Instability after hip arthroplasty, whether it is a total (THA) or intermediate (HA), poses a major risk, however arthroplasty is the standard treatment for displaced intracapsular fractures of the femoral neck of the elderly. Three types of arthroplasties can be proposed: total prostheses with or without a dual mobility cup (DM THA) reducing the risk of dislocation, and hemiarthroplasties. In the absence of clear recommendations regarding the type of implant to be used and the scarcity of studies comparing HA and DM THA, we conducted a monocentric comparative retrospective study using the propensity score method to compare DM THA versus HA on recently displaced femoral neck fractures: (1) survival and risk of dislocation, (2) functional results, (3) mortality.

The rate of dislocation of THA fitted with a DM cup is lower than that of HA.

We retrospectively identified 112 patients in the HA group and 153 patients in the DM THA group who underwent an emergency arthroplasty for a displaced cervical fracture between 2010 and 2013. The minimum follow-up was 5 years (range, 5–9 years). The mean age at surgery was 81 years (range, 55–101 years). Elective surgery patients (n=2), hardware fractures (n=10), pathological fractures of the femoral neck (n=6), associated fractures (n=3), and revision surgeries (n=5) were excluded. The primary outcome measure was instability. Clinical follow-up was performed by the WOMAC score and the risk of mortality was determined after adjusting for confounding factors using the propensity score method.

After adjustment by the propensity score, the dislocation rate at 2-years was 2.2% (n=3/153) in the dual mobility THA group and 6.3% (n=7/112) in the HA group (OR=0.34 [95% CI: 0.06–1.96] (p=0.23)). After adjustment by the propensity score, the mean WOMAC score was 8.20 (±6.56) in the THA group, compared to 10.78±3.92 on average in the HA group (p=0.031). After adjustment by the propensity score, we did not find any significant difference in the reoperation rate without changing implants and revisions, and postoperative complications. After adjustment by the propensity score, mortality was significantly higher in the HA group 45.5% (n=69/152) versus 91.5% (n=102/112) in the HA group (OR=0.50 [95% CI: 0.25–0.98] (p=0.042)).

Few studies have compared these two types of implant in the context of trauma. Although the results of our study are not significant regarding the risk of dislocation, the use of a dual mobility cup seems to be a very satisfactory solution in this trauma context.

III; comparative retrospective cohort.