Although they have been thought of as a solution to instability in total hip arthroplasty (THA), dual mobility implants failed to reduce the risk of dislocation in a study presented at the AAOS 2021 Annual Meeting.
The findings were shared by lead author Benjamin Kelley, MD, a resident from the Department of Orthopaedic Surgery at UCLA Health.
Dr. Kelley and coauthors analyzed data and outcomes from 152 patients who underwent a total of 168 consecutive primary THAs. Procedures were performed by a single surgeon between 2011 and 2017. THAs were performed via a posterior approach with a cementless, monoblock, dual mobility implant construct. Patients who were eligible for the analysis had been followed for at least two years to determine incidence of implant failures, rate of complications, and changes in Harris Hip Scores (HHS).
Of note, 30.8% of patients had a body mass index of >30, and the mean age was 67 years. The most common etiologies preceding THA were primary osteoarthritis (81.4%) and hip fracture (7.7%). After an average follow-up of 5.3 years, 10 cases of implant failure requiring revision occurred, for a failure rate of 6.4%.
Five dislocations occurred (3.2%) at an average of 28.4 days after the operation. Two patients with recurrent instability were revised to modular acetabular revision shells with constrained liners. Of the remaining three, two were managed with closed reduction and bracing and one was treated with a modular dual mobility head exchange.
Of the patients who experienced complications postoperatively, however, HHS improved by an average of 44 points. Survivorship rates were also high, at 93% overall and revision-free and dislocation-free survival rates of 93.6% and 96.8%, respectively. In a multivariable analysis, only cup size was significantly associated with an increased risk of implant failure, while obesity and stem type were associated with changes in HHS score.