Bone Pathology and Rehabilitation

Question 1

Adaptation in bone: Loss

Answer 1

• Microgravity leads to significant and progressive bone loss.
• Bone loss in Skylab astronauts was up to -7.9% at the calcaneus (84-day flight).
• Five-year follow up showed the condition had not corrected.
• Rats in their growth phase show arrest lines at the periosteum in cortical bone.
• Osteoblast number and activity , osteoclast number unchanged.
• Bed rest can simulate microgravity.

Question 2

bed rest

Answer 2

Calcium excretion rises (significant after 50 days) • Serum calcium evelated from day 20
• Parathyroid hormone variable
PICP showed significant and large declines; recovers

after 119 days of bedrest, all bone mineralisation decreased except increase in the skull

Question 3

Adaptation in bone: Loss

disuse

Answer 3

In canine metacarpal in 40 weeks of disuse
Periosteal growth suppressed in growing dogs
Endocortical resorption and remodelling accelerated in mature dogs, cortical porosity
also increased.

Question 4

Adaptation in bone: Gain

Answer 4

Distributed bouts of daily loading increase osteogenesis

bone formation in response to mechanical loading is greatest when the total volume of loading is broken up into smaller bouts with rest periods in between - that is, to get a bone growth effect from exercise - you only need short periods of intense activity - not long endurance bouts of loading.

Question 5

Adaptation in bone: Gain factors

Answer 5

Age and gender are important factors: Athletes show greater skeletal responsiveness as juveniles.

past puberty, skeleton becomes less sensitive to bone loading however when getting old (past menopause) skeleton is less adaptable

Question 6

safety factor

Answer 6

Safety Factor =
Maximum force a structure can withstand / Force the structure needs to withstand in life
about 4 - 10x for bones

Question 7

Bone failure – Acute loading

Answer 7

Many different types of bone fracture, and these relate to the direction and relative magnitudes of forces applied, and to the material and structural properties of the bone itself
kids = greenstick fracture most common (not a complete fracture)
* if have high bone mineral density, fracture risk is lower

Question 8

Bone failure – Fatigue loading

Answer 8

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.

Question 9

Bone failure – Fatigue loading - fractrues

Answer 9

Fatigue fracture involves microdamage. If this damage is not repaired by BMUs then it accumulates and may eventually compromise bone integrity.

Question 10

Bone failure - role of mechanotransduction

Answer 10

Mechanotransduction plays a role in ‘identifying’ where bone repair needs to occur. The end result is a secondary osteon of new bone in place of damaged bone.

Question 11

Resistance of cortical bone

Answer 11

• Cortical bone is resistant to crack propagation due to:
voids
lamellae (bony layers)
cement lines
collagen fibrils

Question 12

Bone failure – vertebrae

Answer 12

After compression to 85% original height 96% of original height is regained, indicating that this strain of 0.15 has created some permanent damage, but also the recovery is ‘relatively good’.

Question 13

Bone failure – vertebrae trabeculae

Answer 13

Horizontal trabeculae brace vertical trabeculae and when compressed Vertebral end plates become concave while intervertebral disc volume is maintained. Therefore, Loss or weakness of horizontal trabeculae allow vertical trabeculae to buckle.

Question 14

Change in bone mineral density with age

Answer 14

Increasing and hits max in 20s when puberty has finished then decreases. In women, more rapid drecline after menopause due to hormones

Question 15

Aging of the skeleton

Answer 15

after 20 = decrease in mechanical strength, architecture, ash-density and integrity

Question 16

Summary

Answer 16

Skeletal fragility is determined both by material and structural properties
Bone mechanical requirements and competence change with use and age
Cortical and cancellous bone have to meet different mechanical requirements as their roles in life are quite different

Question 17

why are bones curved

Answer 17

when loaded in the longitudinal direction, the bone will deform in a predictable direction. The second advantage of a curved bone is that it will bend more when the load is increased.

overall can resist deficted loadings and can reduce overall mass concentrating it in the part of the bone that wil be most beneifcial to resist deformation