Purpose of the study: The purpose of the study was compare dislocation rates of total hip arthroplasties (THA) implanted with a dual-mobility cup versus those implanted with a conventional cup.

Material and method: The first series (DM) included 105 patients who underwent first-intention THA implanted by one operator (DS) from January 2005 to June 2007. Dual mobility cups with a 28 mm head were implanted. There were 60 women and 45 men, mean age 76.6±5.65 years (range 53–93). Degenerative disease predominated (n=95, 90.%). The cups were Novae press-fit (SERF) (n=94), Stafit (Zimmer° 5N+5°? Avantage (Biomet) (n=5), and Gyros (Depuy) (n=1). The second series (S) included 108 patients who underwent the same procedure performed by the same operator (DS) from January 2003 to June 200 for the same indication. This series was the control series. There were 56 women and 52 men, mean age 74.19±5.9 years (range 53–87). Degenerative disease predominated (n=100, 92.6%). All implantations used metal-polyethylene bearing with a 28 mm head. The implants were St Nabor cups (Zimmer) (n=44), Cédior cups (Zimmer (n=41), and sealed cups (n=22). The same femoral stem with a 12–14 cone was used in both series. The reduced posterior approach was used in all cases without section of the pyramidal tendon. Inclusion required at least one year follow-up. Fischer’s test was used to compare dislocation rates. Other variables were analysed with the chi-square test.

Results: Regarding the dual-mobility cup series (DM) there were no cases of dislocation. In the conventional cup series (S) there were five early dislocations (< 3 months), giving a rate of 4.63%. although the dislocation rate was obviously higher in the S series, the difference was at the limit of significance (p=0.0597). In addition, the DM population was slightly older than the S series (p=0.0026).