Osteonecrosis and fracture healing

Question 1

Bone structure

Answer 1

Question 2

Composition of bone

Answer 2

Cortical bone

• 80% skeletal
• compact bone
• outer

Cancellous/spongy bone

• trabeculae
• high tunrover

Question 3

Functions of bone

Answer 3

Structural

• Support
• Protection
• Movement

Mineral Storage

• Calcium
• Phosphate

Question 4

Two types of fracture healing

Answer 4

• Indirect healing (secondary)
• Direct healing (primary)

Question 5

Indirect fracture healing stages

Answer 5

Indirect healing (Secondary, via callus formation)

‘Formation of bone via a process of differential tissue formation until skeletal continuity is restored’

INFLAMMATION, REPAIR, REMODELLING

Question 6

Inflammation stage

Answer 6

• blood from broken vessels forms a clot.
• 6-8 hours after injury
• swelling and inflammation to dead bone cells at fracture site
• fracture haematoma

Question 7

Repair stage

Answer 7

FIbrocartilage (soft calluus)

• lasts about three weeks
• new capillaries organise fracture hematoma into granulation tissue - ‘procallus’
• Fibroblasts and osteogenic cells invade procallus.
• Make collagen fibres which connect ends together (type III)
• Chondrocytes begin to produce fibrocartilage

Bony (hard) cartilage

• (after 3 weeks and lasts about 3-4 months)
• osteoblasts make woven bone.
• Calcified type 1

Question 8

Remodelling stage

Answer 8

• Osteoclasts remodel woven bone into compact bone and trabecular bone
• Often no trace of fracture line on X-rays.

Question 9

Direct fracture healing

Answer 9

• Unique ‘artificial’ surgical situation
• Direct formation of bone, without the process of callus formation, to restore skeletal continuity’

Question 10

Blood supply of bone

Answer 10

Endosteal

• Inner 2/3rds

Periosteal

• Outer 1/3rd

Question 11

Compromise of blood supply

Answer 11

• Surgical factors (iatrogenous)
• anatomical factors

Question 12

Anatomical

Answer 12

• Certain fractures are prone to problems with union or necrosis (bone death) because of potential problems with blood supply
  
  • Proximal pole of scaphoid fractures
  • Talar neck fractures
  • Intracapsular hip fractures
  • Surgical neck of humerus fractures

Question 13

Which medications can impair fracture healing

Answer 13

NSAIDS

• NSAIDs reduce local vascularity at fracture site
• Additional reduction in healing effect independent of blood flow

Bisphosphonates

• inhibit osteoclastic activity
• delay fracture healing as a result
• long half-life

Question 14

Osteonecrosis definition

Answer 14

Avascular necrosis, death of a bone/bone infarct near a joint

Question 15

Bone infarct definition

Answer 15

Bone death not near a joint

Question 16

Hip osteonecrosis

Answer 16

Necrotic bone on femoral head gives no congrent surface and therefrore arthrtiis

Question 17

Hip blood supply

Answer 17

medial circumflex femoral artery

Question 18

Examintion of osteoecrotic hip

Answer 18

Examinition

• limb
• tenderness around affected bone
• restriction internal roation and abduction

Question 19

Presentation of osteonecrosis in hip

Answer 19

• groin pain
• worsening with weight bearing
• 2/3rds rest pain
• 1/3 night pain
• normal XR

Question 20

Pathophysiology of osteonecrosis

Answer 20

1. bone is derived of blood supply medullary bone first
2. articular cartilae - receives nutrition from synovial fluid
3. cortex- collateral blood supply - Both spared

Question 21

Causes of osteonecrosis

Answer 21

1. trauma
2. corticosteroids
3. alcohol abuse
4. sickle cell disease

Question 22

X-ray features

Answer 22

• MRI- 90% sensitivity
• later stages - articular surface collapses, joint space narrowing
• may be normal for months
• mild density changes
• Crescent sign (Subchondral radiolucency preceds subchondral collapse)