For the millions of adults undergoing total hip replacement each year, the choice of implant bearing can mean the difference between a successful recovery and a return to the operating room. Dual-mobility implants have been widely adopted under the assumption that their nested ball-in-socket design dramatically reduces post-surgical dislocation — but a well-powered randomized trial now puts that assumption under serious scrutiny.
This multicenter RCT enrolled 555 patients deemed at elevated dislocation risk who underwent primary posterior-approach total hip arthroplasty, randomizing them to either dual-mobility (DM) bearings with a mean 42 mm effective head diameter or standard single-bearing (SB) heads ranging from 28 mm to 44 mm. At a median follow-up of 23 months, dislocation occurred in just 0.7% of the DM group versus 2.1% in the SB group — a threefold relative difference that nonetheless failed to reach statistical significance (P = 0.29). Two-year dislocation-free survivorship was 99.0% versus 97.6% respectively (P = 0.63), and all-cause revision rates were similarly indistinguishable between groups at roughly 2–3.5%.
The findings carry meaningful implications for orthopedic decision-making. DM implants carry a cost premium and introduce a unique failure mode — intraprosthetic dislocation — not present with standard bearings. Their widespread adoption in high-risk patients has outpaced the randomized evidence base, largely driven by observational data and biomechanical rationale. This trial, which is among the largest RCTs to directly compare the two constructs, suggests the real-world dislocation benefit may be substantially smaller than retrospective series implied. That said, the overall dislocation rate in both arms was remarkably low, raising the possibility the trial was underpowered to detect a clinically meaningful difference at this event rate. Additionally, a median follow-up under two years may underestimate late dislocations, particularly in the lumbosacral fusion subgroup where spinopelvic mechanics shift over time. This is incremental rather than paradigm-shifting evidence, but it justifies more selective — rather than blanket — use of DM implants in high-risk primary THA.