Fracture through the Ages Flashcards Preview

Y2 LCRS 2 - Musculoskeletal - Laz COPY > Fracture through the Ages > Flashcards

Flashcards in Fracture through the Ages Deck (34)
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1
Q

Define bone strength

A

The ability of bone to resist fracture

2
Q

What factors contribute to bone strength?

A
  • Density
  • Structure
3
Q

1) What method has been used for diagnosing osteoporosis and what are the limitations of this method?
2) When using this method how do we determine someone who has low bone mass and how do we determine if the patient is osteoporotic?

A

1)

  • DEXA scans
  • This gives a reading of bone mineral density (BMD) but it doesn’t tell you anything about the bone structure

2)

  • When compared to the T-score values taken from a healthy young patients and if the value obtained is > 1 S.D. away then the patient has a low bone mineral density while if > 2.5 S.D. away then the patient is diagnosed as osteoporotic
4
Q

How does trabecular bone density change in response to load?

A

The trabecular bone is remodelled - trabecular bone architecture changes to make it more adapted to the loads the body will undergo

5
Q

What are some risk factors for being osteoporotic?

A
  • Old
  • Post-menopausal
  • Smoking
  • Drinking
  • Little exercise
6
Q

Describe the effects of oestrogen on osteoclasts

A
  • Oestrogen stimulates apoptosis in osteoclasts
7
Q

What are the two main divisions of bone composition and what are some sub-components of these - therefore detail the complete picture of the composition of bone?

A
  1. Cells
  • Osteoblasts
  • Osteoclasts
  • Osteocytes
  • Osteoprogenitors
  1. Matrix
  • Inorganic
    • Hydroxyapatite
    • Calcium
    • Phosphorus
  • Organic
    • Collagen
    • Mucopolysaccharides
    • Non-collagenous proteins
8
Q

What are the two subsets of bone matrix and what falls under each?

A
  • Organic
    • Collagen
    • Non-collagenous proteins
    • Mucopolysaccharides
  • Inorganic
    • Hydroxyapatite crystals (calcium and phosphorus)
9
Q

What are the four types of bone cells?

A
  • Osteoprogenitor cells
  • Osteocytes
  • Osteoblasts
  • Osteoclasts
10
Q

What is the role of osteoprogenitor cells?

A
  • These differentiate into the other types of bone cell
11
Q

What are osteocytes and what is their role?

A
  • An osteoblast that has become embedded within the bone matrix, occupying a bone lacuna and sending, through the canaliculi, slender cytoplasmic processes that make contact with processes of other osteocytes
  • They are involved in bone homeostasis
12
Q

How often does bone normally turnover?

A
  • 120 days
13
Q

Describe normal bone turnover

A
  • The osteoclast will dissolve away the bone
  • Preosteoblasts will move in and differentiate into osteoblasts
  • In a healthy person, the osteoblasts will lay down more bone than the osteoclasts dissolved (so you don’t get any bone loss)
14
Q

How do osteoblasts lay down bone?

A
  • Osteoblast precursors arrive
  • They mature into mature osteoblasts
  • Osteoblasts lay down osteoid which is further mineralised by hydroxyapatite
15
Q

How is bone turnover different in an elderly person?

A
  • There is less apoptosis of osteoclasts and the resorption pits are very big and don’t get filled in by osteoblasts so you get lots of bone loss
16
Q

What effect do bisphosphonates have on osteoclasts?

A
  • Bisphosphonates encourage cell death in osteoclasts
  • Bisphophonates are absorbed into the bone when it is mineralised
  • When osteoclasts come along to resorb the bone, the bisphosphonates are released and internalised into these osteoclasts
  • They damage their cytoskeleton so that the osteoclasts lose their RUFFLED BORDER, and without this they can’t function and secrete their resorptive enzymes
17
Q

What is a major problem with bisphosphonate use?

A
  • Atypical fractures
  • Fatigue microdamage / stress fractures also because bisphosphonate suppresses osteoclastic activity and since this is a key part of bone remodelling, there is decreased remodelling and turnover of damaged bone tissue to repair the fatigue microdamage so it accumulates and you often get fracture due to this often in the sub-trochanteric areas
18
Q

What is the half-life of alendronate?

A

Around 10 years

19
Q

What new drug has come onto the market that has a similar action to bisphosphonates but with a shorter half-life?

A
  • Denosumab - prevents osteoclast activity (but by another different mechanism)
20
Q

1) Describe the mode of action of Denosumab
2) What is a major problem side effect with Denosumab, the same as with bisphosphonates?

A

1)

  • Denosumab prevents the binding of RANK-L molecules binding RANK receptors on precursors to osteoclasts such as macrophages thus preventing its maturation into osteoclasts
  • Therefore it prevents the action of osteoclasts

2)

  • Intereferes with bone remodelling because since it is inhibiting osteoclast activity it also inhibits the whole remodelling process, this prevents the healing process of bone damage thus can lead to fatigue microdamage
21
Q

Describe the action of RANKL

A
  • RANKL binds to RANK receptors on precursors to osteoclasts (such as macrophages) and promotes their maturation to osteoclasts
22
Q

In a healthy person, what protein is responsible for regulating the bone remodelling process and how does it do this?

A
  • Osteoprotegrin (OPG)
  • It prevents the binding of RANKL (often secreted by osteoblasts) to the RANK receptor (this is also what denosumab does)
23
Q

State Wolff’s Law

A
  • Bone remodels according to the stresses applied to it
24
Q

State some factors that contribute to bone mass

A
  • Genetics
  • Nutrition
  • Vitamin D
  • Exercise
25
Q

List, in order, the four stages of fracture healing?

A
  1. Haematoma
  2. Soft callus formation
  3. Hard callus
  4. Remodelling
26
Q

What happens in the first stage of fracture healing and what is this stage called?

A
  • Haematoma
  • (/inflammation) – blood and inflammatory cells at the site of fracture come pouring in
27
Q

What happens in stage 2 of fracture healing and what is this stage called?

A
  • Soft callus
  • Cartilage develops to form this soft callus at the site of fracture (type 2 collagen is layed down) but mineralisation has not occured yet (as prevented by proteoglycans)
28
Q

1) Which type of collagen is deposited in the soft callous?
2) Which type of collagen is deposited in the hard callous?

A

1)

  • Type 2 collagen

2)

  • Type 1 collagen
29
Q

What prevents mineralisation in the soft callous?

A
  • Proteoglycans
30
Q

What happens in stage 3 of fracture healing and what is this stage called?

A
  • Hard callus
  • The soft callus is invaded by blood vessels
  • Chondroblasts break down the calcified callous
  • It is replaced by osteoid (type I collagen) produced by osteoblasts and you get woven bone being layed down (mineralisation begins to occur)
  • Osteoid calcifies to form woven bone
31
Q

What happens in stage 4 of fracture healing and name this stage?

A
  • Remodelling
  • Bone properly heals
  • Woven bone remodels to lamellar bone
  • It is shaped relative to the load (Wolff’s law)
  • Medullary canal reforms
32
Q

Name four types of fracture

A
  • Spiral
  • Oblique
  • Comminuted (e.g. butterfly fragment)
  • Transverse
33
Q

What type of fracture can occur in the bones of children due to their plasticity?

A
  • Greenstick fractures
  • Cortical fracture on one side and sparing on the other side – often in children
34
Q

What type of forces cause the 4 different types of bone fractures?

A
  • Spiral fracture - caused by rotational forces
  • Oblique fracture - caused by compression forces
  • Comminuted fracture - caused by bending forces and impact
  • Transverse fracture - caused by tension forces