Osteoarthritis develops after damage to the cranial cruciate ligament (CCL). Treatment with conventional intraarticular and extraarticular techniques does not appear to stop its radiographic progression. It has been claimed that tibial plateau leveling osteotomy (TPLO) provides functional stability for the stifle and can reduce, or stop, the progression of osteoarthritis. Plain radiography, however, is limited with respect to evaluating and staging this condition. Biochemical markers are released from joint tissues and may provide another means to measure the status of articular cartilage. Information on synovial fluid biochemical markers in dogs is, however, limited. This study evaluated 2 hypotheses: 1) that the concentrations of 3 potential synovial fluid biochemical markers from dogs with CCL injury would be affected by TPLO and 2) that medial meniscal release or meniscal injury would alter the expression of these potential markers. Synovial fluid was collected from 41 dogs with CCL disease before TPLO surgery and again 6 weeks and 6 months after surgery. The fluids were assayed for 1/20/5D4 epitope of keratin sulfate (KS-5D4), cartilage oligomeric matrix protein (COMP) concentration, and sulfated glycosaminoglycans (S-GAG). Synovial levels of S-GAG, KS-5D4, and COMP did not significantly change during the 6 months after TPLO surgery, which may reflect the minimal impact on joint metabolism of a limited arthrotomy or that TPLO does not influence the expression of these potential markers. The study results showed no evidence that TPLO affects cartilage metabolism and also found that dogs with medial meniscal injury at the time of study entry had decreased concentrations of synovial fluid COMP. However, further studies would be necessary to validate these findings.

COMMENTARY: More important than this study's lack of evidence for TPLO as disease-modifying surgery are the interesting findings regarding potential biochemical markers for canine osteoarthritis. This is the first report to document a significant correlation between synovial fluid COMP and naturally occurring meniscal injury in dogs. Serum COMP in humans is one of the most promising biochemical markers for predicting hip osteoarthritis before radiographic diagnosis. It also reflects disease severity and progression in knee osteoarthritis. Previous studies have suggested that synovial fluid COMP concentrations might be altered in dogs with osteoarthritis, but results have varied from those reported here. Because of the potential confounding variables in these studies, including disease duration, additional studies are needed to better define the relationship between synovial fluid COMP levels and changes in canine articular cartilage in osteoarthritis.

Use of biochemical markers of osteoarthritis to investigate the potential disease-modifying effect of tibial plateau leveling osteotomy. Girling SL, Bell SC, Whitelock RG, et al. J SMALL ANIM PRACT 47:708-714, 2006.