Fractures Flashcards
how is the structure of bone assessed?
DEXA scans
what are the scores used in the DEXA scan and what do they mean?
T and Z scores
T score= how much your bone mass differs from the bone mass of an average healthy 30 year old adult.
Z score= compares your bone density to the average bone density of people your own age and gender
what T scores indicate pathology?
T score 2.5 SD below normal (score < -2.5)–> osteoporosis
T score 1.0-2.5 SD below normal (score between -1.0 and -2.5) –> osteopenia, low bone mass
what is main composition of bone?
- matrix and cells
- matrix is organic (e.g. collagen) and inorganic (Ca, P)
what are the cells that make up bone?
o Osteoclasts
– break down bone
– big and have a ruffled border
o Osteoblasts
– lay down new bone
o Osteocytes
– mature osteoblasts
– act as mechanoreceptors.
o Osteoprogenitors
what is the bone remodelling cycle?
1) resorption: osteoclasts break down bone
2) reversal: osteoclasts apoptose while preosteoblasts line the bone
3) formation: mature osteoblasts form osteoid and mineralisation occurs
4) resting: osteocytes line the bone
what is contained in the ruffled borders of osteoclasts?
the digestive bone enzymes
what are bisphosphonates, what do they do?
induce osteoclast apoptosis:
destroy the osteoclast cytoskeleton which breaks down the ruffled border so they no longer can release digestive enzymes
inhibit the constant bone remodelling (so limit the bone reabsorption)
name an example of a bisphosphonate
alendronate
what is the negative effect of using bisphosphonates over time?
build-up of microfractures that can lead to spontaneous fractures (of the shaft typically)
what drug inhibits osteoclast activation?
Denosumab
an RANK/OPG analogue
what cell normally exhibits the RANK receptor?
osteoclast
what cells normally exhibits the RANK ligand (RANKL)?
osteoblasts
what effect does osteoprotegrin have?
acts to supress osteoclast activation.
what period of someone life is most bone laid down?
pre-pubertal
what does Wolff’s Law describe? how can this be applied to remodelling
bone remodels according to the stresses applied to it
bone can remodel according to the stresses applied to e.g exercises
what are the 4 stages of fracture healing?
1. Haematoma/Inflammation – up-to 1 week. 2. Soft callus formation – 1-4 weeks. 3. Hard callus formation – 1-4 months 4. Remodelling – up-to several years.
what happens at the haematoma stage of fracture healing?
a. Macrophages, leucocytes, IL-1-6, BMPs to promote healing
b. Granulation tissue formation.
c. Progenitor cell invasion
what happens in soft callus formation in fracture healing?
a. Chondroblasts –> collagen, fibroblasts –> fibrous tissue.
b. Proteoglycans produced (prevent mineralisation).
c. Chondrocytes release calcium + enzymes to break down proteoglycans (allows mineralisation).
soft callous stabilises the disorganised bone
the bone is not yet at optimal strength but can have some use
what happens in hard callous formation in fracture healing?
a. Blood vessel invasion of soft callus.
b. Chondroclasts break down calcified callus and this is replaced by osteoid (T1 collagen) from osteoblasts.
c. Osteoid calcified into WOVEN bone.
what happens in remodelling in fracture healing?
a. Woven –> lamellar bone.
b. Shapes according to Wolff’s law.
c. Medullary canals form.
how do children compare to adults in bone healing ability?
children are much quicker in the healing process
what are 4 types of general fracture?
o Spiral fracture (twist)
o Oblique fracture (compressive on bone)
o Butterfly fragment fracture – blow to one side.
o Transverse fracture (perpendicular to long axis)
What is a typical children’s bone fracture?
o Greenstick (one side broken, the other intact)
visually like slumped tree trunk
