Limits of the MSK System - Cartilage

Question 1

state 3 functions of articular cartilage

Answer 1

1) transfers forces between articular joints
2) distributes force within a joint
3) allows relative movement between articular surfaces with minimal friction

Question 2

how is cartilage made up?

Answer 2

1) cells (5-10% of cartilage)
- chondrocytes

2) intracellular metric (90-95%)
- water (65-80% of IM)
- structural macro molecules (20-35% IM) (type 2 collagen and proteoglycans)

Question 3

state 3 additional characteristics about cartilage

Answer 3

1) avascular (no blood supply)
2) aneural (no nerves)
3) synovial fluid (essential to the healthy function of the synovial joint)

Question 4

what is collagen ?

Answer 4

collagen is the structural framework of cartilage, tendons, and ligaments

Question 5

what are the functions of collagen ?

Answer 5

1) provides tensile stiffness and strength
2) has little resistance to compression or shear
3) arranged to exploit tensile strength

Question 6

what is the tensile strength of collagen ?

Answer 6

100 MPa (like nylon)

Question 7

explain the 3 layers of collagen

Answer 7

1) close to bone is perpendicular to the bone - prevents collagen being pulled away from bone via tensile forces
2) at articular surface is oriented parallel to the surface - prevents collagen being pulled sideways - keeps shape of cartilage - allows friction free movement
3) in the middle - randomly aligned - is a framework for proteoglycans

Question 8

state 3 characteristics of Proteoglycans

Answer 8

1) give cartilage its viso-elastic properties (dependent on the rate at which force is applied)
2) highly negative electrostatic charge (same as each other) keeps stiffness as want to repal each other
3) hydrophilic - draws water into material - keeps plump and cushiony

Question 9

state the 4 physical properties of cartilage

Answer 9

1) tensile properties
2) compressive properties
3) shear properties
4) viso-elastic properties

Question 10

state 2 facts about the tensile properties of cartilage

Answer 10

• determined by the arrangement of collagen

- tensile strength higher parallel to surface than perpendicular

Question 11

state 2 facts about the compressive properties of cartilage

Answer 11

• determined by the proteoglycan content

- compressive stiffness less at surface and greater in the middle zones

Question 12

state 2 facts about the shear properties of cartilage

Answer 12

• provided by the arrangement of collagen

- resistance to being pulled side to side

Question 13

state 3 facts about the visco-elastic properties of cartilage

Answer 13

• associated with the flow of water in to the muscle
• the higher the pressure and compressive strains, the less permeable the cartilage becomes
• display ‘creep’

Question 14

what 2 reasons makes mechanical loading and unloading essential for cartilage health

Answer 14

1) influx of nutrients

2) efflux of waste product

Question 15

state 2 facts about cartilage remodelling

Answer 15

1) remodelling response occurs when the cartilage is damaged, but is very limited
2) chondrocytes synthesis new matrix components, but fail to restore matrix to normal, even if the damage is minimal

Question 16

state the two causes of acute cartilage failure

Answer 16

1) active forces (i.e. - heavy lifting)

2) impact forces (i.e. - collisions)

Question 17

state the 2 causes of chronic cartilage failure

Answer 17

1) interfacial wear caused by a lack of lubrication I abnormal or degenerative joints
2) fatigue wear (occurs when proteoglycan-collagen matrix is damaged by cyclical stressing)

Question 18

state 2 additional facts about how ‘fatigue wear’ leads to chronic failure of cartilage

Answer 18

• caused by the application of high active or impact forces over a long period of time (e.g. - running)
• important factors are magnitude/intensity of stress, loafing frequency, and duration

Question 19

state what it is meant by the key term - ‘osteoarthritis’

Answer 19

osteoarthritis is a degenerative condition of cartilage and the underlying bone

Question 20

where is osteoarthritis most common?

Answer 20

hip, knee, lower back, and fingers

Question 21

what is the incidence rate of osteoarthritis in those aged 60 and above?

Answer 21

15%

Question 22

what is the thought cause of osteoarthritis?

Answer 22

thought to be caused by mechanical stress with insufficient wear of the tissue

Question 23

when is osteoarthritis most likely?

Answer 23

when sportspeople have had a previous injury to that area

Question 24

state 3 treatments for osteoarthritis

Answer 24

1) lifestyle/gait modification
2) pain medication
3) joint replacement (includes partial joint replacement)

Question 25

state what it is meant by the key term - menisci

Answer 25

menisci are fibrocartilage semi-lunar discs located between the tibial and femoral condyles and are connected by a transverse ligament

Question 26

state 2 functional properties of the menisci

Answer 26

• increase the connectivity of the tibial plateaus

- distribute load in the knee over a large surface area and play a key role in shock absorption

Question 27

state 2 additional facts about the menisci

Answer 27

• thickest part at the peripheral boarders and then taper down towards the middle
• medial menisci merges with the joint capsule and the medial collateral ligament

Question 28

state 4 facts about menisci injuries

Answer 28

1) associated with ligament injuries at the knee
2) result in mechanical constraint to movement
3) occur due to wear and tear or acute damage
4) most common acute damage is due to ligament damage (medial collateral ligament is connected to the medial menisci)

Question 29

explain the basic physics behind an MRI scan (3 points)

Answer 29

1) strong magnetic field align the protons in H2O in the body
2) perpendicular magnetic field pulses at different frequencies to disturb protons from alignment
3) different tissues of the body re-align at different speeds emitting different radio frequencies

Question 30

what radiation is an MRI scan ?

Answer 30

non-ionising radiation

Question 31

what type of image does an MRI scan produce?

Answer 31

3D imaging

much greater contrast of different soft tissue injuries than CT

Question 32

what reasons could make MRI not possible for all patients ?

Answer 32

1. pacemaker
2. stimulator implant
3. claustrophobia (most common)

Question 33

state 4 facts about Arthroscopy (keyhole surgery)

Answer 33

1) a structural technique for viewing inside of joints
2) invasive - only done of there is a known problem which needs fixing
3) minimally invasive way of solving a problem - but with minimal view
4) surgeon can manipulate what is going on in the joint

Question 34

state 4 facts about the repair of cartilage

Answer 34

1) chondrocytes can regenerate new proteoglycans and matrix
2) avascular - no blood supply
3) cannot regenerate to the same degree as before
4) damage occurring is faster than remodelling so accumulates over time - cartilage is most likely to degenerate out of the tissues in the MSK system