0624 - Fracture Healing

Question 1

What are the two primary forms of bone? Outline each.

Answer 1

Woven and Lamellar bone

Woven - Immature, randomly arranged collagen (Type 1) in osteoid. Seen in rapid osteoid production (foetal bone, healing fracture).

Lamellar - Regular parallel bands of collagen arranged in sheets. Can be compact or cancellous. Most healthy adult bone, stronger and more resilient than woven bone.

Woven is eventually remodelled to form lamellar.

Question 2

What are the three main bone cells? What is the function of each?

Answer 2

Osteoblasts - Make osteoid and mediate mineralisation.

Osteocytes - Inactive osteoblasts trapped within formed bone.

Osteoclasts - Capable of eroding bone and remodelling bone. Monocyte derived.

Question 3

How are osteoclasts activated?

Answer 3

RANK-Ligand and RANK
RANK activation causes osteoclast activation. RANKL inhibitors important for treating Paget’s and metastatic disease - strengthens bone and decreases risk of fracture.

Question 4

What are the broad components of bone?

Answer 4

Cells and ECM

Cells - Osteoblasts/cytes/clasts

ECM - Osteoid (type I collagen), calcium hydroxyapatite, and non-fibrillar proteins (osteopontin, osteonectin)

Question 5

What are the two types of bone development

Answer 5

Endochondral ossification - Form bone from a cartilage matrix - how bones grow in length, making cartilage that turns into bone. Via hypertrophy of chondroblasts.

Intramembranous ossification - Primitive mesenchymal matrix (laid by periosteum) which then forms bone by mesenchymal preosteoblasts differentiating directly into osteoblasts (without a cartilage matrix) - how bones grow in width and in foetus.

Question 6

Define Fracture

Answer 6

A discontinuity in the bone

Question 7

What are the types of fracture? (5)

Answer 7

Comminuted - Multiple fragments

Transverse - straight across

Oblique - Oblique line

Spiral - around the bone

Segmental - 2 or more fractures in one bone.

Question 8

What is the difference between a Linear and a Comminuted fracture?

Answer 8

Linear - Oblique or transverse line of fracture.

Comminuted - more complex, may involve shattered bones.

Question 9

What is the difference between Complete and incomplete fracture?

Answer 9

Complete - the fracture line proceeds across the entire plane of the bone.

Incomplete - there is an element of continuity that is contiguous with the fracture line.

Question 10

What is the difference between displaced and non-displaced fractures?

Answer 10

Displaced - edges are no longer opposed, possible laceration of vessels/nerves in vicinity.

Non-displaced - edges are opposed allowing for better healing.

Question 11

What is the difference between Open vs Closed fractures?

Answer 11

Open - through the skin

Closed - contained within.

Question 12

What are the three causes of fracture?

Answer 12

Trauma - mechanical force

Pathological - Bone weakened by another primary process (low-impact)

Stress - repeated, chronic, comparatively low stress.

Question 13

What are the two types of fracture healing?

Answer 13

Primary and secondary.

No different to any other tissue (requires lots of granulation tissue) except that bone needs to form too.

Question 14

Describe primary fracture healing

Answer 14

Occurs with reduction and/or rigid internal fixation (oppose the ends or fix it in place).

Minimal periosteal response, so no callus formation. Attempt by cortex to re-establish new Haversian systems (normal bone homeostasis)

Question 15

Describe secondary fracture healing

Answer 15

Occurs in majority of fractures. There is a periosteal reaction, forming a callous.

Involves both endochondral and intramembranous ossification.

Need rigid fixation to minimise the callous.

Question 16

What are the temporal stages of fracture healing (brief)

Answer 16

Inflammatory - Haematoma formation, inflammation, granulation tissue formation

Reparative - Soft callous, becoming hard callous

Remodeling - Reshaping bone to normal contour.

Question 17

Outline the 6 physiological stages of fracture healing.

Answer 17

1 - Haematoma - Stimulated by bone necrosis and hyposia, phagocytes and lysosomes clear debris, fibrin mesh forms scaffold, and new capillaries grow in from periosteum.

2 - Cellular/Granulation - Formation of granulation tissue (new CT and angiogenesis)

3 - Soft Callus - Influx of fibroblasts and osteoblasts form periosteum, produce a fibrocartilagenous (soft) callus of woven bone. Lasts for 3 weeks

4 - Hard Callus - Connects bone filament to woven bone. Gains strength, but without immobilisation, cartilage will form instead of bone.

5 - Ossification (mineralisation) - Starts by 2-3 weeks, lasts 3 months. Requires immobilisation, allowing bone ends to cross over and develop new Haversian system.

6 - Remodeling - Hard callus is remodeled to compact bone. May take months-years.

Question 18

What are the broad causes of non-healing fractures?

Answer 18

Local - Poor blood supply, poor immobilisation, infection, soft tissue injury, bone death

Systemic - Malnutrition (reduces osteochondral cells, decreases callous formation), smoking (inhibits osteoblasts, nicotine vasoconstriction), Diabetes (collagen defects, microvascular disease), anti-inflammatory medications (cause temporary reduction in bone healing).