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Athena's Armor

By: David Levin Date: Sep 8, 2017
Athena

Michael Crisp is used to taking in strays. For years, he and his family have fed cats living on the street, given them new homes, and provided them with medical care at the vet. Most of his rescues have just needed a meal and a basic checkup—but one kitten, who he quickly named Athena, seemed different.

“She just appeared at my feet one day, and when I picked her up, I could feel her heart beating right under her skin. It was really strange,” he said.

Crisp immediately scheduled an appointment with Dr. Chistine Kirnos, his vet in Media, PA, who confirmed that something was very wrong. Athena’s rib cage had never fully closed, leaving an inch-wide gap where her sternum would normally be. Instead of hard bone protecting her heart, only a few millimeters of flesh lay between it and the outside world. It was a disaster waiting to happen.

“We knew we had to do something. A scratch or even a bump in the wrong spot could have been deadly, but doing surgery to fix it was going to be complicated. That’s why Dr. Kirnos referred us to Penn Vet,” said Crisp.

A CT scan of Athena's ribcage shows the unfused sternumAt Ryan Hospital, Crisp met with Professor of Surgery Dr. Lillian Aronson, a veteran clinician who has been operating on animals for more than 20 years. Aronson realized that the problem wasn’t just Athena’s ribs. The cat’s diaphragm, a major muscle that normally separates lungs and heart from the abdominal cavity, was also deformed, creating a large hole that Athena’s internal organs could move through freely.

“This cat had some very unusual defects,” said Aronson. “Her liver had actually pushed through into the pericardium, the sac surrounding the heart. I had never seen that in conjunction with a split sternum before.”

Not that Athena seemed to mind. Although she had major birth defects internally, she behaved as if nothing was wrong, and stayed eager to explore the outside world. At home, Crisp said, she would often beg to go outdoors, and would urinate near the front door to protest being closed up in the house.

“Outwardly, she seemed completely fine,” added Aronson. “So one option was to do nothing, and let her live her life. We were concerned, though, that if she was determined to go outdoors or wrestle with other cats, the consequences could be catastrophic. So we decided we needed to protect her heart.”

Novel Surgery

Titanium mesh was implanted into Athena's chest to protect her heart.Doing that was no easy task. After searching through a mountain of veterinary journals, Aronson found only one case similar to Athena’s, in a five-month-old German Shepherd many times her size. In order to fix this chest defect on a cat, the Penn Vet team would have to invent a new procedure from the ground up.

At first, Aronson considered suturing Athena’s rib cage closed, but given the size of the hole in her sternum, that could have compressed her lungs, causing additional damage. The best course of action, Aronson reasoned, would be to rebuild the sternum entirely using titanium surgical mesh.

Dr. Aronson also enlisted the help of Dr. Jonathan Wood, a veterinary neurosurgeon at Ryan Hospital, who has worked with similar mesh implants in the past to rebuild injured animal’s skulls. To plan the surgery, he and Aronson took images from a digital CT scan of Athena’s chest, isolated her bone structure, and created a full-scale model of her rib cage using a 3D printer.

The finished model, Wood said, could be used to precisely measure how to bend the mesh to fit Athena’s unique rib cage, and determine where it could be anchored along her existing bone.

An x-ray of Athena's chest shows her heart about the titanium mesh implant (at red arrow) “You can’t just pop the mesh in and hope it stays put,” said Wood. “A 3D print like this provides a really useful tool to learn exactly where to place a suture or wire before you ever make a single cut.”

It also let Aronson spot potential issues before the surgery began. After looking closely at both the model and CT scans, she and Wood determined that Athena’s heart might rub against the titanium mesh once it was in place, irritating the muscle and causing additional damage with every beat. To solve this, Aronson covered the mesh with a membrane called Vet BioSiSt, which is made of intestinal tissue from pigs, to create a smooth barrier between the metal implant and the cat’s tiny heart. With time, she says, scar tissue will surround the material, providing even more protection.

A Close Call

Athena in the ICU after her first surgeryAfter repairing the cat’s diaphragm and affixing mesh to her rib cage, Athena seemed as good as new, said Crisp. She played, wrestled, and explored with other cats, seemingly oblivious to her once life-threatening condition.

Nearly six months after her surgery, however, the protective nature of her new metal breastplate was unexpectedly put to the test. Relatives visiting Crisp’s neighbors brought a pair of adult pit bulls with them—and Athena, ever curious, found her way into their yard. One dog attacked, biting her around her chest and abdomen.

After a violent fight, Athena somehow managed to wriggle free and hide. Crisp found her in a neighbor’s garage more than two hours later, bloody but alive, and rushed her back to Ryan Hospital for treatment.

As emergency room vets stitched up Athena’s wounds, the extent of her injuries became clear. One of the dog’s teeth had penetrated between her ribs, causing minor damage to her lung. Other bites, however, were deflected by her new titanium breastplate—leaving her previously vulnerable heart untouched. Athena would live to see another day.

“If she didn’t have the mesh in place, she never would have survived that fight,” said Crisp. “Dr. Aronson saved her life. We feel really fortunate to live so close to such an outstanding facility that can perform a surgery as unique as Athena's."

Athena recuperating at home after her implant surgery