Patho-1-Fracture healing Flashcards Preview

Block 6 - MSK > Patho-1-Fracture healing > Flashcards

Flashcards in Patho-1-Fracture healing Deck (36):
1

2 main forms of bone

  • Woven
  • Lamellar

2

Difference between woven bone & lamellar bone

Woven bone: immature form with randomly arranged collagen fibres in osteoid

  • fetal bone development, healing fracture, Paget's disease of bone
  • eventually remodelled to form lamellar bone

Lamellar bone: regular parallel bands of collagen arranged in sheets

  • 2 main types: compact & cancellous

 

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3

4 features of woven bone

  • immature bone
  • randomly arranged collagen fibres in osteoid
  • eventually remodelled to form lamellar
  • made when osteoid produced rapidly e.g. fetal bone, healing fracture

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4

Disease associated with woven bone?

Paget's disease - causes the abnormal enlargement and weakening of bone

5

3 features of lamellar bone

  • mature bone
  • regular parallel bands of collagen fibres in osteoid
  • stronger & more resistance than woven

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6

2 types of lamellar bone

  1. cancellous
  2. compact

7

Difference between compact & cancellous bone?

Compact bone - solidly filled with ground substance & inorganic salts

  • external layer
  • arranged in osteons
  • lamellae found in periphery & between osteons
  • central canals connected to each other by perforating canals

Cancellous bone - spongy bone with irregular lamellae

  • no osteons
  • arranged in trabeculae
  • major tissue type = short, flat, irregular bone
  • ligher than compact bone
  • supports red BM

8

Composition of bone

Cells:

  • osteoblasts (make matrix components)
  • osteocytes (resting osteoblasts)
  • osteoclasts (resorption of bone)

ECM:

  • organic osteoid (collagen type I)
  • inorganic Ca2+ & phosphate
  • non-fibrillar proteins e.g. osteopontin

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9

Name the 4 main types of bone cells & their function

Osteoblasts 'bulid bone' - make osteoid & mediate mineralisation

Osteocytes - inactivate osteoblasts trapped within formed bone

Osteoclasts 'crash bone' - capable of eroding bone & bone remodelling phagocytic cells

  • ruffled border & multiple nuclei

Osteoprogenitor - precursor to osteoblast

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10

What activates osteoclasts?

RANKL & RANK

11

2 types of bone development

  1. Endochondral ossification
  2. Intramembranous ossification

12

What is endochondral ossification?

  • forms bone from a cartilage matrix
  • bone replaces cartilage e.g. long bones - growth plate, vertebrae, pelvis
  • helps bones grow length ways

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13

What is Intramembranous ossification?

  • direct replacement of primitive mesenchymal by bone e.g vault of skull, maxilla, most of mandible
  • mesenchymal matrix
  • helps bone grow in width

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14

Mechanism of endochondral bone formation

  • osteoblasts line cartilage precursor
  • chondrocytes hypertrophy, degnerate & calcify (area of low O2 tension)
  • vascular invasion of cartiage occurs then ossification (increasing O2 tension)
  • bone grows in length

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15

Mechanism of Intra-membranous (Periosteal) bone formation

  • pre-osteoblasts --> osteblasts --> lay down seams of osteoid
  • doesn't involve cartilage
  • bone grows in width

16

Growth plate layers

Zone 1: resting cartilage

Zone 2: proliferating cartilage

Zone 3: hypertrophic cartilage

Zone 4: calcified cartilage

Zone 5: ossification

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17

Zone of proliferative cartilage role?

zone where growth length is created via active cartilage cells

18

Failure of zone of proliferative cartilage to work causes?

growth cessation

19

Hypertrophy layer

  • no active growth
  • chrondrocytes become enlarged, swollen and vacuolated in process of maturation leading to cell death

20

Zone of provisional calcification

  • Death of chrondrocyte
  • Longitudinal bars of cartilage matrix becomes calcified

21

Define fracture

break in continuity of bone

22

Different types of fractures (x5)

DOGS-C

  • greenstick (half breaks)
  • complete (through entire bone)
  • displaced (shift)
  • open (through skin)
  • segmental (multiple areas)

 

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23

Causes of fracture

  • trauma - mechanical force
  • pathological - bone weakened by another primary process
    • neoplastic & non-neoplastic can be causes
  • stress

24

What is a key sign that the fracture is pathological?

low impact

25

Fracture healing

mechanism that allows fracture to repair

fracture healing divided into:

  • direct (primary)
  • indriect (secondary)

26

Primary fracture healing

  • occurs with anatomic reduction & rigid internal fixation
  • attempt by cortex to re-establish new Haversian systems
  • little or no periosteal response
  • no callus formation

27

Secondary fracture healing

  • periosteal reaction --> callus formation
  • involves endochondral & intramembranous (periosteal) ossification
  • enhanced by movement - inhibited by rigid fixation

28

Callus

composite mass of tissue that forms at a fracture site to establish continuity at bone ends 

  • sometimes felt as a mass

29

Problem with external fixation

huge infection risk

30

3 healing phases

1. Reactive phase

  • haematoma formation --> inflammation --> granulation tissue formation

2. Reparative phase

  • soft callus --> hard callus

3. Remodelling phase - bone reshaped to normal contour

31

6 stages of fracture healing - describe

  1. haematoma - haemorrhage, clot formation within hrs/days
  2. inflammatory - starts within 48hrs, inflammatory cells appear; organisation & resorption of clot
  3. granulation - 2-12 days - presence of mesenchymal cells, fibroblasts, new capillaries
  4. soft callus - 1 week - several months - callus grows & bridges fracture site; cartilage & trabecular bone laid down
  5. hard callus - 1 week - several months - when callus has sealed bone ends, trabecular bone
  6. remodelling - continues for several months - reorganisation of bone, original cortex restored

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32

Conditions that interfere with fracture healing

  • poor blood supply  --> avascular or aseptic necrosis
  • poor immobilisation --> misalignment/deformity
  • infection - common with open fractures

33

Anatomic factures that influence fracture healing (x4)

  • soft tissue injury
  • interruption of local blood supply
  • interposition of soft tissue at fracture site
  • bone death due to radiation, thermal or chemical burns or infection

34

Systemic features that reduce fracture healing (x4)

  • malnutrition - reduces activity & proliferation of osteochondral cells; reduces callus formation
  • smoking - inhibits osteoblasts; nicotine causes vasoconstriction
  • DM - collagen defects
  • anti-inflammatory medications - temporary reduction in bone healing

35

Outcomes of fracture healing?

  • restoration of original tissue
  • scar
  • excessive repair
  • failure of healing/reapir
    • non-union
    • malunion
    • excessive bone formation

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36

Non-union of fracture - causes & management

  • displaced/comminuted/infection
  • inadequate immobilisation
  • management - rigid internal fixation
  • patient factors