Patho-1-Fracture healing Flashcards
2 main forms of bone
- Woven
- Lamellar
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
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
Disease associated with woven bone?
Paget’s disease - causes the abnormal enlargement and weakening of bone
3 features of lamellar bone
- mature bone
- regular parallel bands of collagen fibres in osteoid
- stronger & more resistance than woven
2 types of lamellar bone
- cancellous
- compact
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
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
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
What activates osteoclasts?
RANKL & RANK
2 types of bone development
- Endochondral ossification
- Intramembranous ossification
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
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
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
Mechanism of Intra-membranous (Periosteal) bone formation
- pre-osteoblasts –> osteblasts –> lay down seams of osteoid
- doesn’t involve cartilage
- bone grows in width
Growth plate layers
Zone 1: resting cartilage
Zone 2: proliferating cartilage
Zone 3: hypertrophic cartilage
Zone 4: calcified cartilage
Zone 5: ossification
Zone of proliferative cartilage role?
zone where growth length is created via active cartilage cells
Failure of zone of proliferative cartilage to work causes?
growth cessation
Hypertrophy layer
- no active growth
- chrondrocytes become enlarged, swollen and vacuolated in process of maturation leading to cell death
Zone of provisional calcification
- Death of chrondrocyte
- Longitudinal bars of cartilage matrix becomes calcified
Define fracture
break in continuity of bone
Different types of fractures (x5)
DOGS-C
- greenstick (half breaks)
- complete (through entire bone)
- displaced (shift)
- open (through skin)
- segmental (multiple areas)
Causes of fracture
- trauma - mechanical force
-
pathological - bone weakened by another primary process
- neoplastic & non-neoplastic can be causes
- stress
What is a key sign that the fracture is pathological?
low impact
Fracture healing
mechanism that allows fracture to repair
fracture healing divided into:
- direct (primary)
- indriect (secondary)
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
Secondary fracture healing
- periosteal reaction –> callus formation
- involves endochondral & intramembranous (periosteal) ossification
- enhanced by movement - inhibited by rigid fixation
Callus
composite mass of tissue that forms at a fracture site to establish continuity at bone ends
- sometimes felt as a mass
Problem with external fixation
huge infection risk
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
6 stages of fracture healing - describe
- haematoma - haemorrhage, clot formation within hrs/days
- inflammatory - starts within 48hrs, inflammatory cells appear; organisation & resorption of clot
- granulation - 2-12 days - presence of mesenchymal cells, fibroblasts, new capillaries
- soft callus - 1 week - several months - callus grows & bridges fracture site; cartilage & trabecular bone laid down
- hard callus - 1 week - several months - when callus has sealed bone ends, trabecular bone
- remodelling - continues for several months - reorganisation of bone, original cortex restored
Conditions that interfere with fracture healing
- poor blood supply –> avascular or aseptic necrosis
- poor immobilisation –> misalignment/deformity
- infection - common with open fractures
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
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
Outcomes of fracture healing?
- restoration of original tissue
- scar
- excessive repair
- failure of healing/reapir
- non-union
- malunion
- excessive bone formation
Non-union of fracture - causes & management
- displaced/comminuted/infection
- inadequate immobilisation
- management - rigid internal fixation
- patient factors
