Results of hip resurfacing.

Background: The renewed popularity of resurfacing hip arthroplasty in the last 10 years has generated a remarkable quantity of scientific contributions based on mid- and short-term follow-up. More than one paper has reported a consistent early revision rate as a consequence of biological or biomechanical failure. Two major complications are commonly described with resurfacing implants: avascular necrosis and femoral-neck fracture. A close relationship between these two events has been suggested, but not firmly demonstrated, whereas cementing technique seems to be better understood as potential cause of failure.

Methods: We performed an in vitro study in which four different resurfacing implants were evaluated with a simulated femoral head, two types of cement, (low and high viscosity) and two cementing techniques: direct (cement apposition directly on the femoral head) and indirect (cement poured into the femoral component).

Results: High-viscosity cement showed homogeneous distribution over the entire femoral head. Low-viscosity cement showed a massive polar concentration with insufficient, if not absent, distribution in the equatorial zone.

Conclusion: Polar cement concentration could be a risk factor for early implant failure due to two effects on the femoral head: biological (excessive local exothermic reaction could cause osteocyte necrosis) and biomechanical (which could lead to uneven load distribution on the femoral head).