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Plaster Applications and Orthopaedic
What is plaster of paris?
Plaster of Paris is a hemi hydrated calcium phosphate. To make plaster of Paris, gypsum is heated to drive off water. When water is added to the resulting powder original mineral forms and is set hard. Plaster bandages and splints are made by impregnating crinoline with plaster of Paris [CaSO4)2H2O]. When this material is dipped into water, the powdery plaster of Paris is transformed into a solid crystalline form of gypsum. The amount of heat given off is determined by the amount of plaster applied and the temperature of the water.
Stages of plaster application
1.First Stage
- The first stage involves the application of POP slab or cast.
2. Second stage or cast –setting stage
- Change of pop to gypsum
- Defined as the time taken to form rigid dressing after contact with water.
3.Third stage or Green stage
- The just set wet cast.
4. Fourth Stage or cast Drying
- By evaporation of excess of water when the cast dries.
- This results in a mature cast with multiple air pockets through which the skin breathes.
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Types of plaster of paris
1.Indigenous
- Prepared from ordinary cotton bandage role smeared with POP powder.
2.Commercial
- Plaster of Paris rolls commercially prepared consists of rolls of muslin stiffened by starch POP powder and an accelerator substance like alum.
- This commercial preparation sets very fast and gives a neat finish unlike the indigenous ones.
After the Cast is Removed
Once the cast is removed you may notice that the body part which was casted looks different to the other side. It may appear smaller and paler and the hair growth may also be different. This is all quite normal and is due to muscle wasting and a lack of sunlight to the skin. The colour and hair growth will slowly return to normal.
Muscle wasting occurs because the body part has been immobilised and so the muscles have not been working. A rehabilitation programme should be prescribed for you to help regain muscle strength and size.