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The different ways that wounds heal...

DIFFERENT WAYS WOUNDS HEAL

Before we discuss specific wounds, we will discuss the way that wounds heal.  The better we understand the nature of wound healing, the easier it will be to understand recommendations on treating specific wounds.  It is better to suture some wounds, while others may heal just as well with less stress to the patient by being left open and/or bandaged.  Soon we will discuss wounds in specific areas and the best approach for them.  But, just as in school, we must build a foundation before we can discuss specifics.

The ideal wound healing is by “first intention.”   First intention healing is when the skin edges reattach to each other.  This is our objective in wound management after the bleeding is controlled and contamination is removed.  This means the treatment of the wound must be started very soon after the accident.  The normal guideline is for closure of the wound within four hours.  Of course, we stretch this guideline by many hours.   The longer the time until closure, the more we have to do to counteract the retraction of skin, more debriding (removing dead tissue), and more care in preventing infection.

Once a wound occurs, the underlying tissue is exposed to the air.  This is destructive to this tissue and it rapidly dies.  This dead tissue must then be removed before closing the skin over it.  Dead tissue will be replaced by new tissue and is part of the drainage normal to all wounds.  If this dead tissue is trapped under a closed wound, it will build up in volume and put pressure on the overlying skin and the sutures holding it.   By removing the dead tissue, the fresh tissue beneath will form a bond with the skin through the blood components we discussed last week.

So to summarize:
First intention healing is accomplished by closing a wound while still fresh.
The skin will reattach to itself and the underlying (subcutaneous) tissue.
This may be aided with the help of a bandage, if it’s location makes this possible.
There is a minimum of scarring, and healing time is rapid, usually within two weeks.

If the wound is not found immediately, if procrastination interferes with the decision to seek treatment, or if the veterinarian is treating other emergencies, the time that lapses may make “second intention” healing necessary.  The horse has a unique approach to second intention healing, brought about by the need for rapid closure of the wound.  Back in the days before veterinarians, the inability to move out with the herd made the straggler an easy meal!  

Second intention healing occurs when the skin edges do not reattach to each other:
The blood resulting from the injury forms a clot.
The clot consists of a mesh of fibers that trap blood cells.
These form a dam to prevent further bleeding.
The fibers then contract, squeezing the “juice” out of the cells and forming a firm layer between the skin edges.
This layer helps to protect the subcutaneous tissue, and is the first step in second intention healing.
It also provides a healthy bed for new cells.
As these new cells form, they migrate towards the center of the wound, from the edges of the wound, in single layers.
To give you an idea of how thin this layer is,  just visualize the thinnest sheet of anything you can imagine: this cell layer is even thinner: just a few cells deep.
Once the first layer has developed, the next layer spreads out over it, and so on...
The clot holds the edges of the skin together, so that they do not spread any further, which would disrupt the clot and tear the cells free.

This sounds like a very fragile tissue covering the wound, and it is.  We must keep this in mind when we decide on treatment.  The initial treatment of the wound is necessarily:
to remove contamination
tie off blood vessels
trim away deteriorating tissue separated from the blood supply, and
apply the appropriate medication.

Each time the wound is even touched, literally, the outer cell layers are damaged.  Therefore, with our initial treatment we have disrupted the wound’s attempt to heal itself.  This is forgivable because the measures we then take will result in more efficient healing process.  From this point on we must use treatments that are beneficial to the wound and do not repeatedly destroy those fragile cells.  We will stop at this point with this morsel of food for thought:

What effect does our favorite treatment have on wound healing?

The list of products frequently used would be long, and in some cases amazing.  Hopefully, after the next article we will better understand the differences between natural healing and closure of the wound with the much slower scar tissue.

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