Cartilage markers in synovial fluid in symptomatic knee osteoarthritis.

Objective: To investigate if the relative content of aggrecan and cartilage oligomeric matrix protein (COMP) in synovial fluid lavage samples differs between individuals with knee pain with or without evidence of radiological knee osteoarthritis (joint space narrowing).

Methods: In a community based cohort of 204 individuals aged 35-54 years with chronic (> 3 months duration) knee pain, a subgroup of 45 subjects with radiographic osteoarthritis, grade I according to the Ahlbäck classification, was randomly chosen; 45 individuals, age and sex matched from the same cohort with chronic knee pain but with normal radiographs, served as controls, Knee joint fluid was obtained by a standardised lavage procedure. The concentrations of aggrecan core protein epitopes and a cartilage matrix protein (COMP) were determined by immunoassays and the aggrecan/COMP concentration ratio was calculated.