Pathology of OA

Question 1

Name the 6 progressive characteristics of OA?

Answer 1

1. Progressive degradation of articular cartilage
2. Synovitis (begins as intermittent bouts –> becomes chronic)
3. Soft tissue length changes (capsular fibrosis)
   o Ligaments
   o Tendons
   o Fibrocartilaginous joint capsule
4. Formation of new bone at the joint surface and edges (subchondral sclerosis and osteophyte formation)
5. Cyst formation in the subchondral bone
6. Collapse of the joint surfaces

Question 2

What is the clinical presentation of OA?

Answer 2

Increased pain 
Joint swelling
Progressive loss of ROM
Muscle inhibition/insufficiency/atrophy
Joint deformity and body enlargement
Functional limitations

Question 3

What is primary OA?

Answer 3

No known cause

Contribution of genetic factors, chondrocyte dysfunction and initiating factors from the bone/synovium

Question 4

What makes up the cellular components of cartilage?

Answer 4

Immature chondroblasts

Mature chondrocytes

Question 5

What makes up the extracellular matrix of cartilage?

Answer 5

water (60%)
Proteoglycans
Collagen

Question 6

What is the role of chondrocytes?

Answer 6

synthesis and maintain the ECM - normal turnover occurs

Question 7

What is the role of proteoglycans?

Answer 7

brush like structure acts as a molecular sponge - to bind water

Protien core with side chains of chondroitin sulphate and keratin sulphate

Question 8

What is the role and organisation of collagen in cartilage?

Answer 8

Hold the ECM and cells in place

 Superficial horizontal collagen fibres
 Intermediate collagen arcade
 Deep vertical collagen fibres

Question 9

What are the 4 functions fo the hyaline cartilage?

Answer 9

• Low friction self-lubricating surface for joint movement
• Distribution of load – acts as a shock absorber
• Protects the subchondral bone
• Durable, strong and resilient – resistant to wear

Question 10

How is nutrition supplied to cartilage?

Answer 10

Avasular - nutrition via the sweep and squeeze mechanism and the underlying subchondral bone

Question 11

What is are the two phases of early OA?

Answer 11

Cartilage matrix dysfunction and cartilage fibrilation

Question 12

What occurs during cartilage matrix dysfunction?

Answer 12

o Degrading enzymes - produced by chondrocytes and synovial cells
o Cause the break down in structure of proteoglycans –> water is released
o Decreased water content –> softening of the cartilage –> decreased tissue stiffness –> Cartilage becomes less resilient to normal stresses
o Breakdown of collagen fibres –> loosens the collagen arcade –> weakens the cartilage framework
o Cartilage begins to split up

Question 13

What occurs during the fibrillation phase?

Answer 13

o Drying out of the cartilage causes it to be more fragile – breaking off of small parts of collagen
o Tiny particles of cartilage which have broken off cause synovial irritation
o Leads to inflammatory response by synovial membrane –> Increase in synovial cell activity
• Increased amounts of mucin & increased volume and viscosity of the fluid
o Intermittent bouts of this ‘inflammatory synovitis’ causes joint effusion

Question 14

Why might a patient feel grating or crepitus?

Answer 14

Due to fibrillation - as disease progresses there is a change from fine grating to coarse grating

Question 15

What are the 7 stages of late OA?

Answer 15

1. recurrent and chronic synovitis
2. progressive and uneven loss of cartilage thickness
3. fissuring in deep vertical collagen fibres
4. Increased sclerosis of subchondral bone
5. Marginal osteophytes
6. Subchondral cysts
7. Flattening and collapse of joint surfaces

Question 16

What occurs as a result of chronic synovitis?

Answer 16

Joint capsule fibrosis due to consistent stretch from the swelling

Question 17

What is the result of progressive uneven loss of cartilage?

Answer 17

• Reduced ROM
• Contraction or lengthening of surrounding soft tissues – resulting in weakness
  • Knee held in loose pack position - Lengthening of quads, Shortening of hamstrings
• Increased sclerosis of subchondral bone due to increased stress

Question 18

What occurs to cause fissuring of cartilage?

Answer 18

increased loss of water means more collagen fibres are displaced - fissures deep vertical collagen fibres - may extend into the bone causing subchondral microfractures

Question 19

What is sclerosis and why does it occur?

Answer 19

Increased bone density – since there is no cartilage to distribute load, there is increased load on the underling bone – it compensates by increasing in density

Question 20

What are subchondral cysts?

Answer 20

Progression of fissures allows synovial fluid to leak into the bone

Question 21

What is the result of osteophytes?

Answer 21

usually form on joint edges - limit the end of ROM

Question 22

What is the presentation of a patient with medial compartment OA knee?

Answer 22

Varus deformity

Question 23

What is the presentation of OA hip?

Answer 23

FFD

Question 24

Why does degeneration occur during OA?

Answer 24

Imbalance in sythesis and degradation of the matrix - due to biomechanics or biochemical changes in the joint

Changes in the loading of the chondrocytes or chondrocyte dysfunction

Question 25

What limits cartilage repair in OA?

Answer 25

Sparse arrangements of chondrocytes
Chondrocyte dysfunction
Avascular nature