ROUTINE POST-OPERATIVE X-RAY EXPOSURE AND POLYETHYLENE WEAR

Abstract

The purpose of this study was to determine if routine x-ray exposure produced any chemical oxidation of Ultra High Molecular Weight Polyethylene (UHMWPE), used for joint arthroplasty.

Three different polyethylene polymers were obtained from Biomet, Depuys and Howmedica. These samples had undergone sterilisation and packaging methods. Rectangular shapes of polymer were cut according to the standards specified by the ASTM (American Society For Testing and Materials). Eight samples of each polymer were obtained and divided randomly in to test and control subgroups. The test samples were exposed to ten x-rays with the standard dose used for the hip joint.

Polyethylene oxidation was measured using Fourier transform infrared spectroscopy. This technique can assess the incorporation of oxygen within the carbonyl region. Radiated and non-irradiated samples were compared in each polymer group.

Oxidation from the Fourier transform infrared spectroscopy was quantified by calculating the area under a signature absorption peak for UHMWPE (methylene band at 1370 cm-1) and an oxidation absorption peak (carbonyl band at 1720 cm-1). The ratio of the area of the oxidation peak to the area of the signature peak yields the carbonyl content, or oxidation, relative to the amount of polyethylene. There was no significant difference in oxidation after exposure to x-rays between test and control UHMWPE samples.

Although numerous studies have looked in to the effects of high dose radiation exposure on polyethylene, effects of routine x-rays have not been studied before. It is common practice to follow-up patients with joint replacements over a long period with xrays at each visit. Present study examined the effects of routine x-rays on oxidation of polyethylene. However there was no detectable oxidation after exposure to x-rays. This study paves way for further research in this direction.