Granulation tissue is the smooth, pink, shiny tissue that forms over the bed of an open wound in the initial stages of healing. When all goes well, this tissue stays even with the level of the skin. As healing progresses, it begins to shrink and the skin edges grow closer together until they meet in the midline, with only a thin layer of pale granulation tissue, i.e. a scar, remaining.
Proud flesh is granulation tissue gone wild. It grows up higher than skin edges and in excessive amounts that keep the skin edges apart. The surface may be smooth or bumpy, even cauliflower-like. Proud flesh is limited almost exclusively to the legs at or below the knee and hock. Interestingly enough, it’s usually only a problem for horses. Ponies aren’t frequently plagued by proud flesh.
The condition is similar in many ways to a human form of abnormal scarring called keloid formation. Although treatment of both the human form and equine form is difficult and frustrating, it can be done successfully, and the human research is helping to direct veterinary studies.
Some of the most recent information that helps us to understand proud flesh, and some treatment options include:
• Inflammatory Responses
The first stage of healing after an injury involves an inflammatory response. This ”cleans up” any foreign material, dead tissue and bacteria in the area, eventually sets the stage for production of tissue growth factors that trigger healing.
A 2003 study from the University of Utrecht, Netherlands, found that ponies have a much stronger initial inflammatory response to wounds both on the body and on the legs than horses do.
This was a good fit for the data from a 2001 study performed at the same university, also published in the Equine Veterinary Journal, that showed fibroblasts (connective tissue/scar producing cells) from horses and ponies had the same inherent capacity to contract (”shrink”), and that leg and upper body fibroblasts did not differ.
That study had concluded that there must be something different about the chemical environment of the cells to explain why they behaved differently.
With the results of the studies above, the question then becomes why do ponies have a stronger inflammatory response in their leg wounds, and why do horses only have frequent problems with proud flesh in their lower legs’
One possible explanation is poor delivery of blood to the healing tissues. This got a bit confusing because proud flesh has more blood vessels than normal scar tissue, bleeds more easy and was found to have higher levels of growth factors that stimulate blood vessel growth. That seems contradictory but those same high levels of blood vessel growth factors had been found in human keloids, too.
Turns out the reason the levels of growth factors for new blood vessels is so high is that the cells lining the existing blood vessels are swollen to the point they are restricting or even cutting off blood flow to the cells. The blood is making it into the larger vessels, but not all the way through down to capillaries where the cells actually get fed.
A study from the University of Montreal, just released in the Canadian Journal of Veterinary Research, found exactly the same thing in horse wounds. The tiny vessels supplying oxygen and other nutrients to the cells had swollen linings and were partially or completely blocked.
The best way to minimize the chance of proud flesh developing is to have wounds sutured closed shortly after they occur. Unfortunately, the skin of the lower legs is pulled tight and there sometimes isn’t enough healthy skin left after a wound to do this.
Bandaging has become a bit controversial since a 2003 study in the American Journal of Veterinary Research found that bandaged wounds were actually more likely to develop proud flesh. They also found that as long as the proud flesh was removed as it developed, those wounds healed as well and as quickly as ones that did not develop proud flesh. While this study does suggest that bandaging of fresh wounds on the lower legs might not be a good idea, most vets do continue to use pressure bandaging, after removing the excess granulation tissue, when treating older wounds that have developed proud flesh.
Surgical removal of human keloids isn’t recommended, because they often grow back larger, but it’s an important part of the treatment of proud flesh. The veterinarian will use a scalpel to shave off the layers of tissue that are above the level of the skin. This causes bleeding but isn’t painful since the tissue has no nerve endings.
• Surgery Alternatives
An alternative to surgery that has been around for a long time is the use of caustic materials that dissolve the excess tissue, usually copper sulfate powders or ointments such as Proudsoff ointment from Creative Science (check with your local dealer), about $5.50 for a 3 oz. jar, or Farnam’s Wonder Dust Powder (www.farnamhorse.com 800-234-2269) about $5/4 oz..
To use these products, it’s necessary to clean the area then use a gauze sponge briskly across the surface of the granulating tissue, until there is some oozing of blood. Repeat this daily until the tissue is down below skin level and the wound starting to shrink.
• Silicone Sheets
Although how they work is unknown, there is some evidence that applying sheets of silicone may help prevent or shrink human keloids. A 2005 University of Montreal study tried this with surgically created lower-leg wounds in horses and found the silicone helped prevent excessive granulation tissue when compared to conventional bandaging. However, this approach still needs to be compared side-by-side to wounds that receive no bandaging at all since other studies found conventional bandaging on fresh wounds may increase proud flesh. The jury is still out on this approach.
• Preparation H
The human hemorrhoid cream, Preparation H, was evaluated as a wound treatment in a report presented at the 2005 meeting of the Italian Society of Veterinary Practitioners (SIVE). Those researchers described more rapid healing of surgically created open wounds on the lower leg when they were treated with Preparation H. Why this would help isn’t immediately clear but keeping the wounds pliable may be a factor.
• Other Topical Treatments
A variety of topicals, including antibiotics, propylene glycol gel (Solugel by Johnson and Johnson Medical) and collagen gels, have been evaluated on lower-leg wounds and not found to have any effect one way or the other on healing and granulation tissue formation.
Put It To Use
• Wounds on the lower legs of horses are susceptible to developing excessive granulation tissue/scarring, commonly called ”proud flesh.”• Suturing of wounds shortly after they occur minimizes the risk, but isn’t always possible.• One Italian study suggests that use of Preparation H as a wound dressing that can result in more rapid healing. No effect has been found with topical antibiotics or other types of wound ointments and gels.• Bandaging open lower-leg wounds is controversial and may increase the risk of excessive granulation tissue , but this must be weighed against the need to protect wounds and keep them clean. If excess granulation does develop in bandaged wounds, it will not increase healing time if it is surgically removed.
• Surgical removal of proud flesh and/or use of caustic
powders is still the cornerstone of treatment.