Obesity is no longer a risk factor for dislocation after total hip arthroplasty with a double-mobility cup

Purpose Dislocation is one of the most feared complications after total hip arthroplasty (THA). This risk is greater in obese patients compared with the general population. Methods We performed a retrospective cohort study in which the main objective was to compare the dislocation rate between obese patients (BMI>30 kg/m(2)) (exposed group) and non-obese patients (BMI <= 30 kg/m(2)) (unexposed group) after primary THA with a double-mobility acetabular cup. The patients had a minimum follow-up of 24 months. Results The 'obese' group consisted of 77 THA cases and the 'non-obese' group of 425 cases; the two groups were similar in terms of age, gender and ASA score. After a mean follow-up of 58.3 +/- 27 months (range 27-159), 43 patients had been lost to follow-up and 56 had died; the two groups had similar mean values. One patient in the 'obese' group had suffered a dislocation due to a fall 16 months after the THA. One patient in the 'non-obese' group had suffered a dislocation after a periprosthetic femur fracture with stem subsidence two months after the THA procedure. Both patients underwent surgical revision where the double-mobility cup was preserved; there were no further dislocation events as of the last follow-up. The dislocation rate in the two groups was similar (1.3 % versus 0.23 %, p>0.05). No cases of loosening were found. Revisions were secondary to deep or superficial infection (n=22), periprosthetic femur fracture (n=10) or haematoma (n=3). Conclusion These findings imply that double-mobility cups are a reliable way of reducing the risk of dislocation in obese patients after primary THA.