Osteoporosis Flashcards
What is osteoporosis?
- progressive loss of bone mass associated with change in bone micro-architecture
- associated with reduced cross linking within trabecular cone resulting in cortical thinning
How common is osteoporosis?
One third of women over 50 will sustain in osteoporotic fracture in their lifetime
What is remodelling?
- a normal process continually taking place within the bone
- allows bone to adapt to stressors and repair microdamage
- the net product of bone formation and reabsorption
What are the stages of bone remodelling?
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- activation of osteoclasts from circulating precursor cells, mediated by receptor binding of NF-kB ligand
- aggregation and adherence of osteoclasts to regions of active bone reabsorption on the trabecular plate
- osteoblastic breakdown of bone matrix, releasing calcium, minerals and active growth factors
- simultaneous osteoblastic deposition of osteoid with subsequent mineralization as calcium and phosphate
What happens to bone remodelling in postmenopausal women?
- Shifts towards bone reabsorption, leading to net bone loss
- Osteoclasts function in a less regulated manner , perforating through the trabecular plate
- There is no framework for osteoblast activity and structural integrity is lost
- This loss of connectivity between the trabecular plates is typical of the microstructure changes associated with osteoporosis
What are the risk factors for primary osteoporosis?
Female gender Previous fragility fracture Maternal history of hip fracture Current smoker Alcohol intake >3 units/day Glucocorticoids >3 months at more than 5 mg/day Low calcium and vitamin D deficiency Low BMI (<19 kg/m2)
What are the causes of secondary osteoporosis?
Rheumatoid arthritis Hyperthyroidism/hyperparathyroidism Premature menopause (<45yo) Chronic malabsorption or malnutrition (e.g. coeliac) Chronic liver disease
What risk stratification tool is used?
The FRAX tool was developed by the WHO to calculate 10 year fracture risk
What investigations are used in osteoporosis?
Blood tests - FBC, UE, LFT, TFT, Ca, vitamin D, PTH, coeliac serology, myeloma screen
What is a DEXA scan?
Gold standard investigation used to establish a formal diagnosis of osteoporosis by measuring bone mineral density
How is a DEXA scan reported?
T score - the number of standard deviations (SDs) above or below the bone mineral density for an average 25 year old
What T score indicated osteoporosis?
T score of 2.5 SDs below normal represents osteoporosis
What is a Z score?
A Z score coressponds to the number of SDs above or below the bone mineral density in age-matched controls
When would a whole spine X-ray be useful?
To establish the presence of asymptomatic fracture
1/3 of vertebral fractures fall into this group
Which bone turnover markers are used in specialist clinics to establish compliance and effectiveness ?
serum C-terminal telopeptide (CTX) levels
What supplement should osteoporosis patients be commenced on?
Vitamin D
Co administration with calcium will depend on baseline serum calcium levels and dietary intake
What is the mainstay of treatment for osteoporosis?
Bisphosphonates
What is the mechanism of action of bisphosphonates?
They inhibit osteoclastic bone reabsorption, which in turn results in reduced bone formation and turnover as a whole is reduced
For how long do patients usually receive bisphosphonates?
3-5 years
Why are bisphosphonates stopped after 3-5 years?
Beyond this the benefits of therapy must be balanced against the risk of atypical subtrochanteric fractures and osteonecrosis of the jaw
What is alendronate?
Oral bisphosphonate
When is zolendronic acid used?
Intolerant to oral bisphosphonate
What is zolendronic acid?
An IV bisphosphonate
What is denosumab?
monoclonal antibody to RANK-L
reducing its availability at receptor sites at the osteoclast surface
