Osteoporosis Flashcards
What are the seven important functions of bones?
- Support
- Protect
- Movement
- Mineral and growth factor storage
- Blood cell formation
- Triglyceride storage
- Hormone production
What are osteogenic stem cells?
Progenitor cells that differentiate into osteoblasts
What part of the bone is most affected by osteoporosis?
Cancellous (spongy) bone
What do osteoblasts secrete?
Osteoid (unmineralised matrix)
What cells line the bone? What is their role?
Periosteal and endosteal cells maintain matrix
What do osteocytes sense?
Sense stress and strain
What are the organic components of bone?
- Osteogenic cells
- Osteoblasts
- Osteocytes
- Bone-lining cells
- Osteoclasts
- Osteoid
What is osteoid made up of?
Ground substances and collagen fibres
What gives bone resilience?
Sacrificial bonds in or between collagen molecules
What is the inorganic component of bone? What percentage of the total bone mass does it make up?
Hydroxyampatites (mineral salts), 65% of bone mass
What hormones are responsible for regulation of bone growth?
- Growth hormone
- Thyroid hormone
- Testosterone and oestrogen
What percentage of bone mass is “recycled” due to bone homestasis each week?
5-7%
How often is spongy bone and compact bone replaced by bone homeostasis?
Spongy bone: every 3-4 years
Compact bone: every 10 years
Where in the bone does bone remodelling occur?
- Periosteum
- Endosteum
What is the function of osteoclasts?
- Create depressions or grooves as break down of matrix occurs
- Secretes lysosomal enzymes that digest matrix and protons
- Acidity converts calcium salts to soluble form
What does osteoclast activation depend on?
Parathyroid and thyroid cell-secreted proteins
What are the functions of calcium in the body?
- Nerve impulse transmission
- Muscle contraction
- Blood coagulation
- Secretion by glands and nerve cells
- Cell division
How much calcium is in the body normally?
1200-1400g of calcium in body
What vitamin is required to absorb calcium?
Vitamin D
What effect does parathyroid hormone have on calcium?
Removes calcium from bone, regardless of bone integrity
What effect does calcitonin have?
In high doses, lowers blood calcium levels temporarily
What is involved in the negative feedback hormonal loop for blood calcium homeostasis?
- Calcitonin secreted by the thyroid gland
- Stimulates osteoblasts and inhibits osteoclasts
- Blood calcium decreases
- Parathyroid hormone secreted by parathyroid glands
- Stimulates osteoclasts and inhibits osteoblasts
- Blood calcium increases
What is osteoporosis?
A reduction in bone mineral density 2.5 SD below the young adult mean (age 30)
What is osteopaenia?
A reduction in bone mineral density 1 - 2.5 SD below the adult mean (age 30)
What bone changes occur with the development of osteoporosis?
Loss of microarchitecture of bone
- total bone mass
- trabecular volume
- trabecular connectivity/separation
- trabecular plate thickness, and number
How is osteoporosis severity scored?
T-score
What are the risk factors for osteoporosis?
- Age
- Post-menopausal women
- Older men
- Petite body form
- Insufficient exercise
- Poor diet
- Low Vitamin D and C
- Smoking
- Hormone conditions
- Immobility
- Prostate cancer (androgen-suppressing drugs)
What other pathologies are also considered to increase the risk of osteoporosis?
- Rheumatoid arthritis
- Coeliac disease
- Chronic lung diseases
- Chronic renal failure
- Chronic liver failure
How often is someone admitted to an Australian hospital with an osteoporotic fracture?
Every 5-6 minutes
How is osteoporosis diagnosed?
Dual Energy X-ray Absorptiometry or bone densitometry
What sites are used to measure bone density? What kind of fractures are they best at predicting?
- Femoral neck: best site for predicting hip fractures
- Vertebra: best site for predicting spinal fractures
- Radius
How many women and men over 60 years of age will suffer an osteoporotic fracture in their lifetime?
- 60% of women
- 30% of men
What is the incidence of further fracture in women with an osteoporotic spinal fracture?
Women with spinal fractures are 4 times more likely to have another fracture within the next year, compared to women who have never had an osteoporotic fracture
What are the outcomes after osteoporotic hip fractures?
- 20-25% will be permanently disabled
- 50% never regain their former independence, and will require long-term nursing care
- 1 in 3 return to activity and independence
- 12-15% mortality within 6 months
- 25% mortality at 12 months as a result of subsequent immobility.
What does osteoporosis treatment involve?
- Calcium supplements
- VItamin D supplements
- Weight bearing exercise
- Hormone replacement therapy
What drugs are used in the treatment of osteoporosis?
- Bisphosphonates: inhibit osteoclast activity and number
- Selective oestrogen receptor modulators: mimic oestrogen
- Parathyroid hormone
- Denosumab
- Strontium injections
What prevention strategies are used in the management of osteoporosis?
- Maximise peak bone mass
- Limit the gradient of decline
- Prevent falls and fractures
What are the roles of Vitamin D?
- Regulation of paslam calcium and bone mineralisation
- Maintains function of neuromuscular junctions
- Effects on other systems
What food sources have Vitamin D?
Most: fatty fish
Less: eggs, some low-fat milk, fortified products
What does Wolff’s law indicate?
Wolff’s law indicates that bone strength increases and decreases as the functional forces on the bone increase and decrease.
What are the general principles of exercise for osteoporosis?
- Long term
- Ongoing, but changing
- Site specific
- Tension or force producing
- Consideration of falls risk, balance and reaction time
What aspects need to be considered for exercise prescription in osteoporosis?
- Specificity: site-specific
- Overload: must exceed typical everyday loads
- Reversibility
- Initial values: lower start, progress
- Diminished returns: quick response, then slow
What movements should be avoid by individuals who are severely osteoporotic?
Avoid flexion, twisting and asymmetrical loading
What did Bailey and Wavell (2010) and Daly et al conclude about weighbearing and impact exercise?
Higher frequency and repetitions result in greater bone mineral density
What is the incidence of further osteoporotic fractures in those who have already had 2 or more and 3 or more previously, compared to someone who has no previous history?
2 or more: 9 times more likely to have another fracture
3 or more: 11 times more likely to have another fracture
