Amnion: A Miracle of Birth for Wound Management
We still don't know how it happened. The only clues were a smear of blood on the inside of the stall door and a bent handle on the water bucket. We could only guess that sometime during the night our Morgan yearling, Minnie, had rehearsed one of her airs above the ground and somehow managed to come down with her left foreleg caught between the bucket and the wall. Not knowing the cause wasn't nearly as gut-wrenching as our failure to notice the injury as soon as we arrived at the barn. As usual, our morning chores were done in predawn darkness, and Minnie, with a gaping laceration and two dangling flaps of skin on her cannon bone, was turned out in a muddy spring paddock. The guilt still haunts us.
It wasn't until feeding time that evening that we saw the laceration, and it might have been missed even then if I hadn't noticed Minnie shivering out of the corner of my eye. We called the veterinarian and started cleaning away the mud-laced-with-manure mixture that caked Minnie's legs up to her knees. My husband, Jim, ran relays to the house for hot water while I sponged and flushed. By the time John Cole, DVM, the on-call veterinarian that evening, arrived, we knew this was a serious injury. The total surface area was probably 20 square inches; the wound had been grossly contaminated and was already at least 12 hours old. Cole sedated Minnie and took over the cleaning. As extensive as the skin damage was, the tendon appeared to be uninjured. That was the good news. The bad news was that the edges of the torn skin were curled and dried and did not appear viable.
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After considerable debate, we decided to have the skin flaps removed and allow the wound to heal by secondary intention, meaning that the deeper layers of flesh would mend first, then the skin would regenerate in the final stages of repair. Without the natural restriction imposed by the skin, this type of healing sometimes produces "proud flesh," excessive amounts of the shiny, pink granulation tissue that first fills gaping wounds. Lacerations on horses' lower legs are particularly prone to proud flesh, and we realized that our choice meant possible disfigurement and skin grafting at some point down the line. Yet the risk of infection after so much contamination and elapsed time made closing the wound with stitches an even greater and more immediate threat. Before beginning work on the wound, Cole injected her with a broad-spectrum antibiotic.
I watched quietly as the scalpel sliced away Minnie's future. Sired by a Grand Prix dressage stallion out of my best producer, she was destined for fame. An incredibly athletic filly, Minnie much preferred walking on her hind legs while her pasturemates played tag and other more fillylike games. She could trot 10-meter circles with her tail over her back and her nose on the ground, bouncing a foot with each stride. But her career as a dressage horse was fading with each stroke of the blade. "She'll make a dynamite broodmare," I kept telling myself.
The debridement complete, Minnie was bandaged with a standard three-layer dressing -- a nonstick pad against the wound, a protective layer of padding and an outer wrap. Cole left instructions for stall confinement and daily dressing changes. He also warned us we were facing many months of treatment even if the recovery proceeded without complication.
Four days after the original injury, Lou Calabrese, DVM, the equine specialist of the practice, examined Minnie's wound and was no happier than I about its appearance. Each dressing change revealed huge amounts of dripping exudate, and the proud flesh was already out of control. I didn't even want to look at the wound; looking Minnie in the eye was harder still. With some hesitation, I broached the subject of trying amnion dressings before the filly's condition got any worse.
I had learned of the practice of using this placental membrane, the source of the amniotic fluid that supports fetal life, as a natural bandage the previous year. One of my broodmares had developed severe purpura hemorrhagica, a hyperimmune reaction, after a mild bout of mastitis. The mare had survived, but large areas of hide had sloughed off her hind legs as a result of massive edema. At the time, with the mare near death, scarring was the least of our concerns, but once the mare recovered, I regretted having made no effort to promote cosmetic healing. A concerned friend had mentioned to her veterinarians at the Aeolian Veterinary Hospital that extensive scarring seemed inevitable if my mare managed to survive. They generously sent me several articles on wound healing, one of which dealt with the experimental use of amnion dressings on lower-leg wounds in horses.
Based on similar amnion use in treatment of human wounds, the study was conducted almost 10 years ago by veterinarians at Auburn University. They compared healing of surgically acquired lacerations dressed with standard bandages and managed in three different ways: no treatment, dressing with amnion, dressing with a live yeast-cell derivative (contained in a popular hemorrhoid ointment). The amnion-covered wounds had healed faster, with reduced infection and much less proud flesh, than the two other treatment groups.
But the Auburn study had been performed in a hospital environment by experienced technicians; could the procedure be adapted to a field situation and carried out by a layperson? Calabrese studied the articles overnight and gave me his blessing in the morning. He said he'd spread the word that I was looking for a fresh amnion suitable for my project. He was encouraging, but I couldn't help wondering if he was just trying to bolster my spirits; I don't think he really believed amnion could help this horrendous injury.
The phone was ringing the next day as I returned from work. Calabrese had just completed a neonatal exam on a Paint foal, and the mare had been passing the placenta as he was summoned to another emergency. He had asked the foal's owners to save the placenta for me and to keep it as clean as possible. I hurried to the home of these unknown benefactors, where, I'm afraid, I showed more interest in the placenta than the new foal.
I think I noticed a few green faces as I pulled out my scissors and chopped the amnion, the transparent innermost membrane of the placenta, free from the rest of the afterbirth and stuffed it into a plastic bag. With a quick thanks to the healthy colt and his mama, I was out the door with my prize.
Twenty-four hours later I had the dressings ready to apply, using my kitchen modifications of Auburn's technique (see "Recipe for Success," on the next page). At Auburn, the experimental horses had been sedated for the removal of the proud flesh, and local anesthesia had numbed the lacerated legs while the amnion was secured to the surrounding healthy tissues with skin staples. For each dressing change, the veterinarians again sedated the horse, cut a window in the amnion dressing to examine the wound and then used Superglue to affix a replacement section to the original dressing, the edges of which remained stapled in place.
On the following page, you'll find detailed descriptions of both the Auburn and the author's modified methods of this procedure, as well as photographs of wounds during treatment.
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