Wear of articular cartilage: the effect of crystals.

An investigation of the effect of crystals in a lubricant on the wear of articular cartilage in vitro was carried out in order to examine the hypothesis that crystals present in synovial fluid could cause abrasive damage of the articular surface. Plugs of cartilage were worn against a stainless steel counterface in a pin-on-disc wear rig. The concentration of cartilage debris present in the lubricant was assessed by measuring the bound sulphate originating from the glycosaminoglycans by ion chromatography. Results indicated that the presence of crystals in the lubricant significantly increased the concentration of wear debris and that the crystal size and morphology influenced the type of damage sustained by the cartilage. Other experimental evidence suggested that cartilage scratched in vivo was no more susceptible to further in vitro damage in this experimental model than normal cartilage. These results implied that crystals present in the synovial fluid of arthritic joints have the potential to cause excessive wear of the articular surface, but that if such crystals are removed the scratched cartilage may not be susceptible to any further damage by abrasive wear.