Saws cut material by exerting a sheer force at the corners of their teeth causing failure of the material being cut. The modern cast saw was invented by Robert Stryker in 1945 (www.google.com/patents/US2427580). The design of this device was unique as it utilized high-frequency small-amplitude blade oscillation to cut materials. The small motion arc through which the blade oscillates allows soft tissues to move back and forth with the blade, dissipating the sheer forces, and thus preventing injury (Fig. 1). However, once the blade encounters a stationary material that is unable to move with the blade’s oscillations, sheer forces are generated and the fixed material is cut. This explains, in theory at least, how these devices are capable of preferentially removing (fixed) casting material without injuring the skin underneath (Supplement Digital Content Video 1, The author demonstrating how the cast saw can cut through an immobile object such as a sawbones model. Copyright 2015. Reprinted with permission from Matthew A. Halanski, MD, Supplement Digital Content 1, http://links.lww.com/BPO/A57 and Supplement Digital Content Video 2, The author demonstrating how relaxed soft tissue can oscillate with the saw blade preventing injury. Copyright 2015. Reprinted with permission from Matthew A. Halanski, MD, Supplement Digital Content 2, http://links.lww.com/BPO/A58).
Seventy years after being patented, these oscillating cast saws are still commonly used throughout orthopaedic clinics today. Despite their design, iatrogenic cast saw injuries occur with an incidence of 0.1% to 0.72%.1,2 In addition to direct patient harm, these injuries can have considerable medico-legal cost with injuries reported at a single institution over a 1-year period to average $445,144 or $15,898/patient.1 These injuries may be the result of both thermal and/or abrasive damage to the skin.1–5
Thermal injury is thought to occur when friction between the blade and the cast elevate the cast blade temperatures above 50°C where permanent dermal injury can occur (Fig. 2).6 Shuler and Grisafi5 reported an average cast saw blade temperature of 55.7°C during the removal of fiberglass casts, while others have recorded cast blade temperatures from 40.5 to 101.6°C.4
Ansari et al1 found the incidence of abrasive injuries was 3 times higher than that of the incidence of burns. These injuries presumably occur when the downward pressure exerted on the cast saw prevents the underlying skin from oscillating back and forth with the saw blade. In such a scenario, the skin becomes immobile and is susceptible to being cut by the blade (Fig. 3).
PRINCIPLES OF MANAGEMENT
Risk Factors for Thermal Injury
Multiple factors related to the cast-cutting device itself can increase or decrease the risk of thermal injury. Different cast saw manufacturers differ in their strategies used to minimize heat produced during cast removal. In addition to eliminating debris, vacuum attachments seems to decrease the overall temperatures generated during cast removal.4,7 Factors related to the cast saw blade may affect the risk of thermal injury.4 Used or worn blades have been shown to generate significantly more heat (20 to 40°F) compared with new blades4 (Fig. 4).
Cast factors also influence the risk of thermal injury during cast removal. Fiberglass casts generate more heat during cast removal than plaster4 for any given saw type. Casts >0.5 inches (12.7 mm) have been reported to generate temperatures up to 210°F. Keeping casts <3/8 inches (9.5 mm) thick is felt to be safer.4,5 Locations such as the concavities of casts, where cast thickness may be increased should be avoided if possible8 (Fig. 5). In contrast to cast thickness, cast padding (≥4 layers) is protective from thermal injury.5
Risk Factors for Abrasive Injury
Although dull cast saw blades increase the temperature of the blades during cast removal, increased sharpness of the blades can increase the risk of abrasive injury.1 These sharp blades cut through casting material efficiently and can injury the underlying skin if care is not taken. Insufficient cast padding can increase the risk of injury as well.
Perhaps initially counter-intuitive, softer casting materials increase the risk for injury. When a cast is hard and immobile, the saw blade cleanly cuts the material; however, when the cast is soft, the casting material in a sense becomes similar to soft tissue. Thus one must press very hard to get the saw to cut the casting material. This increased pressure and decreased tactile feel (between cast and underlying tissue) increase the likelihood that the skin under the cast will be damaged. This scenario may occur if insufficient time is given for a cast to “set,” if an insufficient thickness of materials is used, or if a plaster cast gets wet. This may partially explain the increased incidence of cast saw injuries in the emergency room, where caregivers may be more hurried to split or remove a cast.2
Ulnar styloid, humeral epicondyles, malleoli, are anatomically more at risk than more well-padded areas. These locals have skin overlying bone with very little subcutaneous fat. If the skin in these areas pushed down by the cast saw, it can easily become pinned between the saw blade and the underlying bone and unable to oscillate with the blades motion. Once the skin becomes immobile it is cut [Supplemental Digital Content Video 3, An example of how pinning the tissue against a boney prominence (in this case the metacarpal head), can prevent soft tissue motion resulting in an injury. Copyright 2015. Reprinted with permission from Matthew A. Halanski, MD, Supplemental Digital Content 3, http://links.lww.com/BPO/A59].
Human factors play a significant role in cast saw injuries. Both user errors and patient factors can increase the likelihood of cast saw injury. Very young, sedated, or otherwise nonverbal patients cannot communicate that they are having pain during cast removal. Any patient complaints of pain or burning during cast cutting should be taken seriously.
Blade to skin contact occurs commonly during cast removal. Surprisingly the number of times the blade touches the skin appears independent of user experience or education.9 However, clinical experience and other studies have demonstrated that poor user technique increases risk of injury.1,2,5 At first glance, these data may appear in opposition to one another; however, they highlight perhaps the most important factor in cast saw injuries, the duration of blade to skin contact. By minimizing the time that the blade is in contact with the skin (using the recommended in-out technique), the risk of thermal injury and abrasive injury can be nearly eliminated. Thermal injuries are a function of time and temperature, thus minimizing the time that blade touches the skin, prevents thermal injury (in the same manner a candle can be quickly put out with fingertips without injury). Similarly, by pushing down and pulling out the saw blade (using the in-out technique), the skin under the cast may pushed down but not “dragged,” with the blade. “Dragging” the blade along the cast can drag the padding and skin underneath the cast. Such skin is under tension and cannot oscillate with the blade increasing the risk for abrasive injury.
Proper use of the cast saw involves assessing potential risk factors and using proper technique to minimize injury. Each time the cast saw is used the user should check the saw blade to ensure it is not dull and that the teeth are free of casting material. Next the ideal path to cut should be decided. Paths avoiding concavities and boney prominences should be chosen, if at all possible. If this is not possible, a high level of caution should be used in these areas. Placing a line on the cast demonstrating the path may be useful for inexperienced users. If removing a Gortex, waterproof cast, the cast saw operator must stay over the blue safety strip to prevent thermal injury. Similar zip strips may be placed down the cast during removal, regardless of padding type, to further protect the skin from injury. If a cast is to be “windowed,” the operator must remember to not “bend” the blade trying to make curved edges to the window, doing so will increase the friction on the blade and thus increase its temperature.
Proper cast saw technique eliminates most cast saw injuries. Perhaps instead of viewing the process as “cutting a cast off with a saw,” it would be better to explain this as “perforating the cast.” Naturally, the former evokes images of the use of a circular saw cutting wood in which the blade is pushed through the wood to cut rather than the proper “in-out” technique that is required for safe cast removal. To begin, the user should comfortably position the cast saw in the hand so that the hand can be stabilized on the cast to allow precise control of the depth of the cast saw blade penetration. Ideally the stabilizing finger can be positioned to be in contact with the side of the blade to assess blade temperature during the removal process. With the saw on and the blade stabilized, the user perforates the cast with downward pressure (the “in” part of the in-out technique) and then removes the blade without advancing the blade forward (the “out” part of the in-out technique). With the blade above (and outside of the casting material) the operator’s hand and the cast saw blade are advanced 1 to 2 cm in the direction the cast is going to be cut and the same procedure is performed. This process is repeated until the cast is fully cut. Penetration and removal of the blade from the cast material should be done quickly to minimize the duration of any blade to skin contact, minimizing thermal injury. The depth and pressure of blade penetration should be controlled and minimized to prevent abrasive type injuries. Thus the importance of stabilizing the cast saw with the hand. Furthermore, completely removing the blade from the casting material between each penetration prevents dragging the skin underneath and allows the blade to cool. Depending on the length and thickness of the cast, the blade temperature should be intermittently assessed by the operator by touching the sides of the cast saw blade. If the blade is too hot (causes discomfort to the operator’s fingers), the blade should be given time to cool. This is especially important in longer casts, that is, spica, long arm, and long leg casts. Finally, cast spreaders are used to pry open the edges of the cast and break any small connections remaining between the perforations. Examples of proper and improper technique can be found in (Supplemental Digital Content Video 4, Proper in-out cast saw technique. Notice, the cast saw is steadied and supported by a finger on the cast. This helps control the depth of penetration and allows blade temperature to be assessed during removal. The blade is completely removed from the material before advancing and brief pauses taken to assess blade temperature. Copyright 2015. Reprinted with permission from Matthew A. Halanski, MD, Supplemental Digital Content 4, http://links.lww.com/BPO/A60 and Supplemental Digital Content Video 5, Improper “dragging” technique. Copyright 2015. Reprinted with permission from Matthew A. Halanski, MD, Supplemental Digital Content 5, http://links.lww.com/BPO/A61).
Despite many technical advances in orthopaedics, cast immobilization remains an important treatment option. Recent focus on improving quality and safety has brought to light the iatrogenic injuries caused by casting and cast removal.2 In addition to better recognition and standard education to reduce these injuries, other strategies are being utilized in hopes to eliminate them all together.
One strategy to decrease the injuries caused by casting and cast saws is to decrease the use of casts. Based on level I evidence, fractures that were once treated with long arm cast immobilization are now treated with short arm casts and still others with removal splints. Similarly, with the increased use of flexible nails in the lower extremities, hips spica, and long leg cast use may be decreasing as well. Although decreasing cast use should decrease the number of cast-related complications, this may have an unwanted effect in further limiting the experience that trainees have learning appropriate techniques.
To counter this, several institutions are utilizing simulation to study and help educate trainees.2,9 In addition to being used for research purposes, cast simulation exercises can be used to objectively measure and document user proficiency.2,10 Although these educational programs may decrease iatrogenic injuries over time, they have thus far been unable to completely eliminate all such injuries.2
Finally, in the future, we expect advances in technology to further decrease the risk of cast saw injuries. By eliminating blade to skin contact, providing a safety mechanism to prevent injury, or by eliminating the cast saw all together, the author believes the vast majority of these injuries will be eliminated, making cast removal a safe experience for everyone.
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