Which of the following is a direct contributor to cartilage matrix degradation in OA?

• A. Increased activity of matrix metalloproteinases and ADAMTS enzymes
• B. Increased bone formation
• C. Decreased blood supply
• D. Increased cartilage synthesis

Answer: (A)

Direct cartilage matrix degradation in osteoarthritis happens when catabolic enzymes break down the extracellular matrix. Matrix metalloproteinases, especially MMP-13, cut collagen type II, which provides the cartilage’s structural framework. Aggrecanases from the ADAMTS family, particularly ADAMTS-4 and ADAMTS-5, cleave aggrecan, the proteoglycan responsible for cartilage’s ability to resist compression. When these enzymes are upregulated by inflammatory signals within the joint, the matrix of cartilage is degraded directly, leading to thinning and fissuring of the tissue.

Other changes in osteoarthritis, like increased bone formation or osteophyte development, reflect secondary remodeling of subchondral bone and joint surfaces rather than direct degradation of the cartilage matrix. Cartilage is avascular, so changes in blood supply aren’t the primary driver of matrix breakdown, and increased cartilage synthesis would oppose degradation rather than cause it.