Theory of tissue mechanics

Question 1

Bone healing

Answer 1

• Organic compound 20-25% of wet bone weight
• Inorganic compound 65-70% of wet bone weight
• Water component 10% of wet weight

Question 2

Types of bones

Answer 2

Cortical bone: External part of long bone
Trabecular bone: Found in metaphases and epiphysis

Question 3

Basic forces causing fractures

Answer 3

• Compression
• Tension
• Transverse loading
• Torsion
• Bone is anisotropic

Question 4

Bone likes and dislikes

Answer 4

Like:
- Compression
Dislikes:
- Torsion
- Shear

Question 5

Remodelling

Answer 5

Balancing between bone absorption by osteoclasts and bone formation

Question 6

Osteoporosis

Answer 6

Increase porosity of bone, decrease in density and strength, increase vulnerability to fractures

Question 7

Piezoelectric effect

Answer 7

Electrical potential created when collagen fibres in bone slip relative to another one, facilitates bone growth

Question 8

Bone healing with fixation

Answer 8

• Pins and plates
• Prevent movement around…
• Reduce mechanotherapy
• Longer healing time
• More stability earlier

Question 9

Bone healing without internal fixation

Answer 9

• Heal through callus formation
• Unstable in early stages
• No hardware issues

Question 10

Two contractile proteins

Answer 10

• Actin: thin
• Myosin: thick

Question 11

Muscle architecture

Answer 11

• Typical diameter 50-70
• Length varies from mm to 10cm+
• Attach to tendon plates
• Geometric arrangement differs

Question 12

Types of contraction: Lengthening

Answer 12

• Addition of sarcomeres to muscle fibres
• In region on myotendinous junction

Question 13

Types of contraction: Strength

Answer 13

• Max strength between 20-30yrs
• Cross sectional area of muscle is greatest
• Resistance training increases myofibrillar diameter

Question 14

Types of contraction: Cross-sectional area

Answer 14

• Female is 75% of male
• Response to resistance training in males via hypertrophy

Question 15

Muscle regeneration

Answer 15

• Satellite cells
• Fuse with adjacent myofibres to repair and regenerate muscles
• Restore and replace muscles cells damaged by injury

Question 16

Tendons

Answer 16

• Similar to ligaments in composition
• Predominantly made of collagen 70-80%
• Lesser % of elastin
• Connect muscle to bone
• Synovial component to assist gliding

Question 17

Tendon continuum

Answer 17

Reactive:
- PG absorb water
- Tenocytes change shape
- Fibres widen (swll)
Disrepair:
- Angiogensis
- Type I to Type III
- Increase PG
Degenerative:
- Less cellular
- Type III predominates
- More permanent

Question 18

Tendon Recap

Answer 18

Tendons:
- Transmits muscle load
Failure:
- Bone-tendon
- Muscle-tendon
- Mid-tendon
Elastic region:
- 1.5-4% stretch
Plastic region:
- Causes 10-15% stretch

Question 19

Ligament composition

Answer 19

• Similar to tendons in composition
• Predominantly made of collagen 70-80%
• Higher % of elastin
• Connects bone to bone
• Structure regulated by fibroblastic activity

Question 20

Ligament immobilisarion

Answer 20

• Major deterioration occurs within a few weeks
• Ligament cells produce inferior quality ligament material
• Structural weakening of ligament complex

Question 21

Aims of ligament healing

Answer 21

• Increase cross-sectional area
• To maintain ligamentous length
• Encourage remodelling

Question 22

Cartilage

Answer 22

Layer of hydrated soft tissue covers the ends of bones of diathrodial joints

Question 23

Articular cartilage reaction to force

Answer 23

• Cartilage has a natural tendency to swell
• Cartilage susceptible to constant load
• Excessive load can be destructive to matrix