Microstructural modifications induced by accelerated aging and lipid absorption in remelted and annealed UHMWPEs for total hip arthroplasty

Three types of commercially available ultra-high molecular weight polyethylene (UHMWPE) acetabular cups currently used in total hip arthroplasty have been studied by means of Raman micro-spectroscopy to unfold the microstructural modification induced by the oxidative degradation after accelerated aging with and without lipid absorption. The three investigated materials were produced by three different manufacturing procedures, as follows: irradiation followed by remelting, one-step irradiation followed by annealing, 3-step irradiation and annealing. Clear microstructural differences were observed in terms of phase contents (i.e. amorphous, crystalline and intermediate phase fraction). The three-step annealed material showed the highest crystallinity fraction in the bulk, while the remelted polyethylene is clearly characterized by the lowest content of crystalline phase and the highest content of amorphous phase. After accelerated aging either with or without lipids, the amount of amorphous phase decreased in all the samples as a consequence of the oxidation-induced recrystallization. The most remarkable variations of phase contents were detected in the remelted and in the single-step annealed materials. The presence of lipids triggered oxidative degradation especially in the remelted polyethylene. Such experimental evidence might be explained by the highest amount of amorphous phase in which lipids can be absorbed prior to accelerated aging. The results of these spectroscopic characterizations help to rationalize the complex effect of different irradiation and post-irradiation treatments on the UHMWPE microstructure and gives useful information on how significantly any single step of the manufacturing procedures might affect the oxidative degradation of the polymer

Eleven-year results of the ABG I hip replacement

The ABG I uncemented hip prosthesis has demonstrated an unacceptably high failure rate and poor functional outcome in our patients. A prospective review was performed of 38 implanted hips with a mean follow-up of 11 years. Sixteen hips have been revised or are candidates for revision hip surgery, due principally to polyethylene wear and pelvic osteolysis. Contributing factors were likely to be the poor wear characteristics of the polyethylene liners—which were gamma irradiated in air—and the thinness of these liners. Of further concern were the poor pain and function scores in the remaining hips [mean Harris Hip Scores (HHS) of 70 (SD 22) at 11-year follow-up]. The influence of the surgical learning curve on clinical results may have been an important factor. Undersized femoral components were associated with poor pain and functional scores in five patients with HHS < 60. All ABG I hip implants must remain under careful, long-term review

Behavior of Hylamer polyethylene in hip arthroplasty: comparison of two gamma sterilization techniques

Hylamer polyethylene was introduced in the 1990s as an alternative to conventional polyethylene. Its chemical and physical properties, and especially its high crystallinity, were claimed to improve resistance to wear. Initially Hylamer devices were sterilized by gamma radiation in air, then the technique was changed and gamma radiation was performed in the absence of oxygen. Clinical experience has shown the early loosening of some devices made from Hylamer. The aim of this study was to ascertain whether early wear and consequent osteolysis was linked to the sterilization method. We retrospectively compared 31 patients with hip prostheses with Hylamer liners sterilized by gamma radiation in air (group 1) with 30 patients with the same prosthesis, but sterilized in the absence of oxygen (group 2). The groups were similar for sex, age, disease, head diameter and material. Mean follow-up was 84 months and no clinical signs of failure were present. Radiographic measurement revealed that wear of group 1 was significantly greater than that of group 2 (0.23 mm/year vs 0.09 mm/year, p=0.001). Periacetabular and femoral osteolysis in group 1 was significantly greater than group 2. In conclusion, the method of sterilization might have influenced the outcome of Hylamer polyethylene liners