Dual Mobility Acetabular Systems for Total Hip Arthroplasty: A Multicenter Study and Technique Report.

INTRODUCTION Dual mobility constructs for THA have been a tremendous advancement for hip arthroplasty surgeons, especially in scenarios where instability is a possibility. While some researchers have reported events of malseating with their use, the authors of the current study believe that this may be avoided by ensuring appropriate surgical technique. Therefore, the purpose of this study was to: (1) describe the surgical techniques that we employ to ensure that the liner is adequately seated; and (2) report the rates of malseating, dislocation, and aseptic loosening among our collective cohort of dual mobility THA patients. MATERIALS AND METHODS All patients who underwent THA with a dual mobility construct between January 1, 2010 and December 31, 2018 at four institutions were identified. Those who had less than two years of follow up were excluded. Outcomes of interest included radiographic evidence of liner malseating, aseptic loosening, and dislocation. A total of 1,826 patients who underwent THA with a dual mobility construct were identified. Among these patients, 504 had less than two years of follow up and were excluded from our analysis. The remaining 1,322 patients met our criteria including 941 primary THAs (71.2%) and 381 revision THAs (28.8%). RESULTS After a minimum follow-up period of two years, there were only two cases of malseated liners (0.15%). Serial follow ups have demonstrated no movement or changes in the position of the liners over time for both patients. In addition, they have been shown to have normal serum metal ion levels and no clinical complaints after 5.3- and 7.1-year follow up. Seven of 1,322 patients (0.53%) experienced a dislocation. Aseptic loosening of the acetabular cup was diagnosed in one patient 3.4 years postoperatively. In three patients, femoral component loosening occurred after a mean follow-up period of 2.3 years, (1.3 to 3.1 years). Among the 941 primary cases, the incidence of liner malseating was 0.21%, as both patients who experienced this complication were in this subgroup. As stated above, these patients have demonstrated normal serum metal ion levels and no clinical or radiographic sequelae as a result of the liner malseating. The dislocation rate among primary cases was 0.21% (2 of 941). Aseptic loosening of the acetabular component occurred in two (0.21%) while one patient (0.1%) was found to have femoral component loosening at final follow up. Of the 381 revision THAs, there were no cases of liner malseating. Five revision THA patients (1.3%) experienced a dislocation over our study period. Two revision THA patients experienced aseptic loosening of the femoral component (0.79%) at final follow up. CONCLUSIONS The results of this paper demonstrate that malseating is not a prevalent issue with dual mobility THA when appropriate surgical techniques are used. It is hoped that that this paper clarifies the techniques for implantation of these implants and that excellent results can be achieved when care is taken to ensure that liners are well-seated intraoperatively.