Physicochemical and biomechanical examination of surfaces of retrieved polyethylene heads from total hip prostheses with rotating polyethylene head system.

Abstract

In order to assess whether hydrodynamic lubrication occurs in total hip prostheses with a rotating polyethylene (PE) head system (R-THP), several physicochemical, morphological, and biomechanical tests were carried out. R-THPs have been used in more than 1000 patients since 1970, and 12 PE heads, retrieved from 10 patients after an average of 24.5 years since total hip arthroplasty (THA), were employed for the tests. The weight-bearing area of the PE surface was light yellow in color and considerably oxidized, but no wear scars were observed. In the non-weight-bearing area, in contrast, discoloration and oxidation were hard to detect. The weight-bearing surface of the PE head became smoother with time after THA, and the friction coefficient did not differ significantly from that of an unused PE head. The radial clearance between head and socket decreased at a temperature of 17 degrees C, which is equivalent to the difference between room temperature and the temperature of the human body. Scanning electron microscopy showed a fine undulating pattern, which suggested that hydrodynamic lubrication could occur in the rotating PE head system.