Casts and Casting

Kenneth J. Noonan, MD, MHCDS

Matthew A. Halanski, MD¹

Benjamin J. Shore, MD¹

¹Gurus:

General Considerations

A lot has changed in orthopaedics over the past 50 years. Our specialty has morphed from one where traction and cast immobilization played a large role in managing patients of all ages for trauma, congenital conditions, and the aftermath of polio. We have witnessed advances in internal fixation, intraoperative imaging, and surgical techniques. For example, adult femur fractures are now treated with intramedullary fixation and are no longer treated with weeks of traction followed by walking spica casts. Simply put, we are no longer managing many adult fractures with closed methods. Even in children, advances in fixation have decreased our dependency on external methods of stabilization. Furthermore, changes in health care delivery have left casting to technicians and nurses (and who can do a great job), but this leaves even fewer opportunities for residents to learn the art of casting. There will always be a role for cast and splint immobilization, and in pediatric orthopaedics the need for these measures is not likely to change. While over 90% of adult forearm fractures are treated with surgery, 90% of pediatric forearm fractures are treated with reduction and cast immobilization. This is due in part to the remodeling potential of pediatric bones, where acceptable alignment rather than exact anatomic reduction is sufficient for many fractures. Similarly, joint stiffness is not typically a long-term problem for children treated with a cast.

Although casting is often viewed as “conservative” treatment, the physician and family should recognize that this does not imply that this treatment is without potential complications and pitfalls. The lay population have seen casts on other people’s kids their whole lives and are biased to think that nothing wrong could happen to their kid. Although the true incidence of cast complications is unknown, a litigation history of a large multispecialty multilocation pediatric group showed that casts were the number one cause of litigation. When using a cast, it’s important that a frank discussion of the risks and pitfalls of casting be explained to patients and families. I explain that cast sores occur in 1 per 100 patients and that together we have to be vigilant in preventing them. At the very least, this is important for protecting oneself from litigious and angry parents who can’t understand why their child got a sore from a cast. Yet more importantly, we need to educate them that pain in high-risk areas such as the heel, dorsum of the foot and ankle, popliteal fossa, patella, and olecranon may be an impending sore. Stay out of trouble and tell them where the incision is on the child’s extremity, if they have pain anywhere else they need to come in. ORTHOPAEDICS 101: There are no hypochondriacs in casts. If a child in a cast develops pain under the cast that persists longer than 12 hours, the cast needs to be removed or windowed and the skin inspected. This should be explained clearly to all parents and caregivers.

Certain pediatric patients may be at a higher risk for cast complications. Discerning problems in the very young or developmentally delayed may be quite difficult, and cast sores can occur despite appropriate and careful application. Many of these patients have comorbidities such as spasticity, malnutrition, altered sensation, and poor communication which increase difficulty of developing, detecting, and articulating cast problems.

Problems with casts can arise when they are used to obtain reductions; some of these can be minor and some can be limb threatening (Fig. 4-1). Fundamentally, when it comes to fracture care, its critical to remember that “reduction,” whether it be open or closed, is not the same as stabilization, which is what casts and
splints do. If you need a cast to obtain a reduction, you need a different plan or an implant. Similarly, if you chose an implant that requires a cast to maintain a reduction, one should consider a more stable implant. A good example is the 10-year-old with a femur fracture that undergoes flexible nailing and the surgeon is concerned about stability and uses a long leg cast that ends at the fracture site. (The long lever arm of the cast actually makes it more unstable.) In this situation, a spica cast would be a better external immobilization method, yet a plate or a locked nail is likely the best choice for this fracture. Nobody likes spica casting.

Figure 4-1 A: In the past, femur fractures were treated by first applying a spica cast to all portions except the broken femur. When these portions were hard, the fracture was reduced by applying traction through the casted lower leg; the thigh portion was the last part to be incorporated. B: Although apparently a simple method, a series of patients (including the one pictured) developed compartment syndrome in the leg. Lesson: Using a cast to reduce a fracture is dangerous. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

Where does cast wedging for trauma come into play? Casts can be wedged with good results if done within certain time limits depending on the location of the fracture, the bone that is angulated, and the age of the patient. It is reasonable to consider cast wedging within 10 days for distal radius fractures; 14 days for both bone forearm fractures (Figs. 4-2 and 4-3); and 3 weeks for femur and tibia fractures. The reason cast wedging is acceptable is because we are not trying to obtain a reduction we are trying to restore a reduction that was lost in the cast. Where you can hurt a child is when you try to wedge an unreduced fracture acutely or try to wedge a fracture that will not move because it has “flexible” rod in it, or when the fracture is beyond the time windows outlined above (Fig. 4-4). Many of these fractures are very sticky and hard to move; in addition, radiographs of the fracture through cast material often hide signs of healing.

When wedging, the clinician needs to ensure that no excessive focal pressure is exerted at the bridge causing a pressure ulcer or nerve compression. A disadvantage of a “closing wedge” is that it may pinch soft tissue.

Figure 4-2 A: This 5-year-old boy was 10 days out from a both bone forearm fracture that had sagged into an unacceptable ulnar bow as the swelling decreased. B: Cast wedging restored the alignment. Be aware of the contralateral side of the cast; there is subtle buckling of the plaster, which can cause a pressure ulcer on the opposite side of the wedge. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics).

Figure 4-3 A: A 10-year-old girl with a tibia and fibula fracture treated with a long leg cast. Initial visit demonstrated valgus angulation. B: Angulation was corrected with an opening wedge cork spacer of about 1.5 cm.

Figure 4-4 You cannot wedge a greenstick fracture. If you feel that the angulation needs to be corrected this needs to be done with a closed reduction and not wedging of the cast. A: This child with a greenstick forearm fracture had acceptable alignment; yet the provider was bullied into improving it by anxious parents. B: The child had his cast wedged without improvement of alignment. Note the fulcrum on the skin on the volar surface. This child developed a Volkmann ischemic contracture as a result of the compartment syndrome that ensued from this.

What about using casts to stretch joints and correct deformity that is not trauma related? The answer is “maybe,” but be careful! In casting clubfeet, you get into trouble when you apply a cast in a position of correction beyond that which you obtain with manipulation. It is not uncommon to lengthen the hamstrings of a child with cerebral palsy who also has a knee flexion contracture. One can apply a long leg cast than do serial wedging to stretch the knee. Even if extra padding is placed on the heel and the knee, sores can happen—be careful (Fig. 4-5).

Pitfalls in Cast Application

It is important to have ready and in easy access the needed padding (cast lining and stockinette), water (lukewarm, not hot), cast material (plaster and fiberglass in rolls and reinforcing slabs), and needed instruments (C-arm imaging and X-rays clearly visible in line of sight, scissors, cast saws, spreaders etc.). This is key as cast application is a timely undertaking with materials that cure and harden in a short period, and the application may depend on a short window of time available for comfort or sedation of the child. It is further recognized that all needed personnel need to be ready, and this will ideally include a sedation team and child life specialists, in addition to the one to three people needed to apply a cast.

MATERIAL SELECTION

The two main choices for cast application are plaster of Paris and synthetic cast material like fiberglass. Plaster of Paris is cheaper and allows one to intimately
mold the material to the extremity being treated. It is also twice as heavy and not nearly as strong as fiberglass. There are different rates at which plaster can cure; the faster curing plasters tend to be much more exothermic and can lead to potential cast burns. Dip water temperatures of 50°C and thicknesses of 24 ply can yield temperatures high enough to cause burns. Placing a curing plaster cast on pillows can also lead to high temperatures in the area of pillow contact; these temperatures can be high enough to cause thermal damage. Overwrapping a curing plaster cast with fiberglass can also insulate and direct the heat back into the limb (Fig. 4-6). Fiberglass tape is commonly used and has several benefits in comparison to plaster such as being light weight, radiolucent, waterproof, and having lower peak temperatures of curing. The peak temperature of curing rarely exceeds 45°C, and thus, the risk of thermal injury from synthetic fiberglass tape is substantially less than plaster.

Figure 4-5 Heel ulcer that occurred during stretching cast for knee flexion contracture in a patient with spastic diplegia. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

THE GURU SAYS…

Focus on the edges of a cast when fiberglass is used. The edges can be sharp, leading to abrasions of the thumb or dorsum of the foot or toes in children. Let the parents know they can use a fingernail file to smooth any rough edges not found at the time of application to prevent an injury. It is important to place stockinette, padding, and the casting tape to the desired site of application and then fold the stockinette over the most distal edge of the casting tape to give a well-padded edge. Often stockinette and padding will be folded back and then the casting tape applied, leading to a very sharp, unpa dded edge with cast wear.

MATTHEW HALANSKI

Dr. Skaggs Adds

I may be in the minority, but I find fiberglass holds a mold better than plaster. As fiberglass casts are also stronger, lighter, longer lasting, and better tolerated by patients, I have not used plaster in well over a decade. Jon Davids and Steve Frick taught us that when a fiberglass cast is properly applied, with the stretch-relax technique, it generates less skin pressure than a plaster cast and better accommodates swelling without the need to sacrifice structural integrity. I suspect synthetic liners, padding, and casting material will continue to improve, and less cotton and plaster will be used in the future.

PROBLEMS WITH PADDING

Stockinette or liner may be applied against the skin, under the cast and cast padding. Although not essential, these liners minimize skin irritation; allow nice well-padded and polished edges to the cast to be applied. They also minimize the tendency of some children to “pick out” their cast padding. These liners are made of cotton, water-friendly synthetic materials such as polyester, sliver-impregnated cotton (to minimize bacterial growth), or Gore-Tex (W.L. Gore & Associates; Newark, Delaware). Some in the care of children who require spica cast application favor water-permeable liners such as Gore-Tex. In addition to being more convenient for patients, these newer synthetic materials have been shown to minimize skin irritation.

Ideally, the limb should be held in the desired position of immobilization prior to padding application. A common pitfall is when casting material is applied for a
short leg cast with the ankle in less than 90° of ankle flexion; if the ankle is then flexed to 90° during the application or curing of the cast, the material will bunch up and will impinge on the dorsum of the ankle. Stay out of trouble by not using circumferential gauze under perioperative casts, which can become tourniquets as they shrink from dried blood combined with the limb swelling. It’s better to cover wounds with noncircumferential sterile 4 × 4s and then wrap with cotton rolls, which can stretch or tear with swelling.

Figure 4-6 Recipe for disaster: Short leg plaster cast is covered with fiberglass and placed on a pillow while curing. Research has shown that this combination can yield temperatures high enough to burn the patient. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

Pressure sores are not necessarily prevented by extra cotton padding; in fact, extra padding can lead to loss of reduction as swelling goes down, which can lead to shear forces and subsequent sores. Cast padding should be applied between three and five layers thick over the limb being casted. Bony prominences and cast edges should be additionally padded to prevent irritation yet allow a cast to be molded to fit snugly without undue pressure. The heel, malleoli, patella, anterior superior iliac spine (ASIS), and olecranon are areas that may require additional padding. The use of foam or felt padding in such areas may help decrease the incidence of pressure sores.

Figure 4-7 Classic example of excessive plaster in the concavity (blue arrow) and minimal plaster along convexity (red arrow). (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

PITFALLS IN CAST APPLICATION AND MOLDING

Plaster is dipped in water appropriate in temperature, some water is squeezed out, and then the plaster is progressively applied to the limb with circumferential wraps that overlap by 50%. Avoid wrapping too tight by taking tucks as you wrap around the convexities of a limb. ORTHOPAEDICS 101: When wrapping any type of cast material (cotton roll, fiberglass, or plaster), there is a natural tendency to have excessive material in the concavities of a joint (Fig. 4-7). We have seen burns from curing plaster in front of the ankle when the plaster becomes inadvertently too thick (Fig. 4-8). Stay out of trouble by keeping plaster uniform by using splints in back of the ankle and elbow and then incorporating with circumferential plaster (Fig. 4-9). Although similar problems wrapping fiberglass around convexities can occur, the relative strength of the material does not seem to lead to the same problems as plaster. One problem unique to fiberglass casting is inadvertent tightness that sometimes occurs as a result of the increased tackiness of
the material as the roll is unwound. This can increase in older fiberglass that is more challenging to unroll. To avoid this, fiberglass should be applied in a stretch relaxation manner; the fiberglass roll is lifted off of the limb (in contradistinction to plaster which stays in contact); unrolled first then wrapped around the limb (Fig. 4-10). Difficulty exists when wrapping a wide roll into a concavity (anterior elbow or ankle), as the fiberglass can only lay flat if pulled too tight. Small relaxing cuts in the fiberglass may be needed, as fiberglass does not tuck as easily as plaster of Paris. Remember that fiberglass begins to cure as it exposed to air; don’t open the package until you need it.

Figure 4-8 A: Research has shown that temperatures can get high enough to burn the skin in the concavity of a joint undergoing plaster application. B: Full-thickness burn over the anterior ankle from a plaster cast. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

Figure 4-9 After the cotton has been applied to this short leg cast, a posterior plaster slab splint is applied then incorporated with circumferential plaster wraps. With this methodology, concave overwrapping is decreased. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

Plaster goes through stages of curing until it reaches full hardness 24 hours later. It’s convenient to frame discussions about the stages of plaster molding as the initial stage, terminal stage, and final hardness. Initially as the plaster is being applied, it’s critical to mold the plaster wraps together to incorporate the gypsum and the cotton fabric together to increase the strength of the cast. Merely wrapping plaster without incorporating it is a recipe for failure. Your hands and fingers should constantly be rubbing and incorporating the material in this initial phase, and you don’t have to worry too much about pressure points, as the cast material is too soft to remain permanently deformed. We teach the residents that if you see fibers after wrapping the plaster you aren’t molding enough! As the plaster begins to cure, however, you will notice that the material will become warm and firm and does not spring back. This is the terminal stage, when your final mold is produced, and this also the time where fingertips and pointy objects can leave permanent plaster indentations, which can lead pressure sores (Fig. 4-11). The same stages of initial and terminal molding also apply to fiberglass, yet less initial molding is required to incorporate the fiberglass, as it tends to cure faster. Both fiberglass and plaster can get divots during the terminal molding stages, and the cast should be held with open palms and not
fingertips. When you are done applying a plaster leg cast (and its cool), rest it on a pillow with the heel hanging free (Fig. 4-12). Even though plaster appears hard, it can deform gradually over the next several hours until it fully hardens. It’s a good idea to tell patients to abstain from weight bearing on a plaster cast for 24 hours.

Figure 4-10 Stretch relax fiberglass application can decrease tightness. Unwinding the fiberglass and then wrapping the fiberglass will overcome the adhesive nature of the fiberglass roll as it is applied. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

Figure 4-11 In the terminal molding stage, the surgeon’s belly is a good place to support the foot in neutral while final molding is performed with the flat of the hand to avoid pressure spots. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)

Figure 4-12 After the plaster cast has cured, it is placed on a pillow with the heel hanging free to prevent gradual deformation of the heel. (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)