Bone adaptation to mechanical loading Flashcards
What is Strain?
The amount of deformation in the material relative to its original length is the strain in the material
How many microstrain is normal activity?
1000microstrain
What happens to the bone when strain is intensified and lowered?
intensified: new bone forms
lowered: bone resorption takes place
What is customary strain?
Normal feeling of strain
What frequency and magnitude do:
-Vibration
-Walking/running
- Impact/resistance
Vibration-High freq, low magnitude
Walking/running- both moderate
Impact/resistance- Low freq, high magnitude
What happens to the bone when its disused?
microstrain- below 800
Remodelling (bone adaptation), bone mass and strength reduced
What happens to the bone when its in a adaptive state?
Microstrain- between 800 and 1500
Bone remodelling (repair). bone mass and strength stays constant (bone resorption and formation are at a constant)
What happens to the bone when it in overload?
Microstrain- over 1500
Modelling (bone growth), bone mass and strength increased
What happens to the bone in a fracture?
Microstrain- over 15000
Maximum elastically deformation exceeded resulting in bone fracture
Whats special about osteocytes?
The a putative mechanosensing cells, 95% of bone cells are osteocytes, Osteocytes have many projections to the osteoblasts which help communication to occur
What does mechanical loading do to the bone?
Mechanical loading reduces osteocytes apoptosis
mechanical loading increases bone formation and decreases sclerostin staining—> less expression when loading
What stimulates Bone resorption?
RANKL
What are the 4 levels of fracture resistance?
1- Fall avoidance
2- Architecture
3- Bone structural unit, osteocytes organisation
4- Material properties
With age do you have less or more bone formation and resorption?
Less
What happens to the adaptive capacity to load with age?
Decline in the number of and fucntionof osteocytes
Decline in osteoblasts differentiation
Impaired activation of WNT signalling
