Cross-sectional comparison of synovial fluid biochemical markers in equine osteoarthritis and the correlation of these markers with articular cartilage damage

Objective: To investigate the relationship between biochemical markers in the synovial fluid of osteoarthritic and contralateral equine joints and gross articular cartilage pathology. Design: Twenty-two horses underwent bilateral arthroscopy of their carpal or metacarpophalangeal joints following recent onset lameness. The degree of cartilage damage in each joint was scored and synovial fluid, from both the clinically affected and the contralateral joint, was collected. Bone specific alkaline phosphatase (BAP), 5D4 epitope of keratan sulphate (KS), total glycosaminoglycans (GAG) and hyaluronan (HA) were measured. Results: The mean age of the horses was 4.1 years and the maximum duration of lameness was three months. Joints examined were midcarpal, antebrachiocarpal and metacarpophalangeal. The median concentration (semi-interquartile range) of BAP was significantly higher in the clinically active joint than in the contralateral joint, 21.75 (6.22) vs. 12.35 (4.07) units, while the other biomarkers measured were significantly lower in the clinically active joint than in the contralateral joint, i.e. KS 8.79 (1.96) mug/ml vs. 16.39 (5.65) mug/ml, KS:GAG ratio 0.19 (0.04) vs. 0.31 (0.10) and HA 741.6 (222) mug/ml vs. 1061.75 (325) mug/ml. BAP was positively (R=0.57), and KS (R= -0.57) and KS:GAG ratio (R=-0.49) were negatively correlated to the degree of cartilage damage within the joint. Conclusion: The correlation between articular cartilage damage and synovial fluid BAP and KS imparts validity to their potential use as non-invasive diagnostic aids in equine osteoarthritis (OA). The positive correlation between BAP and cartilage damage suggests that there is a link between bone turnover and cartilage damage in OA. (C) 2001 OsteoArthritis Research Society international.