MSK 2 - Articular Structure and Pathology Flashcards
What is a synovial joint composed of?
Joint capsule: Fibrous joint capsule (outer layer) and synovial membrane (inner layer)
Joint space
Synovial fluid
Articular cartilage
What is the outer layer of the joint capusule?
Fibrous capsule or stratum fibrosum
What kind of blood supply does the fibrous capsule have?
Poor blood supply BUT rich in joint receptors (sensory receptors)
What is the function of the synovium?
produce synovial fluid
What do type B cells of the synovium do?
Secrete hyaluronate (HA) = gel that improves viscosity of synovial fluid and attracts H2O
Secrete lubricin (glycoprotein) = reduce friction
What do type A cells of the synovium do?
Secrete immunoglobulins
Secrete lysosomal enzymes
What is synovial fluid?
Clear viscous fluid
Provides lubrication for joint surface –> frictionless surfaces between bones
What are thixotrophic properties?
Viscosity varies inversely w/ velocity of movement:
Rest - synovial fluid resists movement of joint
Movement - synovial fluid provides less resistance to movement
What is hyaline articular cartilage?
Thin covering on the ends of most bones
What does hyaline articular cartilage do?
Reduces friction
Absorb/disperse compressive forces
What is articular cartilage composed of?
Cellular component
Extra-cellular matrix
What is the cellular component of articular cartilage?
Chondroblasts (chondrocytes)
What do chondrocytes to?
Produce/maintain extra-cellular matrix
How much of cartilage do chondrocytes make up?
2%
What makes up the non-fibrous component of the extra-cellular matrix?
Proteins
Proteoglycans
(makes up 5 - 10%)
What does the non-fibrous component of the extra-cellular matrix do?
Regulate fluid flow in/out of cartilage (water = 60 - 80% of cartilage)
What makes up the fibrous component of the extra-cellular matrix?
Collagen fibers
What do collagen fibers do in the extra-cellular matrix?
Arranged to absorb mechanical stress
How much of the cartilage is made of collagen?
10 - 30%
What is zone 1 of the cartilage-bone interface?
Smooth surface –> reduce friction of joint surface
What are zone 2 and zone 3 of the cartilage-bone interface?
Transitional zones –? absorb compressive forces
What is the tidemark of the cartilage - bone interface?
Interface between uncalcified and calcified layers
What is zone 4 of the cartilage-bone interface?
Calcified cartilage –> anchors cartilage to bone
What are the stimuli for matrix turnover?
Enzymes from chondrocytes
Hormones: GH/IGF
Mechanical Load: weight bearing
What does weight bearing activity do in healthy cartilage?
Push fluid (water/synovial fluid) out of cartilage
What happens to fluid flow during weight bearing activity in healthy cartilage as the cartilage becomes more compressed?
Fluid flow out becomes slower and resistnace becomes exponentially harder
**prevent ALL of the fluid from flowing out of the cartilage
What is responsible for regulating fluid flow in/out of cartilage?
Proteoglycans
What is the net result of fluid flow in/out of cartilage w/ compression?
Protects against compressive forces
Allows for nutrients to pass in/out of cartilage to reach chondrocytes
Does articular cartilage have blood/nerve supply?
No
**pain results from inflammation/swelling/irritation of pain sensitive tissues such as joint capsule/synovium, periosteum
How does articular cartilage heal after its been injured?
Poor ability to regenerate d/t poor blood supply
What is the most common joint disease?
Osteoarthritis
What is the primary defect of osteoarthritis?
Loss/disruption of articular cartilage –> matrix destruction involving chondrocytes, collagen and proteoglycans
What are the enzymatic changes seen in osteoarthritis?
Excessive enzyme secretion from chondrycytes –> matrix breakdown
Ezymes from synovium also contribute to matrix (collagen) breakdown
**loss of proteoglycans in cartilage disrupts fluid regulation (H2O flows in/out too easily)
What are the hormone changes seen in osteoarthritis?
Chondrocytes become less sensitive to GH/IGF
What are the cytokine changes seen in osteoarthritis?
Excessive production of IL-1 –> inhibition of normal cytokine regulation of matrix turnover
- *IL-1 facilitates NO synthesis
- *IL-1 = inflammatory cytokine
What is found in synovial fluid and synovium in the joints of pts w/ osteoarthritis that is not found in normal joints?
Nitric Oxide
What does nitric oxide do in the joints of pts w/ osteoarthritis?
Chondrycyte apoptosis
What are the fluid changes @ rest that occur w/ osteoarthritis?
Increased volume of water w/ in cartilage
What are the fluid changes during weight bearing activity that occur w/ osteoarthritis?
Fluid is pushed out rapidly
Cartilage is easily compressed w/o much resistance
**relase of wt bearing allows increased volume of fluid to re-enter cartilage
What is the net result of the fluid changes during weight bearing activity that occur w/ osteoarthritis?
Cartilage has limited ability to absorb foces and provide adequate nutrients to chondrocytes
How does osteoarthritis effect surrounding structures (besides articular cartilage)?
Cause bone sclerosis and bone cysts
Osteophyte formation –> irritation
Synovial thickening –> loss of gross movement
What are the risk factors of osteoarthritis?
Trauma/Genetics = largest risk
Joint/ligament laxity
Inflammatory conditions
Neurological disorders –> abnormal movements –> damage joints
Exercise –> high impact sports