Bone health

Question 1

Bone distribution

Answer 1

cortical 80%

Trabecular 20%

Question 2

Cortical bone function

Answer 2

biomechanical strength
attachment site for tendon and muscle
trauma protection

Low turnover rate - Haversian remodelling, periosteal appositional growth

Question 3

Trabecular bone function

Answer 3

mineral metabolism
strength
elasticity

higher turnover rate
frequent remodelling

Question 4

Bone matrix composition

Answer 4

90% collagen

10% proteins - osteocalcin, osteonectin, osteopontin

Question 5

Bone mineral composition

Answer 5

hydroxyapatite - calcium and phosphate

Question 6

bone mass imaging

Answer 6

X-ray - not good, need to lose 30% before it is evident
High resolution CT: can do finite element analysis
- allows prediction of force required to break structure

Dual-energy X-ray absorptiometry (DXA) - typically used

Question 7

Fracture epidemilogy

Answer 7

bimodal distribution
adolescence - more males, due to trauma to long bones
elderly - more females, mostly low-trauma

Question 8

Fracture risks

Answer 8

previous fractures - doesn’t matter which joint
Age

synergistic with bone density

Question 9

DXA

Answer 9

low dose radiation

measures amount of calcium in hip/spine

Question 10

BMD

Answer 10

relates patient’s bone mass density to normal distribution in population
standard deviations from normal

Question 11

bone formation markers in blood

Answer 11

Bone-associated alkaline phosphatase
Collagen type I propeptidases
Osteocalcin

Question 12

bone resorption markers in blood

Answer 12

calcium
hydroxyproline
hydroxylysine glycosides
pyridinium crosslinks

Question 13

Bone biopsy

Answer 13

rarely used

Question 14

Peak bone mass

Answer 14

different sites in the body reach peak at different times

Question 15

WHO definition of osteoporosis

Answer 15

more than -2.5 SD below population average

Question 16

WHO classification of osteoporosis for postmenopausal women

Answer 16

also used for men >50
stratify based on t scores

Normal >-1.0
Low bone mass/osteopenia -2.5 to -1.0
Osteoporosis <-2.5 with lower fracture

Question 17

FRAX score

Answer 17

determines fracture risk within 10 years
useful for men and women >50, all ethnicities
Other risk factors:
- previous fracture
- parental hip fracture
- current smoking
- GC use
- RA or other secondary causes
- alcohol intake - >3 units/d

Question 18

Osteoporosis scoring in younger men/women

Answer 18

Use age-matched Z scores instead of t scores

Use clinical diagnostic features over bone mass

Question 19

Clinical diagnosis of osteoporosis

Answer 19

Presence of a fragility fracture

Question 20

Fragility fracture

Answer 20

Caused by an injury that would be insufficient to fracture normal bone
Could be due to minimal or no injury

Question 21

Calcium supplementation

Answer 21

1000 mg/day 19-50, 1200 >50
do not prevent fractures
not enough to treat osteoporosis
only need to supplement to sufficiency
CV risk unclear

Question 22

vitamin D supplementation recommendation

Answer 22

infants - 400 IU
children/adults - 600
adults > 70 - 800

Question 23

Clinical manifestations of severe vit D deficiency

Answer 23

<25 nmol/L
osteomalacia
Ricketts
proximal myopathy, sway, falls

Question 24

Clinical manifestations of moderate vit D insufficiency

Answer 24

25-75 nmol/L
secondary hyperparathyroidism
muscle weakness, falls
increase fracture risk
potential for increased risk of cancers, inflammatory arthritis, MS, type I diabetes, TB, influenza
Prevalence of vitamin D deficiency is extremely high in the population

Question 25

Disuse osteoporosis

Answer 25

Reduce the stress on bone due to casting, reduced activity --> increased resorption/impaired bone formation

Question 26

Bone scan

Answer 26

bone scintigraphy tracer most commonly used = Tc-99m MDP MDP becomes incorporated in the mineral phase of bone and visualized via gammacamera increased tracer uptake with increase in blood flow/osseous remodelling Causes of increased uptake: - tumour (primary/metastatic) - infection - trauma (mechanical stress)

Question 27

Bone scintigraphy indication

Answer 27

``` osteomyelitis stress fractures occult fractures metastases staging for tumours AVN ```

Question 28

3-phase bone scans

Answer 28

Blood flow phase: arterial bloodflow - e.g. hypervascularity Blood pool: equilibrium in the extracellular space - soft tissue Delayed: 2-24 hours after injection of tracer