Osteoporosis Flashcards
What is osteoporosis?
Reduced bone mass and bone mineral density
Micro-architectural deterioration of bone tissue
Bone is increasingly fragile
Predisposition to fractures
Define an osteoporotic fracture?
A fracture associated with low bone mineral density
Resulting from mechanical forces that would not usually result in fractures
Commonly in the spine, forearm, hip and shoulder
Pathophysiology of osteoporosis?
What is the official definition?
Imbalance of bone resorption and bone formation
Loss of inner trabecular bone
- excessive bone resorption
- inadequate formation of new bone during remodelling
- inadequate peak bone mass (during growth)
Bone mineral density more than 2.5 standard deviations below the young adult mean value (T score)
So this is T score less than or equal to -2.5
What’s the process of bone remodelling?
Osteocytes send signal to blasts and clasts
Osteoclasts breakdown bone by released H+ and lysosomal enzymes which remove and resorb mineral and collagen matrix
They undergo apoptosis
Osteoblasts build new bone by producing type 1 collagen and regulate mineralisation
They then either undergo apoptosis or become osteocytes
What is bone made of?
70% mineral: hydroxyapatite (salt of calcium and phosphate)
30% organic matrix: type 1 collagen fibres
What is RANK ligand?
A protein released by osteoblasts that triggers certain monocytes to differentiate into osteoclasts
What’s the link between PTH and vitamin D?
PTH raises calcium levels
- increases bone resorption
- increases Ca reabsorption in kidneys
- increases conversion to active vitamin D (cholecalciferol)
Cholecalciferol then increases Ca absorption in the small intestine
What’s active vitamin D also known as?
What’s the formula?
Cholecalciferol
1,25-(OH)2D
Risk factors of osteoporosis?
Think of FRAX
Age
Female
Previous fracture
Parental hip fracture
SHATTERED
Steroids
Hyperthyroidism, hyperparathyroidism, hypercalciuria
Alcohol and tobacco
Thin (BMI<22)
Testosterone reduced
Early menopause, late menarche
Renal or liver failure
Erosive/inflammatory bone disease: RA, myeloma
Dietary Ca low, malabsorption, diabetes 1
What’s the causes of primary and secondary osteoporosis?
Primary: age related
Secondary: drugs, diseases like RA, diabetes 1 etc
Why does early menopause cause osteoporosis?
They have less oestrogen
Oestrogen inhibits bone resorption
With estrogen deficiency, the osteoclasts live longer and are therefore able to resorb more bone.
Investigations of osteoporosis?
X-ray
Bone densitometry DEXA scan
Bloods: Ca, phosph, ALP should be normal. consider other investigations if suspect secondary
How do patients with osteoporosis present?
Asymptomatic until fracture
Low trauma
Spine Proximal femur Distal radius (Humerus) (Pelvis) (Ribs)
Management of osteoporosis?
Lifestyle:
- stop smoking and alcohol
- exercise improves BMD
- falls prevention programme
- diet: increase Ca and vit D
Drugs:
- bisphosphonates
- calcium (adcal) or vit D supplements
- Strontium ranelate
- HRT
- Denosumab
Which bisphosphonates are given?
How do they work?
1st line: Alendronate
2nd line: risedronate, etidronate
These can be taken once a day or once a week
If can’t tolerate oral you can give Zolendronic acid, which is a single IV infusion once a year
They inhibit the action of osteclasts
