Casts and braces

A cast is a splint which sets hard around the limb. Plaster of Paris - POP - is the most widely used material.

Cast splintage is used primarily for distal limb fractures and in children. The cast keeps the fracture straight and immobile. It does not hold the fracture out to length and is unsuited to fractures associated with limb shortening. Articular fractures put in plaster may also become very stiff as adhesions form between muscle fibres, and between muscle and bone, and the lack of movement may impair healing of cartilage.

The timing of plastering is important. Stiffness can be kept to a minimum by using traction until some movement is possible in the joint. Alternatively, start with a conventional cast and later replace by a functional brace once healing has started. Casts applied immediately are liable to loosen as the swelling of the injury subsides and muscle wastage sets in.

For mid-shaft fractures of long bones, three point pressure is used to maintain alignment of the reduced fracture, pressure being exerted above, below and around the fracture. To control rotation, immobilise the joints above and below.

The main complications of plaster immobilisation arise from the cast being too tight - circulation is impaired and the limb is painful, numb, cold or discoloured; from pressure sores - pressure over bony prominences; and from removal - the skin may be abraded or lacerated.

Functional braces reduce joint stiffness. The plaster is applied as segments with the joint left free. The technique is well suited to fractures of the femur and tibia. However, since the cast is less rigid, the brace should be delayed until healing as started.