Abstract
Introduction
Several devices based upon the dual mobility (DM) concept have recently been FDA approved. However, little is available on the efficiency of current DM on THA instability prevention, and on specific complications. The aim of this retrospective study was to report on the minimal 5-year follow-up results of a cementless DM socket.
Methods
Between January 2000 and June 2002, 168 primary consecutive non selected THAs were performed in 92 females and 76 males. The average age at surgery was 67.3 years. A single DM socket design was used (Tregor, Aston Medical, France) consisting of a Ti-sprayed and HA-coated CoCr shell with a highly polished inner surface articulating with a mobile intermediate polyethylene component. The opening diameter of the mobile insert was 6% smaller than that of the femoral head. In 115 hips, the modular femoral head completely covered the Morse taper, whereas a long-neck option leaved the base of the Morse taper uncovered in the remaining 53 hips.
Results
At the minimum 5-year follow-up, 119 patients were still alive and had not been revised at a mean of 7.2 years (5-8.9 years), 4 hips were revised for dislocation between the femoral head and the mobile insert (intra-prosthetic dislocation) at a mean of 5.9 years, 22 patients were deceased, and 23 patients were lost to follow-up. Intra-prosthetic dislocation occurred in 4 of the 53 hips (7.5%) with an incompletely covered Morse taper, whereas no dislocation were reported in the remaining 115 hips (p = 0.009).
Discussion and Conclusion
A current cementless DM socket was highly effective in the prevention of dislocation following primary THA. However, fatigue damage and wear of the mobile insert at the capturing area can lead to intra-prosthetic dislocation requiring revision.
Surgeons should be aware of this specific complication and efforts should be made to avoid aggressive contact at the femoral neck to mobile insert articulation (“3rd articulation”).
