Our aim is to develop a strategy that reduces the risk of dislocations after total hip arthroplasty surgery performed due to femoral neck fracture. We therefore perform a register-nested, pragmatic, randomized controlled trial to investigate the safety and efficacy of dual mobility cups that were designed to minimize the risk of dislocation in the large and fragile group of elderly patients with femoral neck fractures.

Total hip arthroplasty (THA) is regularly performed in patients with a femoral neck fracture. However, dislocation is very common after THA in hip fracture patients, and this complication is deleterious to health and quality of life. The dual mobility cup offers a technical solution that potentially reduces the risk of dislocation. There is however no high-level evidence to support the general use of dual mobility cups in patients with displaced femoral neck fractures, and the purpose of the proposed study is to provide evidence to support or refute the use of this concept in the very large group of hip fracture patients.

We a register-nested, pragmatic randomized controlled trial (RCT) to investigate the safety and efficacy of dual mobility cups that were designed to minimize the risk of dislocation after THA. Our aim is thus to investigate whether the incidence of dislocations after THA surgery performed due to femoral neck fracture can be reduced by the use of this device.

The intervention group receives a dual mobility cup (of any brand that is in general use in Sweden), and the control group receives a standard cup (of any brand that is in general use in Sweden). The choice of cup or stem fixation (cemented or uncemented), femoral head size, brand of stem type, surgical approach, antibiotic prophylaxis, and postoperative mobilization are up to the surgeon's choice and the routines that are relevant at each study site.

The necessary infrastructure for this register-nested RCT is present within the Swedish Hip Arthroplasty Register (SHAR) and the Swedish Fracture Register (SFR). Pre-operative registration of fractures is already established within the SFR, and an online platform to screen, include and randomize eligible patients is established. Cross-matching of data from the SFR and the SHAR with the database of the Swedish Patient Register (SPR) is performed in order to catch endpoint not routinely collected by the SHAR.

Expanded recruitment in collaboration with UK, WHITE 12-Duality, started 10/09/2022. https://www.isrctn.com/ISRCTN11895196

Inclusion Criteria:

• Written informed consent
• Diagnosis: displaced femoral neck fracture type AO 31-B2 or B3/Garden type 3 or 4
• Eligible for THA according to local guidelines and routines

Exclusion Criteria:

• Previous inclusion of contralateral hip
• Delayed fracture surgery (date of injury >7 days prior to date of randomization)
• Pathological or stress fracture of the femoral neck, or fracture adjacent to a previous ipsilateral hip implant
• Inability or unwillingness to give written consent
• Dementia (as diagnosed by the screening physician)
• Unavailability of both interventions for a study subject (e.g., implants being out of stock, or lack of the individual surgeon's expertise to perform either procedure)