Bone L3: Bone Pathology and Rehabilitation

Question 1

What are some adaptation in bone loss?

Answer 1

• Microgravity leads to significant and progressive bone loss
• Bone loss in Skylab astronauts -7.9% (84 day flight)
  
  • 5yr follow up = condition had not been corrected
• Rats in growth phase show arrest lines at periosteum in cortical bone
• Decreased osteoblast number and activity
• Unchanged osteoclast number

Question 2

Immobolisation: 120 days of bed-rest (6o head-down posture) Bone resorption markers (urine or serum)

Answer 2

• Pyridinoline (PYR) and Deoxypyridino (DPYR)
  
  • Indication of bone collagen breakdown
• N-Telopeptide (NTx)
  
  • Biomarker for bone turnover (varies spontaneously)
• Tartrate-resistant acid phosphatase (TRAP)
  
  • Highly expressed by osteoclasts
  • Parathyroid hormone
    
    • blood Ca2+
• Calcium concentration

Question 3

Immobolisation: 120 days of bed-rest (6o head-down posture) Bone formation marker (serum)

Answer 3

• Carboxy-terminal propeptide or Type I collagen (PICP)

Question 4

What is bone disuse?

Answer 4

• Periosteal growth suppressed in growing dogs
• Endocortical resorption and remodeling accelerated in mature dogs
• Decreased cortical porosity

Question 5

What are some adaptation in bone gain?

Answer 5

• Bones (curved) when applied loading, can bend and have adaptive tissue to resist
• Studies showed that bone formation in response to mechanical loading is greatest when total volume of loading is broken up into smaller bouts with rest periods in between
• Bone growth effect from exercise
  
  • Need short periods of intense activity
  • NOT long endurance bouts of loading
• Age and gender are important factors
  
  • Athletes show greater skeletal responsiveness as juveniles

Question 6

What is the safety factor?

Answer 6

Safety factor = Maximum force a structure can withstand/ Force the structure needs to withstand in life • Bones are 4-10 times stronger than necessary = safety factor o Not including injury

Question 7

Different types of bone fracture

Answer 7

• Relate to the direction and relative magnitudes of force applied,
• Material and structural properties of the bone itself
• Brittle- high energy fracture (pieces)
• Greenstick- not fully fractured

Question 8

What is bone failure through fatigue loading?

Answer 8

• Stress fracture = fatigue (internally compromised)
• In most materials, repeated loading of a specimen at stresses lower than failure stress, can cause fracture
• During repetitive loading (under constant load), bone shows a progressive degradation in stiffness until fatigue failure occurs
• Fatigue fracture involves microdamage
  
  • If not repaired by BMUs then accumulates and eventually compromise bone integrity
• Mechanotransduction plays a role in ‘identifying’ where bone repair needs to occur
  
  • End result is a secondary osteon of new bone in place of damaged bone
• Cortical bone is resistant to crack propagation due to:
  
  • Voids: cracks holt void and go outwards = energy = stop crack
  • Lamellae (bony layers) o Cement lines o Collagen fibrils

Question 9

Explain if bone failure is likely to occur in the vertebrae.

Answer 9

• After compression to 85% of original height 96% of original height is regained
  
  • Indicating that this strain of 0.15 has created permanent damage, but recovery is ‘relatively good’
• Cortical bone would likely fracture at = 0.01

Question 10

What are changes in ageing of the skeleton?

Answer 10

• Discrepancy between male and female
• Exercise can change rate of decline
• >1 BMD- okay
• <1 BMD- bad effect

Question 11

Ageing of the skeleton- 50 years

Answer 11

Integrity is still maintained

Question 12

Ageing of skeleton- 80 years

Answer 12

Decreased integrity

Question 13

Skeletal fragility is determined by both material and structural properties. What are the material characteristics?

Answer 13

• Bone mineral content (BMC)
  
  • Ratio of collagen to hydroapatite

Question 14

Skeletal fragility is determined by both material and structural properties. What are the structural characteristics?

Answer 14

• Amount of bone
• Size and shape
• Internal organization of bone

Question 15

What happens to Ca²⁺ excretion; Serum Ca²⁺ and Parathyroid hormone during bed rest and immobilisation?

Answer 15

• Increased Ca²⁺ excretion
• Increased Serum Ca²⁺
• Parathyroid hormone variable
• Significant decreased PICP
• Different changes depending on stage
  
  • Growing OR natural

Question 16

Ageing of skeleton- 20 years

Answer 16