Osteoarthritis Flashcards
Define osteoarthritis.
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)
How does osteoarthritis develop?
Osteoarthritis develops due to defective articular cartilage and damage to underlying bone as a result of excessive loading on joints, and abnormal joint components
What are the two key factors that lead to osteoarthritis?
Abnormal stress and abnormal cartilage
What can lead to “abnormal stress”
Genetic predisposition Trauma Dysplasia Obesity Mis-alignment Muscle weakness Loss of proprioception
What can lead to “abnormal cartilage”
Genetic predisposition Ageing Inflammation Metabolic changes Endocrine factors
Which joints are most commonly affected in osteoarthritis?
Distal interphalangeal joint (DIP) proximal interphalangeal joint (PIP) First metacarpophalangeal joint Spine Knees Hips First metatarsophalangeal joint
What are the names given to the osteophytes found on the hand in osteoarthritis?
Bouchard’s nodes for nodes on PIPs Heberden’s nodes for nodes on DIPs
What are the symptoms of osteoarthritis?
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
What are some radiographic features of osteoarthritis?
Joint space narrowing
Osteophytes
Subchondral bony sclerosis
Subchondral cysts
Describe the differences between the radiographic features of rheumatoid arthritis and osteoarthritis.
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
What are the pathological changes in osteoarthritis?
Focal areas of damage to articular cartilage (cartilage fibrillation)
Osteophytosis/osteophyte formation
Subchondral bone sclerosis Irreversible loss of articular cartilage
What is the normal weight-bearing properties of cartilage dependant on? How is this relevant to osteoarthritis?
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
What are proteoglycans?
Glycoproteins containing one or more sulphated glycosaminoglycans (GAGs) - in articular cartilage aggrecan is the major proteoglycan
Describe normal articular cartilage
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
What percent of the net weight of cartilage is water?
80%
What is the most important component of articular cartilage?
Aggrecan
What is aggrecan made up of?
100 Chondroitin sulphate chains
60 Keratan sulphate chains
What is special about hyaluronic acid? What is its role?
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
What changes happen to the cartilage to make it osteoarthritic cartilage?
Reduced proteoglycan => reduced hydration => thinning of cartilage
Reduced collagen
Aggrecan cleavage (by ADAMTS aggrecanases)
Chondrocyte changes (e.g. apoptosis)
What are the chondrocyte changes seen in osteoarthritic cartilage?
- 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
How does aggrecan cleavage happen in osteoarthritic cartilage?
Aggrecan cleavage is mediated by ADAMTS aggrecanases leading to aggrecan fragments being present in osteoarthritic cartilage
What are the bone changes in osteoarthritis?
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)
What is more likely to be the cause of osteoarthritis in a younger patient and in an older patient?
Young = more likely to have more of a genetic component
Old = more like to have more of a mechanical ("wear and tear") componentHow is osteoarthritis managed?
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
What are the clinical features of osteoarthritis?
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
