Fracture through the Ages Flashcards
Define bone strength.
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
Measures bone mineral density (BMD) but doesn’t tell anything about 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 + phosphorus)
What are the four types of bone cells?
Osteoprogenitor cells
Osteocytes
Osteoblasts
Osteoclasts
What is the role of osteoprogenitor cells?
Differentiate into the other types of bone cell
What is the role of osteocytes?
Bone homeostasis (found in the lacunae + have projections into the canaliculi)
How often does bone normally turnover?
120 days
Describe normal bone turnover.
Osteoclasts dissolve away old bone
Preosteoblasts move in + differentiate into osteoblasts
Osteoblasts will lay down more bone than the osteoclasts dissolved (so no bone loss)
How is bone turnover different in an elderly person?
Less apoptosis of osteoclasts + resorption pits are very big + don’t get filled in by osteoblasts = loss of bone
What effect do bisphosphonates have on osteoclasts?
Encourage cell death in osteoclasts
Damage their cytoskeleton they lose their RUFFLED BORDER, without which they can’t function
What is a major problem with bisphosphonate use?
What causes this?
Atypical fractures:
Reduce bone remodelling (which replaces old + damaged bone) results in premature ageing of the bone
Microcracks
Form due to day-to-day use + if not filled in they eventually join + cause stress fractures
What is the half-life of alendronate? (bisphosphonate)
Long ~ 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 osteoclast precursors + promotes maturation to osteoclasts
What protein is responsible for regulating the bone remodelling process and how does it do this?
Osteoprotegrin
Prevents RANKL binding to RANK receptor (same as denusomab)
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 4 factors that contribute to bone mass
Genetics
Nutrition
Vitamin D
Exercise
What are the 4 stages of callus fracture healing? What are the relative time periods from date of fracture?
Haematoma + Inflammation (1 week) Soft Callus (1-4 weeks) Hard Callus (1-4 months) Remodelling (up to several years)
Which type of collagen is deposited in the soft callus?
Type 2 collagen
What prevents mineralisation in the soft callus?
Proteoglycans
What happens in stage 3 of callus fracture healing?
Hard callus
Soft callus is invaded by blood vessels
Chondroblasts break down calcified callus
It is replaced by osteoid (type I collagen) produced by osteoblasts
Osteoid calcifies to form woven bone
What happens in stage 4 of callus 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 and their common causes
Spiral (twisting)
Oblique (compression)
Butterfly (direct impact)
Transverse (pulling)
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 + stay intact
What are the 2 ways in which fractures can heal?
Surgical: rigid fixation, 2 bones compressed against each other with a plate
Callus: non rigid fixation, when there is a degree of movement at the fracture site e.g. a rod inserted
What happens in stage 1 of callus fracture healing?
Haematoma containing macrophages, leukocytes etc.
Granulation tissue forms
Progenitor cells invade
What happens in stage 2 of callus fracture healing?
Soft callus
Chondroblasts + fibroblasts differentiate to form type II collagen + fibrous tissue
Proteoglycans produced to prevent mineralisation
Chondrocytes release calcium into ECM + degrading enzymes to breakdown proteoglycans to allow mineralisation
