WOUND HEALING

One thing certain about life: we can all expect to experience some wounds. The good news is that we are fundamentally designed to heal.

While the statement above has philosophical implications, we will be sticking to the physical ones in this discussion. In particular, we will be considering the skin and the wounds experienced in the skin and underlying tissues. 

Drawing showing the different layers of the epidermis (skin)
(Photo Credit: Public Domain via Wikimedia Commons)

The skin and its associated tissues exist in layers: the epidermis on the outside (layered in and of itself), the dermis below, the subcutis below that, and fat and muscle below that. When we are injured, these areas may be cleanly cut, punctured, scraped, ulcerated or even burned. These wounds can be sterile, unclean (relatively clean but not sterile), or even heavily contaminated. The body is designed to address all of these situations and often, as caregivers, we can help.

The healing process starts as soon as the wound is inflicted.

There are four phases of wound healing: Inflammation, Debridement, Repair, and Maturation.

INFLAMMATION (Starts immediately)

This is the first phase of healing and is all about controlling bleeding and activating the immune system. Without going into too much biochemical detail, blood clots are forming and blood vessels are constricting to limit blood loss in the area of the wound. This process also calls in “clean up” cells of the immune system to address contaminating bacteria and any dead tissue.

DEBRIDEMENT (Starts in a few hours)

Wound fluid, dead tissue, and immunologic cells form pus which is designed to flow as a liquid from the wound and carry debris with it. The cells that were called to the wound in the inflammation phase are now actively working on consuming dead tissue and cleansing the area.

REPAIR (Starts in a couple of days)

Collagen begins to fill in the wound to bind the torn tissues, a process that will take several weeks to complete. New blood vessels begin to grow into the area from the uninjured blood vessels nearby. The wound edge begins to produce “granulation tissue,” the moist pink tissue that will ultimately fill in the wound. The wound will actually shrink in a process called “wound contraction” so that new skin can form and cover it.

MATURATION (Starts in 2-3 weeks and can take months or even years)

Once plenty of collagen has been deposited, the final phase of scarring can form. The scar becomes stronger and stronger over time as new blood vessels and nerves grow in and the tissue reorganizes. The final result will never be as strong as un-injured tissue but should ultimately achieve approximately 80% of the original strength.

SECONDARY INTENTION

If the wound cannot be closed with sutures (it is too big, there is too much tension on the wound margins pulling them apart, the wound is too infected etc.), then a process called “second intention” comes into play. This is the part of wound healing where granulation tissue must form to fill in the gap. Once the wound is filling with granulation tissue, contraction is soon to follow which means the wound will be getting smaller and smaller. Eventually it can be allowed to simply close on its own or, when it is small enough, the margins can be trimmed and the wound surgically closed by primary intention for a smaller scar and better fur coverage. In the right circumstances, skin grafts can be applied but only if a healthy granulation bed is present.

HOW CAN WE HELP?

The body is actually pretty good at healing but there are some things that can go wrong as well as ways that we can facilitate the healing process.

• Deeper pus pockets must be drained. Eventually these will probably rupture out on their own (it can be a disaster if they rupture in instead of out), but often they will take a great deal of overlying tissue with them if left to their own devices. If the pus can be drained by lancing and flushing, this will usually prevent a large tissue slough if the abscess is allowed to rupture on its own. Sometimes in-dwelling drains must be placed surgically to assist in removing harmful fluids.
• The wound must be kept moist. This can be accomplished with bandages and/or ointments. A moist wound has better blood flow and can complete the healing process more effectively.
• Gross contamination should be cleaned up. Dirt, hair, pus and other bacteria rich substances should be flushed from the wound. Antibiotics may be needed either orally, topically, or both to address infection.
• Dead tissue should be trimmed. If there is non-viable tissue present in the wound, it should be removed so the body will not have to liquefy it. This can be done through surgery, through special types of bandages or by topical applications depending on the type of wound.
• Wound enhancing topicals can be applied. There are a number of topical products touted to reduce infection and/or enhance the formation of granulation tissue. It often seems like new products are available annually so we will not attempt to review them all but your veterinarian may select one to potentially assist the body’s wound healing efforts.

First Aid Tip: If your pet’s wound is fresh and your pet will allow it, try to wash out large debris particles with tap water (saline flush as for eyes is even better as it is balanced for tissue exposure). Cover the wound with clean, dry bandage material, if possible. See your veterinarian for professional wound care.

UNHEALING WOUNDS

If a wound seems to be on-going, either making healing progress and then getting worse again or simply not showing signs of healing, then be sure to bring your pet to the veterinarian. Unhealing wounds may have tumor involvement or may simply be infected. Do not try to “do-it-yourself” and end up with an advanced and possibly untreatable problem.

Page posted: 11/15/2013
Page last updated: 5/1/2022