Fracture through the Ages Flashcards
Define bone strength.
The ability of bone to resist fracture
What factors contribute to bone strength?
Density
Structure
What method has been used for diagnosing osteoporosis and what are the limitations of this method?
DEXA scans
This gives a reading of bone mineral density (BMD) but it doesn’t tell you anything about the bone structure
Describe the effects of oestrogen on osteoclasts.
Oestrogen stimulates apoptosis in osteoclasts
What are the two main divisions of bone composition?
Cell (10% of volume)
Matrix (90%)
What are the two subsets of bone matrix and what falls undereach?
Organic – collagen, non-collagenous proteins, mucopolysaccharides
Inorganic – hydroxyapatite crystals (calcium and phosphorus)
What are the four types of bone cells?
Osteoprogenitor cells
Osteocytes
Osteoblasts
Osteoclasts
What is the role of osteoprogenitor cells?
These differentiate into the other types of bone cell
What is the role of osteocytes?
They are involved in bone homeostasis (they are found in the lacunae and have projections into the canaliculi)
How often does bone normally turnover?
120 days
Describe normal bone turnover.
The osteoclast will dissolve away the bone
Preosteoblasts will move in and differentiate into osteoblasts
In a healthy person, the osteoblasts will lay down more bone than the osteoclasts dissolved (so you don’t get any bone loss)
How is bone turnover different in an elderly person?
There is less apoptosis of osteoclasts and the resorption pits are very big and don’t get filled in by osteoblasts so you get loss of bone
What effect do bisphosphonates have on osteoblasts and osteoclasts?
Bisphosphonates encourage cell death in osteoclasts
They damage their cytoskeleton so that the osteoblasts lose their RUFFLED BORDER, and without this they can’t function
What is a major problem with bisphosphonate use?
Atypical fractures
What causes this?
Bisphosphonates also have an effect on osteoblasts
They reduce bone remodelling (which replaces old and damaged bone) so you get premature ageing of the bone
Furthermore, microcracks form in the bones due to day-to-day use and if these microcracks are not filled in by bone remodelling they will eventually join up and cause stress fractures
What is the half-life of alendronate?
Around 10 years
What new drug has come onto the market that has a similar action to bisphosphonates but with a shorter half-life?
Denusomab (half-life = 6 months)
Describe the action of RANKL.
RANKL binds to RANK receptors on precursors to osteoclasts and promotes their maturation to osteoclasts
In a healthy person, what protein is responsible for regulating the bone remodelling process and how does it do this?
Osteoprotegrin
It prevents the binding to RANKL to the RANK receptor (this is what denusomab also does)
State Wolff’s Law.
Bone remodels according to the stresses applied to it
At what age is peak bone mass reached?
30-40 years
State some other factors that contribute to bone mass
Genetics
Nutrition
Vitamin D
Exercise
What are the five stages of fracture healing?
Haematoma Inflammation Soft Callous Hard Callous Remodelling
Which type of collagen is deposited in the soft callous?
Type 2 collagen
What prevents mineralisation in the soft callous?
Proteoglycans
What happens in stage 3 of fracture healing?
The soft callous is invaded by blood vessels
Chondroblasts break down the calcified callous
It is replaced by osteoid (type I collagen) produced by osteoblasts
Osteoid calcifies to form woven bone
What happens in stage 4 of fracture healing?
Woven bone remodels to lamellar bone
It is shaped relative to the load (Wolff’s law)
Medullar canal reforms
Name four types of fracture
Spiral
Oblique
Comminuted
Transverse
What type of fracture can occur in the bones of children due to their plasticity?
Greenstick fractures
One cortex could break but the other cortex could bend but stay intact
