Cartilage

Question 1

Role of articular cartilage

Answer 1

Transfers forces between articulating bones

Distributes forces in joints

Allows relative movement between articular surfaces with minimal friction

Question 2

Articular cartilage

Answer 2

Cells (5-10%) - chondrocytes

Intracellular matrix (90-95%)

• Water
• Structural macromolecules —-> Type II collagen
  - —> Proteoglycans

Avascular

Aneural

Synovial fluid

Question 3

Collagen

Answer 3

Structural framework, tendon and ligament

Provides tensile stiffness and strength

Tensile strength of tendon ~100 MPa

Little resistance to compression or shear

Arranged to exploit tensile strength

Question 4

Proteoglycans

Answer 4

Give cartilage visco-elastic properties - dependent on load and rate which it is applied

Highly negative electro-static charge

Attracted to water

Results in compressive strength

Question 5

Physical properties

Answer 5

Tensile properties

• Determined by arrangement of collagen
• Tensile strength higher parallel to surface than perpendicular

Compressive properties

• Determined by proteoglycan content
• Least at surface, greatest in middle

Shear properties
- Provided by arrangement of collagen

Visco-elasticity

• Associated with movement of water in the tissue
• The higher the pressure and compressive strains, the less permeable cartilage becomes

Question 6

Failure of cartilage

Answer 6

Mechanical loading and unloading essential to keep cartilage healthy

• influx of nutrients
• efflux of waste products

Limited remodelling response

Chondrocytes synthesise new matrix components but fail to restore matrix to normal

Question 7

Acute failure

Answer 7

Active forces

Impact forces

Question 8

Chronic failure

Answer 8

Interfacial wear caused by lack of lubrication in abnormal/regenerative joints

Fatigue wear

• Caused by application of high active/impact forces
• Magnitude/intensity, frequency, duration

Question 9

Menisci

Answer 9

Fibrocartilage

Spaces and stabilisers

Shock absorbers

Question 10

Basic physics of MRI

Answer 10

Strong magnetic field align protons in the body

Perpendicular magnetic field pulses at different frequencies to disturb protons from alignment

Different tissues of the body re-align at different speeds emitting different radio frequencies

Question 11

What does MRI stand for?

Answer 11

Magnetic Resonance Imaging

Question 12

MRI

Answer 12

3D image of all structures of the body

Much greater contrast of different soft tissues than CT

Takes 40-60 mins

Expensive - £350 per scan

No ionising radiation

Not possible for all patients

• Pacemaker
• Stimulator implant
• Claustrophobia

Question 13

Arthroscopy

Answer 13

Surgical technique for viewing inside joints

Question 14

Osteoarthritic Knee

Answer 14

Degenerative condition of cartilage and underlying bone

Can occur at any joint in the body but most common at hip, knee, lower back and fingers

Occurs ~15% of the population over 60

Thought to be caused by mechanical stress with insufficient repair

Treatment

• lifestyle modification
• pain medication
• joint replacement