Limits of the musculoskeletal system 2 - Lecture 4

Question 1

What is the role of articular cartilage?

Answer 1

1. Transfers forces between articulating bones
2. Distributes forces in joints
3. Allows relative movement between articular surfaces with minimal friction

Question 2

What are some characteristics of collagen?

Answer 2

1. provides tensile stiffness and strength
2. Tensile strength of 100MPa (similar to nylon)
3. Little resistance of shear

Question 3

What are some characteristics of proteoglycans?

Answer 3

1. Give cartilage disco-elastic properties
2. Highly negative electro-static charge
3. Attracted to water

Question 4

What are some physical properties of cartilage?

Answer 4

Tensile properties (determined by arrangement of collagen - parallel better than perpendicular)
Compressive properties (determined by proteoglycan content - stiffness lower at surface and greatest in middle zones)
Shear properties
Visco-elasticity (associated with movement of water in the tissue)

Question 5

What happens in the failure of cartilage?

Answer 5

Remodelling response when damaged is limited as chondrocytes synthesise new matrix but it never returns to normal strength even if damage is minor

Question 6

Why does cartilage fail?

Answer 6

Acute injury (heavy lifting)
Chronic Injury (interfacial wear form lack of lubrication, fatigue wear from cyclic stress)

Question 7

What are the menisci?

Answer 7

Fibrocartilage (spacers and stabilisers and shock absorbers)

Question 8

What happens in a magnetic resonance imaging machine? (MRI)

Answer 8

Strong magnetic field aligns the protons.
Perpendicular magnetic field pulses at different frequencies to disturb protons form alignment.
Different tissues of the body re-align at different speeds emitting different radio-frequencies

Question 9

Why choose an MRI?

Answer 9

3D image
Great contrast of different soft tissues
Lengthy (40-60 mins)
Expensive (£350)
No ionising radiation

Question 10

Why could an MRI kill a patient?

Answer 10

Loose metal e.g in eye of brain
Pacemakers
Spinal stimulators
Cochlear implants
Some valves and stents
Chlostrophobia

Question 11

What is an arthroscopy?

Answer 11

Surgical technique to view inside the joints

Question 12

What is an osteoarthritic knee?

Answer 12

Degenerative condition of cartilage and underlying bone
Most common in hip, knee and lower back
Occurs in -15% of population over 60
Caused by mechanical stress with insufficient repair

Question 13

What is a ligament?

Answer 13

Bone to bone
Stabilise joint
Restrict movement

Question 14

What is a tendon?

Answer 14

Muscle to bone
Store and retain elastic energy
create moevement

Question 15

What are ligaments and tendons made up of?

Answer 15

Cells - Fibroblasts
Water
Collagen
Proteoglycans
Elastin

Question 16

Mechanical limits of the ligament/tendon?

Answer 16

The more collagen fibres to greater the resistance to stretch

Question 17

What are some common ligament injuries?

Answer 17

ACL
MCL
Calceaneal fibrular ligament
Anterior Talo fibular ligament

Question 18

How does a ligament heal?

Answer 18

Influx of blood cells to damaged area cause inflammation and pain
New collagen fibrils laid down
Scar tissue forms
Scar tissue remodels
Can take years

Question 19

What architectural parameters make muscles different?

Answer 19

Size
Fibre length
Pennation length
Fibre type
Tendon length