Dual-mobility Cups Compared to Unipolar Cups on Dislocation and Cost-effectiveness After Primary Total Hip Arthroplasty.

Rationale: Dislocation is the leading reason for early revision surgery. To address the problem of dislocation, the dual-mobility (DM) cup was developed in France in the 1970's. This cup should provide more stability and biomechanically reduce the risk of dislocation. In the Netherlands, most DM cups are placed in specific patients, e.g. with cognitive impairment and for revisions due to recurrent dislocations. Despite the increased and, in some countries, broad use of DM cups, high quality evidence of their (cost)effectiveness is lacking. This study aims to perform a trial to fill this gap in knowledge. Much of the information needed to judge the effectiveness of DM cups is already incorporated in the Dutch Arthroplasty Register (LROI). This register lends itself perfectly for a nested RCT towards this aim.

Objective: The primary objective is to investigate whether there is a difference in the number of hip dislocations following primary total hip arthroplasty (THA), using the posterolateral approach, with a DM cup compared to a unipolar cup in elderly patients 1 year after surgery. The secondary objectives are: to investigate whether there is a difference in the number of revisions; to investigate what the cost-effectiveness and cost-utility is of a DM cup compared to a unipolar cup at 1 year follow-up; to investigate whether there is a difference in the number of hip dislocations and revisions between a DM cup and a unipolar cup 2 years after surgery; to investigate whether there is a difference in patient reported outcomes between a DM cup compared to a unipolar cup 1 and 2 years after surgery; to compare the number of hip dislocations, revisions and PROM data between patients in the randomized DM group and patients in an observational cohort DM group. Finally, long-term survival of DM and unipolar cups will be evaluated based on revision and mortality data registered in the LROI.

Study design: Prospective multi-center nation wide, single blinded RCT nested in the LROI.

Study population: Patients ≥ 70 years old, undergoing an elective primary cemented THA.

Intervention (if applicable): The intervention group receives a THA with a dual mobility cup, the control group receives a THA with a unipolar cup.

Main study parameters/endpoints: Primary: The number of dislocations. Secondary: costs, patient reported outcomes and implant survival.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: In addition to the benefits from regular care, the primary hip arthroplasty procedure, patients might benefit from randomization to receiving a DM cup. DM cups are designed to reduce the risk of hip dislocation, compared to a unipolar cup. Patients may undergo more thorough follow-up than non-study patients and may benefit from this increased surveillance compared with regular care. The only burden associated with study participation is the time needed to complete the cost questionnaires (all other outcomes are part of standard care).

• Number of revision surgeries [Time frame: 1 year postoperative]
• cost-effectiveness questionnaire [Time frame: 1 year postoperative]
• Number of dislocations [Time frame: 2 years postoperative]
• Patient Reported Outcomes on physical functioning [Time frame: 1 and 2 years postoperative]
• Patient Reported Outcomes on pain [Time frame: 1 and 2 years postoperative]
• Patient Reported Outcomes on quality of life [Time frame: 1 and 2 years postoperative]
• Implant survival [Time frame: 5 - 10 years postoperative]