Osteoarthritis Flashcards
What age group experiences osteoarthritis?
Usually starts around age 50 with highest incidence after 70. Proteoglycan and collagen synthesis decreases with age.
Who’s more affected by osteoarthritis? Men or women?
Men more often than women
What are the cells that make the extracellular matrix of the cartilage?
Chondrocytes
What is the function of cartilage?
Reduce friction and absorb shock
What sort of joints does osteoarthritis affect?
Synovial joints - freely moving joints. Synovial fluid hydrates, oxygenates and feeds articular cartilage.
Are there blood vessels or nerves in articular cartilage?
No - so insensitive to pain, can’t regenerate much and gets fed from synovial fluid.
Cartilage is made of these protein core and polysaccharide chains called glycosaminoglycans (or GAG’s) that make up what..?
Proteoglycans
What binds one proteoglycan to another to form a complex?
Hyaluronate binds them to form complexes and proteoglycans aggregates with collagen fibres
How do GAG’s attract cations?
Negatively charged GAG’s attarct cations like Na+ and water which makes cartilage resilient and it also regulates synovial fluid movement within the cartilage because where Na+ goes, water follows.
What two things break cartilage down?
1) Cytokines stimulate the synthesis of degradative enymes (that’s why there’s a lot of IL-1 in inflammed joints).
2) Matrix metalloproteinases breakdown collagen and inhibit proteoglycan production.
What makes cartilage?
1) Growth factors like the insulin like growth factor (IGF-1) and the transforming growth factor (TGF - beta) which stimulate proteoglycan and collagen synthesis and activate proteinase inhibitors (inhibit degradative enzymes)
Do genetics and environmental factors have anything to do with osteoarthritis?
Yes.
What’s primary osteoarthritis?
It’s associated with aging. Accumulates with effects of wear and tear. Happens as the quantity and quality of proteoglycans in cartilage decrease with age.
What is secondary osteoarthritis?
Happens because of wear and tear due to chronic or excessive joint stress, joint instability, or direct damage to cartilage. Example: obesity, occupational, repetitive use, athletes or sport injury, congenital - like leg length discrepency, abnormal gait d/t neuromuscular disease, neuropathy
What are some hematologic disorders that cause osteoarthritis?
Hemophilia and hemochromatosis
What are 5 steps that lead to the pathogenesis of OA?
1) Erosion of articular cartilage
2) subchondral sclerosis (scarring)
3) Formation of subchondral cysts
4) Formation of bone osteophytes
5) Secondary inflammation (mild synovitis)
(Damage, sclerosis, cysts, spurs, inflammation)
What’s the hallmark sign of OA?
Loss of proteoglycans
When do cytokines get released in response to joint injury or stress and activate proteinases?
When articular cartilage erodes.
What happens as cartilage erodes?
It starts as proteoglycans are lost and collagen gets broken down. Worsens as proteoglycan and collagen synthesis can’t keep up with age. Cytokines get released due to join injury and then cartilage loses strength due to loss of collagen, and loss of resilience (loss of proteoglycans)
What does the eroded cartilage look like?
Softened (chondromalacia), surface defects (rough appearance), superficial cracks (fibrillation), and progressive erosion to the underlying bone.
What is subchondral sclerosis?
Thickening or hardening of the subchodnral bone. Cartilage is lost and so the bone is exposed. Bone rubs against bone. And bone remodeling increases density in this area (making it look more white on an Xray)
What causes subchondral cysts to be formed?
Happens with advanced disease. Synovial fluid seeds into subchondral bone through microfractures. Trapped fluid forms cysts and increass pressure can cause pain.
Where do osteophytes form?
At the edges of the articular surfaces in response to bone stress. They enlarge and deform joins which causes pain and limits movement. Example: bouchards nodules
What are joint mice?
Pieces of cartilage and bone that break off into the synovial cavity
