Physiology of Joints Flashcards
3 types of joints?
- Synovial (AKA diarthrosis)
- Fibrous (AKA synarthrosis)
- Cartilaginous (AKA amphiarthrosis)
What are fibrous joints?
Bones are united by fibrous tissue and so no movement is allowed, e.g: bones of the skull in adults
What are cartilaginous joints?
Bones are united by cartilage and allow limited movement, e.g: intervertebral discs, pubic symphisis, part of the sacroiliac joint and the costochondral joints
What are synovial joints?
Bones are separated by a cavity, filled with synovial fluid, and united by a fibrous capsule and other extra-articular structures, e.g: ligaments, tendons and bursae
Describe the synovial membrane
Lines the inner aspect of the fibrous capsule; it is a vascular connective tissue, with capillary networks and lymphatics
Fibroblasts (synovial cells) produce synovial fluid
2 types of synovial joints?
Simple synovial joint (one pair of articular surfaces), e.g: metacarpophalangeal joint
Compound synovial joint (more than one pair of articular surfaces), e.g: elbow joint
Functions of joints?
Provide structural support and allow purposeful motion of the MSK system
3 roles of joints during purposeful motion?
Stress distribution
Confer stability
Joint lubrication
How do joints confer stability?
Shape of the articular component, e.g: the hip joint
Ligaments provide a second major stabilising force
Synovial fluid acts as an adhesive seal, freely permitting sliding motion between cartilaginous surfaces
What provides joint lubrication?
Cartilage interstitial fluid
Synovium (the synovial membrane) is a polymer of disaccharides and is lubricated with hyaluronic acid (mucin)
Synovium-derived lubrcin (glycoprotein)
Functions of synovial fluid?
- Lubricates joint
- Facilitates joint movements, reducing friction
- Helps minimise wear-and-tear via lubrication
- Aids in nutrition of articular cartilage
- Supplies chondrocytes with O2 and nutrients and removes CO2 and waste products
The synovial fluid not a static pool. How?
Continuously replenished and absorbed by the synovial membrane
Thickness of synovial fluid?
High viscosity due to hyaluronic acid (mucin), which is produced by the synovial cells
Viscosity varies with joint movement but this is impaired in a diseased joint
Constituents of the synovial fluid?
- Hyaluronic acid (mucin)
- Uric acid - derived from dialysis of blood plasma
- Few cells (mainly mononuclear leukocytes)
How do the viscosity and elasticity of the synovial fluid vary?
Rapid movement:
Decreased viscosity
Increased elasticity
Appearance of synovial fluid in different scenarios?
Normal: viscous, clear and colourless
Red: traumatic synovial tap and in haemorrhagic arthritis
Leukocytes in synovial fluid?
< 200 WBC/mm3
Of this, <25/mm3 comprises polymorph cells
When does WBC increase in synovial fluid?
Inflammatory and septic arthritis
Compare normal, inflammatory and septic synovial fluid in the following aspects:
Viscosity
Colour
Clarity
Total WBC
PMN leukocytes ?
Describe the synovial fluid in each of the test tubes
A: normal synovial fluid that is viscous and clear
B: from joint with mild synovial inflammation
C: from joint with mild synovial inflammation; blood stain is caused by trauma
D: from a severely inflamed joint; thin and opaque due to a very high polymorph count
Main functions of articular cartilage?
- Provides a low friction lubricated gliding surface to help prevent wear-and-tear of joints
- Distributes contact pressure to subchondral bone
How are the mechanical properties of cartilage determined?
Composition of cartilage ECM and the interaction between the fluid and solid phase plays a role in determining mechanical properties of cartilage
Name the different zones of the articular cartilage?
How do the different zones of articular cartilage vary?
Organisation of collagen fibres
Relative content of cartilage components
Type of cartilage that is normally articular?
Hyaline (elastic and sponge-like)
Components of hyaline cartilage?
Extracellular matrix (ECM):
- Water (70%) - maintain resiliency of tissue and contribute to nutrition and lubrication
- Collagen (20%) - mainly type II; contributes to the elastic behaviour of cartilage, tensile stiffness and strength
- Proteoglycans (10%) - provides compressive properties assoc. with load-bearing
Variation in water content of articular cartilage?
Uneven distribution (most is near the articular surface)
Cartilage water content decreases with AGE
Types of proteoglycan in articular cartilage?
Mainly GAGs, e.g: chondroitin sulphate
Composition changes with age, e.g: chondroitin decreases with age
Formation and composition of the ECM of articular cartilage?
Synthesised, organised and degraded and maintained by chrondrocytes; usually, constitutes <2% of the total volume >98% is ECM
Rate of ECM degradation compared to rate of replacement?
In normal joints, rate of degradation does not exceed rate of replacement In joint disease, rate of degradation exceeds rate of synthesis
How is ECM degraded?
Using metalloproteinase proteolytic enzymes, e.g: collagenase and stromelysin
How can the mechanical properties of cartilage be changed?
Change relative amounts of water, cartilage, proteoglycan
Catabolic factors of cartilage matrix turnover?
Stimulate proteolytic enzymes and inhibit proteoglycan synthesis:
- TNFα
- IL-1
Anabolic factors of cartilage matrix turnover?
Stimulate proteoglycan synthesis and counteract effect of IL-1:
- TGF-β
- Insulin-like growth factor (IGF-1)
Markers of cartilage degradation?
Serum and synovial keratin sulphate, e.g: with age and in osteoarthritis
Type II collagen in synovial fluid - useful for evaluating cartilage erosion, e.g: osteoarthritis and rheumatoid arthritis
Describe osteoarthritis
Cartilage and synovial composition and function deteriorate with age and repeated wear and tear
Describe rheumatoid arthritis
Synovial cell proliferation and inflammation
Describe gouty arthritis
Deposition of salt crystals of uric acid
Describe pseudogout
Deposition of rhomboid shaped calcium pyrophosphate crystals
Describe soft tissue rheumatism
Injury and inflammation to peri-articular structures, e.g. injury to the tendon causes tendonitis
Radiological appearance of osteoarthritis?
Subchrondral sclerosis
Subchondral cyst
Early osteocyte formation
…these may be seen
