Casting over Kirschner (K) wires requires some consideration of the technical demands of the treatment. The cast is used to support the injured limb while the clinician placed K wire(s) are used to keep the fracture fragments aligned and in close proximity during the time they are healing and forming new bone.
Perhaps one could be forgiven for thinking that the cast did not have to fit the injured limb closely because the fracture site was being supported by the metalwork support of the K wires. It should not be necessary to tell cast technicians that an ill-fitting cast will cause pressure injuries at the very least and they may permit fracture fragment movement at the worst.
Once the fracture site has become infected, the patient will usually complain of constant pain at and they will often present with frank exudate at the pin sites. Rubor, calor and ascending lymphangitis will serve to underline the presence of a significant infection. This often arises where the K wires have become mobile.
Skin microflora include Staphylococcus aureus and Pseudomonas aeruginosa and these skin commensals may become pathogenic. The K wires may also migrate under the skin, thereby making the wire removal a far more difficult proposition.
The radiograph above shows an AP view of the distal half of the radius and ulna, the carpals and the proximal third of the metacarpals. Additionally, there is a K wire placed axially through the epiphysis and the distal metaphysis to fix the transverse metaphyseal fracture of the radius. The developmental stage of the bones depicted suggests that this patient is aged between 11 and 14 years.
The cast edges are shown and at the level of the start of the epiphyses, the cast is seen to widen. There is almost one centimetre of space between the cast and soft tissues at the distal end. This was likely to have been caused by wrapping extensive layers of padding around the wire, in the mistaken belief that the padding of the wire was more important than creating an accurately fitted cast.
The lateral radiograph demonstrates a dorsally displaced fragment of metaphyseal radius. The K wire was placed dorsally and it penetrates an angle of 25 degrees until it reaches the volar cortex of the radius. At the point of skin entry of the K wire, the cast edge is distant from the soft tissues by around 2 centimetres. At the level of the distal wrist crease, the volar cast edge is around 1 centimetre distant from the soft tissue.
Too much undercast padding and dressing material is the reason that this cast did not fit the patient. The requirement to apply a lightweight cast over a freshly inserted K wire is often seen. Wires may be properly finished with soft metal caps or plastic end protectors and the distal end may also be turned through 90 to 180 degrees at the time they are placed by the clinician.
Where the K wires are placed without any attempt at protecting the distal end, the wire may be sharp and occasionally it will be pressing rather too hard on the skin at the point of entry. This will cause soft tissue breakdown and infection so it is important to correct any external skin pressure.
Often, the case is that one may turn an inserted wire to change the orientation of a K wire distal end to prevent it pressing the skin. Occasionally, one my also carefully bend the wire using two pairs of pliers or Spencer Wells pattern haemostats so that it cannot press on the skin. Using a piece of self-adhesive felt (Delta Terry Net/Hapla) over the stockinette but under and around the K wire, will be sufficient to protect the skin. Placing another piece of felt over the visible K wire will secure it, prevent it moving and keep the cast padding to a minimum.
Remember, the first priority is to support the injured limb and the examples depicted here are not capable of supporting the injured limb. Too much padding is not a kindness and it may easily lead to infection of the K wire and pressure injuries. There may be too much movement at the fracture site and it is possible to see this type of fixation collapse and become ineffective.