Fixation failures of dual mobility cups: a mid-term study of 2601 hip replacements

Abstract

Background: The use of dual-mobility cups has increased because of a low rate of dislocations combined with a 96% 15-year survival rate. However, late cup migrations have been attributed to their fixation (tripod - exact fit with two pegs and one extraacetabular screw) and the absence of porous coating. In a second-generation device, the designs were modified to achieve press-fit fixation and a layer of titanium beads was sintered on stainless steel cups.

Questions/purposes: We therefore (1) determined the midterm survival of press-fit, grit-blasted, second-generation cups with or without additional screws, compared with original tripod and (2) compared survival of grit-blasted dual-mobility cups with bimetallic porous-coated cups.

Methods: From a multiinstitutional trial, we reviewed 2408 patients with osteoarthritis implanted with 2601 prostheses of seven designs of a second-generation dual-mobility cup. The criteria for failure were migration, widening radiolucencies in any zone of the interface, or revision for cup loosening. The minimum followup was 5 years (mean, 7.7 years; range, 5-11 years).

Results: The 8-year survival rate of press-fit, grit-blasted cups was lower than that for press-fit, grit-blasted cups fixed with screws (91% versus 100%) and for tripod fixation (98%). The 8-year survival rate of press-fit, grit-blasted cups was less than that for press-fit, porous-coated cups made of the same alloy (91% versus 95%).

Conclusions: The data suggested primary fixation of grit-blasted dual-mobility cups should be secured with screws. Porous coating sintered on the convex side improved midterm survivorship. No deleterious effect of metallosis resulted from sintered titanium beads on stainless steel. Long-term followup is required to confirm these findings.

Fig. 1A–C

(A) A tripod grit-blasted cup designed according to the original Bousquet model (Novae^® cup, photograph published with permission from Serf dedienne santé, Décines, France), (B) a press-fit cup designed for equatorial press fit (Sunfit^®, photograph published with permission from Serf dedienne santé, Décines, France), and (C) a grit-blasted cup with flanges allowing extraacetabular screw fixation (POLARCUP^®, photograph published with permission from Smith & Nephew Orthopaedic AG, Aarau, Switzerland) are shown.

Fig. 2

A histogram shows the number of dual mobility cups implanted per year.

Fig. 3

A histogram shows the number of mechanical fixation failures (revised or not) in relation to postoperative followup.

Fig. 4A–C

(A) A postoperative radiograph shows a press-fit, grit-blasted tripod dual-mobility cup implanted in a 65-year-old active woman during THA for advanced primary osteoarthritis. (B) Seven years later, the patient reported excellent hip function and radiographic control looked optimal. (C) In the eighth postoperative year, hip function deteriorated slightly, and the cup migrated medially. The upper fixation screw broke, while bone density at the acetabular roof increased. The patient has declined reoperation.

Fig. 5A–C

(A) A postoperative radiograph shows a press-fit, grit-blasted, dual-mobility cup implanted in a 72-year-old active woman for advanced primary osteoarthritis. The patient, who initially was pain free, reported acute groin pain during the third postoperative year. (B) The radiograph shows radiolucency at the bottom of the cup and bone condensation at its top, although there is no measurable migration. (C) She received a larger press-fit, porous-coated dual-mobility cup seen in this radiograph obtained 3 years after revision surgery. She acknowledged immediate and complete pain relief.