A comparative study about the incidence of dislocation and peri-prosthetic fracture between dual mobility versus standard cups after primary total hip arthroplasty.

PURPOSE: Dislocation and peri-prosthetic fracture (PPF) are major reasons for revision THA (total hip arthroplasty). The main advantage of dual mobility (DM) cups is to minimize the incidence of dislocation compared to single mobility (SM) cups. We hypothesized that the use of DM would lead to an increased risk of PPF because of its greater stability. In contrast, standard cups would be at higher risk of dislocation.

METHODS: A retrospective comparative study was performed in our institution including 126 revision THAs between January 2013 and December 2017. Collected data included gender, age, BMI, Parker score, ASA score, the etiology for primary THA, type of cup (SM or DM), cortical index, Noble index, and the stem fixation.

RESULTS: Overall, 53 standard and 73 DM cups were included for study. In the dislocation group, 29 had standard cups (83%) and 6 had DM cups (17%). Dislocation was 12-fold higher in SM cups (p < 0.001). In the PPF group, 24 had standard cups (26%) and 67 had DM cups (74%). PFF was 12-fold higher for DM cups (p < 0.001). A higher Parker score and a higher cortical index had a protective effect on the risk of PPF (OR = 0.76 (p = 0.03), OR = 0.57 (p = 0.048)).

CONCLUSION: The use of DM increased hip stability but led to a higher rate of PPF by load transfer on the femur. Further studies with larger cohort and follow-up are needed to confirm these findings and measure the incidence of these complications.