Flashcards in Bone Growth and Repair Deck (32)
What is the anatomy of a long bone?
-Metaphysis (Flare at the end of shaft)
-Physis (growth plate)
-Epiphysis (On joint side of physis)
Briefly describe bone growth.
-Hyaline cartilage model
-Primary ossification centre
-Secondary ossification centre
-Formation of bone (compact bone, periosteum, spongy bone, articular cartilage and epiphyseal growth plate)
What are the features of cortical bone?
-Resists bending and torsion
-Laid down circumferentially
-Less biologically active
What are the features of cancellous bone?
-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 or buckle
Why do fractures occur?
-High energy transfer in normal bones
-Repetitive stress in normal bones can result in stress fractures
-Low energy transfer in abnormal bones (osteoporosis, osteomalacia, metastatic tumour, other bone disorders)
What is the biology behind fractures?
-Mechanical and structural failure of bone
-Disruption of blood supply
-Regenerative process (no scar within the substance of the bone)
What are the 4 stages of fracture healing?
What takes place during stage 1 of fracture healing?
-Begins immediately after fracture
-Formation of haematoma and fibrin clot
-Aggregation of platelets, PMNs, neutrophils, monocytes and macrophages
-By product of cell death= lysosomal enzymes
-Action of fibroblasts
-Mesenchymal and osteoprogenitor cells
What role do mesenchymal and osteoprogenitor cells play in fracture healing?
-Transformed endothelial cells from medullary canal and/or periosteum
-Osteogenic induction of cells from muscle and soft tissues
How does angiogenesis occur?
-Oxygen gradient required (low)
-Macrophages – produce angiogenic factors under hypoxic conditions
How stage 1 of fracture healing be affected?
-Very of for pain relief by act against inflammation increasing recovery time
Loss of haematoma
-Can occur in open fractures and surgery
-Slows down recovery process as haematoma kick starts the process
Extensive tissue damage
-Poor blood supply
What can be injected if haematoma is loss/want to speed up healing?
Platelet concetrates= Buffy coat
-Platelet-derived growth factor (PDGF)
-Transforming growth factor-beta (TGF-B)
-Insulin like growth factor (IGF)
-Vascular endothelial growth factor (VEGF)
When does stage 2 begin?
When the pain and swelling subside
How long does stage 2 last?
Until the bony fragments are united by cartilage or fibrous tissue
Describe the state of the fracture during stage 2.
-Angulation can still occur
-Continued increase in vascularity
How can stage 2 of fracture healing be affected?
-Demineralised bone matrix
Jump straight to bone
Why is autogenous cancellous bone graft gold standard?
-Best choice for the majority of bone graft needs
What types of allograft bone is there?
What are the features of allograft bone?
-Risk of Disease transmission
What occurs during stage 3?
-Conversion of cartilage to woven bone
-Typical long bone fracture (endochondrial and membranous bone formation)
Describe the state of the fracture in stage 3.
-Secondary bone healing
What takes place during stage 4?
-Conversion of woven bone to lamellar bone
-Medullary canal is reconstituted
-Bone responds to loading characteristics Wolff’s Law
What is critical for the progression of fracture healing?
Mechanical properties of tissue and their environment
How is degree of instability expressed?
Magnitude of strain (% change of initial dimension)
What happens if strain is too low?
Mechanical induction of tissue differentiation fails
What happens if strain is too high?
Healing process does not progress to bone formation
Failure to heal in expected time
What are the causes of delayed union?
-High energy injury
-Distraction (increased osteogenic jumping)