An elegant repair
The solution to a mare’s recurring post-surgical hernia is a new technique that uses an ancient fiber.
Lily’s colic surgery went smoothly. The 8-year-old mare had been rushed to Tufts University in Massachusetts with acute gut pain, and exploratory surgery revealed a left dorsal displacement of her large colon. The surgeons corrected the displacement, sutured the incision in the mare’s abdomen and sent her home a few days later.
That’s when the complications began. “When you’re opening and closing an abdomen, there’s a lot that can go wrong,” says Jose Garcia-Lopez, VMD, DACVS. “There are multiple layers of muscle to suture, along an incision line that can be 40 centimeters long. Then, after you’re done, the horse stands up, and gravity puts hundreds of pounds of viscera right on the incision you’ve just sutured. To put it in context, imagine if after you had major abdominal surgery, your doctor told you to get on all fours and crawl around. That’s exactly what we ask horses to do.”
That’s why hernias---the protrusion of an organ or body tissue through an opening in the abdominal wall---are a relatively common complication of colic surgery. Surgeons have developed a variety of techniques to suture incisions as securely as possible, but hernias still develop in 10 to 20 percent of horses. “Surgical hernias occur when the linea alba, the fibrous band of tissue that runs along the midline, fails at the site of the incision,” says Garcia-Lopez. “Infection increases the risk of this happening, but it can happen in a healthy wound, too. Essentially, the abdominal wall pulls apart at a weak spot, creating a pouch of sorts.”
That pouch can then fill with fluid and expand, creating space for abdominal structures to slip in. “What you see from the outside is a bulge along the midline,” says Garcia-Lopez. “If you touch it, it will usually feel soft.”
Some hernias are inconsequential ---they may look unpleasant, but they do no harm to the horse. “Many times the bulge is created by a small piece of fat or omentum that slips down into the pouch,” says Garcia-Lopez. “That isn’t too worrisome.” A horse with a benign hernia may even be ridden, although a pendulous bulge may interfere with more athletic efforts.
Other hernias, however, can be quite dangerous. “If a portion of bowel or intestine slips down into the space, particularly through a small opening, it can become strangulated, with the blood cut off, and begin to die,” says GarciaLopez. “Then you’ve got a potentially deadly colic emergency on your hands.”
Hernias can usually be corrected surgically, although it may not be necessary if the abnormality poses no harm to the horse. Typically, a veterinarian will examine the bulge with ultrasound to determine its contents to assess any potential dangers. “Most owners, in my experience, opt to repair hernias,” says Garcia-Lopez. “It does involve another surgery, but in many ways that is better than worrying about what might happen down the road.”
A failed fix
A fist-size bulge appeared along Lily’s midline within weeks of her colic surgery, prompting her owners to call in their regular veterinarian. “Her owners still rode her regularly and were planning on using her as a broodmare,” says Garcia-Lopez. “They weren’t worried about aesthetics, but they were concerned about what might happen with the hernia through pregnancies.”
After conferring with their veterinarian, Lily’s owners agreed to a hernia repair procedure done on the farm. The mare was anesthetized and laid down in a clean grassy area. The veterinarian then reopened the failed incision line, repositioned the bulging tissues and sutured the abdomen closed once again. Lily woke from the anesthetic and stood up without any complications.
To help prevent a recurrence, the veterinarian outfitted Lily with a hernia belt. “These are stretchy belly wraps that secure with strong Velcro,” says Garcia-Lopez. “They are cut to particular sizes to fit certain measurements
and fit very tightly. These wraps are essentially corsets that you leave on a horse for several weeks after the surgery. Studies have shown that using them immediately post-surgery can reduce the stress on the incision line as well as the amount of edema or swelling present, which, potentially, reduces the risk of a hernia.”
For a time, the repair seemed to have worked. But when the hernia belt was removed, the defect in the incision line slowly reappeared. Within months, another bulge emerged in the exact same location. Frustrated, but determined to help their mare, Lily’s owners loaded her up and headed back to Tufts.
Once she arrived, Garcia-Lopez conducted a complete examination of the mare. But beyond the bulge in her midline---about three inches long and one-and-a-half inches wide---Lily was in good health and spirits. Although the ultrasound did reveal large bowel within the hernia, there was no evidence of immediate danger of an intestinal strangulation. This was good news, GarciaLopez explained to Lily’s owners, because the best approach to the problem was to wait about six months from when the hernia reoccurred before attempting another repair.
“When you repair a hernia, you want a very, thick fibrous ring of scar tissue around the defect,” he says. “The thicker it is, the better able it will be to hold the new sutures. I think that may have contributed to the first repair failure---it was simply done too soon. I told [Lily’s owners] we needed to wait for the scar tissue to form, and then we could attempt another repair.” They agreed, loaded the mare and headed back home to wait.
Silky solution
When Lily returned to Tufts two months later, says Garcia-Lopez, “the ring of scar tissue around the hernia appeared thick enough on ultrasound to hold more sutures.” However, the veterinarian also offered the mare’s owners an alternative---to try out a new, still-experimental method of repair.
In human medicine, plastic or reconstructive surgeons may suture a flexible mesh into the tissues to help provide strong support for healing with reduced risk of complications. “Historically, polyester and polypropylene meshes have been used,” says Garcia-Lopez. “They are good and strong, but they last forever as a foreign substance in the body, and if an infection develops, you have to remove all of it as part of the treatment.”
However, Garcia-Lopez had been working with a research group in the development of a new type of mesh made with silk. “Silk mesh is conducive to bringing new fibroblasts into the area, which leads to the growth of fibrous tissue,” he says. “As this is happening, the silk deteriorates, so ultimately it is replaced by native tissue. Treating infections doesn’t necessitate removing the silk mesh, either. Silk has been around for centuries, obviously, but only in the last decade or so have we known how to weave it together to be strong enough for surgical applications such as this.”
Prior to Lily, Garcia-Lopez had used silk mesh in surgical trials on sheep, and he had conducted a few preliminary trials in horses, but he hadn’t yet used it on a large and persistent hernia. However, the mare’s owners agreed it was worth a try, and the surgery was scheduled for the following day.
With Lily fully anesthetized and positioned on the surgical table, Garcia-Lopez cut a two-inch-wide elliptical-shaped incision to the right of the hernia on her midline. He then carefully separated the muscular layers of the body wall to examine the tissue around the hernia.
“You have to take into consideration how much you’ll be able to pull the body wall back together, given the strength of the area and the amount of fibrous tissue you have to work with,” says Garcia-Lopez. By manually manipulating the tissues, he was able to reduce the size of the hernia to about
two inches. Next, he stretched the silk mesh across the gap, anchoring it within the layers of muscle tissue in the abdominal wall. He then sutured the outer layers of skin closed and placed a tight hernia band on the mare before waking her up.
“There’s always a moment of worry as the horse scrambles back to its feet,” says Garcia-Lopez. “That can pull all your work apart immediately.” But
between the silk mesh and the hernia belt, Lily’s hernia repair remained strong for the three days she stayed at the clinic for continued observation. She also received treatment with antibiotics and anti-inflammatories.
“The belt offers support but also reduces edema in the area,” says Garcia-Lopez. “If you can keep the edema down, there is less stretching of the tissues.” Lily’s hernia belt
remained in place after she went home; it was removed only for short periods each day for grooming and adjustment. The mare returned to Tufts for two follow-up exams, at eight and 20 weeks after her surgery.
At each visit, ultrasound examinations showed that the mesh was holding strong and fibrous tissue was quickly forming around it. Externally, Lily’s midline remained flat and smooth, with no sign of a returning bulge. After the second visit, the hernia belt was removed for good, and the repair continued holding strong.
Lily went on to fulfill her new role as a broodmare. “We were fortunate to be able to keep track of her,” says Garcia-Lopez. “She had at least two foals, one of which had to come into the clinic for a small problem. We were able to take a close look at her then and saw no issues at all with her hernia. Two foals later, she still looked great. There’s no reason to think it won’t hold forever.”