Positioning in undisplaced fractures
In undisplaced fractures, reduction is not necessary. The plaster cast will be applied on the hanging leg (knee flexed to 90 degrees and ankle held at 90 degrees).
Application of the padding
First, apply the padding. This needs to be thicker over the malleoli and around the fibular head.
The cast should reach from the MTP joints of the toes to just below the knee joint, avoiding the upper end of the plaster’s being at the level of the neck of the fibula, where the common peroneal nerve crosses.
Handling of plaster bandages
It is important to hold the plaster rolls correctly during application, so that they can be rolled on, rather than pulled on.
Application of plaster bandages
It is easier to start proximally, overlapping by half the width of the roll and moving down the lower leg to around the ankle and foot.
After the application of the second roll, whilst the plaster is still soft, final manipulation is done and the reduction held, with appropriate molding, until the plaster hardens. This may take 4 to 5 minutes, depending on the temperature of the water – colder water gives you more time.
The final two rolls are then applied, and further molding is performed to achieve the desired 3-point fixation.
Molding of the cast: 3-point cast fixation
When molding the cast, the same action as for reduction is repeated and held until the plaster is firm.
The principle of 3-point fixation within the cast needs to be applied. The two main molding points are created by gentle pressure below the buttressing malleolus and above over the opposite supramalleolar part of the lower leg.
The third point is created by molding the upper end of the cast firmly around the leg, on the aspect of the leg opposite to the supramalleolar molding.
In suprasyndesmotic fractures, with disruption of the syndesmosis, firm molding around and even over the lateral malleolus helps to close the diastasis and allows the syndesmosis to heal.
These fractures will require extension to an above-knee cast as discussed shortly.