CHAPTER 8 Updated by Yvonne A. Elce, DVM, Diplomate ACVS Selection of the optimal way to manage a wound should not be based on rigid rules relating to time or conditions, but rather, it should rely on careful examination of the wound and consideration of factors relating to the patient. Each wound is unique and requires individualized care. Wounds may be closed immediately after cleansing and debridement (referred to as primary closure) or closure may be deferred for a few days to allow continued debridement and treatment (referred to as delayed primary closure). Alternatively, wounds may be revised and closed after granulation tissue has formed (referred to as delayed secondary closure) or left to heal without suturing (referred to as second‐intention healing). Primary closure should be considered in all cases, and particularly when tissues underlying the skin, such as bone or tendon, are exposed, because this approach is most likely to provide the best cosmetic and functional outcome. When a horse incurs a wound, the goals of treatment are to reduce pain and restore a normal appearance and function to the wounded area, as rapidly as possible. The manner in which this goal is achieved varies because many options exist. Careful examination of the horse in general, and of the wound specifically, should always be performed before any therapeutic decisions are made. A complete medical history must be obtained and should include the status of tetanus vaccination, as well as details pertaining to when and how the wound occurred. The owner’s goals and limitations (financial, time, technical, or facility‐related) must be discussed. After a thorough history has been obtained and the horse physically examined to rule out any noteworthy systemic problems, a detailed examination of the wound may begin. Administering some form of sedation that simultaneously provides analgesia and diminishes the anxiety of the patient, thereby facilitating a careful examination and protecting the veterinarian, is helpful. While examining the wound, special attention should be paid to the following: the involvement of underlying structures, such as joints, body cavities, bone, and tendon; the amount of gross contamination; an estimation of the manner in which the wound was incurred and the time elapsed since wounding, if not clear from the medical history (e.g., crushing or sharp trauma; fresh or chronic appearing); the location, shape, and depth of the wound; and the integrity of the local vascular supply. Because these factors contribute to the overall status of the wounded tissues, rigid guidelines based on the age or degree of contamination of a wound should not be used to dictate whether or not the wound can be sutured or must be left to heal by second intention. The options for wound management are primary closure, delayed closure (either primary or secondary), and leaving the wound unsutured to heal by second intention, with or without some form of skin grafting. Whenever possible, wounds should be managed by primary closure because this leads to a superior cosmetic and functional outcome. Many veterinarians were taught that a wound is suitable for primary closure, without risk of infection and subsequent dehiscence, if it is less than 6–8 hours old. This “golden period” relates to the time that it takes multiplying bacteria in a surgical wound, created experimentally in laboratory animals, to reach an infective concentration, considered to be more than 105 organisms per gram of tissue or milliliter of exudate.1 In fact, we now know that this time may be longer than 6–8 hours in very clean, minimally contaminated wounds, and it may be shorter in heavily contaminated, contused tissues.2 Consequently, the concept of a “golden period” is inaccurate,3 and the outcome of primary closure is now considered to depend predominantly on the adequacy of the host’s immune response, the virulence of contaminating bacteria, and local environmental factors that might potentiate the virulence of bacteria.4 For more information on the bacterial impact on wound healing, the reader is referred to Chapter 3. In the horse, primary closure is considered ideal for fresh, minimally contaminated wounds of the extremities, wounds of the head, and flap wounds with a good blood supply, such as those found, for example, on the neck, the flank, the thorax, or the proximal aspect of the limb. Wounds caused by contact with sharp objects often heal successfully after primary closure because this type of injury inflicts minimal trauma to the tissues and their blood supply (Figure 8.1). Figure 8.1 Example of a fresh skin wound on the medial surface of the right hock, with sharp edges, caused by a metal gate. The wound was partially closed primarily, leaving its ventral extent unsutured to allow drainage. A vertical mattress suture pattern, with tubing used as stents, was selected to counter the tension that results from flexion of the hock. The sutured wound was then supported by a full limb bandage. Placing a bandage over stents can result in pressure necrosis, so the wound should be monitored closely for signs of this complication. Pressure on the bandage overlying the wound should be reduced to decrease the likelihood of pressure necrosis from developing beneath the stents. If damage to skin beneath the stents appears, the limb should be left unbandaged, or the stents should be removed in a staged approach. Delayed primary closure is defined as that carried out days after injury, but before granulation tissue begins to appear, usually 4–5 days after injury. Delayed secondary closure (secondary closure) typically refers to wound apposition, with suture, after granulation tissue is grossly apparent, usually more than 5 days after injury. Although others have suggested that delayed primary and delayed secondary closure be referred to simply as delayed closure,5 these forms of wound management are considered, in this chapter, as distinct because the presence or absence of granulation tissue exerts an influence on the method of closure.5 Delayed primary closure is often selected as an approach to manage fresh wounds that are moderately contaminated, contused, and swollen. Closure is achieved in a fashion similar to primary closure but after a short duration (1–3 days) of treatment aimed at diminishing swelling and/or contamination. Recent meta‐analyses of the human medical literature suggest that delaying primary skin closure may reduce the incidence of infection of contaminated and dirty abdominal incisions (mostly relating to complicated appendicitis), but this trend cannot be confirmed due to a paucity of well‐designed, large‐numbered, randomized clinical trials.6,7 No comparable studies have been conducted on horses to determine whether delayed primary closure leads to an outcome superior to that associated with primary closure of contaminated, accidental wounds. Nevertheless, experience in the human medical field suggests that the low incidence of infection of dirty wounds managed by delayed primary closure is attributable to repeated irrigation and debridement of the wound prior to suturing, rendered possible by delaying closure.7,8 Delayed secondary closure is usually appropriate for wounds that are contaminated or have a compromised blood supply. The wound is closed after it develops a healthy bed of granulation tissue. The granulating wound often must be revised to enable firm apposition of the skin edges. Granulation tissue is debulked, if necessary, the skin surrounding the wound often must be undermined, and a thin margin of skin is removed from the periphery of the wound to create fresh edges that are more likely to heal once apposed and sutured. Examples of wounds that are usually amenable to delayed secondary closure are heel bulb lacerations and wounds of the body that can be revised (Figure 8.2). “Degloving” injuries, which usually involve the metacarpal/metatarsal area, are often very contaminated and have a compromised blood supply, and so, theoretically, these wounds would be good candidates for delayed secondary closure. The metacarpal/metatarsal area, however, has very little redundant skin, and consequently, revising these wounds in view of performing a delayed secondary closure is often difficult or impossible. Based on personal experience, the author recommends that degloving wounds of the metacarpus/metatarsus be sutured as early as possible, either via primary or delayed primary closure, to avoid the extended duration associated with second‐intention healing and to maintain a humid healing environment to prevent desiccation of structures exposed by wounding, such as bone and tendon.9 Because degloving injuries that are sutured are at risk of suffering partial or complete dehiscence as a result of wound infection,10 owners must understand the reasons for electing this approach and should be made aware of the possibility of failure of the primary closure. More information on the management of degloving injuries can be found in Chapter 14. Figure 8.2 Heel bulb laceration of several days duration that was managed by delayed secondary closure. The cause was barbed wire. The horse was severely lame on the affected limb, and the wound was exudative and swollen, indicating infection. Second‐intention healing (i.e., by formation of granulation tissue, contraction, and epithelialization) is often the favored approach for the management of large wounds located over highly mobile regions (e.g., pectoral, axillary, groin, gluteal, etc.) (Figure 8.3) or for wounds that cannot be closed because of damage to surrounding soft tissues or because of loss of skin. These conditions are, unfortunately, common in horses. Skin grafting is useful in cases in which the tissue deficit exceeds the capability of wound contraction and epithelialization. For more information regarding skin grafting, see Chapter 18. Reconstructive surgery and revision of scar tissue may be used to achieve a superior cosmetic and functional outcome in a wound that has already healed. For more information regarding reconstructive surgery, see Chapter 10. Figure 8.3 Example of a large wound in the axillary area that was managed by second‐intention healing. At the time the horse was presented, granulation tissue had already filled the wound bed, and subcutaneous emphysema, which commonly accompanies wounds in the axillary region, was not observed. Examination and preparation of the wound are the first steps required to identify the most appropriate method of closure (See Box 8.1). The horse should be sedated to facilitate the examination, and analgesic medication may also be administered systemically, if required, to improve the patient’s comfort. More information on the effects of anti‐inflammatory drugs on wound healing is available in Chapter 4. Antimicrobial drugs are commonly included in the management regimen when treating wounds at risk of becoming infected, such as contaminated wounds, penetrating wounds, wounds with devitalized tissue, or open fractures. Acute or superficial wound infections in horses are usually the result of one dominating microorganism. Conversely, chronic or deep wound infections in horses are often polymicrobial.10,11 Antibiotics selected for use should reflect this microbial epidemiology,10,11 bearing in mind the emergence of antimicrobial resistance and the importance of using a narrow‐spectrum antibiotic, the selection of which is based on antibiotic sensitivity testing. Table 19.1 in Chapter 19 lists the common bacteria isolated from various types of wounds in horses, and Table 19.3 in Chapter 19 lists likely antibiotic sensitivities for each pathogen, as a basis for empiric antimicrobial therapy most probable to be useful. For a full discussion regarding the use of antimicrobial drugs for the management of wounds, the reader is referred to Chapter 4. Whether local administration of an anesthetic agent to desensitize the wound precedes or follows clipping of hair at the wound’s periphery and cleansing of the wound depends on the horse’s demeanor, the condition of the wound, and of the skin surrounding the wound. Ideally, the local anesthetic agent is administered after clipping and cleansing, but for horses that do not tolerate clipping and cleansing, the area may be desensitized after removing only gross debris. The wound may be desensitized by local, regional, or intralesional anesthesia. A wound on a limb can be desensitized by placing a line or ring block proximal to the wound or by administering regional (i.e., perineural) anesthesia proximal to the wound. For wounds of the body, the local anesthetic agent can be placed in a curved line cranial to the wound; the line is extended slightly caudally around the edges of the wound to ensure complete desensitization. Wounds of the head may be desensitized by administering the local anesthetic agent subcutaneously, caudal to the wound or with more targeted perineural anesthesia.12 Alternatively, a wound may be desensitized by direct intralesional placement of local anesthetic solution, although this should be done only after clipping and cleansing to minimize seeding of contaminants into deeper tissues. Two percent lidocaine or mepivacaine hydrochloride is commonly used as a local anesthetic agent and provides desensitization for a sufficient time for examining, debriding, and closing the wound. Mepivacaine, rather than lidocaine, should be used if the wound is extensive and apt to require a long intervention because desensitization resulting from mepivacaine lasts longer than that from lidocaine. The duration of anesthesia, however, depends on the location and the vascularity of the wounded area; consequently, the horse must be monitored closely for signs of discomfort during manipulations. Commercially available topical anesthetic creams or gels [e.g., Emla CreamTM, containing lidocaine (2.5%) and prilocaine (2.5%), Oak Pharmaceuticals] may provide sufficient desensitization of the wound because they have been shown to be as effective as infiltration with lidocaine in providing desensitization when performing episioplasty in mares.13 The slower onset of blockade provided by creams and gels (around 45 minutes), however, may limit their usefulness. General anesthesia is rarely required for initial examination and cleansing of the wound, but it may be useful for foals or for horses with a large and heavily contaminated wound, or for horses with a wound that involves a critical structure underlying the skin, such as a joint or tendon. General anesthesia, administered intravenously, may be used for all stages of examination, cleansing, and treatment if the horse is not accustomed to being handled, to ensure the safety of both the horse and the veterinarian. The skin adjacent to an open wound should be prepared as for aseptic surgery; this is usually done immediately prior to cleansing and debriding the wound. Involved personnel should don sterile gloves, after surgical hand antisepsis, to avoid further contaminating the wound. Three types of solutions are available for surgical hand antisepsis: aqueous scrubs; alcohol rubs; and alcohol rubs containing additional active ingredients. Although aqueous scrubs containing chlorhexidine and povidone–iodine (PI) have withstood the test of time, newer alcohol‐based rubs offer the advantage of rapid and immediate action, as well as reduced skin damage after repeated use. The clinical use of an alcohol‐based hand rub (Avagard, 3M Healthcare) was tested in the environment of an equine hospital and found to be as effective for presurgical hand antisepsis as the traditional water‐based chlorhexidine hand scrubs in reducing the number of colony‐forming units on the hands of surgeons prior to elective equine surgeries.14 Verwilghen et al. recently found that a commercial alcohol‐based hand rub (Sterillium, Bode‐Chemie) was as effective as 4% chlorhexidine digluconate (Hibiscrub, Regent Medical) and superior to 7.5% PI (Vetclean, Ecuphar) in reducing the number of colony‐forming bacterial units on the hands of equine and small animal surgeons and showed a superior sustained effect.15 There are important differences between the various commercial alcohol‐based hand rubs (concentration of alcohol, method of application, etc.); consequently, the manufacturers’ guidelines for time and method of application should be followed. Using an alcohol rub may be more practical than using an aqueous scrub for achieving hand antisepsis in the field situation. Sterile lubricating gel should be placed within the wound prior to clipping the hair on the surrounding skin. This prevents tiny hairs from accumulating within the wound, and the gel can be easily rinsed away after clipping. Placing gauzes impregnated with isotonic saline solution within the wound prior to clipping is an acceptable alternative to using a gel. The skin surrounding the wound should be scrubbed using an antiseptic detergent, such as chlorhexidine or PI, and then rinsed with sterile isotonic saline solution. Because surgical scrubs contain a cytotoxic detergent, they should not be allowed to contact the wound’s surface. For more information regarding skin preparation (for both the surgeon and the patient), the reader is referred to Chapter 4. Wound cleansing involves the use of fluid, applied in a steady flow across the surface of the wound, to remove loosely attached cellular debris, contaminants contained in exudate, and residue from topically applied wound‐care products.16 The technique is also referred to as “irrigation” and this term is used interchangeably with wound cleansing within this textbook. Irrigating the wound is more effective than scrubbing its surface with gauze or sponges; the negative effects of the latter technique, which damages the fragile new tissues in the wound bed, no doubt outweigh the benefits of decreasing contamination of the wound.17,18 Pressurized wound irrigation is likely to be beneficial in reducing the bacterial count, as well as in eliminating dirt and tissue debris in heavily contaminated wounds,19 such as those often seen in equine practice. In the author’s experience, pressures ranging from 8–15 psi are beneficial in achieving the objectives of irrigation when managing wounds in horses; moreover, wound‐care experts in the field of human healthcare claim that this range of pressure is strong enough to overcome adhesive forces of bacteria.20 Pressures of 8–15 psi are unachievable with gravity flow but can be attained by using a 35‐ or 60‐mL syringe and an 18‐ or 19‐gauge needle.21 Commercial irrigation devices are capable of delivering fluid under pressure and may be interesting alternatives. The volume of fluid should reflect the size and the degree of contamination of the wound. Irrigation should continue until the wound is rid of gross contaminants but stopped before the tissues take on a gray, waterlogged, edematous appearance. The wound should initially be cleansed using sterile, isotonic, non‐toxic fluids, delivered at body temperature. Unadulterated polyionic fluids, such as 0.9% saline solution or lactated Ringer’s solution, are readily available and certainly appropriate but can be expensive when large volumes are required. A systematic review, conducted in human medicine, concluded that tap water offers a low‐cost yet equally effective irrigation solution for acute and chronic wounds and does not seem to increase the risk of infection or delay healing beyond that which occurs when using isotonic saline solution.22 The authors of that review, however, caution that the tap water must be of good quality (i.e., potable).22 If large volumes of tap water are used, the wound must be monitored carefully for the development of edema. Some veterinarians perform an initial cleansing with tap water to remove the gross contamination of dirt and debris and then use polyionic fluids for a final irrigation, commonly performed in conjunction with some debridement. Some veterinarians may opt to add an antimicrobial drug to the irrigation fluids when cleansing chronic or severely contaminated/infected wounds. Antiseptics have a broad range of activity and are less likely to induce bacterial resistance than are antibiotics. Nevertheless, concentrations of PI or chlorhexidine must be kept very low to avoid the toxic effect of the antiseptic on cells and deleterious effects on healing, though what constitutes an ideal concentration remains controversial.23–25 The concentration of PI should not exceed 0.2% (20 mL per litre of fluid), and that of chlorhexidine should be 0.05% (25 mL of the 2% concentrate diluted with 975 mL of fluid).20,25,26 The addition of an antibiotic to irrigation fluids goes against current antibiotic stewardship, except possibly when cleansing wounds suffering from ischemia or in which the presence of a biofilm is suspected.10,11,27 The earlier a wound is cleansed the better, because in chronic wounds, bacteria may have formed a biofilm resistant to mechanical disruption. After a biofilm has formed, debridement is more effective than irrigation in ridding the wound of bacteria.10 The reader is referred to Chapters 4 and 5 for more information regarding techniques of wound cleansing and solutions used for irrigation. Debridement, ideally performed simultaneously with irrigation, consists of trimming jagged skin edges and removing necrotic debris and heavily contaminated tissue to reduce the bacterial load of the wound, thereby enhancing healing. Although autolytic debridement occurs naturally, wounds of horses are often so heavily contaminated that this particular mode of debridement is rapidly overwhelmed, making a complementary means of debridement necessary. Sharp surgical debridement, using a scalpel, a curette, or a hydrosurgical device,28,29 is an excellent method for rapidly cleaning wounds containing a large amount of devitalized tissue and/or bioburden and is less traumatic than is scraping the tissues with a scalpel blade or rubbing them with gauze. A narrow margin of skin at the wound’s edge should be trimmed; this is followed by removal of devitalized tissues, often using a “layered” approach that begins at the wound’s surface and progresses to its depths. The criteria governing removal of tissue are the tissue’s color and attachment; the aim of debridement is to remove discolored and poorly attached tissue, leaving only healthy, bleeding tissue. Nevertheless, skin of questionable viability should be spared because the horse does not have an abundant supply of it and because skin contributes the most to healing. Dressing‐enhanced autolytic debridement, enzymatic debridement, and biosurgical debridement (i.e., maggot debridement therapy) can be useful in wounds that are not closed primarily. More information regarding the various methods of debridement is available in Chapter 4. After the wound is clean, it is explored to determine the extent of damage to structures deep to the skin, including bone, tendon, ligament, synovial cavity, sinus, or body cavity (thoracic, abdominal), and to rule out the presence of a foreign body. A common method of exploration is to palpate the wound with a sterile probe or a gloved finger. Particular attention should be paid to the presence of fluid within a wound located near a synovial structure. Plain or contrast radiographic examination of the region surrounding a deep wound or a wound suspected of involving bone, can be helpful; ultrasound may be used to identify an accumulation of gas or fluid or the presence of a radiolucent foreign body. More information regarding the techniques of exploration can be found in Chapter 4. Involvement of deeper structures influences the approach to closing the wound. For example, primary closure may be preferred when the injury involves the thoracic or abdominal cavity, bone, tendon, paranasal sinuses, or synovial cavity, whereas delayed primary closure may be more appropriate if one or more of these structures are involved but heavily contaminated.
Approaches to Wound Closure
Summary
Introduction
Evaluation and preparation of the wound
Local anesthesia and analgesia
Cleansing and debridement
Surgeon and patient preparation
Wound cleansing/irrigation
Wound debridement
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