Introduction This multicenter randomized controlled trial (RCT) sought to determine if dual-mobility bearings (DM) reduce dislocation risk in patients at high-risk for instability undergoing primary total hip arthroplasty (THA) compared to standard bearings (SB). Methods A total of 555 patients undergoing primary THA via posterior approach were randomized to DM (n=271; 42mm mean effective head, range 36-55mm) or SB (n=284; head sizes: 28mm n=2, 32mm n=42, 36mm n=168, 40mm n=61, 44mm n=11). Stratified randomization was based on high-risk criteria: 1) prior lumbosacral fusion (n=170) 2) other inclusions; (age ≥75, preoperative combined flexion-adduction-internal rotation ≥115°, substance abuse, inflammatory arthritis, neuromuscular disorder, removal of hardware, cognitive impairment, acute displaced femoral neck fracture, and kyphosis/scoliosis; n=385). A priori power analysis determined 206 patients were required per group (alpha=0.05; power=0.80) to show a reduction in the risk of dislocation from 8% to 2%. Twenty-eight patients (5.0%) were lost to follow-up before 90 days, leaving 527 patients followed for a median of 23 months (range, 3.0 to 87.2 months). Results There were six dislocations in the SB group and two in the DM group (2.1% vs. 0.7%). There was no difference in 2-year dislocation-free survivorship between cohorts (SB: 97.6% vs. DM: 99.0%; p=0.63). Sixteen hips were revised (SB: 3.5% vs. DM: 2.2%; p=0.45), with no difference in 2-year all-cause revision-free survivorship (SB: 96.4% vs. DM: 97.5%; p=0.53). Infection was the most common revision indication (5 SB 1.8% and 2 DM 0.7%). There were no differences in HHS or HOOS JR at any time point (p>0.05). Mean effective head size was larger in the DM cohort (42mm vs. 36mm, p<0.001). Conclusion In this multicenter RCT, DM bearings reduced the risk of dislocation by 3-fold but given the lower than anticipated dislocation rate overall this difference did not reach statistical significance. Further follow-up will be required to fully understand how dual mobility bearings affect the rate of dislocation in high-risk patients. Keywords: DM, conventional bearing, THA, RCT, instability
Potluri et al. (Thu,) studied this question.