Joints, Articular cartilage and Synovial fluid L2: Hyaline cartilage & synovial joint pathology

Question 1

Hyaline cartilage is vascular/avascular

Answer 1

Avascular

Question 2

When is hyaline cartilage highly vulnerable?

Answer 2

Excessive, impulsive high loading

Question 3

Hyaline cartilage health depends on ______.

Answer 3

Loading patterns.

Question 4

Alterated loading patterns (for hyaline cartilage) such as ____, _____ and _____ can lead to altered compositional properties.

Answer 4

Excessive, Prolonged and Absence

Question 5

The _______ contributes directly to interstitial fluid pressurization –> attract H2O and offer______ resistance to interstitial fluid flow.

Answer 5

proteoglycan network strong

Question 6

Most curved surfaces compressed by ____ forces (eg. compression)

Answer 6

external

Question 7

What 2 types of loading alter chondrocytes metabolism?

Answer 7

1. Increased intermittent hydrostatic pressure
2. Shear stress

Question 8

How does increased intermittent hydrostatic pressure alter chondrocytes metabolism?

Answer 8

• Aggrecan
• Type II collagen
• macromolecule

Question 9

How does shear stress alter chondrocytes metabolism?

Answer 9

• increased the release of the proinflammatory mediator,
• decreased aggrecan and Type II collagen expression, and
• induced molecular changes associated with apoptosis (self-destruction, pre-programmed cell-death)

Question 10

What are the 5 changes that occur in ECM during ageing?

Answer 10

1. hypertrophic changes in chondrocytes
   
   • chondrocytes hypertrophy before they die- aging chondrocytes hypertrophy
2. loss of glycosaminoglycans (associated with aging and OA)
3. calcification of the ECM
4. increased number of tidemarks > 60 years age
5. movement of the tide mark to the cartilage surface = replacement of the lower calcified cartilage by bone
   
   • Tide mark = the line marking the border between the calcified cartilage and the non-calcified cartilage

Question 11

What are the 4 causes of hyaline cartilage patholgy?

Answer 11

1. Acute trauma
   
   • Impulsive high rate of application
2. Altered kinematics
3. Prolonged overloading
   
   • Obesity ( body weight)
4. Prolonged immobilization
   
   • Lack of stimulus

Question 12

How are ACL ruptures associated with primary cartilage damage & development of OA?

Answer 12

• Mechanism = simultaneously valgus + rotation = dynamic loading in multiple planes
• Often associated with
  
  • Meniscal damage (non-contact, rapid deceleration, valgus force rapid change of direction)
    
    • Primary or secondary
    • Medial meniscus (most common injury)
• Direct articular cartilage lesion
  
  • Usually femoral condyles (split, impact lesion on femoral condyle = change in ECM)
• Collateral ligament tears (MCL)
• Bone marrow lesion (change in stiffness)
• Haemarthosis
  
  • Bleeding, rapid swelling –> 2nd reaction –> irritation of inflammatory mediators (eg. synovial)

Question 13

What are the 2 changes (in proteogylcans) that occur in hyaline cartilage during immobilisation?

Answer 13

1. • Significant ↓ Proteoglycans ipsilateral side
2. Significant ↑ Proteoglycans contralateral side
   
   • Increase in loading of contralateral side

• Even after 50 weeks, ipsilateral side did not fully recover

Question 14

What are the 4 reasons why hyaline cartilage is unable to spontaneously repair?

Answer 14

*not normal post-inflammatory response

1. avascular & aneural
2. low cellular density
   
   • less cells to maintain
3. low metabolic activity
4. inability to migrate to the site of injury (chondrocytes can’t move around)

Question 15

Why is OA a ‘whole joint disease’?

Answer 15

It affects:

• Cartilage
• Bone
• Intra-articular & periarticular structures

Question 16

What causes OA?

Answer 16

A result of excessive mechanical stress applied in the context of systemic susceptibility

Question 17

What are 6 factors that can increase the risk of OA?

Answer 17

1. Age
   
   • Thinning of cartilage
   • Poor proteoglycan
   • Changes in synovial fluid
2. Obesity
3. Previous injury
4. Female gender
   
   • hormonal, biomechanics- pelvis, strength
5. Genetic inheritance
6. Nutritional factors

Question 18

What are 4 various theories of pathological changes due to previous injury or disease (sequelae)/

Answer 18

1. Mechanical wear &tear
   
   • Bearing surface failure under repeated high loads
   • Altered lubrication
     
     • Change in quality of synovial fluid
     • Loss of fluid film between articular surface
2. Alteration in chondrocyte activity
3. Alteration in ECM
4. Altered subchondral bone stiffness

Question 19

What is the chondrocytes theory?

Answer 19

There are 2 types of hyaline cartilage:Temporary and permanent

Question 20

How does the chondrocytes theory affect endochondral ossification (default pathway)?

Answer 20

• Mesenchymal cells differentiate into chondrocytes
• Chondrocytes undergo terminal differentiation
• Hypertrophy & apoptosis
• Cartilage –> bone

Question 21

How does the chondrocytes theory affect the normal articular hyaline cartilage?

Answer 21

the terminal differentiation of chondrocytes is halted

Question 22

What are the 2 types of inflammatory theories?

Answer 22

1. Local
2. Systemic

Question 23

What is the local inflammatory theory?

Answer 23

• Synovium irritated by cartilage fragments
  
  • inflammatory response
  • Inflammatory markers in synovial fluid
  • activate superficial chondrocytes
  • Proteases
  • Cartilage breakdown
• Abnormal mechanical stress / increase in shear stress
• Mechanotransduction
• synthesis of inflammatory mediators by chondrocytes & subchondral osteocytes

Question 24

What is the systemic inflammatory theory?

Answer 24

• Metabolic syndrome
• Age

Question 25

75% of knee OA affects the ______ compartment.

Answer 25

Medial

Question 26

How does the hip-knee-angle alignment affect OA/

Answer 26

* contributes to the load distribution across the knee articular surface * proportionately divides load between the medial and lateral compartments The load-bearing mechanical axis = a line from the centre of femoral head to the center of the talus

Question 27

What occurs in varus knee? Is there a higher or lower progression of OA?

Answer 27

* mechanical axis passes medial to the knee * creates a moment arm * further increases load on the medial compartment. Higher tibiofemoral adduction moment --\> OA progression

Question 28

What is the role of muscles in knee OA?

Answer 28

To balance external adduction (varus) moment

Question 29

Which muscles help to balance the external adduction (varus) moment of the knee?

Answer 29

* quadriceps \*rectus femoris, (early stance) * sartorius, * long head biceps femoris, * lateral gastrocnemius (late stance) **Decrease varus force = decreased progression of OA**

Question 30

What muscles control eccentric knee flexion @ HS to control loading rate?

Answer 30

Quadriceps

Question 31

What muscles ensure pelvic control? Why is this important?

Answer 31

* hip abductors - gluteus medius & minimus * Contralateral hip drop moves CoM toward swing limb i.e. further from centre of stance knee --\> increases moment arm of ground reaction force

Question 32

Stance limb hip _______ eccentrically control the femur. Why is this important?

Answer 32

Adductors * “lift” medial femoral condyle to resist varus

Question 33

What are 4 possible articular cartilage repair procedures ?

Answer 33

1. Arthroscopic lavage and debridement * cleaning out and evening up the joint surface * short-term relief 2. Marrow stimulating techniques 3. Osteochondral autografts and allografts 4. Autologous chondrocyte implantation

Question 34

How does the marrow stimulating techniques work in repairing cartilage?

Answer 34

* removing damaged cartilage – drilling holes in the underlying bone to cause bleeding * natural replacement of hyaline cartilage with fibrocartilage * quick recovery time * effective articulating surface than hyaline cartilage

Question 35

How does the osteochondral autografts and allografts work in repairing cartilage? What are the advantages and disadvantages?

Answer 35

* Remove injured cartilage and the underlying bone * Replace with cartilage & bone from another site * within the joint (autograft) * a tissue donor (allograft) * The replacement core is gently tapped into place until it lines up with the surrounding tissue. * No screws or other devices are typically needed to hold the replacement core in place since it fits tightly. * start to weight-bear within 4-6 weeks of surgery * gradually activity * return to sport typically after 6-9 months * **advantage** = the ability to replace both cartilage and bone with similar tissue. * **limitation** = amount of tissue that can be taken from within a patient’s own joint

Question 36

What is the advantage of using osteochondral autografts and allografts to repair cartilage?

Answer 36

the ability to replace both cartilage and bone with similar tissue.

Question 37

What is the disadvantage of using osteochondral autografts and allografts to repair cartilage?

Answer 37

amount of tissue that can be taken from within a patient’s own joint