Characterization of wear debris of polyethylene Hylamer insert gamma irradiated in air.

Hylamer polyethylene insert was used in the early 1990's to make hip joint components and, compared with traditional UHMWPE, claimed to have doubled elastic modulus, increased compressive and tensile strengths and greater resistance to crack propagation and creep. Based on favorable pre-clinical evaluations, Hylamer was preferentially selected by surgeons. Clinical experience has shown that Hylamer insert if sterilized by gamma rays in the presence of oxygen, are easily affected by wear, which leads to osteolysis. The aim of this study was to analyze the morphology of Hylamer polyethylene wear debris with wear debris from traditional polyethylene inserts sterilized by the same method.. -Periprosthetic tissue was obtained from : 7 patients with Hylamer inserts gamma sterilized in air (Duraloc cup, Depuy Orthopedics, Indiana, USA) 6 patients with traditional UHMWPE (PCA cup, Stryker Howmedica, New Jersey, USA) sterilized by the same method. -Joint capsule biopsy was paraffin embedded. -20 micron thick slices were placed onto the polycarbonate (size pore 0.2 micron) filter placed onto a polypropylene holder. -Slice were de-waxed and digested with hypochlorite. -Double distilled water was flushed through the filter. -Filters were observed by SEM at 10.000X. -Particles were counted and measured. -Comparisons between the means of the number of particles and their shape descriptions were made by Student's t test, or the Kolmogorov-Smirnov test according to the variance of data. Sections of the newly formed joint capsule were characterized by the presence of a fibrous layer of variable thickness, many mononuclear phagocytes and sometimes a few giant cells. The frequency distribution of globular and fibrillar particles was similar in both groups. The globular particles in the Hylamer samples had a mean area of 0.12 micron2, which was significantly less than that of controls (0.30 micron2) . The width of fibrillar particles in the Hylamer samples was significantly lower than that of controls. The two materials, despite undergoing the same type of sterilization, produced different types of wear, connected to their different properties. The difference in morphology of Hylamer polyethylene wear particles in comparison with traditional UHMWPE might have caused a more intensive biological response, early and massive osteolysis, and therefore, early loosening.