Musc 10 - Fractures through the ages

Question 1

What is the ratio of matrix to cells in bone

Answer 1

90% matrix, 10% cells

Question 2

Which part of the osteoclast secretes enzymes which dissolves bone?

Answer 2

Ruffled border

Question 3

Explain normal bone turnover

In young healthy adult, more bone formation than resorption

Answer 3

1. Signal arrives (e.g. bone damage, hormones, etc)
2. Osteoclasts resorb bone
3. Osteoblasts lay down osteoid (inorganic matrix)
4. Osteoid mineralised by hydroxyapatite
5. Normal bone achieved and cells return to resting state

Question 4

What are bisphosphonates and what do they do

Answer 4

Class of drugs that prevent osteoclasts from resorbing bone

Osteoclasts absorb bisphosphonates and their cell cytoskeleton is damaged (particularly ruffled border)

Used to treat osteoporosis

Question 5

How can long term use of bisphosphonates cause femoral fractures

Answer 5

Osteoclastic activity suppressed - which also suppresses osteoblastic activity. Bone remodelling hindered

Question 6

How does denosumab work

Answer 6

Mimics molecule (osteoprotegerin) that interferes with RANKL pathway - prevents osteoclast precursors from becoming osteoclasts

May also lead to stress fractures

Denosumab has only a half life of 6 months compared to 10 years for bisphosphonates

Question 7

What is the precursor OG of osteoclasts

Answer 7

Macrophages

Question 8

Name 3 functions of calcium in the blood

Answer 8

Nerve function
Muscle function
Clotting

Question 9

What are the requirements for bone healing

Answer 9

1. Vascularity
2. Adequate mechanical stability of fracture

Also bone requires some load

Question 10

Explain callus healing (this is the form of healing if someones in a cast)

FRACTURE IS THE SAME AS A BREAK

Answer 10

Week 1 - haematoma / inflammation. Macrophages, etc. Granulation tissue forms. Progenitor cells invade.

Week 2-3 - Soft callus. Chondroblasts and fibroblasts differentiate - form collagen (2) and fibrous tissue. Proteoglycans produced –> prevent mineralisation. Chondrocytes release Ca into ECM and degradation enzymes to break down proteoglycans - allows mineralisation

Week 4-16 - Hard callus. Soft callus invaded by blood vessels. Chondroblasts breakdown calcified callus. Replaced by osteoid (Type 1 collagen) from osteoblasts. osteoid calcifies –> woven bone

Weeks 17+ - remodelling. Woven becomes lamellar bone. Shape relative to stresses - Wolffs law. Medullary canal forms.

Question 11

Rates of remodelling are highest in?

Answer 11

Children and adults

Question 12

Describe fracture patterns

Answer 12

1. Spiral fracture = twisting
2. Oblique fracture = direct result of compression
3. Butterfly fragment - from a bending force (very high energy)
4. Transverse fracture = tension. e.g. patella, olecranon