Page 198 - ASOP ROT Study Guide

5. CHANGING PLASTERS

Once swelling has settled, a cast may have lost its effectiveness either because it no longer makes a
good overall contact or because it has lost its three point contact (see section - Trauma): It is
essential that a cast is changed as soon as these possibilities are recognized.
Signs that a cast is loose include:

♦ Complaints of discomfort because of movement of the cast
♦ The ability to move the cast vertically relative to the limb
♦ The ability to rotate a cast slightly on the skin

The risks of cast change are:

♦ Pain for the patient during removal
♦ Loss of position of the fracture

A balance has to be struck between these risks. Plasters should be changed without anesthetic
provided the patient will co-operate (children may not). This has the advantage that muscle tone
will tend to maintain fracture position. Often a simple painkiller such as oral codeine or injected
morphine half an hour before the procedure will reduce discomfort to acceptable levels. Doctors
can also block sensation by injecting local anesthetic around nerves.

After changing the cast it is essential that an X-ray is taken immediately afterwards to ensure the
position of the fracture has not been lost.

6. BREAKAGES AND REPAIRS

Casts tend to break at predictable points, relating to how they are used and loaded. They break due
to bending and impact forces.

Bending is a particular problem in the lower limb. As we walk we inevitably tend to alternately bend
the cast backwards and forwards. Points where bending causes maximum compression are at the
front around the joints - particularly the knee and ankle. Plaster particularly is susceptible to being
crushed here and, once the material has been disrupted, it needs to be repaired.

Impact forces predictably occur at the heel and to a lesser extent at the elbow.

A cast should be repaired with the same material as it was made where possible as this will bind
more efficiently to give a good repair.

In your plaster room, when the next three patients with below knee plaster of Paris splints return
for an appointment, inspect their casts to see where they are soft or worn. Do the same for the
next three patients with arm casts.

7. WEDGING TECHNIQUE

Wedging of a cast may be carried out to correct the alignment - particularly an angulation but
occasionally a rotation. Wedging does not correct shift and occasionally makes shift worse.
Wedging should always be done under medical supervision.

It is always better to perform an opening wedge - adding material - and not a closing wedge which
removes material. The former tends to increase cast volume which is unlikely to cause pressure
problems.