Bone Pathology Flashcards Preview

Module 7: Skin & bones > Bone Pathology > Flashcards

Flashcards in Bone Pathology Deck (13)
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1
Q

What is the role of osteocytes?

A

Detect changes in fluid flow in the ECF caused by altered stress and strain and/or microcracks and signal to osteoblasts to initiate bone formation or resorption

2
Q

What are the factors that can complicate fracture repair?

A
  • Malnutrition
  • Bacterial osteomyelitis
  • Interposition of large fragments of necrotic bone or soft tissue
  • Age
  • Pseudoarthrosis
3
Q

What are the types if fracture?

A
  1. Traumatic - excessive force
  2. Pathological - abnormal bone broken by minimal trauma or normal weight bearing e.g. osteomyelitis, neoplasia, metabolic bone disease
4
Q

Draw pictures to illustrate how fractures at the growth plate can occur

A

Type I and II - minimal complications

Type V - growth plate is crushed, damages resting cell layer or epiphyseal artery that nourishes them

*premature growth plate closure leads to limb deformity*

5
Q

How are fractures classified?

A
  • Infraction - only the trabecular bone is damaged without cortical deformation. Inflammation and necrosis predispose to this

Cortical fracture:

  • Simple/closed - skin is unbroken
  • Compound - skin is broken and bone exposed to external environment
  • Comminuted - several small fragments
  • Avulsed - caused by the pull of a ligament
  • Greenstick - one side broken, other side bent
  • Transervse or spiral - orientation of fracture line
6
Q

Define ‘stable fracture’

A

Fracture ends are immobilised by natural processes, not surgically fixed, to give relative stability. Due to formation of a callus.

7
Q

What are the stages in stable fracture repair?

A
  1. Necrosis of bone and marrow can occur at the broken ends
  2. Growth factors are released by macrophages and platelets in the clot and from dead bone (important for stimulating tissue repair)
  3. After 24-48hrs undifferentiated mesenchymal cells proliferate and neovascularisation occurs. A loose collagenous tissue forms
  4. 36hrs - new woven bone forms a callus
  5. Over months to years woven bone is replaced by strong, mature, lamellar bone (secondary callus)
  6. Callus size can be reduced over a period of years by osteoclastic activity to restore the bone to its normal shape
8
Q

What is a callus?

A

An unorganised meshwork of bone that forms after a fracture. Primary callus contains woven bone, cartilage can form from 4-6wks but it doesn’t get converted to bone (if blood supply is inadequate).

  • External part - formed by periosteum
  • Internal part - forms between ends of fragments and in medullary cavity
  • Should bridge the gap, encircle the fracture and stabilise the area
9
Q

Define rigid fracture repair

A

Surgical application of a device to repair a fracture

  • Ideally there is contact healing - direct osteonal bridging with no callus formation
  • Gap between bone ends should be <1mm to enable bone cells to migrate from the ends and form lamellar bones at right angles to the fracture line
  • If gap >1mm, woven bone that forms will be remodelled into osteonal bone
10
Q

What are the complications of rigid fracture repair?

A
  • Inadequate blood supply - cartilage formation, necrosis if there is anoxia
  • Instability - excessive movement and tension favours callus formation
11
Q

Define osteitis, periostitis, osteomyelitis, sequestrum

A

Osteitis - bone inflammation

Periostitis - inflammation of periosteum

Osteomyelitis - inflammation of bone including the medullary cavity

Sequestrum - fragment of dead bone isolated from blood supply and surrounded by a pool of exudate

12
Q

What are the portals of entry into bone?

A
  1. Direct entry - through periosteum and cortex, via trauma, direct extension
  2. Haematogenous - blood gains access to the marrow cavity of diaphysis and metaphysis via a nutrient foramen
    3.
13
Q

Describe embolic osteomyelitis

A
  1. Embolus lodges in capillary loop at the metaphysis
  2. Inflammation causes lysis of metaphyseal bone and growth plate cartilage
  3. Causes mechanical instability - periosteum responds by producing woven bone
  4. Exudate can lyse the cortex at its thinnest point - metaphyseal cut back zone
  5. Exudate can extend into the periosteum and cause periostitis
  6. Exudates can also extend into joints and onto the surface of the skin