Review Question - QID 218172

Highly cross-linked polyethylene (XLPE) bearing surfaces were developed to address the problems of wear and osteolysis associated with conventional, non-crosslinked ultra-high molecular weight polyethylene (UHMWPE) liners. Overall, high-quality data have demonstrated that XLPE liners exhibit significantly reduced wear and are associated with greater implant survival at 10 years when compared to UHMWPE liners (Answer 2).

It is well-known that wear represents a process through which particulate debris forms. In response to this debris, the body generates a cell-mediated response, which has the ability to trigger a variety of downstream effects. With respect to polyethylene, the presence of polyethylene particles triggers macrophage activation and subsequent macrophage recruitment. These macrophages then release a variety of osteolytic factors including, but not limited to, TNF-alpha, hydrogen peroxide, IL-1, IL6, and prostaglandins. Second to the release of these factors, RANK production is increased, leading to osteolysis, prosthesis micromotion, and particulate debris dissemination.

In response to concerns regarding osteolysis, much research has been performed regarding the optimal manufacturing and storage process for polyethylene - the material most utilized for smoothe articulation between metal/ceramic shell and head bearing surfaces. Irradiation, used to sterilize polyethylene, was historically performed in an oxygen-rich environment, which led to early bearing failure secondary to the effects of oxidation. Irradiation in an oxygen-depleted environment, however, leads to cross-link formation, which greatly improves material resistance to adhesive and abrasive wear, at the expense of decreased ductility and fatigue resistance.

Calvert et al. performed a double-blind, prospective, randomized controlled trial comparing XLPE and UHMWPE liners in total hip arthroplasty. Their study ultimately enrolled 119 patients, and the primary outcomes were linear, three-dimensional, and volumetric wear. Overall, all three wear rates were lower in the XLPE cohort between 6 months and 4 years postoperatively (p < .05), leading the authors to conclude that XLPE reduces short-term polyethylene wear.

Devane et al. also performed a double-blind, prospective, randomized controlled trial investigating XLPE and conventional UHMWPE liners in total hip arthroplasty. Their study randomized 122 patients and their cohorts were followed for a minimum of 10 years, with 100% of patients available for 10-year follow-up. At a minimum of ten years, three-dimensional wear, osteolysis, and revision rates were lower in the XLPE group versus the UHMWPE group, with no appreciable difference in patient-reported outcomes. Overall, the authors concluded that XLPE liners exhibit significantly reduced wear and greater implant survival at ten years when compared with conventional UHMWPE liners.

Incorrect Answers
Answer 1: XLPE liners generate smaller, not larger, wear particles, and are more resistant to wear than UHMWPE liners.
Answer 3: Conventional UHMEPE liners exhibit a wear rate of 0.1-0.2 mm/yr.
Answer 4: THA liners less than 6mm in thickness are associated with greater wear rates.
Answer 5: XLPE liners exhibit less wear and greater implant survival at ten years when compared to conventional UHMEPE liners.