Physiology of Joints Flashcards
What are some features of fibrous joints (synarthrosis)?
Bones united by fibrous tissue, doesn’t allow any movement (e.g skull in adults)
What are some features of cartilaginous joints (amphiarthrosis)?
Bones united by cartilage, allow limited movement (e.g intervertebral discs, pubic symphysis, part of sacroiliac joints, costochondral joints)
What are some features of synovial joints (diarthrosis)?
Bones separated by a cavity (containing synovial fluid) and united by a fibrous capsule (and other extra-articular structures e.g tendons, bursae)
Where is the synovial membrane located and what is it?
Lines the inner aspect of the fibrous capsule; is a vascular connective tissue with capillary networks and lymphatics
What does the synovial membrane contain?
Synovial cells (fibroblast) which produce synovial fluid
What lines the articular surface of bones in synovial joints?
Cartilage
What are the two classes of synovial joint?
Simple = one pair of articular surfaces Complicated = more than one pair of articular surfaces
What are the physiological functions of joints?
Structural support
Purposeful motion = stress distribution, conferring stability, joint lubrication
What components of the joint take up the greatest share of stress?
Muscles and tendons crossing over the joint
How do joints confer stability?
Shape of articular compartment, ligaments provide secondary stabilising influence, synovial fluid acts as adhesive seal that freely permits sliding motion between cartilaginous surfaces
What elements provide joint lubrication?
Cartilage interstitial fluid, synovium (derived hyaluronic acid), synovium-derived lubran
What are the functions of synovial fluid?
Lubricates joint and facilitates movement by reducing friction
Helps minimise wear and tear of joints
Aids in nutrition of articular cartilage
Supplies chondrocytes with O2 and nutrients, and removes CO2 and waste products
What is the volume of the joint cavity filled by synovial fluid in the adult knee?
<3.5ml
What continuously replenishes and absorbs synovial fluid?
Synovial membrane
Why does synovial fluid have a high viscosity?
Mainly due to presence of hyaluronic acid (mucin) produced by synovial cells
How does rapid movement affect the viscosity of synovial fluid?
It decreases the viscosity but increases the elasticity
How are the other constituents of synovial fluid derived?
By dialysis of blood plasma
Does the synovial fluid contain many cells?
No - only contains very few, mainly mononuclear leucocytes
What is the normal appearance and cell count of synovial fluid?
Normally clear and colourless; it has <200 WNC/cubic millimetre, of which polymorphs are usually <25/cubic millimetre
What can increase the cell count of synovial fluid?
Inflammatory and septic arthritis
What can turn the synovial fluid red?
Haemorrhagic arthritis and trauma
What is the role of articular cartilage?
Provides low friction lubricated gliding surface to prevent wear and tear, distributes contact pressure to subchondral bone
What determines the mechanical properties of cartilage?
Composition of the ECM, interaction between fluid and solid phase of cartilage
How is articular cartilage structured?
Four zones = superficial zone (10-20%), middle zone (40-60%), deep zone (30%) and calcified zone
How do the zones of articular cartilage differ?
In organisation of collagen fibres and relative content of cartilage components
What are the usual properties of articular cartilage?
Hyaline, elastic and has sponge-like property, covers articular surfaces of bone
What are the components of the ECM of articular cartilage?
Water (70%), Collagen (mainly type II, 20%), proteoglycan (10%)
What are some features of the water found in the ECM of the articular cartilage?
Unevenly distributed (highest (80%) near articular surface), decreases with age, maintains the resilience of tissue and contributes to nutrition and lubrication system
What are some features of the collagen that makes up the ECM of the articular cartilage?
Mainly type II collagen, decrease with age, maintains cartilage architecture and provides tensile strength and stiffness
What are some properties of the proteoglycans found in the ECM of the articular cartilage?
Highest concentration found in the middle and deep zones, composed mainly of GAGs, decreases with age, responsible for the compressive properties associated with load bearing
How much of the total articular cartilage volume does the ECM normally constitute?
> 98%
What synthesises and maintains the ECM of the articular cartilage?
Chondrocytes (account for <2% of total cartilage volume)
How do chondrocytes receive O2 and nutrients?
Via the synovial fluid (articular cartilage is avascular)
What is the rate of ECM degradation equal to in normal joints?
The rate at which the ECM is replaced
How can joint disease arise?
Due to changes in the relative amounts of the major components of the ECM, or if the rate of ECM degradation exceeds the rate of its replacement
What are the factors which influence cartilage matrix turnover?
Catabolic factors = stimulate proteolytic enzymes and inhibit proteoglycan synthesis (TNF, IL-1)
Anabolic factors = stimulate proteoglycan synthesis and counteract effects of IL-1 (TGF-beta, IGF-1)
What are some markers of cartilage degradation?
Serum and synovial keratin sulphate = increased levels indicate cartilage breakdowns, levels increase with age and osteoarthritis
Type II collagen in synovial fluid = increased levels indicate cartilage breakdown, useful in evaluating cartilage erosion
How does osteoarthritis arise?
Cartilage and synovial composition and function deteriorate with age and repeated wear and tear
What causes rheumatoid arthritis?
Synovial cell proliferation and inflammation
What can lead to the development of soft tissue rheumatism?
Injury and inflammation to periarticular surfaces
What can deposition of salt crystals in joints cause?
Gout = needle shaped uric acid crystals Pseudogout = rhomboid shaped calcium pyrophosphate crystals
