• Ammar Jobory, Johan Kärrholm, Søren Overgaard, Becic PedersenAlmaADanish Hip Arthroplasty Register, Aarhus, Denmark.Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark., Geir Hallan, Jan-Erik Gjertsen, Keijo Mäkelä, and Cecilia Rogmark.
• Department of Orthopaedics, Lund University, Skåne University Hospital, Malmö, Sweden.
• J Bone Joint Surg Am. 2019 Jul 17; 101 (14): 1278-1285.

BackgroundThe dual-mobility acetabular cup (DMC) has an additional bearing consisting of a mobile polyethylene component between the prosthetic head and the outer metal shell. This design has gained popularity in revision total hip arthroplasty (THA) and in primary treatment of femoral neck fractures with the anticipation of a reduced risk of THA instability. Our primary aim was to evaluate the overall revision risk of these cups on the basis of data from the Nordic Arthroplasty Register Association (NARA) database, and our secondary aim was to study specific revision causes including dislocation.MethodsPropensity score matching for age, sex, fixation of the cup and stem, and the year of surgery (2001 to 2014) was used to match 4,520 hip fractures treated with a DMC to 4,520 hip fractures treated with conventional THA (control group). Competing risk regression analyses with revision or death as the end point were used. Revision was defined as a secondary surgical procedure in which any component of the implant was removed or exchanged. In addition, revision of the cup was analyzed.ResultsThe DMCs had a lower risk of revision compared with conventional THA, with an adjusted hazard ratio (AHR) of 0.75 (95% confidence interval [CI] = 0.62 to 0.92). This was consistent after adjusting for surgical approach. DMCs had a lower risk of revision due to dislocation (AHR = 0.45 [95% CI = 0.30 to 0.68]) but we found no difference regarding revision for deep infection. Revision of the acetabular component, both in general and due to dislocation, was more frequent with the use of conventional cups. The risk of death was higher in the DMC group (AHR = 1.49 [95% CI = 1.40 to 1.59]).ConclusionsThe use of a DMC as primary treatment for hip fracture was associated with a lower risk of revision in general and due to dislocation in particular. The total number of DMCs analyzed (4,520) likely exceeds any cohort of DMC-treated fractures published to date.Level Of EvidenceTherapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

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