Physiology of Joints

Question 1

what are the three types of joint in the body

Answer 1

synovial
fibrous
cartilaginous

Question 2

describe fibrous joints (synarthrosis) and give an example of one

Answer 2

when bone are united with fibrous tissue, dont allow movement

bones of the skull in adults

Question 3

describe cartilaginous joints (amphiarthrosis) and give 5 examples

Answer 3

bones united by cartilage, allow little movement

intervertebral discs
pubic symphsis
part of the sacroiliac joints
costochondral joints

Question 4

describe synovial joints (diarthrosis)

Answer 4

when bones are separated by a cavity (containing synovial fluid) and united by a fibrous capsule (+ other extra articular structures: ligaments, tendons and bursae)

Question 5

what lines the inner aspect of a synovial fibrous capsule

Answer 5

synovial membrane (60 microM thick)

Question 6

what is the synovial membrane

Answer 6

vascular connective tissue with capillary networks and lymphatics

Question 7

what does the synovial membrane contain that produces synovial fluid

Answer 7

fibroblasts (synovial cells)

Question 8

what covers the articular surfaces of bones in synovial joints

Answer 8

cartilage

Question 9

describe the two types of synovial joints

Answer 9

simple- one pair of articular surfaces

compound- more than one pair of articular surfaces (e.g elbow)

Question 10

what extra articular surfaces support joints

Answer 10

ligaments, tendons and bursae

Question 11

what are the physiological functions of joints

Answer 11

to serve the functional requirements of the MKS

structural support and purposeful movement

Question 12

what is an additional role of the joint during purposeful movement

Answer 12

stress distrubution

Question 13

how does the joint remain stable

Answer 13

the shape of the articular component

ligaments stabilise

synovial fluid acts as an adhesive seal that freely permits sliding motion between cartilaginous joints

Question 14

what provides joint lubrication

Answer 14

cartilage interstitial fluid

synovium- derived hyaluronic acid (mucin- a polymer of disaccharides)

synovium- derived lubrcin (a glycoprotein)

Question 15

what are the 6 roles of synovial fluid

Answer 15

lubricates joint

facilitates joints movements (reduced friction)

help minimise wear and tear

aids in the nutrition of articular cartilage

supplies the chondrocytes (cartilage cells) with O2 and nutrients

removes Co2 and waste products

Question 16

what does the synovial fluid fill

Answer 16

the joint cavity

Question 17

is the synovial fluid a static pool- explain

Answer 17

no- synovial fluid is continuously replenished and absorbed by the synovial membrane

Question 18

why does synovial fluid have a high viscosity

Answer 18

due to the presence of hyaluronic acid (mucin) produced by the synovial cells

Question 19

does the viscosity of synovial fluid vary

Answer 19

yes, with joint movement

Question 20

what role does the blood play in synovial fluid

Answer 20

constituents such as uric acid are derived from by dialysis of blood plasma

Question 21

what cells are contained within the synovial fluid

Answer 21

not many- mostly mononuclear leucocytes

<200 WBC/mm3 (0f which polymorphs are usually <25/mm3)

Question 22

what happens to the synovial fluid during joint movement (especially rapid movement)

Answer 22

the viscosity and elasticity change

rapid movement=
viscosity descreased
elasticity increased

Question 23

what properties of synovial fluid become defective in diseased joints (e.g. osteoarthritis)

Answer 23

its ability to decrease in viscosity and increase in elasticity during rapid movement

Question 24

what does synovial fluid look like

Answer 24

clear and colourless

Question 25

when does synovial blood count increase from more than <200WBC/mm3

Answer 25

in inflammatory and septic arthritis

Question 26

when does synovial fluid turn red

Answer 26

in traumatic synovial tap and in haemorrhagic arthritis

Question 27

when does synovial fluid go straw to yellow colour

Answer 27

inflammatory synovial fluid

Question 28

when does synovial fluid go opaque

Answer 28

septic synovial fluid

Question 29

when, other than during movement, is synovial viscosity low

Answer 29

inflammatory synovial fluid

Question 30

when is synovial fluid total cell count highest

Answer 30

septic synovial fluid

Question 31

what are the roles (2) of articular cartilage

Answer 31

provides a low friction lubricated gliding surface which helps prevent wear and tear of joints distributes contact pressure to subchodral bone

Question 32

what plays a key role in determining the mechanical properties of cartilage

Answer 32

the composition of the cartilage ECM and the interaction between the fluid and solid phase of the cartilage

Question 33

list the different zone of articular cartilage from outwards to inwards

Answer 33

``` articular surface superficial zone middle zone deep zone calcified zone (subchondral bone) ```

Question 34

what do the zones of articular cartilage differ in

Answer 34

organisation of collagen fibres and relative content of cartilage components

Question 35

what type of cartilage is articular cartilage usually

Answer 35

hyaline

Question 36

describe the properties of articular cartilage

Answer 36

elastic and spongey

Question 37

what parts of bone does the articular cartilage cover

Answer 37

articular surfaces

Question 38

what makes up the extracellular matrix of articular cartilage

Answer 38

water (70%) collagen (20%, mainly type II, contributes to the elastic behaviour) proteoglycans (10%)

Question 39

describe 4 key properties of water in cartilage

Answer 39

70% of cartilage wet weight unevenly distributed, 80% near articular surface content decreases with age maintains the resiliency of the tissue and contributes to the nutrition and lubrication system

Question 40

describe 5 key properties of collagen in cartilage

Answer 40

20% of wet weight mainly type II decreases with age maintain cartilage architecture provides tensile stiffness and strength

Question 41

describe the 5 key properties of proteoglycan

Answer 41

10% of cartilage wet weight highest concentration in middle and deep zone composed mainly of glycosaminoglycan e.g. chondroitin sulphate composition changes with age (chondroitin decreases with age) responsible for the compressive properties associates with load bearing

Question 42

how much of cartilage volume is ECM (extracellular matrix)

Answer 42

>98% of cartilage volume

Question 43

what synthesises, degrades and maintains the ECM

Answer 43

chondrocytes (usually <2% of the total cartilage volume)

Question 44

how does articular cartilage and chondrocytes receive nutrients and O2

Answer 44

articular cartilage is avascular- gets it from synovial fluid

Question 45

how does the rates of ECM degradation and replacement compare in normal joints

Answer 45

degradation doesn't exceed replacement

Question 46

how do chondrocytes degrade ECM components (e.g. collagen and proteoglycan)

Answer 46

metalloproteinase PROTEOLYTIC ENZYMES e.g. collagenase and stomelysin

Question 47

what can change the mechanical properties of the knee

Answer 47

changes in the relative amounts of the components (water, collagen and proteoglycans) or if ECM degradation exceed rate of synthesis

Question 48

what do the catabolic factors of cartilage matrix turnover do, give 2 examples of them

Answer 48

stimulate proteolytic enzymes and inhibit proteoglycan synthesis TNF alpha Interleukin - 1

Question 49

what do the anabolic factors of cartilage matrix turnover do, give 2 examples of them

Answer 49

stimulate proteoglycan synthesis and counteract effects of IL-1 tumour growth factor (TGF- beta) insulin like growth factor (IGF-1)

Question 50

what are the two markers of cartilage degradation and why are they present

Answer 50

serum and synovial keratin sulphate - increased levels indicate cartilage breakdown - level increses in patients with osteoarthritis type II collagen in synovial fluid - increased levels indicate cartilage breakdown - useful in evaluating cartilage erosion (e.g. in osteoarthritis and rheumatoid arthritis)

Question 51

what is osteoarthritis caused by

Answer 51

cartilage and synovial composition and function deteriorate with age and repeated wear and tear

Question 52

what causes rheumatoid arthritis

Answer 52

synovial cell proliferation and inflammation

Question 53

what causes gouty arthritis

Answer 53

deposition of salt crystals (e.g. uric acid) in the joint

Question 54

what causes soft tissue rheumatism

Answer 54

injury and inflammation to periarticular structures (e.g. injury to tendon causes tendonitis

Question 55

what effects on the bone can be seen following cartilage wear and tear

Answer 55

cyst formation sclerosis in subchondral bone osteophyte formation

Question 56

what shaped needles in gouty arthritis

Answer 56

needle shaped

Question 57

what type and shape of needles in pseudo gout

Answer 57

rhomboid shaped calcium pyrophosphate crystals