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Fracture classification
- Traumatic - normal bone broken by excessive force
- Pathologic - abnormal bone broken by minimal or no trauma
- E.g. due to osteomyelitis, bone neoplasia
- Closed - overlying skin and soft tissue is intact
- Compound - overlying skin and soft tissue are perforated
- Comminuted - bone is shattered at fracture site
- Compresses - the ends of the fracture are impacted into each other
- Avulsed - due to pull of a ligament
- Transverse
- Spiral
Fracture repair
- Fracture
- Ruptured blood vessels -> haemorrhage and clot formation, some ischaemic necrosis
- Dead marrow liquefies and is phagocytosed
- Dead bone is removed by osteoclasts
- Continues long after bone has been united by callus
- Periosteum tears, fragments displaced
- Ruptured blood vessels -> haemorrhage and clot formation, some ischaemic necrosis
- -> Haematoma formation, necrosis of any isolated fragments
- -> Mesenchymal cells proliferate in haematoma - granulation tissue
- Invading cells: endothelial, fibroblasts, osteoprogenitor
- -> Loose collagenous tissue (primary callus)
- -> Mesenchymal cells differentiate to osteoblasts and chondroblasts
- -> Woven bone (secondary callus)
- External callus - from periosteum
- Periosteal growth eventually bridges the gap between the fracture ends
- Blood supply is outstripped
- Cartilage is produced instead of osteoid
- Blood vessels invade cartilage -> endochondral ossification
- Osteoid becomes ossified
- Internal callus - from endosteum
- Rarely forms cartilage
- May occlude the medullary cavity
- Osteoid remodelled by osteoclastic resorption
- External callus - from periosteum
- -> Mature lamellar bone
- Early reactive fracture repair may be mistaken for osteosarcoma on biopsy
Complications of fracture repair
- Malnutrition
- Lack of adequate blood supply (leads to hypoxia)
- Leads to excess cartilage in callus
- Healing can still occur since this can turn to bone
- Excess movement
- Leads to excess fibrous tissue in callus adn formation of false joint (below)
- Presence of necrotic bone (may form a sequestrum)
- Poor alignment
- Bacterial infection
Pseudoarthrosis
- False joint
- Non-osseus union
- From infection, poor imobilisation, avascularity, extensive tearing damage to periosteum
- Composed of fibrous tissue
- If mobility continues -> hyaline cartilage forms -> neoarthrosis (formation of new joint)
- In Osteodystrophia fibrosa, osteomalacia and rickets - callus forms but does not mineralise
Head and neck of femur fracture
- Vascularisation from joint capsule -> if complete separation -> bone and marrow undergo avascular necrosis
- Fibrovascular tissue and osteogenic cells invade -> deposit new bone
- Resorption of articular cartilage and subchondral bone -> osteoarthropathy commonly develops
Sore shins
- Dorsal metacarpal disease of racehorses
- In 2-3 year olds
- Excessive compressive stress on dorsal cortex of third metacarpal -> microfractures
- Hyperaemic overlying periosteum - -> new bone production to cover the lesion
Also see Repair in the Bones - Pathology