10. Fractures through the ages

Question 1

How does the amount of bone in a given sample of lumbar vertebra change in utero and after birth?

Answer 1

• Increase in utero

* Decrease after birth, but bone becomes more ordered (trabecular bone forms)

Question 2

What percentage of bone is matrix?

Answer 2

90%

Question 3

When in life does modelling stop and just remodelling takes place?

Answer 3

As you reach adulthood

Question 4

Why is it important for bone to remodel and repair?

Answer 4

The bone can become the required shape to withstand loads and to prevent weak spots from forming due to fatigue micro-damage

Question 5

Outline the order of sequence of bone repair

Answer 5

1) Damage occurs and lining cells become activated, causing macrophages to differentiate into osteoclasts
2) Osteoclasts have a ruffled border with the bone - where enzymes are secreted to destroy the bone
3) Osteoblasts fill the hole that the osteoclasts have formed, and secrete osteoid
4) Osteoid becomes mineralised by hydroxyapatite, normal bone is formed, and cells return to resting state

Question 6

What happens to the bone repair process as you get older?

Answer 6

• Process becomes unbalanced
• Normally, more bone is formed than removed
• This is controlled by testosterone and oestrogen, which is not produced as much in older age

Question 7

What happens to the bone cells during menopause?

Answer 7

• Oestrogen causes osteoclastic cell apoptosis (less osteoclasts)
• When oestrogen stop during menopause, osteoclasts can keep resorbing bone
• Osteoclast > osteoblast - so more bone is removed
• Bone density decreases - weak and brittle

Question 8

What are the most common fragility fractures?

Answer 8

• Hip fractures - high mortality
• Vertebral fractures - stooped posture in elderly people
• Distal radial fractures

Question 9

Why is exercise important for bones?

Answer 9

• More force applied => more bone put down => stronger bone
• When elderly people make their lives easier and exercise less, it increases loss of bone strength
• If you build a large bone mass early in life, it takes longer for the bone to become fragile when older

Question 10

Outline the 2 ways a bone can heal

Answer 10

Direct healing
• Broken ends are put back together to touch one another, and pressure is applied
• Osteoclasts move forward towards the other bone, with osteoblasts following behind
• Only occurs if there has been surgical prevention (plates and screws)

Callus healing
• More natural - bone is put back to touch or has rods and pins inserted
• Allows some movement at fracture site
• Improved healing

Question 11

Describe callus healing at the following timeframes:
• Week 1
• Weeks 2-3
• Weeks 4-16
• Over 12-18 months

Answer 11

Week 1
• blood vessels damaged
• haematoma
• increase blood supply - pro-inflammatory, bringing osteoclasts/blasts

Weeks 2-3
• soft callus formed
• mainly formed from cartilage and fibrous tissue - restricted movement

Weeks 4-16 (usually week 6)
• cartilage => bone
• becomes mineralised and collagen type I is formed
• bone is disorganised and weak (hard callus)

Over 12-18 months
• bone remodels to form trabecular bone that can withstand the forces applied to it, better

Question 12

What causes the following type of fracture/fragment patterns:
• Spiral fracture
• Oblique fracture
• Butterfly fragment
• Transverse fracture

Answer 12

• Spiral fracture - rotational/twisting force
• Oblique fracture - compression
• Butterfly fragment - high impact bending force, small part of bone thrown off (e.g. hit by car)
• Transverse fracture - tension, usually caused by own muscles and tendons

Question 13

What is a Greenstick fracture?

Answer 13

• Cortex breaks on one side but not the other
• Occurs in children, because the bone is less mineralised and more flexible
• Easy to realign but can end up breaking on the other side