Polyethylene is generally used as a component in the majority of hip joint prostheses. A very important downside of this material is excessive wearing of some of the polyethylene cups leading to premature loosening of the hip prostheses.
Based on numerous observations, it has been determined that polyethylene wear is not always identical. Differences observed in the polyethylene wear are not easily explained, as they neither depend on the period of use nor on the factors that may affect the value of load on hip prosthesis such as weight and physical mobility of patients
A question arises whether in cases of premature and excessive wear of polyethylene bearings which cannot be explained by exclusively mechanical factors, the chemical structure of implanted material has changed making the material more susceptible to mechanical tear and wear.
To answer that question the authors made IR spectophotometric studies of 13 samples collected from used ultra-high molecular weight - UHMWPE (DIN 58834) - polyethylene cups removed from patients after several years of use. The results of spectophotometric studies on used polyethylene samples have been compared with 8 samples of new, not yet used polyethylene cups.
The analysis of infrared spectra demonstrates a conspicuous difference in the chemical structure of both types of polyethylene cups. In the spectrum of the exploited material the presence of additional, complex carbonyl band ranging from 1800 to 1600 has been observed, corresponding to the stretching vibrations of the groups >C=O, which does not occur in the spectrum of an unused bearing. It may be concluded that the cause of premature wear-off of polyethylene cups is oxidation and accompanying polymer degradation. Chemical degradation and oxidation of the material lower its mechanical resistance and may accelerate the process of polyethylene cup wear-off.

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