Physiology of cartilage

Question 1

what are the main types of cartilage in the body?

Answer 1

hyaline
elastic
fibro

Question 2

where is hyaline cartilage found?

Answer 2

skeletal
-articular cartilage
-costal cartilage
-epophyseal growth plates
extra-skeletal
-trachea
-larynx
-nose

Question 3

where is elastic cartilage found?

Answer 3

ear
epiglottis

Question 4

where is fibrocartilage found?

Answer 4

menisci
intervertebral discs

Question 5

what is the function of articular cartilage?

Answer 5

creating a smooth lubricated surface for articulation
facilitating load transmission and creating a low friction environment

Question 6

what is the composition of articular cartilage?

Answer 6

chondrocytes cells
collagen
water
proteoglycans/proteins

Question 7

how does the arrangement of chondrocytes change from superficial to deep?

Answer 7

-very elongated, thin (1-3 cells thick) run parallel to the joint. allows it to be resistant to shear forces
-middle zone, become larger and hypertrophic
-in deeper zone, stacked onto of each other

Question 8

what are some key properties of articular cartilage?

Answer 8

avascular
neural
non-immunogenic

Question 9

how does the collagen fibre arrangement change and why is it important?

Answer 9

collagen fibres change from being oblique to vertical. transition from middle to the deep zone is how collagen resists compression forces

Question 10

what is the tidemark?

Answer 10

histological feature that marks the border between the calcified zone and non-calcified zone

Question 11

what is the function of chondrocytes?

Answer 11

synthesise and maintain ECM

Question 12

what is the function of ECM?

Answer 12

mainly collagen type II, embedded in a gel of negatively charged proteoglycans (important ones being hyaluronan and aggrecan), protects chondrocytes and loading forces

Question 13

how does articular cartilage heal?

Answer 13

cannot be synthesised
to heal it must penetrate the subchondral bone as cartilage does not have a blood supply
bleeding allows mesenchymal stem cells to come into zone and synthesise fibrocartilage

Question 14

what happens if the injury is above the tidemark?

Answer 14

the chondrocytes can try to synthesise more matrix, but they cannot migrate to ‘plug the gap’

Question 15

outline the main factors involved in cartilage homeostasis

Question 16

what is the composition of fibrocartilage?

Answer 16

cells - fibrochondrocytes
ECM- collagen type I, water, proteoglycans. glycoproteins, elastin

Question 17

what is the problem with meniscal tears?

Answer 17

menisci are poorly vascularised. above age 17 the outer 10-20% has a blood supply. any injury inside can’t really heal

Question 18

how do cartilage injuries happen?

Answer 18

trauma
sports
infection
OA
previous injury

Question 19

how can physio help cartilage injuries?

Answer 19

exchange of nutrients happens via diffusion. as long as you are moving the joint you create pressure changes to allow the diffusion to happen. muscles surrounding the joint also stay strong and keeps the joint mobile and biomechanicaslly in line

Question 20

what are the medical treatment for cartilage injury?

Answer 20

-standard analgesia
-NSAIDs
-oral glucosamine and chronroitin sulphate
-steroid injections/viscosupplementation- injecting hyaluronic acid to replenish it

Question 21

what is meant by mature bone?

Answer 21

all cortical and cancellous bone
osteoblasts lay down bone matrix in sheets
parallel organised collagen fibres orientated via the stress on bones

Question 22

what is immature bone?

Answer 22

also known as woven bone
only seen when someone has an injury and is healing
see in children
randomly aligned collagen fibres

Question 23

what are the functions of bone?

Answer 23

biggest store of calcium
protects viscera
tendon/ligamrnt attachment

Question 24

describe the structure of the cortical bone?

Answer 24

mature bone laid down in concentric rings
80% of skeleton
slower turnover rate/metabolic activity

Question 25

describe the structure of cancellous bone?

Answer 25

osteoblasts lay down bone in a trabecular pattern like a lattice
lighter
higher turnover and undergoes greater remodelling

Question 26

what are the modes of blood supply to bone?

Answer 26

nutrient artery enters centre of diaphysis
vessels enter around
periostea blood supply

Question 27

what happens when the artery centres the centre of the diaphysis?

Answer 27

high pressure, comes from systemic circulation. divides into ascending and descending arterioles to supply the bones

Question 28

what are the 2 ways in which bone heal?

Answer 28

indirect healing
direct healing

Question 29

what is the process of fracture healing?

Answer 29

-haematoma
-soft callus
-hard callus
remodelling

Question 30

what happens during haematoma stage?

Answer 30

harmopoetic cells are great secrete growth factors
fibroblasts, osteoprogenitors and mesenchymal cells

Question 31

what is thew soft callus stage?

Answer 31

woven, disorganised bone is made, strain starts to go down
1 week -> 1 month
10% strain at failure

Question 32

what is the remodelling phase?

Answer 32

osteoclasts break down the disorganised, woven bone dissolving the hard callus
osteoblasts then lay down organised, lamellar bone
can take place for a number of years after injury

Question 33

what is direct fracture healing?

Answer 33

unique surgical situation
direct formation of bone without the process of callus formation
fracture is stable
no movement under physiological load
relies upon compression of the bone ends
no callus formed
direct formation of bone via oseoclastic absorption (cutting cones)

Question 34

what does a bone need to heal?

Answer 34

blood supply