Lecture 17 MSK Theme - Osteoporosis and Hip Fracture Flashcards
What is osteoporosis?
A common condition found amongst older people and is associated with fractures that cause significant morbidity and mortality.
What is osteoporosis characterised by?
A skeletal disorder.
Characterised by compromised bone strength predisposing a person to increased risk of fracture.
Describe the pattern of bone mineral density throughout a persons life time.
BMD in the late 20s up until the 50s when (especially in women) there is a rapid decline in BMD and then a more gradual decline in older age.
What scans can be used to look at BMD?
DEXA
What is an important balance in keeping bone structure healthy?
Balance between bone resorption and formation.
In adults there is daily removal of small amount of bone minerals but this is balanced out by the equal deposition of new mineral to maintain bone density.
What are the 3 important structural cells in bone?
Osteoblasts
Osteoclasts
Osteocytes
What are osteoblasts for?
Responsible for bone formation.
What are osteoclasts for?
Responsible for bone resorption.
What are osteocytes for?
Responsible for forming structural integrity of the skeleton, mechanical transduction and recruitment of new bone.
What happens when the balance between bone resorption and bone formation goes wrong?
If the bone resorption of minerals exceeds the rate of new mineral formation then bones weaken and become more prone to fracture.
This is a key hallmark of osteoporosis.
What are the clinical features of osteoporosis?
Fractures.
Symptoms of osteoporosis are not there unless a bone is broken.
What is the Z and T score comparing?
T scores compare bone density with that of a healthy person.
Z scores uses the average bone density of the people of the same age, sex and size as a comparator.
Describe the T and Z scores in elderly people.
Significant proportion of adults in their 80s+ have a T score below -25.
However, only 50% of people with a sustained low trauma fracture have a T score less than -2.5 so BMD is not a perfect clinical indicator of fracture risk.
What did twin studies show regarding osteoporosis?
Strong genetic predisposition.
Twin studies = 80% of bone structural characteristics are predictable.
What genes are implicated in rarer forms of osteoporosis?
Collagen A1 gene - relevant biological mechanisms accountable for fracture risk.
LDL receptor related protein (LRP5) - candidate gene for genetic osteoporosis because it has found implications with high BMD phenotypes.
What is the relationship between hormones, the menopause and BMD in women?
Loss of oestrogen in women from the menopause maps clearly to the effects on BMD as deficiency is related to increased bone turnover and resorption.
What is NOGG and FRAX?
Routine in clinical practice to establish fracture risk.
FRAX algorithm available from a website where the output is an estimated 10 year fracture risk, including hip fractures.
Using the 10 year fracture risk, can plot the risk on a NOGG graph to tell whether the estimation of BMD using a DEXA scanner is likely to be useful in refining fracture risk.
What are some methods to prevent fracture risk?
Target bone resorption by decreasing the activity of osteoclasts.
Increase bone formation by stimulating osteoblasts.
Oestrogen replacement therapy.
Biphosphates.
Calcium and vitamin D focus on decreasing bone resorption.
Teriparatide - anabolic/bone building agent but promoting osteoblast activity.
Strontium ranelate - affects bone formation and resorption in a beneficial way.
How do biphosphonates work?
Antiresorptive.
Switch off osteoclasts and decrease fracture risk.
How does denosumab work?
Competes to precent differentiation of osteoclast precursors by inhibiting the RNAK-ligand receptor.
How do antiresorptive drugs work?
Suppress bone respiration due to coupling of osteoblast and osteoclast function.
