Abstract
BACKGROUND: With dislocation as a leading cause for revision after total hip arthroplasty (THA), modular dual-mobility (MDM) constructs are more commonly used at present in an attempt to decrease postoperative instability. With modularity, there is potential for additional complications, including malseating of the liner. The goal of this study was to perform a radiographic analysis on the incidence of MDM liner malseating. METHODS: We retrospectively identified 305 patients (305 THAs) who underwent primary THA with an MDM liner from a single manufacturer inserted by a single surgeon. One hundred fifty-six (51%) patients were male. The mean age was 68 years, and the mean body mass index was 31 kg/m(2). Only patients with both anteroposterior and cross-table lateral radiographs at a minimum of 6 weeks postoperatively were included. Dislocations and reoperations were determined at 1 year after the procedure. All MDM liners were routinely tested intraoperatively with a "4-quadrant test" to assess for proper seating. RESULTS: Four (4/305, 1.3%) MDM liners were noted to be radiographically malseated at early follow-up with three (3/147, 2.0%) occurring in a thinner two dimentional (2D) ongrowth shell and only one (1/158, 0.6%) observed in a thicker three dimentional (3D) additively manufactured shell. They were inferiorly prominent by a median of 1.2 mm, best seen on the cross-table lateral radiograph. In patients with at least 1-year follow-up, no MDM liners dissociated and no patients sustained a dislocation. Five (1.6%) patients required reoperation unrelated to the acetabular or MDM construct. CONCLUSIONS: Surgeons should be aware that malseating of dual-mobility liners may occur. However, with utilization of a consistent surgical technique to test for seating of the liner, the radiographic incidence of MDM liner malseating was low at 1%. Although there were no short-term clinical implications of liner malseating, long-term follow-up is needed.