Osteoarthritis

Question 1

Define osteoarthritis.

Answer 1

Chronic slowly progressive disorder due to failure of articular cartilage that typically affects the hands (especially those involved in the pinch grip), spine and weight-bearing joints (hips and knees)

Question 2

How does osteoarthritis develop?

Answer 2

Osteoarthritis develops due to defective articular cartilage and damage to underlying bone as a result of excessive loading on joints, and abnormal joint components

Question 3

What are the two key factors that lead to osteoarthritis?

Answer 3

Abnormal stress and abnormal cartilage

Question 4

What can lead to “abnormal stress”

Answer 4

Genetic predisposition
Trauma 
Dysplasia
Obesity
Mis-alignment
Muscle weakness
Loss of proprioception

Question 5

What can lead to “abnormal cartilage”

Answer 5

Genetic predisposition
Ageing
Inflammation
Metabolic changes
Endocrine factors

Question 6

Which joints are most commonly affected in osteoarthritis?

Answer 6

Distal interphalangeal joint (DIP) 
proximal interphalangeal joint (PIP) 
First metacarpophalangeal joint 
Spine 
Knees 
Hips 
First metatarsophalangeal joint

Question 7

What are the names given to the osteophytes found on the hand in osteoarthritis?

Answer 7

Bouchard’s nodes for nodes on PIPs Heberden’s nodes for nodes on DIPs

Question 8

What are the symptoms of osteoarthritis?

Answer 8

Joint pain (worse with activity) 
Joint crepitus (crackling and grinding sounds on moving affected joint)
Joint instability 
Joint enlargement 
Joint stiffness after immobility 
Limitation of motion

Question 9

What are some radiographic features of osteoarthritis?

Answer 9

Joint space narrowing
Osteophytes
Subchondral bony sclerosis
Subchondral cysts

Question 10

Describe the differences between the radiographic features of rheumatoid arthritis and osteoarthritis.

Answer 10

Rheumatoid arthritis also has joint space narrowing but it doesn’t have subchondral sclerosis or osteophytes
There is osteopenia and there are bone erosions in rheumatoid arthritis but not in osteoarthritis

Question 11

What are the pathological changes in osteoarthritis?

Answer 11

Focal areas of damage to articular cartilage (cartilage fibrillation)
Osteophytosis/osteophyte formation
Subchondral bone sclerosis Irreversible loss of articular cartilage

Question 12

What is the normal weight-bearing properties of cartilage dependant on? How is this relevant to osteoarthritis?

Answer 12

It depends on intact collagen scaffolding and high aggrecan content. However, collagen and aggrecan turnover is very slow: collagen half life is decades and aggrecan half life is 3-4 years

Question 13

What are proteoglycans?

Answer 13

Glycoproteins containing one or more sulphated glycosaminoglycans (GAGs) - in articular cartilage aggrecan is the major proteoglycan

Question 14

Describe normal articular cartilage

Answer 14

It is an avascular and aneural structure containing collagen (90% of it is type II collagen) + proteoglycan monomers (aggrecan) + chondrocytes
Aggrecans are arranged into supramolecular aggregates consisting of a central hyaluronic acid filament with aggrecan non-covalently linked to it => negative charge of GAGs attract cations which draw water (by osmosis) into cartilage giving the cartilage its load-bearing function

Question 15

What percent of the net weight of cartilage is water?

Answer 15

80%

Question 16

What is the most important component of articular cartilage?

Answer 16

Aggrecan

Question 17

What is aggrecan made up of?

Answer 17

100 Chondroitin sulphate chains

60 Keratan sulphate chains

Question 18

What is special about hyaluronic acid? What is its role?

Answer 18

It is the only non-sulphated GAG

Hyaluronic acid is a major component of the synovial fluid where it has a major role in synovial fluid viscosity

Question 19

What changes happen to the cartilage to make it osteoarthritic cartilage?

Answer 19

Reduced proteoglycan => reduced hydration => thinning of cartilage
Reduced collagen
Aggrecan cleavage (by ADAMTS aggrecanases)
Chondrocyte changes (e.g. apoptosis)

Question 20

What are the chondrocyte changes seen in osteoarthritic cartilage?

Answer 20

• Increased chondrocyte proliferation - this is an intrinsic repair mechanism when cartilage is reduced but abnormal mechanical stress causes chondrocytes to produce inflammatory mediators which may have a role in OA
• Other cytokines that promote cartilage matrix degradation cause focal areas of chondrocyte apoptosis

Question 21

How does aggrecan cleavage happen in osteoarthritic cartilage?

Answer 21

Aggrecan cleavage is mediated by ADAMTS aggrecanases leading to aggrecan fragments being present in osteoarthritic cartilage

Question 22

What are the bone changes in osteoarthritis?

Answer 22

Changes in denuded sub-articular bone
- Proliferation of superficial osteoblasts results in production of sclerotic bone
- Focal stress on sclerotic bone results in superficial necrosis
New bone formation in joint margins
- This causes formation of nodes (Heberden’s and Bouchard’s)

Question 23

What is more likely to be the cause of osteoarthritis in a younger patient and in an older patient?

Answer 23

Young = more likely to have more of a genetic component
Old = more like to have more of a mechanical ("wear and tear") component

Question 24

How is osteoarthritis managed?

Answer 24

No disease modifying therapy - prevention and symptomatic treatment:

• Education
• Physiotherapy
• Occupational therapy
• Weight loss and exercise
• Analgesia (NSAIDs; paracetamol; intra-articular corticosteroids)
• Joint replacement surgery

Question 25

What are the clinical features of osteoarthritis?

Answer 25

Patients present with mechanical pain that worsens with activity
Bony enlargements, but no true swelling, warmth, or erythema
• Osteophytes at the DIP joints are termed Heberden’s nodes
• Osteophytes at the PIP joints are termed Bouchard’s nodes
Progressive loss of joint range of motion
Short-term stiffness (less than 30 minutes) in the morning and after rest