC in primary total hip arthroplasty (THA) are published in national registries. The Swedish Hip Arthroplasty Register has reported on 287 primary DMC hips of 78,098 THAs. No dislocations were reported. We conclude that DMC decreases dislocation rate, and the national registry of Lithuania also reports a significant decrease in the rate of revision for dislocation in the DMC group. These data-available online-allow us to monitor DMC in real time, although they lack short-term follow-up.
Keywords: Dislocation; Dual-mobility cup; Register; Total hip arthroplasty.