17 Aug 2015
Justine Kane-Smyth
Job Title
Figure 1. Thorough but gentle lavage, performed promptly using isotonic saline can be of enormous benefit.
It is probably fair to suggest horses possess a unique talent for getting themselves into all sorts of unimaginable trouble, picking up a myriad of injuries along the way.
Many practitioners would attest the most common equine emergency encountered in practice involves a wound. It has been reported 40% of horses in one UK population sustained traumatic injury within a 12-month period (Owen et al, 2012).
The folklore of equine wound management is shrouded in mystery, with various recipes for success passed down the generations.
While some principles have stood the test of time and deserve their place in contemporary wound management, others have been shown to be detrimental. There is a surge of interest in wound management that is transforming the way equine wounds are considered and treated. This article aims to explore how some of this new thinking may be implemented on a practical level.
Provided the wound is not found to involve any vital structures on initial assessment (Table 1), the following approach may be implemented and adjusted as necessary.
All traumatic wounds should be classified as contaminated at first, but, left unattended, infection ensues in the majority of cases. The first goal is to convert the wound to clean or clean-contaminated status. Debridement aims to remove all foreign material, devitalised, crushed tissues and reduce the bacterial load, while preserving all viable tissue.
Lavage is the simplest form of debridement and, if performed early, can greatly reduce contamination and bacterial numbers (Figure 1). However, it is important to remain sympathetic to the tissues, as aggressive lavage with excessive pressures can traumatise and “waterlog” tissues. A shower head, 30ml syringe with a 19G needle, or a one-litre water bottle with holes pierced in the lid, can be an ideal lavage system.
Tap water is noxious to fibroblasts, so isotonic saline (0.9%) is the ideal solution. It doesn’t necessarily need to be sterile – adding one tablespoon of table salt to 600ml water is inexpensive and easily done. If necessary, the wound may be cleansed with dilute solutions (0.05%) of chlorhexidine or povidone iodine, but this should ideally be followed by rinsing with saline to remove the detergents. All scrub solutions (that is, anything that lathers) are best avoided. The old adage “if you wouldn’t put it in your eye, don’t put it on the wound” applies here.
Autolytic wound debridement, otherwise known as allowing it to fester, is the most selective debridement method – preserving all vital tissue and healing factors. Leaving the naturally produced tissue fluid in contact with the wound allows leucocyte phagocytosis and enzymatic reactions to clear away necrotic tissue and microorganisms. The process is easily overwhelmed, however, and it is important to assist nature by using some form of physical debridement (lavage with or without surgical debridement) first.
Sharp surgical debridement is the next best option in terms of selectivity (Figure 2). Performed judiciously, it is the least traumatic option the clinician can implement. It is often best to be conservative initially, when the margins between the vital and devitalised tissues may not be clear. Always give tissue the benefit of the doubt; however, sequential repeat debridement, as and when necessary, can hugely improve the wound and hasten healing.
Mechanical debridement with gauze swabs or wet-to-dry dressings is the most traumatic method and is rarely, if ever, appropriate. It is entirely non-selective, removing not just contamination, but also vital healing factors and even fibroblasts. Additionally, the associated trauma is likely to create a vicious cycle of persistent inflammation.
Current opinion favours primary closure whenever possible, provided there is no gross evidence of infection, it is possible to clean the wound up well enough and there is sufficient viable tissue to close. However, it should be closed promptly – the 12-hour “golden period” is no longer considered relevant. Left open, the wound surface area increases during the first 24 hours due to skin edge retraction, which may be prevented by adopting this approach.
There may be greater risk of eventual dehiscence of the repair, but it offers the potential to salvage more tissue (skin in particular) and creates a biological bandage over subcutaneous tissues. Ultimately, the aim is to reduce the overall healing time, even if healing by second intention is required for some of the wound. It is important to manage the client’s expectations carefully – a forewarning of possible/likely breakdown will prevent disappointment.
Tension-relieving suture patterns are usually required and, even if there is no skin deficit, local swelling is often well established by the time the wound is examined. Guidelines for appropriate suture selection are listed in Table 2. Ideally, choose monofilament, non-absorbable material or absorbable suture that is monofilament or coated. Taking larger bites will minimise skin trauma and improve the holding strength of the repair, as the skin edges will be weaker for the first seven to 10 days.
Adding quills made from an intravenous giving set can help to dissipate tension and protect the skin edges when used with a mattress suture pattern (Figure 3).
If it is not possible to convert the wound to a clean or clean-contaminated status, or if infection is already established, primary closure should be postponed. Delayed primary closure may be considered once the wound appears healthy. By being initially patient, debriding as much as possible and allowing healing by second intention to begin, it may then be possible to sharply debride the wound and perform closure of at least part of it.
The aims of an appropriate dressing and good bandage are to:
Dressing technology is very sophisticated and advancing rapidly all the time. The selection of primary dressings available is, however, bewildering. While some are appropriate for a variety of wound environments, others have been specially designed for very specific circumstances and may be detrimental if used inappropriately.
A brief résumé of the more commonly used primary dressings are listed in Table 3.
Maintaining a moist wound environment is now considered of paramount importance. Maintaining optimum moisture at the wound surface should result in progressive re-epithelialisation in a healthy wound healing by second intention within 12 to 14 days. If the wound is desiccated, then moisture needs to be added – for example, using a hydrogel. If the wound is exudative, a dressing should be chosen based on its capacity to cope with the expected amount of discharge.
Consider what is going on in every part of the wound
Balancing act
Mix it up
Conditions within the wound change rapidly. Ideally, wounds should be reassessed frequently and the management protocol tweaked accordingly. The horse and the wound environment should be reappraised on each occasion to determine how to optimise conditions within the wound.
Implementing the rules listed in Panel 1 may be more labour intensive, but worth considering to potentially lessen the overall time for healing to complete.
The secondary layer holds the primary dressing in place and absorbs exudate. The number of layers should be sufficient to provide adequate support or immobilisation where necessary.
The third layer secures the bandage and can provide additional limb support. Careful application of firm, even pressure is important to avoid bandaging complications.
Bandages should be applied very carefully as horses are very prone to developing skin rubs and tendon bows that may produce lesions worse than the original injury. Particular care should be taken over bony prominences (Figure 4) and especially at the following sites:
Measures should be taken promptly to prevent further deterioration if rubs or bows develop. Affected areas may be offloaded or padded out, but it may be necessary to remove the bandage completely if they become severe.
Distal limb casts can be very useful, providing an economical method of immobilisation. Bandage casts are a more user-friendly alternative – a thin bandage is placed initially and then several layers of casting material applied on top. The cast may be split and reused, allowing the wound to be monitored more closely.
The potential for any factors that may impede healing (Table 4) should be considered and measures taken to eliminate (or at least limit) them in advance. For example, a wound that is initially infected and heavily exudative requires a primary dressing with sufficient absorptive capacity to prevent the wound and adjacent skin becoming macerated. It is important to recognise when the wound exudation subsides, as it may become necessary to provide some moisture to avoid desiccation.
If the wound is deteriorating or even if progress is just slow, critically analyse the situation to identify and then deal with any factors likely to delay wound healing.
Infection results in a prolonged and less effective inflammatory phase. Many bacterial species produce collagenases, which further contribute to delays in healing. Factors that predispose to infection and lead to persistent wound infection include:
Systemic antimicrobial therapy alone is often ineffectual and may result in selection for multiresistant bacterial strains. Physical removal of all foreign material is essential to reduce the bacterial load within the wound environment; this includes any foreign bodies and debris, but also all necrotic and devitalised tissue. Topical antimicrobial therapies (for example, manuka honey and silver-impregnated dressings) may then be appropriate to further reduce the numbers of microorganisms on the wound surface.
Intravenous perfusion techniques for regional administration of antimicrobials may also be considered, but are not always practical in the field as they should ideally be repeated at 36-hour to 48-hour intervals.
The maturation of fibroblasts to collagen-producing type cells is slower in horses than ponies, and particularly in the distal limb (compared with the trunk, for example) leading to problematic proud flesh. As the granulation bed becomes more prominent it impedes the already slow migration of epithelial cells across its surface and considerably contributes to delays in wound resolution. Measures to minimise and even prevent its development are listed in Table 5.
Once established, treatment is simple, but may need to be repeated every three to 10 days until healing is complete. The granulation bed should be surgically excised to approximately 0.5cm below the skin edge – paying particular care to avoid disturbing the epithelial margin (Figure 5).
Removal of darkly discoloured or irregular areas is also beneficial, aiming to create a smooth and uniform bed of tissue. The wound should remain bandaged to apply pressure to the surface and to provide limb immobilisation.
Topical therapies are generally not necessary and the majority are contraindicated. Judicious use of topical corticosteroid ointment can be considered in some situations (for example, where it is impossible to sufficiently reduce movement), but should only be used on a completely healthy granulation bed, avoiding the epithelial margins.
In cases where proud flesh becomes persistently problematic, consider the possibility of underlying disease – for example, sarcoid transformation or an unidentified focus of necrotic tissue.
Although, in principle, the same rules of wound healing apply, the hoof wall and coronary band region is specialised as it has a lower healing rate due to constant movement, its proximity to the ground and, therefore, contamination, and little scope for wound contraction due to the rigid hoof wall.
Preservation of the germinal layer of the coronary corium is essential for future hoof wall growth as serious damage may result in a permanent hoof wall defect. A partially avulsed hoof wall will not just heal back into place and should be debrided.
Casts are enormously beneficial for these injuries, providing effective immobilisation and accelerating healing. They should only be applied once infection is controlled and exudation is minimal to avoid soiling. The heel bulbs should be padded for protection and, provided the horse remains comfortable, the cast may be left in place for two weeks.
