70.3 Splitting and spreading a cast

Always pad the prominent bony parts of a patient’s limb, shown in Fig. 70-2, or the cast will cause pressure sores. You can choose whether or not you will put a layer of cotton wool or orthopaedic felt over the rest of his injured limb. Padding a cast completely: (1) makes it less likely to obstruct his circulation, (2) compensates to some extent for shrinkage of his limb because the padding expands a little as his limb shrinks, (3) makes the cast less likely to cause pressure sores, (4) makes it easier to remove, and (5) makes it easier to wedge. The only disadvantage of a padded cast is that it does not hold the bony fragments quite as still as an unpadded one. Be safe and pad all casts. The only exception is a cast for the scaphoid (Fig. 74-10).

If you have decided to apply a circular cast, the next question is whether or not you should split it, so that it can open as the tissues under it swell. If you put a circular cast on a freshly reduced fracture without splitting it immediately, the cast may restrict the swelling of the tissues, increase the pressure in the limb, obstruct its circulation, and cause either ischaemic gangren e needing amputation, or the compartment syndrome followed by Volkmann’s ischaemic contracture (70.4). This can happen even if ischaemia lasts less than an hour, and is a particular danger with fractures of the forearm and lower leg. It is not a danger in casts for the scaphoid or Bennett’s fracture, so there is no need to split these casts. An unsplit circular cast is especially dangerous if a patient already has signs of circulatory impairment (70.4). A hundred unsplit long leg casts may give no trouble, but the hundred–and–first may obstruct a patient’s venous return, cause gangrene, and require that his leg be amputated. When you make rounds the following morning, it may be too late! Gangrene or Volkmann’s contracture may have started at midnight!

Splitting a cast with a scalpel will not destroy its capacity to hold the bony fragments, and is easy if you do it while a cast is still soft. Spreading a split cast with a blunt object such as a screwdriver, so that its edges open, is a separate procedure. It is only necessary on the rare occasions when the circulation to a limb is impaired.