Casts and splints are frequently used for stabilization of musculoskeletal injuries, including fractures and postsurgical support of sites distal to the elbow joint or stifle joint.1–3 However, casts may be associated with soft tissue complications such as pressure sores, edema, and dermatitis.3–5 In a retrospective study,4 it was found that 63% of patients fitted with a cast developed a soft tissue injury.4 Of the injuries that developed as a result of casting, 40% required continued veterinary intervention. These complications usually are minor; however, the cost of managing a cast-related injury can exceed the cost of treatment for the primary injury.4 In some cases, injuries caused by a cast can be severe, which could result in necrosis of the limb and amputation.1,6 Therefore, prevention of these secondary injuries is desirable.
Dermal sores or lesions usually develop at areas of high pressure. These high-pressure areas generally are located over bony prominences such as the calcanei, styloids, or malleoli or at the proximal and distal edges of a cast.7 The reduced compressibility and thinner nature of the tissue over bony prominences can result in nonuniform distribution of pressure over the aforementioned points, which make them extremely susceptible to the adverse effects of pressure.7,8
To achieve adequate stabilization of fractures, it is commonly recommended that a cast should extend to the joints proximal and distal to the fracture site.1,6,9,10 Surprisingly, extremely little information has been provided regarding the location (ie, proximal to the joint that is proximal to the fracture site) at which the rigid material of a cast or splint should terminate. Some authors describe application of cast padding to the level just distal to the nonimmobilized joint.6,9 However, others state that a short cast that does not extend to the elbow joint or stifle joint may be appropriate for treatment of injuries to the distal portions of a limb.11,12 More information is available regarding the forces created when applying external coaptation to humans. A biomechanical concept referred to as a 3-point corrective system theorizes that the rigid material of a cast should always extend as far proximal and distal as possible to minimize the overall forces acting on the limb (Figure 1).7,13 By minimizing these forces, it is expected that pressure points within a cast will be minimized, which will reduce the incidence of pressure sores and other soft tissue injuries. The 3-point corrective system is based on the concept that application of a rigid cast prevents normal joint motion and thereby couples the unaffected skeletal structures proximal and distal to the site of injury.14 During weight bearing, the forces are expected to be largest at bony prominences and termination sites of the cast in locations at which the rigid cast material prevents normal motion (pressure points). The force opposing joint motion during weight bearing has been defined as the CRF. For the tarsus, these forces would occur during flexion and be located caudally at the level of the calcaneus and on the cranial surface proximally and distally at the points where the cast terminates. Two opposing forces (proximal and distal to the CRF) have been defined as CFs. In the example of a 3-point corrective system, 2 CFs oppose 1 CRF and are located opposite each other (ie, if the CRF is acting on the caudal aspect of a limb, the CFs act on the cranial aspect). The forces of both CFs are expected to equate to the force applied at the CRF location.14 Thus, reducing 1 of the CF forces should result in a decrease in the CRF. On the basis of this concept, it has been suggested that by extending the lever arm (ie, extending a cast proximally), the CF will be reduced, thereby reducing the CRF and reducing the incidence of pressure points and sores over the calcaneus.7,14
The introduction of veterinary orthoses and prostheses has resulted in the clinical application of this concept to veterinary patients14; however, to our knowledge, this concept has not been scientifically evaluated for use in small animals.
The purpose of the study reported here was to evaluate the effect of 2 cast configurations on the amount of pressure at various points on the canine pelvic limb. We hypothesized that a cast extending approximately 2.5 cm proximal to the tarsus would create greater pressures at the calcaneus, compared with pressures created by a cast that extended just distal to the tibial tuberosity. A second hypothesis was that pressure over the cranial surface of the tibia at the level of the proximal edge of the cast would be greater for a short cast configuration than for a tall cast configuration.
Supported in part by the Eldred Foundation, the Morris Animal Foundation, and a Young Investigators Grant from the Center for Companion Animal Studies at Colorado State University.
The authors thank Martin Kaufmann for technical assistance and Theresa Wendland for providing Figure 1.
Corrective reaction force
Zonas porous tape, 1-in, Johnson & Johnson, New Brunswick, NJ.
Tubegauz seamless tubular gauze, size No. 34, The Scholl Manufacturing Co Inc, Chicago, Ill.
Cast padding, 2 or 3 in, BSN Medical, Charlotte, NC.
Dermacea gauze roll, 2, 3, or 4 in, Covidien LLC, Mansfield, Mass.
Vetrap bandaging tape, 2 or 4 in, 3M, Maplewood, Minn.
Vetcast casting tape, 2 or 3 in, 3M, Maplewood, Minn.
JobMax 18-volt console multi-tool, Ridgid Inc, Newark, Del.
F-Socket medical sensor 9811E, TekScan Inc, South Boston, Mass.
F-Scan pressure measurement system, version 6.85–29, TekScan Inc, South Boston, Mass.
HRV walkway 6 VersaTek system, 23 in × 130 in, Tekscan Inc, South Boston, Mass.
Excel 2016, Microsoft Corp, Redmond, Wash.
IBM SPSS, IBM Corp, Armonk, NY.
Walkway research Beta, version 7.66-03, TekScan Inc, South Boston, Mass.
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