MSK growth, injury and repair Flashcards
Decsribe cortical bone
○ Diaphysis ○ Resists - Bending - Torsion ○ Laid down circumferentially ○ Less biologically active
Describe cancellous bone
○ Metaphysis ○ Resists/absorbs - compression ○ Site of longitudinal growth (physis) ○ Very biologically active
What is a fracture?
○ Break in structural continuity of bone
○ May be a crack, break, split, crumpling, buckle
○ ( # = shorthand sign for a fracture )
Why do bones fail?
○ High energy transfer in normal bones -Takes a lot ○ Repetitive stress in normal bones - Stress fracture ○ Low energy transfer in abnormal bones - Osteoporosis - Osteomalacia, metastatic tumour § Other bone disorders
What haens in a fracture
○ Mechanical and structural failure of bone ○ Disruption of blood supply ○ Regenerative process - No scar - Four stages
What is strain and how does it affect healing?
□ Degree of instability is best expressed as magnitude of strain (% change of initial dimension)
□ If strain is too low mechanical induction of tissue differentiation fails
□ Too high and healing process does not progress to bone formation
What happens in stage 1 of bone healing?
- Begins immediately after fracture
- Hematoma and fibrin clot
- Platelets, PMN’s, Neutrophils, Monocytes, Macrophages
- Massive increase in blood supply in the first few days
- By products of cell death: lysosomal enzymes
- Starts off with muscle contraction for initial stability
- Fibroblasts come in to stabilise the bone
- Mesenchymal & Osteoprogenitor cells
□ Transformed endothelial cells from medullary canal and/or periosteum
□ Osteogenic induction of cells from muscle and soft tissues - Angiogenesis
□ Oxygen gradient required (low)
□ Macrophages: produce angiogenic factors under hypoxic conditions
How might stage 1 be affetced?
□ NSAIDs ® Potential to slow down fracture repair □ Loss of haematoma ® Open fractures ® Surgery □ Extensive tissue damage ® Fewer live cells to grow back in again ® Poor blood supply
What happens in stage 2 of bone healing?
- Begins when pain and swelling subside
- Lasts until bony fragments are united by cartilage or fibrous tissue
- Some stability of fracture
- Angulation can still occur
- Continued increase in vascularity
□ Falls off after 2 weeks
□ Less so than stage 1
How might stage 2 be affected?
□ Replace cartilage ® DMB (Demineralised bone matrix) □ Jump straight to bone ® Bone graft ® Bone substitutes
What happens in stage 3 of bone healing?
- Fibroblasts convert to osteocyte
- Conversion of cartilage to woven bone
- Typical long bone fracture
□ Endochondral bone formation
□ Membranous bone formation - Increasing rigidity
□ Secondary bone healing (natural healing)
□ Obvious callus - Primary bone healing is when you use surgery to insert a plate
What happens in stage 4 of bone healing?
- Conversion of woven bone to lamellar bone
- Medullary canal is reconstituted
- Bone responds to loading characteristics Wolff’s Law
What are Platelet concentrates?
○ “Buffy coat”
○ Platelet-derived growth factor (PDGF)
○ Transforming growth factor- beta (TGF-B)
○ Insulin like growth factor (IGF)
○ Vascular endothelial growth factor (VEGF)
○ Squirt it in in situations where patients have lost their own haematoma to encourage bone repair
hat is autogenous cancellous bone grafts?
○ Gold standard
○ The patient’s own bone
○ Osteoconductive: bone regrows through it
○ Osteoinductive: stimulates bone growth
○ Best choice for the majority of bone graft needs
What is allograft bone
○ From the bone bank ○ Cortical ○ Cancellous ○ Fresh ○ Prepared ○ Structural ○ Osteoconductive ○ Not osteoinductive ○ Creeping substitution - The osteoclasts work their way through eating the dead bone - The osteoblasts come in and replace the bone ○ Risk of Disease transmission
What is delayed union of bone?
failure to heal in the expected time
What might cause delayed union in bone healing?
○ high energy injury ○ distraction (increased osteogenic jumping!) ○ instability ○ infection ○ steroids ○ immune suppressants ○ Diabetics ○ Smoking (fracture will take 50% longer time to heal if they smoke when they are healing) ○ warfarin ○ NSAID ○ Ciprofloxacin
What might cause non-union failure in bones?
○ failure calcification fibrocartilage ○ instability - excessive osteoclasts ○ abundant callus formation ○ pain + tenderness ○ persistent fracture line ○ sclerosis
