Articular cartilage

Question 1

What cell lineage are chondrocytes derived from?

Answer 1

Mesenchymal cells

Question 2

4 zones of cartilage
Percentage
Orientation of collagen
Shape of chondrycytes
Water / proteglycan content

Answer 2

• Superficial (tangential) – 10%. Smooth, low-friction gliding surface. Resists shear. Collagen is arranged in parallel to surface. Chrondrocytes are oblong along axis of surface. High water, low proteglycan content.
• Middle (transitional) – 40-60%. Disorganized arrangement. Spheroid chondrocytes. Low water, high proteoglycan content.
• Deep (radial) – 30%. Spheroidal columns of chondrocytes. Collagen fibers are oriented vertical to the joint space. Extends into “tidemark” zone above calcified cartilage. Lowest water content and highest proteoglycan content.
• Calcified cartilage – anchored to bone

Question 3

Which zones of cartilage accept compressive loads and produce matrix?

Answer 3

Middle and deep zones

Question 4

Cartilage changes w/ aging

Answer 4

Total chondroitin concentration falls and keratin sulfate increases. Water content decreases. Fewer number of chondrocytes.

Question 5

4 secondary causes of OA

Answer 5

Infection, trauma, and metabolic / neurologic disorders. May occur at any age.

Question 6

Molecular changes in OA

Answer 6

Loss of proteoglycans and increased water. Remaining proteoglycans have shorter chains and are unbound to hyaluronic acid. Collagen loses organization.

Question 7

Imaging findings in OA vs Inflammatory Arthritis

Answer 7

• OA: FOCAL joint space narrowing, osteophyte formation, subchondral sclerosis, subchondral cyst formation, and deformity.
• Inflammatory: SYMMETRIC joint space narrowing, periarticular erosions / ostepenia, and joint subluxation. Osteophytes are RARE.