2.1 Pathology of Fracture Healing

Question 1

What are the 2 forms of bone and how are they arranged?

Answer 1

Woven: immature form with randomly arranged collagen fibres in osteoid

Lamellar: regular parallel bands of collagen arranged in sheets (compact and cancellous)

Question 2

When do you have woven bone?

Answer 2

When you have rapidly produced osteoid such as:

Fetal bone development, Fracture healing, Pagets disease of bone

Question 3

Which cells of bone are multinucleated and what is their function?

Answer 3

Osteoclasts - resorption of bone and bone remodelling

Question 4

What are osteocytes?

Answer 4

Inactive osteoblasts tapped within the formed bone

Question 5

What are osteobasts?

Answer 5

the cells that actively synthesise the matrix and mediate mineralisation (mononucleated)

Question 6

How are osteoclasts activated?

Answer 6

RANKL expressed by osteoblasts binds to RANK on osteoclast precursors. This activates NF-kB which is required for generation and survival of osteoclasts.

Question 7

What occurs in endochondral ossification and in what bones does it occur?

Answer 7

Cartilage is replaced by bone - occurs in long bones, vertebrae and the pelvis
Mechanism by which long bone grows in length

Question 8

What is intramembranous ossification and when does it occur?

Answer 8

Osteoblasts directly form a fibrous layer of tissue that is derived from mesenchyme
Occurs in Vault of skull, mandible and maxilla and also in fracture healing

Question 9

What is a fracture?

Answer 9

A discontinuation of bone

Question 10

What are the 3 causes of fracture?

Answer 10

Trauma, pathological and stress

Question 11

How does a stress fracture occur

Answer 11

Due to constant low level stress which doesnt allow correct remodelling to occur

Question 12

What are the 6 phases of fracture healing?

Answer 12

Haematoma phase 
Cellular and graulation phase 
Soft callus 
Hard calls 
Ossification 
Remodelling

Question 13

What are the inflammatory cells and cytokines involved in fracture healing?

Answer 13

PDGF, TGF-B, IL-1 and 6, PGE2

Question 14

What are the conditions that interfere with fracture healing?

Answer 14

Poor blood supply 
Poor immoblisation 
Infection 
Soft tissue injury 
Interruption of local blood supply 
Interposition of soft tissue at fracture site 
Bone death 
Systemic factors: malnutrition, smoking, diabetes, anti-inflammatory medications