Why is wound healing so slow???
Sometimes we have to search to find a relevant topic to write about in the blog. This month it is a no- brainer; the stars have been misaligned or something worse and we have a dozen current cases with slow healing wounds. If you've never dealt with one on your own horse, consider yourself lucky!
Although horses are professionals at getting injured, most accidents result in mild abrasions that do not go all the way through the skin a.k.a. not full thickness. Handling a much larger laceration can be daunting; but all wounds heal with time. Understanding the underlying process will help guide you through the process of bandaging and wound treatments so that it's not just mystical lotions and potions.
Let's first start by addressing timing; if you find your horse with a freshly lacerated body part - please call your veterinarian to suture the wound. Wound location is the most important variable; you want to rule out joint or synovial structure involvement or communication first. If the wound is able to be sutured- the overall healing time will be greatly reduced! Sometimes we even suture laceration flaps that we know will likely dehisce (come apart) because they serve as a bandaid and greatly shorten the overall length of rest and bandaging.
Phases of Healing:
The first phase of wound healing is when exudate (can be serum, blood, or pus/purulent material) is coming from the wound bed. Depending on the size and extent of the wound this can vary in time from 1 day to weeks or more. Ideally the exudate helps healing and facilitates the next phase, granulation, but excess exudate can be problematic as well. Think flies, serum scald from drainage on skin, and wet bandages. In this stage, we rarely use topicals or ointments unless there is severe contamination in which case we may use medical grade honey or silver sulfadiazene cream. Using medicated bandages with impregnated antibiotics like Kerlix AMD bandages or Kendall COPA pads. Hypertonic saline dressings can also help to "draw" out exudate. This is also the stage where a culture and sensitivity can be run on the wound drainage to help guide antibiotic use.
Granulation tissue is the pink bubbly looking material that horses are experts at forming. So much so that it often becomes exuberant granulation tissue or proud flesh. If the wound has a large amount gap or "dead space" then we will use a counterirritant such as scarlet oil to speed the formation of granulation tissue. Ideally, horses would granulate in the void right up until it's flush with the surrounding skin edges; however, often times the granulation tissue starts to protrude above the skin edges. A wound with proud flesh will not heal until the granulation tissue is addressed. The good thing about granulation tissue is that it's extremely resistant to microbial and fungal infection. When too much of a good thing occurs, we either have to debride/trim the tissue back to flat with skin edges or use a steroid ointment. In general, keeping appropriate bandages on and limiting motion in the healing area will help to reduce the risk of proud flesh formation. A good rule of thumb is that any wound below the carpus (knee) or hock on a horse is going to be at risk of proud flesh formation. Wounds over muscle areas (the rest of the horse's body) with good blood supply don't tend to have the same issue.
3. Epithelialization/Wound Contraction
The final phase of wound healing can be the most prolonged but gratifying part of the process. Once you have a healthy pink granulation bed that's flat, the skin edges will heal from side to side and eventually contract until the whole wound is healed. Contraction takes time, and keeping the wound bed moist seems to be the best way to keep healing active. The use of hydrocolloid or hydrogel dressings (Cica-Care, etc) can help achieve this task. One of the most common hindrances of contraction is going back to phase 2: excessive granulation tissue. Make sure you're addressing any other underlying factors such as Pars Pituitary Intermedia Dysfunction a.k.a. Cushing's.
Let's summarize by stating one super important rule that I learned from Professor Dean Hendrickson at Colorado State University: "Don't put anything in a wound that you wouldn't put in your eye." Which is super helpful to remember when you're standing at Murdoch's wondering which Wonder Wound spray or ointment to purchase. Most products for horses on the market are caustic and can increase proud flesh formation. Dilute betadine (tea colored) saline is the best wound wash to have on hand for new wounds; it decreases contamination and isn't inflammatory to tissues. Then ask your veterinarian for input on what topicals or dressings could help healing.
In extreme cases, we can use skin grafting, regenerative therapies, shockwave therapy, and/or cold laser systems to improve healing time. Even hyperbaric chambers have been used to help wound healing because it can be so lengthy and involved. Just remember- if in doubt, ask for help from a professional!