MPC-grafted highly cross-linked polyethylene liners retrieved from short-term total hip arthroplasty: Further evidences for the unsuitability of the MPC method.

An analysis is presented of four short-term retrieved highly crosslinked polyethylene (HXLPE) hip liners grafted with 2-methacryloyloxyethyl phosphorylcholine (MPC) on their bearing surfaces, which were recently commercialized as a new generation of artificial hip joints. Straightforward evidences by X-ray photoelectron spectroscopy (XPS) confirmed that the MPC layer peeled off on the bearing surface of all short-term liners in both main wear and nonwear zones. Analyses by Fourier-transform infrared spectroscopy with attenuated total reflection assessed the extent of surface oxidation and revealed the type of oxidative species. Electron spin resonance analyses, which compared retrievals and as-received samples, revealed the presence of different species of alkoxyl CO• radicals. This study suggests that MPC grafts on polyethylene do not offer any additional protection from oxidation and can delaminate prematurely after short-term in vivo exposure.