Nature wants to heal wounds, but horses have a particular problem with wound healing, particularly on the lower parts of the limbs, which results in the development of large fleshy outgrowths, known as proud flesh or granulation tissue.
Granulation tissue is a normal component of naturally healing wounds. Normal granulation tissue looks red-pink in colour and has a flat surface without obvious clefts or changes in colour. It is the base upon which the new skin surface cells are supported while they migrate across the wound to provide a healed surface (surface epidermal migration).
While these cells are moving across the wound, they produce chemical signals that encourage the cells in the granulation tissue to contract. This pulls the sides of the wound towards each other. This “wound contraction” is a really important aspect of wound healing. Not only does it reduce the distance the cells have to move, but it also hastens the closure of the wound and squeezes out any dead or foreign matter.
The combination of granulation tissue, epidermal migration and contraction form the main basis of wound healing. Once skin cells cover the surface of a wound, granulation tissue production is switched off and the process of deep remodelling and repair can proceed.
If the process of healing is impaired in any way, the delicate balance between the various processes can be upset. If contraction and the migration of epidermal cells are inhibited then the wound may get bigger because granulation tissue is the only active process in the wound.
There are several reasons why a wound fails to heal. Some of these are associated with the production of proud flesh. Infection, foreign bodies, dead tissues or movement within the wound site, chemical applications and poor blood supply to the wound are known to encourage granulation tissue and inhibit the spread of skin cells across the surface of the wound.
In a few cases there is no obvious reason for the problem but no matter how the problem develops, the principles of management are similar. Where proud flesh develops at sites other than the lower leg regions, there is usually a definable cause.
Proud flesh: treatment and aftercare
A wound with an excess of granulation tissue must be surgically treated. Usually, this involves cutting back any excessive tissue. While this is invariably a very bloody business, it is usually painless because granulation tissue does not have any nerves or nerve endings.
The cutting back of proud flesh can often be done in a standing sedated horse without any need for local anaesthetic. However, general anaesthesia will be needed when surgery is required to deal with very extensive proud flesh and the aggressive control of the copious bleeding that results.
Surgical debridement (cutting back) can serve several purposes. It reduces the bulk of the wound and, at the same time, will remove many of the “blocks” to healing. It is common practice to cut the proud flesh back to just under the skin level. This may allow the skin edges to contract and cells to migrate across the margin of the wound.
However, where proud flesh has been present for some time, the margin of the wound could be unhealthy and the sensitive edges of the wound may have to be cut back. Treatment is focused on creating a healthy wound that wants to heal.
Careful wound dressing management immediately after such surgery is vital — dressings are usually changed at 24hr. At this stage, the vet will reassess the wound and make a decision as to the likelihood that it will heal naturally. Sometimes, immobilisation of the wound site under a firm bandage or even a plaster cast is needed. Infection may need to be controlled with antibiotics.
If the wound shows evidence of healing over the next four to seven days, treatment is continued. But in many cases the process of healing can be hastened by the simple expedient of skin grafting. The easiest form of this elegant yet simple procedure is the use of small skin pieces removed from a healthy site (often the side of the neck under the mane) and depositing these into the granulation bed.
This “imports” normal skin with a strong tendency to heal, and within a few weeks the tiny islands of new skin will be visible in the bed of granulation tissue. The grafts encourage the wound to contract and reduce the flow of new blood vessels, thus encouraging the spread of skin cells across the surface of the wound.
If skin grafting fails, the possibility of other wound healing complications must be considered.
Prevention of proud flesh
Prevention of proud flesh is easier said than done, but it is clear that a healthy, uninfected, clean wound that is properly managed from the outset has fewer tendencies to proud flesh production.
Healing relies upon the migration of the delicate skin cells, so repeated application of strong chemicals and even repeated washing and rubbing of a wound stops these cells. Without the skin cells, the field is clear for granulation tissue to be produced. Nature does not then have anything to stop the wound from over-producing this highly vascular tissue and large volumes of proud flesh are often produced.
Many wounds that have delayed healing have a history of ill-advised interference. A trivial wound may never heal and, remarkably, some wounds heal when we expect that there will be a delay at best. Early action must be taken to address any inhibitor of wound healing.
Horse & Hound (25 November, ’04)