Wear of polyethylene in the total hip prosthesis.

Direct in vivo measurement of wear of total hip prostheses by radiography is not possible. However, improved in vitro approaches have been developed that agree with clinical observations in all salient points. Such measurements show that the wear of the polyethylene component depends crucially on the molecular weight distribution (and probably on other structural variables). Combined with clinical retrievals, there is evidence that relatively high wear may occur even in the absence of acrylic debris. Although sufficient knowledge exists to reduce wear of the total hip prosthesis to a negligible level, for the total knee replacement with higher contact stresses, presently, this is not the case.