Cartilage oligomeric matrix protein (COMP) levels in digital sheath synovial fluid and serum with tendon injury.
Authors: Smith R K, Heinegård D
Journal: Equine veterinary journal
Summary
Smith and Heinegård investigated whether COMP, a non-collagenous extracellular matrix protein abundant in cartilage and connective tissues, could serve as a biomarker for tendon injury in horses, given its established utility in human rheumatological conditions. Using competitive ELISA analysis of synovial fluid from the digital sheath and serum samples, they compared COMP concentrations between healthy controls, horses with tenosynovitis alone, and those with actual tendon damage or sepsis. Digital sheath fluid COMP levels proved substantially more sensitive to pathology, exceeding serum concentrations by over tenfold and rising significantly only when structural tendon damage or sheath infection was present—mild inflammation without tissue damage failed to elevate levels measurably—whilst serum COMP showed age-dependent variation, with foals displaying threefold higher concentrations than adult horses, rendering systemic COMP unhelpful for distinguishing tendinitis from joint disease. These findings establish synovial fluid COMP analysis as a potentially valuable diagnostic tool for practitioners seeking objective confirmation of actual tendon fibre disruption versus non-structural inflammation, though the age-dependency of serum levels warrants caution when interpreting results in young stock. For farriers, veterinarians and physiotherapists managing tendon injuries, local fluid sampling offers superior prognostic insight into tissue integrity and healing trajectory compared to blood-based markers.
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Practical Takeaways
- •Measure COMP in tendon sheath fluid (not serum) to assess active tendon damage or infection; synovial levels reliably distinguish structural damage from simple inflammation
- •Serum COMP is age-dependent and more useful as a joint disease marker than a tendinitis indicator—consider age when interpreting results
- •Elevated sheath fluid COMP supports imaging findings of tendon injury or sepsis and may help guide treatment urgency and prognosis
Key Findings
- •COMP levels in digital sheath synovial fluid were >10-fold higher than serum levels
- •Synovial fluid COMP was significantly elevated with tendon damage or sheath sepsis, but only mildly elevated with tenosynovitis alone
- •Foals (≤1 year) had significantly higher serum COMP than older horses (P<0.001)
- •Serum COMP in tendinitis cases was not significantly different from age-matched controls, indicating serum COMP reflects joint disease rather than tendinitis