MANAGEMENT Why proud flesh forms
Q:I am an original subscriber. Back in the early years---maybe 1979 or 1980--- EQUUS ran an article that described getting rid of proud flesh. It was very timely for me because my horse had just injured his hind leg with a nasty rope burn, and it was not healing. Instead, lumpy, yellow proud flesh had formed. I was at my wits’ end, but with the information in EQUUS, I was able to turn the situation around, and he healed quickly.
Recently my mare sustained a cut on her leg. Fortunately it’s not a huge wound, but I noticed over the weekend that it looked like proud flesh might be forming. I haven’t been able to get my veterinarian out yet, and I am not comfortable with some of the advice I have been getting from my friends, if you know what I mean.
Can you remind me again how to prevent proud flesh in a lower leg wound? And what should I do if I think I see it? This seems to be a topic that affects many horse owners. Cindy Loverde Baltimore, Maryland
A:For many years people held the perception that proud flesh was almost an inevitability in horses, particularly for wounds on the lower (distal) limbs. Textbooks and anecdotes dating to the mid-19th century describe the characteristic features of this distressing failure of wound healing. However, the fact remains that there is no evolutionary advantage for an animal to incur wounds that do not heal, so when proud flesh develops, it indicates some pathology in the wound bed.
In normal healthy healing, the bottom of a wound fills in with granulation tissue, a mix of blood vessels and collagen that has a bumpy red or yellowish appearance. The growth of granulation tissue is stimulated by an inflammatory response within the exposed tissues of the wound. Once the granulation tissue has filled the defect, the inflammation “switches off,” triggering other changes,
including the contraction of the edges of the wound (to begin closing the space) and the growth of epithelial (skin) cells across the gap.
Proud flesh occurs when a lowlevel inflammatory response continues within the wound. Without the “switch off,” the wound edges do not contract properly, new skin does not form, and granulation tissue continues to grow, sometimes forming mounds that rise above the surface of the surrounding skin. Once it reaches this state, both contraction and epithelialization become impossible, and the wound will not heal on its own.
Preventing proud flesh is far better than trying to cure it. Through research, I have identified 12 factors that delay or stop a wound from healing and cause proud flesh to form. These might occur individually or in combination. The reality is that, unless you remove any and all of these obstacles to healing and reinstate the normal inflammatory cascade with its appropriate “switch off” stage, the proud flesh will not go away. Here are the factors that contribute to proud flesh, along with advice for mitigating them:
• Infection. An infected wound is red and angry-looking, exuding pus and/or has a foul odor. For most wounds, topical antibiotics and antiseptics are not required to prevent infection. Simply cleaning a wound to remove debris is likely to be enough. Call your veterinarian if you cannot get an infection under control.
• Movement. Tissues that are stretched and pulled with every step will have a harder time healing. Bandages or casts may be needed to immobilize some wounds. Stall rest may help in some cases, too.
• Foreign bodies. Hair, sand or other contaminants in a wound can cause infection and slow healing. The horse’s body will attempt to expel the foreign
material but healing will be stalled in the meantime. Inspect the wound closely and remove any debris you find. Embedded objects can be difficult to detect. X-rays may be useful to find glass, bone chips or other hard debris.
• Dead tissue. Any tissue within a wound that is dead (necrotic) or is so damaged that it is likely to die quickly will prevent healing and must be removed. In smaller wounds, this may be accomplished by flushing with water or saline, but a veterinarian may need to cut away (debride) the affected tissue.
• Continued trauma. A wound will not heal if it is aggravated by chronic rubbing, scratching or other disruption whether from tack, bandages or activity. To encourage healing, take measures to protect a wound---for example, by keeping the horse on softer footing, giving him time off from training or using a different technique for bandaging.
• Loss of blood supply. Circulation is necessary to nourish healing tissues, but some injuries may compromise blood flow to the area. If this is the case, it may take longer to heal as the blood supply “grows back” into the wound bed.
• Poor oxygenation. To heal, wounds need oxygen, both from the blood supply and from the surrounding air. Leaving a wound uncovered exposes it to air, but bandaging has benefits, too: If a wound doesn’t receive oxygen from the air, the body may compensate by bringing in more through the bloodstream, and that supply will reach the deepest healing tissues. If you’re not sure which approach is best for your horse’s wound, ask your veterinarian for guidance.
• Missing tissue. If a significant amount of tissue was gouged out of a wound, healing will take longer as the normal granulation fills in the defect. Larger wounds may benefit from high-tech wound dressings that create biologic “scaffolds” to help new tissue fill in the defects more efficiently. Call your veterinarian for help with a wound like this.
• Poor health or nutrition. Malnutrition and illnesses such as PPID (pituitary pars intermedia dysfunction, also called Cushing’s disease) can reduce a horse’s immune function, which may slow healing and leave him more susceptible to infections. These days nutritional deficiencies are rare, but a horse does need adequate protein to build new tissue as he heals. Ask your veterinarian to review your horse’s diet if you think he might need more protein.
• Environment. Conditions inside and outside of the wound can influence the rate of healing. Weather extremes--hot or cold, wet or dry---affect the activity of the cells in the wound. Inside the wound, pockets of pus or other fluids or
an uneven tissue bed can impede healing. Each condition needs to be addressed appropriately---such as with warm, moist dressings in a cold dry environment, or by bringing the horse into a dry stall during rainy or humid weather.
• Tumor transformation. In some cases, what looks like proud flesh is actually a tumor. A horse who has sarcoids somewhere else on his body may also develop a sarcoid in a wound. This can look exactly like proud flesh, but it’s important to distinguish between the two conditions because the treatments are diametrically opposite. While proud flesh needs to be debrided, trying to cut out a sarcoid only makes it worse; instead, the tumor needs to be treated with chemotherapy. I think it’s a good idea to have a veterinarian test every suspected case of proud flesh, just to make sure it’s not a tumor.
• Iatrogenic idiocy. In my experience, one of the most common inhibitors of healing is iatrogenic idiocy---my own term for “unnecessary things people put on their horses,” including commercial products as well as homemade preparations that are applied to a wound in the expectation that it will help it to heal. Almost all of the applied materials act as an inhibitor of healing and bias the wound toward a non-healing state. Antiseptic solutions and manuka-honey dressings have benefits in certain situations, but neither is appropriate for use on fresh wounds.
Most wounds need nothing more than flushing with warm water or saline and maybe a simple dressing that contains a water-based gel to keep the surface of the exposed tissues evenly moist. Likewise, once healthy healing is underway, avoid interfering. Scrubbing or pulling off scabs can damage fragile new tissues.
The objective of a clinician attending a wound is to convert an accidental wound into a surgical wound and then close it with appropriate measures to address any of the other inhibitors that could be present. If this is done, the wound will heal---often incredibly well.
Once excessive granulation tissue forms, the wound needs an assessment, based on the healing-inhibitors I have outlined, to determine what went wrong. When any problems are corrected, the wound may be left to heal in a natural way, or, in some cases, surgery
may also be needed to cut away the excess tissue and “reset” the wound to a state where healing can proceed normally. Your veterinarian or veterinary technician can usually give you appropriate guidance.
On the other hand, proud-flesh treatments that attempt to burn back excess tissue with acid, copper sulfate or another caustic material are doomed to fail. Applying caustic chemicals or strong antiseptics and disinfectants do nothing to help the wound---indeed, these treatments would probably cause significant harm.
Thus I recommend that you think very carefully about how you manage this---or any---wound your horse sustains. Treat every one, large or small, as you would treat similar wounds on your own body: If it’s minor, flush the wound, keep it clean and determine whether a bandage would be beneficial; if it is significant, get the advice of a professional and take the appropriate action to get the wound to close quickly and effectively. The longer the wound persists, the bigger the scar will be, and the greater the challenge and the costs, both in terms of subsequent veterinary care and the loss of use. Derek Knottenbelt, BVM&S, PhD,
DECEIM, DACVIM Equine Medical Solutions Stirling, Scotland