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GENERAL WOUND MANAGEMENT
Overview
Horses have a very well-developed “fight or flight” mechanism and when anything happens to startle them, they often react first and think later. If they get caught in something such as a fence or barn wall, their first instinct is to leave; often without regard to whatever body part happens to be caught at the time. Therefore, horses have a well-deserved reputation as being accident-prone.
Signs and Symptoms
Adult horses, weighing approximately 1,000 pounds (450 kg) have more than 10 gallons of blood and can lose up to 40% (approximately 4 gallons) and still survive with aggressive treatment. Four gallons is a lot of blood and the amount of blood loss in a typical equine wound is usually less than what you often first think and therefore less life-threatening. If the bleeding is profuse and pulsating, an artery is likely involved and it will need to be stopped as soon as possible by tourniquet application, direct pressure, or ligation. Profuse bleeding that is not pulsating often responds to direct pressure and a compression wrap, consisting of an elastic bandage material (ElastikonR, VetWrapR, etc.), and an underlying pad (three sheets of sheet cotton, a shipping bandage quilt, an appropriately folded bath towel, or several layers of roll cotton). The compression wrap should be applied in smooth, even layers and firm enough to apply direct pressure to the wound.
Risk Factors
Factors complicating initial wound management include involvement of deep structures such as bone, tendon, ligament, joints, tendon sheaths, vessels, and nerves. Additionally, contamination of the wound with soil, manure, hair, or other foreign material will delay wound healing until these foreign substances are removed. Involvement of deeper structures and significant contamination may compromise blood supply.
When To Seek Veterinary Surgical Advice
Be alert when you first try to handle your horse or try to evaluate the wound of your injured horse. Horses that are normally calm may react completely out of character when they are frightened and in pain. Initially, you should make a quick assessment of the wound to determine if you need veterinary assistance.
Primary reasons to seek veterinary assistance are excessive bleeding, significant contamination, severe lameness, full-thickness wounds (entire skin layer has been penetrated) or wounds involving deeper structures such as bone, muscle, joints, ligaments, tendons, tendon sheaths, vessels and nerves. Full-thickness wounds may be amenable to suture closure which will significantly shorten the healing time of the wound. If closure is to be considered, usually the sooner the wound is closed, the better.
Most wounds should be evaluated by your veterinarian. Thorough knowledge of the underlying anatomy is important to determine the structures involved and the significance of the wound. A very large wound on the upper body that is not close to joints and is not very deep may have a much better prognosis than a small puncture wound into a tendon sheath or joint (Figures 1 and 2).
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Figure 1. Typical shoulder laceration that presented about 24 hours after interaction with barb-wire fence. Although this wound appears to be significant, the only structures involved are skin and muscle, and it should heal with minimal scarring in 2-4 months.
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Figure 2. Small laceration on the inside of the right hock that appears to be insignificant. At this location, the laceration could easily have penetrated into the cunean bursa, the distal tarsal joints and/or the flexor tendon sheath. Additional diagnostic evaluation is warranted to determine if any of these structures are involved.
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Wounds to the head and upper body heal relatively well as long as critical structures are not involved. Head and upper body wounds have a relatively good blood supply compared to distal limb wounds. Upper body wounds have sufficient skin and underlying muscle to allow significant wound contracture to help close even very large defects compared to wounds on the lower limbs. Wounds below the carpus (knee) and hock are complicated by minimal excess skin that is fairly inelastic, lacks underlying muscle tissue, and is subjected to movement during limb flexion. These wounds are also prone to exuberant granulation tissue (“proud flesh”) which will dramatically slow healing and may require surgical intervention.
Examination
The veterinary examination for most wounds consists of a brief physical examination followed by a thorough examination of the wound (Figure 3). The examination of the wound may involve local anesthesia and sedation to allow complete exploration of the wound. Some wounds may need to be evaluated under general anesthesia in order to completely assess the severity or complexity of the wound. The wound will be explored to determine the depth and width of its borders, to determine if there are any foreign bodies in the wound such as wood, wire, pieces of bone or hair, and to determine if any vessels, nerves, tendons, ligaments, muscle, bone or joints are involved. Radiographs of the area may be indicated. An ultrasound examination may also be indicated to evaluate the soft tissues and to locate potential foreign bodies. If joint or tendon sheath penetration is suspected, a site distant to the wound may be prepared in order to insert a needle into the joint or sheath to assess the synovial fluid and, if questionable, saline solution may be injected into the wound to determine if the joint or tendon sheath communicates with the wound. Involvement of a synovial sheath or joint significantly complicates the wound healing process. Repeated lavage or flushing of the synovial structure is generally indicated.
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Figure 3. Severe degloving wound of the right forearm. Although the lateral digital extensor muscle and tendon are exposed and the tendon is obviously transected, there is no joint involvement and the prognosis can be relatively good following immediate veterinary care.
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Treatment Options
Initial wound preparation consists of thorough cleaning and debridement of the wound, followed by suture closure if possible, and bandaging (Figure 4). Very important parts of wound therapy are to clean the wound, remove any foreign bodies, and to remove (debride) damaged or contaminated tissue. Wounds heal much better when all damaged tissue and foreign bodies are removed. The two most commonly used products for wound cleaning include povidone-iodine (BetadineR) and chlorhexidine (HibiclensR or NolvasanR) scrub cleansers. Both of these products are very effective in reducing the bacterial contamination of the wound. The wound must be rinsed thoroughly to remove all soap from the wound as the residual soap can be very irritating and may cause inflammation and delay wound healing. Both products also come in a solution that can be used to lavage wound sites, but must be diluted with sterile saline or equivalent solution to be most effective and to minimize adverse effects from the solutions. Povidone-iodine usually comes in a 10% stock solution and must be diluted to a 0.1% solution (one ml of povidone-iodine per 100 ml of saline) for wound lavage. It usually makes a “weak tea” appearing solution. Chlorhexidine typically comes in a 2% stock solution and is recommended to be diluted to a 0.05% solution (two and one-half ml of 2% chlorhexidine solution per 100 ml of saline) for wound lavage. Please read the appropriate labels for specific concentrations and potential uses of the products.
Figure 4a. Full-thickness skin laceration of the cannon bone region of the right hind limb after clipping and cleaning. No underlying structures are involved.
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Figure 4b. Immediate post-operative photograph of the repaired laceration in Figure 4a.
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Hydrogen peroxide is not recommended for cleaning wounds. For some reason, probably its foaming action, hydrogen peroxide has an undeserved reputation as being a good agent for cleaning wounds. Hydrogen peroxide damages tissues and is not very effective against most bacteria.
Dirt and manure are loaded with bacteria and horses have a habit of getting lots of both in their wounds. Therefore, many wounds of the lower limbs are contaminated and often develop infections in spite of aggressive therapy. The infections cause significant inflammation, dramatically slow or even completely stop wound healing, and result in significant scar tissue formation. Infections of bone, tendons or ligaments may lead to lysis (erosion) of bone, tendons or ligaments.
Following wound cleaning and debriding, a decision will need to be made concerning when and if the laceration should be closed by sutures or if the wound must heal without closure. Ideally, the wounds are closed by suture as soon as possible following the injury (Figure 5). However, wounds with severe contamination or wounds that are more than ~12 hours old are generally not good candidates for immediate closure. The wound may need to be treated and repeatedly cleaned over the next 3-7 days before closure is attempted. Additionally, some wounds are so contaminated or have so much tissue loss or damage that closure may not be appropriate.
Figure 5. Two months post-operative view of Figure 3. Fortunately, the skin flap was broad-based, had sufficient subcutaneous tissue, and adequate blood supply; it was sutured and survived.
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Bandages are usually indicated if the location of the wound is appropriate for bandaging. Bandages are designed to absorb wound fluids, protect the wound from trauma, immobilize the limb, and keep the wound warm and moist. This environment facilitates wound healing.
There are many, many options for bandaging wounds and for the dressing and ointments applied to the wound. Many of these products are beneficial, but some may cause delayed wound healing. Water soluble antibiotic ointments such as silver sulphadiazine, gentamicin, neomycin sulfate, triple antibiotic (bacitracin, neomycin and polymixin), povidone iodine, and chlorhexidine are generally considered positive therapies. Nitrofurazone ointment has been shown to decrease the rate of healing (epithelialization) in some studies.
Lacerations below the fetlock that do not involve joints or tendon sheaths may be best treated by surgery, closure and cast application (Figure 6). This area is highly mobile and is difficult to keep clean. Cast immobilization allows these lacerations to heal with minimal complications provided important underlying structures are not involved.
Figure 6a. Heel bulb laceration of the lateral (outside) aspect of the pastern in the right hind limb. This laceration is fairly typical and usually responds well to surgical closure and cast application. Involvement of the pastern and coffin joints, blood and nerve supply, and the collateral cartilage must be determined. If these structures are not involved, the laceration will usually have a good prognosis.
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Figure 6b. Caudal view of the laceration depicted in Figure 6a, three weeks following repair. The wound has healed well following closure and cast application.
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Systemic antibiotics are often administered until potential infections are under control. Culture of the wound may dictate which specific antibiotic to use. Generally broad spectrum antibiotics, such as penicillin and gentamicin, trimethoprim-sulfa, or ceftiofur, are initially administered. A more specific antibiotic may be selected when results of wound culture are available.
Aftercare
Following initial stabilization and care of the wound, the horse may be restricted to stall rest with hand-walking only, but the level of exercise will be dictated by the wound. Deep wounds in the chest between the front legs or in the flank region between the hind legs are prone to the development of subcutaneous emphysema (air under the skin). When the animal walks, the wound opens and closes, allowing air to enter, but not to leave the depths of the wound. The more the animal moves, the more air is sucked into the wound and the greater the development of subcutaneous emphysema. This air may carry bacteria deep into the tissues causing deep infections that are difficult to manage. For wounds on the distal limb, too much exercise may result in a greater tendency to develop exuberant granulation tissue due to movement at the wound site.
Complications Following Treatment
Complications of the wound healing process include the development of abscesses, cellulitis, hematomas, seromas, habronemiasis, phycomycosis, sarcoids, proud flesh, prolonged healing, and excessive scarring. Habronemiasis (“summer sores”) is caused by a fly larva, which can mimic “proud flesh”. Phycomycosis is a chronic fungal infection that occurs in the Southeast, primarily along the Gulf States, which may also appear to be “proud flesh”. If joints or tendons are involved, additional complications include arthritis, adhesions, mechanical lameness, and scar tissue restrictions of motion. Keeping your veterinarian involved in the ongoing care of severe injuries will help to avoid some of these common complications (Figure 7).
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Figure 7. Severe case of exuberant granulation tissue secondary to a degloving wound of the left hock and metatarsus. The result of this case demonstrates the need for early and continued involvement by your veterinarian.
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Prevention
Finally, protection of the horse against tetanus is easy and one of the most important aspects of wound management. Horses are very susceptible to the toxin produced the tetanus organism which gains entry to the horse through wounds. A tetanus toxoid vaccination with annual boosters is the best way to prevent the disease. Keep good records and know your horses’ vaccination status.
—David Wilson, DVM, MS
Diplomate ACVS
Posted 4/02/2005
Updated 6/17/2008 by Dr. Wilson
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