Minimum Two-Year Outcomes of the Zimmer G7 Modular Dual Mobility Cup in Primary Total Hip Arthroplasty: Survivorship, Complications, Clinical and Radiographic Results

Background/Objectives: Modular dual mobility (MDM) cups are constituted by a cobalt-chromium liner inserted into a standard acetabular shell, allowing for intraoperative indication and supplementary screw fixation of the acetabular component. MDM could face mechanical and biological issues, with the associated risk of elevated blood metal ions levels and adverse local tissue reactions. Methods: This is a monocentric retrospective study on a consecutive series of 105 patients who underwent primary unilateral THA with the G7 Dual Mobility Acetabular System cup (Zimmer Biomet, Warsaw, IN, USA) from March 2019 to April 2023, and who were evaluated clinically and radiographically at a minimum two-year follow-up. All complications and revisions were recorded. Survivorship analysis with any revision surgery as endpoint was performed using Kaplan-Meier survival curves. Results: There were eighty-nine patients (follow-up rate 84.8%) who underwent clinical and radiographic follow-up. The mean follow-up was 2.5 ± 0.8 years. Revision-free survival was 98.0%. Three complications (2.8%) were recorded: one case of posterior dislocation, one periprosthetic joint infection and one post-traumatic periprosthetic femur fracture. Dislocation rate and infection rate were less than 1.0%. None of the patients were revised for adverse local tissue reactions. No cup loosening was observed. No cases of intraprosthetic dislocation, liner malseating or femoral notching were observed. Retroacetabular stress shielding was present in 43.0% of patients. Clinical scores significantly improved at the last follow-up compared with preoperative status (p < 0.0001): the final mean mHHS was 87.5 ± 5.3 and the final mean VAS was 0.5 ± 0.9. Conclusions: The Zimmer G7 modular dual mobility cup appears to be a safe and effective option and does not present specific implant-related mechanical and biological issues in primary total hip arthroplasty at a minimum two-year follow-up.