What is the role of osteocytes?
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
What are the factors that can complicate fracture repair?
- Malnutrition
- Bacterial osteomyelitis
- Interposition of large fragments of necrotic bone or soft tissue
- Age
- Pseudoarthrosis
What are the types if fracture?
- Traumatic - excessive force
- Pathological - abnormal bone broken by minimal trauma or normal weight bearing e.g. osteomyelitis, neoplasia, metabolic bone disease
Draw pictures to illustrate how fractures at the growth plate can occur
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*
How are fractures classified?
- 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
Define ‘stable fracture’
Fracture ends are immobilised by natural processes, not surgically fixed, to give relative stability. Due to formation of a callus.
What are the stages in stable fracture repair?
- Necrosis of bone and marrow can occur at the broken ends
- Growth factors are released by macrophages and platelets in the clot and from dead bone (important for stimulating tissue repair)
- After 24-48hrs undifferentiated mesenchymal cells proliferate and neovascularisation occurs. A loose collagenous tissue forms
- 36hrs - new woven bone forms a callus
- Over months to years woven bone is replaced by strong, mature, lamellar bone (secondary callus)
- Callus size can be reduced over a period of years by osteoclastic activity to restore the bone to its normal shape
What is a callus?
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
Define rigid fracture repair
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
What are the complications of rigid fracture repair?
- Inadequate blood supply - cartilage formation, necrosis if there is anoxia
- Instability - excessive movement and tension favours callus formation
Define osteitis, periostitis, osteomyelitis, sequestrum
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
What are the portals of entry into bone?
- Direct entry - through periosteum and cortex, via trauma, direct extension
- Haematogenous - blood gains access to the marrow cavity of diaphysis and metaphysis via a nutrient foramen
3.
Describe embolic osteomyelitis
- Embolus lodges in capillary loop at the metaphysis
- Inflammation causes lysis of metaphyseal bone and growth plate cartilage
- Causes mechanical instability - periosteum responds by producing woven bone
- Exudate can lyse the cortex at its thinnest point - metaphyseal cut back zone
- Exudate can extend into the periosteum and cause periostitis
- Exudates can also extend into joints and onto the surface of the skin
