Role of free radicals in aseptic loosening of hip arthroplasty.

Fibrous pseudocapsule around hip implants is an invariable finding at revision operations and is believed to release inflammatory mediators that stimulate bone resorption. Reactive oxygen species have been proposed to be causative factors in various disorders with tissue fibrosis. We were interested in investigating whether aseptic loosening is connected with high oxidative stress, and in showing the underlying mechanism of periprosthetic fibrosis and its role in loosening. Levels of oxidative stress markers reduced (GSH) and oxidized (GSSG) gluthatione and malondialdehyde (MDA) were assayed in 28 loose hips and in 12 stable hips revised for high rate of wear and osteolysis. Collagen in the periprosthetic tissues was measured as hydroxyproline content. Osteolysis and polyethylene wear were graded. Increased oxidative stress measured by low GSH/GSSG ratio as well as by increased MDA level was established in patients compared to controls. Oxidative stress markers intercorrelated significantly. MDA and both GSH and GSSG levels correlated significantly with hydroxyproline level. Levels of GSSG and MDA were higher in hips with greater polyethylene wear. The results suggest that high oxidative stress may play a role in formation of a fibrous membrane observed at revision of loose hips. The fibrous pseudocapsule is probably related to high intraarticular pressure and expansion of the effective joint space. This study may elicit some aspects of the pathogenesis of aseptic hip loosening and aid in future investigations aiming at prevention of this complication.