Histological Features of Arthritis in Dogs

Early histological findings in canine osteoarthritis include fragmentation of the cartilage surface (fibrillation) and decreased uptake of metachromatic stains.


Histological signs later in the disease process include identification of vertical clefts in the cartilage, cloning and aggregation of chondrocytes, the formation of osteophytes, which is indicative of remodelling and repair, and regeneration of the tidemark. The tidemark is the transition zone between calcified and non-calcified articular cartilage. In osteoarthritis, the tidemark can be penetrated by tiny blood vessels and in some cases there will be the formation of more than one tidemark.

Early osteophytes made of cartilage, may be present as early as 3-7 days after initiation of osteoarthritis. Because the osteophytes have not calcified into bone yet, they are not able to be observed radiographically. Osteophyte formation may result from a number of factors, they are listed below:

• Joint instability
• Vascular-mediated effects at the marginal zone where the cartilage merges with the synovial membrane
• Synovial membrane inflammation
• Remodelling of the degenerative process associated with structural cartilage changes
• Overexpression of TGF-a (Transforming growth factor; TGF-a’s primary role is to control cellular differentiation and proliferation in most cells)

In severe, progressed cases of canine osteoarthritis, joint biopsy findings will include total loss of cartilage, joint sclerosis, and focal osteonecrosis.

-Dr Caroline