Bricolage IS WRITTEN by Jeff Cable and is based in the United Kingdom.

This blog aspires to provide COHERENT and relevant Material for all cast TECHNICIANS. 

Removable Casts

With the advent of lightweight casting tapes I have been asked to make the occasional removable cast to address specific issues. This type of cast is not an option if one only has access to plaster of Paris (POP).

Some orthopaedic clinicians will request that a cast be constructed in a manner which renders it removable. I suggest that a removable cast is not a desirable treatment modality and its adoption is difficult to pin down. 

When using a removable cast or splint for a comminuted and intra-articular fracture, there is insufficient support for the damaged bone fragments. It would be unethical to subject any patients to a study which determined the absolute value of a removable cast or off-the-shelf splint in such cases. There is a use case to be made for some soft tissue injuries to be fitted with a removable splint for support; even in the very early stages of healing.

The radiographic images of a distal radius and ulna which follow, demonstrate a traumatic injury which may be classified as a 23-C3 injury; using the AO system of long bone fracture classification. The multiple fractures extending into the chondral surface are intra-articular fractures. There is no connection remaining between the articular surface and the diaphysis. The transverse metaphyseal fracture extends for the whole width of the radius. The intra-articular fracture component is described as multi-fragmentary. 

PA distal radius and ulna radiograph

PA distal radius and ulna radiograph

Lateral distal radius and ulna radiograph

Lateral distal radius and ulna radiograph

The following link demonstrates the AO classification and describes the treatment of this injury:

It is clear (from the AO pages) that a relatively undisplaced and stable fracture of this classification would be amenable to conservative treatment with a cast. Anatomic reduction through the means of surgical intervention is their recommended course of action.

The PA radiograph of the example case shows several articular fragments. The position of the bony fragments may be described as being approximately anatomical and quite close to the expected relationship between the relevant bony anatomical features, suggesting stability.

The amount of articular step-off is considered excessive if it reaches 2mm. The step in the articular surface displayed above is probably no more than 1mm. The significance of the comminution present is this; the more comminution there is at any particular fracture site, the more likely is the possibility that the fracture will be unstable.

Instability is also denoted by the presence of fragment displacement. The term instability is considered to mean that there is an increased likelihood of secondary fragment displacement. This secondary displacement occurs after a first adequate fracture reduction has been applied.

I did not appreciate the clinical rationale behind the request for a removable cast. It was the patient's first clinic review. A removable cast was not applied. The patient was flying to their vacation the following week and would be away for some time. A formal below elbow cast was constructed and applied with a single split in the cast down to the skin.

The cast material used was 3M Poly Premium and it was applied lightly enough (to a depth of two layers) so that it could be pulled apart if necessary. The patient having a vacation was unlikely to be the sole clinical reason for applying a removable cast... especially with a specific instruction to the patient not to remove it. This clearly negated the need to make the cast removable.

At this point in the treatment, a full cast would have been the usual prescription for this fracture type. This is notwithstanding the fact that the patient had no other complicating factors or morbidities and so they would have been capable of wearing any type of cast.

The resources required to create a removable cast are often more than those required to create a standard below elbow cast. The creation time difference is roughly 30 minutes for a removable cast and two minutes to construct a below elbow cast.

Another factor for consideration is where an orthopaedic outpatient clinic environment is operating with minimal staff so that patient throughput is affected by delays created by specific work practices. 

The cost of creating a removable cast is several times more than the cost of creating a standard below elbow cast. More adhesive felt, undercast padding, stockinette and the time expended, serve to make the removable cast a relatively expensive treatment proposition. 

Where a cast has been prescribed to be removable, then it is suggested that a simple off-the-shelf splint (such as a futuro pattern splint) is used instead. The splint takes seconds to fit and is not expensive in technician or clinic time. Splints are frequently modified by technicians to fit the patient's anatomy accurately.

Casting materials are not usually a good choice for making into removable splints because of their inherently rough surface and poor flexibility characteristics after the material has set. One notable exception would be a material known as Woodcast casting/splinting material, which has its own system for application and use as a removable splint. There is a whole range of water-bath activated thermoplastic materials that are, generally speaking, easier to use and they tend to be very smooth.

Why do we place fractures in a cast, where they are amenable to non-operative methods of treatment? To answer this question we should return to the fundamentals of bone healing. Remember that fracture healing comprises three distinct phases. One is the inflammation phase, two is the reparative phase and three is the remodelling phase.

The inflammation phase begins immediately after the injury and bone repair rapidly follows this phase. Once the damaged cells and matrix are replaced, a long remodelling phase commences may last for years. Injuries which damage bone also do damage to the soft tissues including the periosteum and blood vessels. Ruptured blood vessels result in a haematoma and this fills the gap in the bone and the surrounding tissues. 

Blood which has clotted provides the mesh framework of fibrin to seal fracture site bleeding and permits the deposition of inflammatory cells and fibroblasts along with new capillary ingrowth. The inflammatory cells release various cytokines which stimulate angiogenesis. Recall that osteoblasts synthesise new bone and osteoclasts absorb bone tissue. 

The definition with which cast technicians are familiar is that a fracture is a break in the continuity of the bone. The AO view is that a fracture is a soft tissue injury which contains a broken bone. This view assists cast technicians to understand that it is the importance of the soft tissue damage which guides clinicians in the treatment of the fracture. 

Cast technicians will be familiar with the urgent surgical fixation which may be cancelled because the soft tissue oedema of the involved limb would prevent adequate skin closure. Where the fracture fragments are displaced and there is extensive soft tissue damage, it is known that fracture healing is retarded. 

It is thought that the extensive tissue damage increases the amount of necrotic tissue; which is an impediment to the migration of mesenchymal cells and vascular invasion of the fracture site. The necrotic tissue is thought to reduce the number of available mesenchymal cells and disrupt the blood supply to the fracture site.

Intra-articular fractures affect joint motion and loading and these factors may cause the fracture fragments to move. Fractured bone alignment restoration and chondral surface congruity along with a full return to function are the aims of treatment. Where the joint articular surface is not restored, the joint may go on to become painful and unstable.

Without rigid fracture stabilisation, the healing may be delayed or go on to progress to non-union. Accurate apposition of the fractured bone fragments decreases the fracture gap. This in turn reduces the volume of repair tissue which is required to heal the fracture. Therefore the position of fracture fragment placement is especially important.

The need to immobilise the fracture site well stems from the requirement to stabilise the fracture. This stabilisation can help to facilitate the fracture site healing by preventing the repeated disruption (by unwanted movement) of the repair tissues. 

Fracture stability is considered to be essential to healing especially where there is a marginal blood supply to the fracture site, or an extensive soft tissue injury. This is also the case where the fracture occurs within a synovial joint. The wrist joint illustrated above is a condyloid synovial joint.

The request for a removable cast does not fit with what is known to be the usual clinical practice for the type of injury depicted. The injury was a few days old and there were the remaining days of the inflammatory response to be considered.

A closely fitting removable cast would inevitably become ill-fitting after another few days with resolution of oedematous soft tissues. With the patient on holiday in a foreign country for some time, it was unlikely that the treatment could have been continued optimally, because of ill-fitting support or where any problem had made itself known.

An ill-fitting cast would imperil the fracture by permitting movement at the fracture site of the multi-fragmentary injury. It would not provide the necessary stabilisation of the fracture site as the removable cast became less well-fitted with each passing day; once the tissue oedema had started to resolve and muscle atrophy had become obvious.

The AO guidance is in favour of operative reduction and fixation. While the option to treat this injury non-operatively is available, it is not considered where the fracture stabilisation is likely to be uncertain.

Provide this type of injury with a cast or a splint but I would try to avoid making a cast into a removable splint. It is most time-consuming and the end result is ill-fitting and no better than an off-the-shelf splint that has been properly fitted. Patients often cannot fit a removable cast to themselves in the same manner in which a cast technician would.

A cast performs a specific job at a specific time during fracture healing. This job is normally unable to be performed by a general purpose splint. e.g. A futuro type wrist splint will not normally prevent the radius from crossing the ulna where the forearm is rotated. A full cast can be constructed which will stop any movement at the wrist joint and prevent the radius from rotating about the ulna. 

It is an integral part of every cast technician's role; to advocate for the patient when they do not know enough to advocate for themselves.

Plaster Room Noise

Woodcast Splinting Material