Effects of Bandage Configuration on Paw Pad Pressure in Dogs: A Preliminary Study
Seven bandage configurations were placed on the right forepaw of six English pointer dogs to evaluate the effects that configurations have on reducing pad pressure. The “clam shell” configuration resulted in less pressure being applied to all palmar pad surfaces. For the major weight-bearing pad, a basic paw bandage with an intermediate compressible foam sponge that had a hole under the major weight-bearing pad, combined with a metal splint paw cup under the sponge, resulted in a significantly lower pressure recording than for other bandage configurations. Digital pads 3 and 5 had the greatest pressure in a basic bandage configuration. Based on pressures on these pads, a basic paw bandage with an intermediate compressible foam sponge under the major weight-bearing pad, with or without a metal splint paw cup under the sponge, helped elevate the digits to relieve pressure on them. Placing a foam sponge pad, with or without a splint paw cup under the palmar paw surface, also provided less pressure on these pads.
Introduction
Wounds of the pads present a special challenge to the veterinary practitioner. Pad healing is more prolonged than healing in other areas of the skin.1 Weight bearing is a contributing factor in the slower healing. The normal function of pad tissue is to serve as a cushion or shock-absorbing tissue. As pressure is placed on the pad tissue, it tends to spread.23 In the presence of open wounds, this spreading counteracts the wound contraction process of the fibroblasts and myofibroblasts that cause reduction in wound size.4 Thus, the wound gets larger. Regardless of the type of reconstructive pad surgery that has been performed, any pad pressure that causes pad tissue to spread results in extrinsic suture tension, which is transferred to tissue outside of the suture to cause it to cut through the tissue.25 In both open and closed wounds, unsupported pad pressure tends to interfere with healing.
Regardless of the type of wound management, bandaging is an important part of the treatment. Bandages provide many functions in wound management, including support and protection.67 When considering the above-mentioned tissue dynamics, wound support and protection from pressure are important considerations for promoting pad wound healing. Reduction of pressure and spreading on pad wounds would promote early healing.
Complete prevention of weight bearing on wounded pad tissue is the ideal for assurance of pad healing. Bandaging the limb up in a non-weight-bearing position such as a Velpeau bandage for the forelimb8 and a Robinson sling for the pelvic limb9 would be means of preventing weight bearing. Placing the paw in flexion by incorporating a splint in a bandage could also be used to prevent weight bearing on the pads.1 Such immobilization is maintained 2 to 4 weeks. A light padded bandage is recommended for 1 to 2 weeks after splint removal.1 With larger dogs, the longer times of nonweight bearing and bandaging would be indicated due to the detrimental effect of greater weight on the pad healing process. However, with nonweight bearing for 2 to 4 weeks, disuse atrophy and a period of lameness follow release from nonweight bearing or flexion. Nonweight bearing for 2 to 4 weeks can be detrimental to limb musculoskeletal structure and function, such as limited joint flexion, type I muscle fiber atrophy,10 and atrophic, destructive, and degenerative articular cartilage changes.11 Joint loading is important in maintaining articular cartilage integrity.12 With canine athletes and working dogs, it is desirable to prevent such changes and the associated lameness in the interest of an early and effective return to activity. Thus, bandaging and splinting techniques for pad injuries that would decrease pad pressure and allow limb use during the healing would be beneficial.
The purpose of this study was to establish some objective preliminary data comparing the effects of some new bandaging techniques based on bandage configuration and new bandage materials on paw pad pressure. These techniques and materials could possibly benefit the practitioner in bandaging paw pad wounds, thus helping to prevent chronic, nonhealing wounds of the pads, especially in large dogs. However, further wound-healing studies would be necessary to establish the actual relationship of pad pressure on pad wound healing.
Materials and Methods
Prestudy Preparations
This study was conducted under protocols approved by the Auburn University Institutional Animal Care and Use Committee. Six English pointer dogs of either sex and weighing from 13.4 to 21.8 kg were selected as representative of large and working dogs (i.e., dogs that would be subject to paw pad lesions). The dogs were given physical and hematological examinations and were treated for external and internal parasites. Additionally, each dog received an orthopedic examination of all limbs and was found to be sound. The dogs were housed in individual runs, fed once daily, and were allowed water ad libitum. The dogs underwent a period of habituation consisting of familiarization with handlers and the study area, walking with a bootie and wire loosely taped to the leg, and manipulation of the right forepaw.
Pressure-Measuring Resistors
Pressure data was collected by affixing a force-sensing resistora to the center of the ground surface of each weight-bearing paw pad [Figures 1, 2]. The resistors were thin polymer film devices that respond to applied surface force by decreasing electrical resistance. Each force-sensing resistor had an active area of 5 mm and was fitted with electrical leads and microconnectors. When assembled, the microconnectors were supported by a thin adhesive tape strip [Figure 1]. A 12-cm length of stranded, 24-gauge, insulated wireb was soldered to electrical tabs of each resistor. A male pin connector was soldered to the other end of the wire. Individual pressure calibration curves were established for each resistor before use, and their function was checked against the curves after use.
Prior to affixing the sensors, the pads were wiped clean with water, dried, cleansed with isopropanol, and air dried. On four dogs, a thin coat of hexamethyldisiloxone acrylate copolymerc was applied to all pads and was allowed to dry before placing the sensors to help assure their adherence. In two dogs, pad sweating interfered with adhesion of a thin adhesive taped patch used to hold the sensors in place. In these dogs, a thin film of cyanoacrylate adhesivee was applied to the pads and allowed to dry before taping a sensor to each pad. The multiple electrical leads were then lightly taped to the metapodium.
Bandage Configurations
After the resistors were in place, seven different bandage configurations were applied sequentially to the right forepaw of each dog. Pad pressure measurements were taken with each configuration as the dog walked. Although bandages were changed, the resistors always remained in place. The types and sequences of bandage application were:
Configuration 1.
Using a secondary bandage wrap,f four circumferential wraps were made around the paw. Two folds of wrap were made over the digit ends, followed by one more circumferential wrap to hold the folds in place. Three, 17.77-cm long strips of 5.08-cm wide adhesive tapeg were applied circumferentially over the secondary wrap, and two, 10.15-cm long strips of the same type of tape were placed at right angles to each other over the digit ends. The final tape strip was like the previous circumferential wraps [Figure 3].
After walking pressures were recorded, Configuration 2 was applied.
Configuration 2.
The paw cup portion of a 19.04-cm long metal splinth was centrally placed on the palmar surface of Configuration 1 [Figure 4] and affixed in place with two circumferential wraps of 5.08-cm wide adhesive tape, 17.77 cm long.
After walking pressures were recorded, the entire bandage of Configuration 1 was removed, using care not to disturb the resistors on the pads.
Configuration 3.
Configuration 1 bandage was applied to the right forepaw. However, a 1.27-cm thick, triangular piece of medium-density foam sponge,i measuring 5.08 cm on a side, was placed centrally under the metacarpal pad on the surface of the secondary bandage wrap. An additional circumferential secondary bandage wrap held it in place [Figure 5]. The outer tape strips were applied over this. After walking pressures were recorded, Configuration 4 was applied.
Configuration 4.
The metal splint paw cup described for Configuration 2 was applied to the palmar surface of the Configuration 3 bandage, as described for Configuration 2 [Figure 4].
After walking pressures were recorded, the bandage was removed, leaving the resistors in place.
Configuration 5.
A Configuration 1 bandage was applied. In addition, a 1.27-cm thick, oblong (9.52 cm × 7.61 cm), medium-density foam sponge pad was placed under the entire palmar surface of the secondary bandage wrap, with the long dimension parallel to the long axis of the paw. The foam had a 2-cm diameter hole in it, which was placed over the resistor on the metacarpal pad. The sponge pad was held in place by an additional, circumferential, secondary bandage wrap [Figure 6]. The outer tape strips were applied over this.
After walking pressures were recorded, Configuration 6 was applied.
Configuration 6.
The metal splint cup was placed on the palmar surface of the Configuration 5 bandage, as described for Configuration 2 [Figure 4].
After walking pressures were recorded, the bandage was removed, leaving the resistors in place.
Configuration 7 (“Clam shell” splints).
After placing a Configuration 1 bandage on the paw, seven wraps of secondary wrap and three strips of 17.77-cm long, 5.08-cm wide adhesive tape were placed around the distal limb proximal to the paw bandage to bring this area up to the same diameter as the paw area. Two, 19.04-cm long, metal splints were placed over the bandage with one splint on the dorsal surface of the bandage and one on the palmar surface of the bandage. The concave surfaces of the paw cups faced each other and extended 2.54 cm beyond the end of the paw bandage [Figure 7A]. The splints were taped in place with four, 17.77-cm long strips of circumferentially wrapped, 5.08-cm wide adhesive tape [Figure 7B]. Two, 10.2-cm long strips of the same type of tape were placed at right angles to each other over the ends of the splints to stabilize them together. In the center of one of these strips, a single-gauze surgical sponge was folded to a 2.54-cm2 size and was placed over the ends of the splints [Figure 7C]. This provided traction on the end of the splints as the dogs walked [Figure 7D].
After walking pressures were recorded, the bandage was removed to complete bandage evaluation for each dog.
Computer Connection, Ambulation, and Pressure Measurements
After application of Configuration 1, connection to a microcomputer was completed by a four-pair, stranded, 24 AWG (American Wire Gauge) networking cable.j The cable was held loosely against the caudal aspect of the limb by circumferential velcro straps and loosely to the hair over the dorsal area by 5.08-cm wide strips of adhesive tape. The cable was suspended by five pulleys from a 9.37-m, overhead-tension wire [Figure 8]. The female sockets of computer light-emitting diodes were used as plugs on the networking cable to receive the male pin connectors. The apparatus allowed the dog to walk from end to end of the gait laboratory. Each force-sensing resistor was supplied with a current of 1.57 milliamperes (mA) at 5 volts direct current (VDC). Output signals were delivered to the analog/digital conversion board of the computer. The oscilloscope feature of a kinematic data collection software programk was used to monitor data during collection and create a store of data. Each dog was led at approximately 1 m per second in a straight line from end to end of the laboratory for three, 20-second periods as data was collected at a rate of 400 Hz.
Data from the stance phase of two sets of five contiguous step cycles during periodic straight-line walking was analyzed. The pressure versus time graphs were examined for form, and those showing excessive electrical noise were not included. Selection of acceptable contiguous step cycles was based on a nonlinear dynamics test applied to the data. With this approach, the step cycles under consideration were related to a series of surrogate step cycles.1314 The surrogate step series were constructed by taking the Fourier transform of the original data, randomizing, and then taking the inverse Fourier transform. Correlation dimensions,15 computed for each surrogate series, were compared statistically using the surrogate-data test.1314 The data selection process evaluated the saturation of correlation dimension contrasted against the embedding dimension.1314
The accepted pressure waves were assembled and averaged. Mean pressures in Newtons per meter2 (N/m2) were compared among digits using a repeated measures analysis of variance (ANOVA). Where significant differences were indicated, the Newman Keul’s multiple comparison test was used for subsequent analysis. A value of P≤0.05 indicated significance.
Results
The data for mean peak pressures on pads with the seven bandage configurations is presented in the Table. When considering the effects of various bandage configurations on metacarpal pad pressure, there were three factors with results of potential clinical interest. First, placement of any additional padding or splint under this pad resulted in increased pressure on the pad, as seen in Configurations 2, 3, and 4, as compared to Configuration 1. The greatest pressure increase was in Configuration 2, where placement of a metal paw splint cup over the wrap of Configuration 1 resulted in significantly greater pressure on this pad. There was also significantly greater pressure than Configurations 5, 6, and 7. The second factor was that in Configuration 6, placement of a foam sponge pad with a hole over the resistor on the metacarpal pad and a metal paw splint cup under the foam sponge pad provided significantly reduced pressure on the metacarpal pad compared to all other configurations except the “clam shell” splints of Configuration 7, where that configuration provided significantly less pressure on the pad. The third factor was that “clam shell” splints of Configuration 7 resulted in significantly less pressure on the metacarpal pad than any other bandage configuration.
With the digital pads, pads 3 and 5 had the greatest pressure in the basic bandage of Configuration 1. Three factors of potential clinical interest were noted. First, the “clam shell” splints of Configuration 7 provided significantly lower pad pressures on all digital pads, with the exception of digital pad 3, compared to all other bandage configurations. The second factor of interest was related to bandage Configurations 2, 3, and 4, where an attempt was made to off-load digital pads, as is done with orthotic devices in humans. To relieve pressure on the digital pads, the metal splint paw cup of Configuration 2, the foam sponge pad of Configuration 3, or the foam sponge pad and metal splint paw cup of Configuration 4 were placed under the metacarpal pad caudal to the digits as additions to the basic bandage configuration of Configuration 1. Thus, the second factor of interest was that digital pads 3 and 5 had instances of significantly lower pressure with these configurations compared to Configuration 1. On digital pad 3 it was Configuration 4 that provided significantly less pressure compared to Configuration 1, and on digital pad 5 Configurations 2, 3, and 4 provided significantly less pressure compared to Configuration 1. Thirdly, unlike the metacarpal pad, placing a foam sponge pad with or without a metal splint paw cup under the palmar paw surface, as seen with Configurations 5 and 6, also provided significantly less pressure on digital pads 3 and 5 compared to Configuration 1.
Discussion
Addition of a metal splint paw cup over a secondary bandage wrap has been stated to help prevent a pad from spreading when weight is placed on the pad.237 Although spreading may be prevented, there may be an increase in pressure on the metacarpal pad when an unyielding device, such as a metal splint paw cup, is added to the bandage. This observation appears to be a manifestation of the phenomenon whereby pressure is increased over convex surfaces when additional padding is placed in a bandage over such a surface,316–18 and the metacarpal pad has a basic convex shape when compared to digital pads. Pressure on a pad tends to spread wound edges apart to interfere with wound healing. A metal splint paw cup tends to confine tissue, but it increases pressure. A wound healing study to evaluate the effects of pressure and confinement by a metal splint paw cup would be necessary to ascertain if such an arrangement would enhance or inhibit healing.
Relief of pressure on a wound can be accomplished by placing padding around the wound.37161719 Configuration 6, with the hole in the foam sponge padding over the metacarpal pad resistor, was an example of such pressure relief used in combination with a metal splint paw cup. The significantly lower metacarpal pad pressure provided by this combination compared to all other configurations, except the “clam shell” splints of Configuration 7, suggests this is a bandage technique that could be used in relieving metacarpal pad pressure when indicated. However, the best pressure relief for the metacarpal pad is provided by the “clam shell” splints of Configuration 7.
When considering the placement of padding around an area for pressure relief (off-loading), it was indicated in this study that the pressure on digital pad wounds could be relieved by additional padding or support under the metacarpal pad to elevate the digits slightly. Configurations 2, 3, and 4 are examples of this, with a metal splint paw cup, foam sponge padding, and foam sponge padding plus a metal splint paw cup under the metacarpal pad, respectively. The significantly lower pressure on digits 3 and 5 produced by Configurations 2, 3, and 4 is indicative that these configurations may be applicable in helping to relieve pressure on these digits if indicated. Although placing a foam sponge pad, with or without a splint paw cup, under the metacarpal pad increases pressure on this pad, these bandage designs (as in Configurations 5 and 6) tend to reduce digital pad pressure; thus, such configurations could also be considered in reducing digital pad pressure.
When a foam sponge is used for bandage padding, a sponge with intermediate compressibility should be used (i.e., such as the sponge that was used in this study), which provides dampening of pressure. If a very soft foam sponge pad (like that used in routine furniture upholstery) or a very firm foam sponge pad (like that used in pipe insulation) is used, sufficient dampening of pressure may not be provided, because either the pad will compress too easily or not easily enough, respectively.
Based on the results of this study, the “clam shell” splints of Configuration 7 compose the best configuration for reduction of pad pressure on all pads while allowing the dog to ambulate. However, the technique does require more time and materials. The technique could be indicated on severe pad wounds or pad salvage surgical procedures. The bandage configuration has been used to attenuate pressure on paw pad grafts placed in a granulation tissue bed over the distal ends of the metatarsal bones of a boxer dog.20 The configuration kept direct pressure off of the grafts as they healed in place; thus, they healed and matured to provide a functional, weight-bearing tissue. The “clam shell” splints of Configuration 7 could be looked upon as a localized crutch for a paw to relieve pressure on wounds or reconstructed tissue as they heal.
Placing exact figures on the amounts of pressure that result in slowed healing or disrupted suture lines would be very difficult. There would be considerable variation depending on individual characteristics (e.g., weight of the animal) and nature of the wound (e.g., deep laceration versus superficial laceration). An underlying factor in such injuries, which has been reported,4 is that such pressure on pad tissue displaces and spreads the tissue and interferes with healing.
The study provided basic information regarding the effects of different bandage configurations on paw pad pressure. For those configurations resulting in less pressure on various pads, the decrease in pressure recorded may have been due to one of two factors. Although the dogs appeared to walk with a similar gait, the configuration of the bandage may have resulted in bearing less weight on the entire limb, which would result in less pressure being applied on the resistors. Alternatively, the bandage configuration may have actually relieved pressure over the palmar pad surfaces. Force plate studies would be necessary to document equal load being applied to the limb during gait with all bandage configurations to establish if the bandage configurations actually relieved pressure over the areas measured or if the decrease in pressure was the result of the bandage configuration causing less weight bearing on the limb. A controlled wound healing study using the bandage configurations would be necessary to make a definitive statement as to the overall effect of any of the bandage configurations on wound healing.
Conclusion
The findings of this study indicate that if a major weight-bearing pad is the primary area of interest, placing additional padding and support over the area increases pressure, especially if only a metal splint paw cup is added to the bandage. However, placing an intermediate compressible foam sponge pad with a hole over this area in combination with a metal splint paw cup will result in less pressure applied to the area. For relief of pressure on digital pads, placing a metal splint paw cup, a piece of foam sponge, or a combination of these under the major weight-bearing pad may help elevate the digits to relieve pressure on these pads. Digital pad pressure could also be reduced by placing a foam sponge pad with or without a metal splint paw cup under the palmar paw surface. The “clam shell” splint of Configuration 7 resulted in less pressure being applied to all pads.
Model 400; Interlink Electronics, Camarillo, CA
Southern Electronics Corp., Opelika, AL
No Sting Barrier Film; 3M Health Care, St. Paul, MN
HypaFix; Smith & Nephew, Inc., Largo, FL
Duro, Super Glue; Loctite Corp., North American Group, Rock Hill, CT
Sof-Band Bulky Bandage; Johnson & Johnson, Arlington, TX
Zonas, Adhesive Tape; Johnson & Johnson, Arlington, TX
Metal splints; Surecraft, Upton, MA
Temperfoam; HiTech Foam, Lincoln, NE
Inmac, Gibbsboro, NJ
PEAK 5; Peak Performance Technologies, Inc., Engelwood, CO
Acknowledgments
The authors thank Drs. Alicia Price and Stanley Carnes and Mr. Daniel Vasile for technical assistance.
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390209
Force-sensing resistor (A) fitted with electrical leads connected by microconnectors and supported by a thin, adhesive tape strip.
Force-sensing resistors taped in place on digital pads and metacarpal pad.
Configuration 1: Basic paw bandage with secondary bandage wrap and a tertiary layer of adhesive tape.
Configurations 2, 4, and 6: Paw cup portion of a metal splint to be taped over bandage configurations 1, 3, and 5, respectively.
Configuration 3: A 1.27-cm thick, triangular, medium-density, foam sponge pad incorporated in the secondary bandage layer under the metacarpal pad.
Configuration 5: A 1.27-cm thick, oblong, medium-density, foam sponge pad incorporated in the secondary bandage layer under the entire palmar paw surface. A 2-cm diameter hole in the pad is placed over the resistor on the metacarpal pad.
Configuration 7: “Clam shell” splints. (A) Two, 19.04-cm long, metal splints placed over the bandage with the paw cups facing each other and extending 2.54 cm beyond the paw bandage. (B) Splints taped in place. (C) End of splints being stabilized together with tape. A 2.54-cm2 surgical gauze sponge is incorporated in the stabilizing tapes. (D) Dog walking with a “clam shell” bandage.
Force-sensing resistors connected to a microcomputer by a four-pair stranded telephone cable supported by five pulleys from a 9.37-m, overhead-tension cable. The apparatus allowed the dogs to walk from end to end of the gait laboratory.
