No Difference in Force Required for Intraprosthetic Dislocation of Mixed Manufacturer vs Same Manufacturer Dual...

To avoid the morbidity of removing well-fixed implants during revision surgery, the off-label practice of mixing femoral heads with dual mobility (DM) polyethylene liners from different manufacturers is commonly performed. The resistance to intraprosthetic dislocation, when the inner prosthetic head disengages from the polyethylene bearing, between mixed and same manufacturer constructs remains unknown.

Between January 2010 and July 2018, 168 DM liners were retrieved. Specimens were excluded for catastrophic wear (n = 14), previously levered-out (n = 17), and cases in legal proceedings (n = 8). Using a validated setup, 129 specimens were uniaxially loaded 100 mm from the femoral head until lever-out failure of the head from the liner. The difference in maximum lever-out force (LOF) was compared for same and mixed manufacturer retrievals (Student t-test). Multivariable regression analysis evaluated the influence of potential confounders (length of implantation, head size, head material, presence of skirt) on LOF.

Ninety-seven same and 32 mixed manufacturer DM constructs were tested. The average LOF for same (272.6 ± 68.7 N) and mixed (299.2 ± 89.0 N) manufacturer specimens was not significantly different (P = .08). An inner head size of 22.2 mm was associated with 184.4-N increase in LOF (P < .001), the presence of a skirt was associated with 63.8-N increase in maximum LOF, and head material (ceramic vs metal) did not influence LOF.

We found no difference in the force required to lever-out same and mixed manufacturer inner heads from DM liners, suggesting that mixing manufacturers when placing DM articulations on well-fixed femoral stems should not increase the risk of intraprosthetic instability.