Abstract
Do we need new polyethylene? Is there a clinical problem with first generation crosslinked polyethylene (XLPE)? Are we being duped into believing that doped polyethylene will solve a problem?
Clinical failures of polyethylene bearing total hip replacements are related to wear and the mechanical properties of the polyethylene. Wear is primarily related to crosslinking. Wear failures are secondary to periprosthetic osteolysis while mechanical failure causes cracking of thin polyethylene. Use of large femoral heads that reduce dislocation may increase wear and mechanical failure in the second decade of XLPE use.
There is no question that XLPE has reduced 2-dimensional (2D) head penetration, volumetric penetration and periprosthetic osteolysis with traditional 28 mm head sizes. Reported 2D penetration rates are 0.03–0.07 mm/year and clinically important polyethylene wear induced osteolysis is nonexistent. However, larger heads with the same 2D head penetration will generate more volumetric debris and could cause osteolysis.
There is no question that retrieved XLPE components have low levels of oxidation at the time of explant. While this is unexpected, the levels are well below levels reported with traditional polyethylene. It remains to be seen if these levels of oxidation will cause mechanical failures.
Currently available versions of polyethylene have focused on eliminating oxidation induced mechanical property reduction and not additional wear reduction. This is accomplished with Vitamin E doping or blending. While the local effects of Vitamin E polyethylene particles at the cellular level have been studied the clinical effect of these chemically new particles remains to be seen.
This author believes that long term volumetric wear with large head size is a greater concern than reduced mechanical properties secondary to in-vivo oxidation. New polyethylene development needs to focus on additional wear reduction. Can we afford to pay more for a new polyethylene in a value based healthcare environment?
