Nonhealing, or difficult to heal wounds in veterinary practice rarely pose an immediate risk to life; however, they can result in prolonged periods of veterinary care which can be very costly to the owner, uncomfortable and stressful for the patient, and potentially may result in euthanasia, or limb amputation in some cases.

There are numerous underlying causes of non-healing wounds and these can generally be divided into wound factors, patient factors and surgeon factors.

Wound Aetiology

Traumatic wounds may be more difficult to heal, dependent on the amount of damage caused to the surrounding skin. Also, when dealing with shearing injuries to the lower limbs, it is not uncommon for exposed bone to be present. Exposed bone is often encountered in distal limb degloving wounds and inhibits wound contraction and epithelialization. When allowed to heal by second intention, a bed of granulation tissue is required for second-intention healing to progress. During the wound healing process the majority of exposed bone will become covered with granulation tissue that arises from the viable periosteum or viable soft tissues adjacent to the bone surfaces, but there is always the risk of potential for osteomyelitis or sequestrum formation.

Contamination

Wounds are commonly classed as clean, clean contaminated, contaminated and dirty. It is important to determine the wound type from this perspective order to plan wound management. Only clean or clean- contaminated wounds should be considered for closure, with all other wounds requiring at least a period of open wound management to convert them to a clean-contaminated state, whereby they may be considered for closure.

Infection

When infection is present within a wound, this will cause inhibition of wound healing throughout all stages of the wound healing process. In order to identify infection a deep tissue culture should be obtained, this is preferable to a surface swab, as surface contaminants do not truly reflect infection. Infection is thought to be present in around 3% of all wounds at the time of suture removal, but infection rates are very variable, dependent on the degree of wound contamination. The aetiology of the wound also will affect the likelihood of infection occurring, with bite wounds having a high probability of infection due to the wound and its surrounding tissues creating the ideal environment for bacterial replication, along with poor drainage and a hypoxic environment. There are also surgical causes of infection: e.g., duration of the procedure, number of theatre staff, placement of surgical drains, suture material, underlying disease and the use of propofol, have all been associated with increased incidence in surgical-site infections in veterinary patients. The following approach has been recommended when dealing with wound infection:

• Investigate and address any underlying causes or contributing factors (e.g., malnutrition, anaemia, systemic disease).
• Maintain an ‘open’ wound environment, while fully exploring any pockets between soft tissue planes using an aseptic technique.
• Debride necrotic, devitalised tissue.
• Ensure thorough lavage of the affected areas with sterile isotonic fluids is performed.
• Obtain deep tissue samples for aerobic and anaerobic bacteriological culture and sensitivity testing.
• Commence empirical antibiotics (which can be changed according to culture results).
• Use bandaging to help with debridement (e.g., wet-to-dry bandages, or antimicrobial dressings).
• Continue open wound management until infection is controlled.

Wound Location

Wounds over joints present a challenge to healing in that they are subject to tension, compression, or shearing forces. The desired result of wound healing is for the two sides of a wound to heal together. If they are exposed to these forces, however, healing is impaired. Wounds over extension surfaces of joints (e.g., carpus, stifle) are subject to tension when joint flexion pulls wound edges apart. Thus, meticulous closure is necessary. Wounds in the axillary and inguinal areas may result from forelimb entrapment in a collar, vehicular trauma, burns, neoplasia, and infections. A primary factor in the impaired healing of such wounds is the shearing movement between the two wound surfaces as the animal ambulates. If such wounds have been present for a long period, it is possible that there may be infection with an atypical organism. Thus, a biopsy for culture and sensitivity testing is indicated.

Patient Factors

Underlying disease can be considered from two viewpoints: disease arising due to the trauma that caused the wound to be sustained, and pre-existing concurrent disease. Trauma can cause a number of issues which will have a knock-on effect in respect to wound healing times including shock, hypoperfusion, or dehydration, concurrent organ dysfunction (e.g., respiratory, renal, gastrointestinal compromise/damage). Patients may also have a concurrent disease process that can hinder wound healing. Hyperadrenocorticism (Cushing’s disease), diabetes mellitus, hypothyroidism, anaemia, are some of the disease processes, which can delay wound healing.

Nutritional Status

Adequate nutritional intake is vital for wound healing to occur, and should be a priority in all critical/ trauma patients. A catabolic state, attributable to malnutrition, is a major contributing factor to nonhealing wounds. In this condition, the body does not have the necessary protein and energy sources (fats and carbohydrates); therefore, existing stores of protein are broken down to maintain basal functions. This means, the increased calorific and protein demands for healing are not available, and the wound becomes quiescent. Glucose and protein are important for normal progression of wound healing. Glucose is the primary source of energy for leukocytes and fibroblasts. It is the integral molecule within the ground substance that is laid down by the fibroblasts. Deposition of this is necessary before collagen formation. Thus, glucose deficiency can affect collagen formation and wound strength. Depletion of protein stores can result in attenuated fibroplasia and prolonged healing time. It is vital that patients receive adequate protein levels, as they are necessary for animals undergoing healing. Sufficient protein levels help to prevent oedema and promote increased fibroplasia with increased wound strength. Zinc deficiency can result in lack of replication of epithelial cells and fibroblasts, causing a weak wound and lack of epithelialization. At the other extreme, an elevated zinc concentration can inhibit macrophages, decrease phagocytosis, and interfere with collagen cross-linking to have a negative effect on healing, and should be considered once other factors have been excluded. Ideally, the patient’s nutritional status on admission to the practice should be noted, including a body condition score and weight and this should be performed daily during the hospitalization period. If there is concern that the patient is unable to achieve its resting energy requirement alone, then assisted feeding techniques such as the placement of oesophagostomy or gastrotomy tubes should be commenced. Many of these patients will require general anaesthesia as part of a wound management protocol (e.g., wound debridement), and so the opportunity for the placement of a feeding tube is likely to be available. For patients requiring sedation or anaesthesia over a prolonged period of time, nutritional status may also need to be addressed in terms of prolonged periods of starvation prior to anaesthesia, and in these cases the patient’s calorific requirements should be calculated and compared against the actual calorie intake of the patient.

Surgeon Factors

The surgeon dealing with the wound management of the patient will ultimately have an effect on the likelihood of complications occurring. There are various issues that can be created during wound closure:

Postoperative Haemorrhage and Haematomas

The presence of postoperative haemorrhage, or haematoma formation, may delay wound healing by putting pressure on suture lines, providing a rich environment for infection and cause discomfort to the patient, thus resulting in self-trauma. In addition to the indirect effect on wound tension, there is experimental evidence that postoperative hematoma formation can directly affect flap survival where reconstructive surgery has been performed. Adherence to Halstead’s principles, including effective haemostasis, can help to prevent this. Minor incisional haemorrhage can be controlled with direct manual pressure for 10 to 15 minutes, but moderate to severe haemorrhage will require further intervention. Conservative management involving placement of pressure bandages, movement restriction and fluid deficit replacement can be instituted initially if the patient is stable. In more severe cases of haemorrhage, or those not responding to conservative management, surgical intervention may be required to identify the source and provide definitive haemostasis.

Wound Dehiscence

Dehiscence is defined as the breakdown of a surgically closed wound. Signs of a problem incision may be erythema, oedema or pain with signs of imminent wound dehiscence including necrosis of the skin edges, extensive cutaneous bruising, the presence of serum beneath the skin and serosanguinous discharge from the suture line. The most common causes of wound dehiscence include:

• Excessive tension
• lschaemic or necrotic wound edges
• Inappropriate suture material or suture pattern selection
• Accumulation of moisture leading to tissue maceration
• Underlying pocket of infection, necrosis, foreign body or neoplasia
• Lack or inappropriate postoperative protection/support (e.g., bandage, Elizabethan collar)
• Premature suture removal
• Delayed healing caused by administration of corticosteroids and other agents

Summary

When dealing with a non-healing wound it is important to re-assess the patient, and consider the various factors that could be contributing to the problem, in order to create an effective and appropriate wound management plan.