Description of cast
- 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
- Complete / incomplete
- Positioning (above and below joint) - to prevent displacement of tracture
- Special casts
- Cast braces
Complications of casts
- Tight casts
- Ridges in cast due to poor application
- Leads to vascular compression / compartment syndrome
- Loose casts
- Skin
- Pressure sores over bony prominences
- Abrasions / lacerations on removal
- FB
- Allergic reactions (rare)