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Description of cast

1. Material

   	Plaster of paris	Newer material
   Structure	Open weave cloth or muslin strip impregnated with dehydrated calcium sulphate Exothermic reaction - calcium sulphate becomes hydrated and rapidly sets Cloth made stiffer using dextrose or starch Hardening rates can be altered using accelerators or inhibitors	Knitted material of cloth or glass fibre impregnated with monomer or polymer or polyurethane with substituted isocyanate terminal groups On addition of water compound polymerises and releases CO2 Highly reactive material packaged in resistant containers
   Advantages		Lighter Stronger More radiolucent Waterproof Resistant to wear and tear
   Disadvantages		Expensive Skin irritation Less deformation after setting, increased risk of neurovascularcompromise of limb if it swells More difficult to apply  Difficult to remove without a proper plaster saw

2. Complete / incomplete
3. Positioning (above and below joint) - to prevent displacement of tracture
4. Special casts
5. Cast braces

Complications of casts

1. Tight casts
   • Ridges in cast due to poor application
   • Leads to vascular compression / compartment syndrome
2. Loose casts
3. Skin
   • Pressure sores over bony prominences
   • Abrasions / lacerations on removal
   • FB
   • Allergic reactions (rare)