On a beautiful spring Saturday when much of Washington was on its knees in the garden, it was hard not to think of planting seeds as surgeon Michael Boyajian gently tucked two tissue expanders beneath the shared skin of Jade and Erin Buckles.

Over the ensuing weeks, the two-inch-long plastic devices would swell and force the infants to grow more skin along the bank of flesh that connects them. More skin -- elastic, protective -- is one of the things these girls need before they can literally go their separate ways. But growing it takes time.

Many things take time when the goal is to safely separate two human beings who've been physically bound to each other since a few days after conception.

Jade and Erin Buckles, the Washington area's first set of surviving conjoined twins in more than 20 years, are scheduled to be surgically separated on June 12 -- 15 weeks after their birth at National Naval Medical Center in Bethesda.

An operation so complicated entails months of preparation, and since mid-April, many dozens of people at Children's Hospital in Northwest Washington have been studying the twins and planning for their arrival. It will be the most thoroughly rehearsed procedure in the hospital's 134-year history.

Conjoined twins are sufficiently rare that nobody ever gets truly experienced in their care. Three separations -- the number that 56-year-old pediatric surgeon Gary E. Hartman can claim when he steps to the table to do the Buckles case -- is a lot, but only in relative terms. It's not safe to view any part of the procedure as even remotely routine.

Nevertheless, the medical team must figure out what constitutes tolerable uncertainty. It must define the line between prudent preparation and pointless data-gathering.

In theory, the entire medical arsenal is available to serve the Buckles twins, who now weigh 18 pounds together. That includes not only the many methods of diagnostic imaging -- CAT scans, MRIs, ultrasound, angiograms -- and countless laboratory tests, but also the tubes, catheters, pumps, oxygenators, monitors and devices that help living flesh survive difficult passages.

And then there are the people.

Separating conjoined twins is like orchestrating a piece of symphonic music. Everyone has a part and must learn the main themes and melodies. A few people get to solo or lead. How to accommodate those players -- their needs, talents and personalities -- while keeping the whole performance coherent has also been the work of the nearly 100 days since Jade and Erin arrived.

Journey of Discovery

"One of the attractions of pediatric surgery is that you're always confronted with the unknown, or a new twist or different twist on the usual version of things," Hartman said, sitting in his corner office that looks down over McMillan Reservoir on Michigan Avenue. "There are going to be unknowns up to the time of surgery."

For many people, this certain uncertainty would be the definition of professional hell. But those people don't go into pediatric surgery.

It is one of the rarest and hardest specialties in medicine, requiring seven years of training after medical school. There are only 670 board-certified pediatric surgeons in the United States. Much of what they do is repair birth defects, which arise from errors in the highly ordered process of fetal development. The major abnormalities are predictable, but the minor variations offer surprises.

Hartman has seen a lot in a quarter-century of practice, first at the University of Oklahoma, then at Stanford, and the last 10 years at Children's. Nevertheless, he said, "Almost every week or every month we run into something that we've never seen before."

Erin and Jade Buckles are "thoraco-omphalopagus twins," or connected from the mid-chest to the mid-abdomen. (About three-quarters of conjoined twins are attached somewhere in that region.) Anatomically, Hartman's three previous cases were roughly similar.

All four children of the first and third sets are alive and healthy. But the babies of the middle set were delivered prematurely, and one died of respiratory failure within several days. Hartman led an emergency operation that saved the surviving twin, but that child died several years later of a heart ailment.

The main thing the Buckles twins share is a liver. The problem isn't apportioning the organ -- each girl has more than she needs -- but dividing it safely. It doesn't have the usual anatomical landmarks that tell a surgeon where crucial structures are, especially the network of large arteries and veins that course through its interior. Hitting one of those vessels could result in catastrophic bleeding.

For Hartman and the pediatric surgeon who will assist him, Capt. Stephen Morrow of the Bethesda naval hospital, getting through the liver will be a journey of exploration. They know that somewhere near where the babies are joined is a plane of tissue unlikely to contain any big blood vessels. "We're going to have to find that plane," Hartman noted calmly.

After the babies are separated, each will be left with what medicine calls -- with uncharacteristic clarity -- "a large defect." Each will lack about one-third of the tissue that normally covers the front of the trunk, the packaging necessary to protect the heart, the liver and the muscles of the abdomen.

The surgeons will have to close this gaping wound in a way that's safe for at least the time being. (It's likely the infants will need future reconstructive surgery as they grow.) This is the part of the job that worries Hartman most. This is where unknowns are guaranteed.

They can patch the babies' diaphragms -- the essential muscles of breathing -- with Gore-Tex, if there are holes in them. If necessary, they can cover the chest wall with other material that, unlike Gore-Tex, will eventually be absorbed by the body. Or if they're lucky, they'll have enough skin. There's no knowing until they get there.

The Heart Dilemma

About 90 percent of chest-attached twins have some connection between their hearts. It may be a trivial bond or it may be a life-threatening one. In late April, when the key players gathered at Children's for the first time to plan the surgery, the hearts were the major topic.

Hartman, sitting at one end of a long mahogany table in the Surgery Department's conference room, guided the conversation in a soft-spoken manner -- the opposite of the stereotyped "surgical personality."

Members of the team summed up what they knew:

The twins shared a single pericardium, the thin Saran Wrap-like sac that surrounded both hearts. The hearts touched but beat separately, so they didn't share chambers. But might they share part of a wall of heart muscle in a way that wasn't visible in early pictures? Might they share coronary arteries, the vessels that supply oxygen-rich blood to the heart muscle? Or do they have only an innocuous, easily clipped bridge of fibrous tissue?

CAT and MRI scans might be able to show, but not with absolute certainty. Cardiac catheterization, which involves injecting a dye into the coronary arteries to delineate their course, would provide extra information, but it also carried extra risk.

The babies' parents -- Melissa Buckles, a high school teacher, and Kevin Buckles, a Marine gunnery sergeant stationed in Washington -- had told the doctors they were willing to have the babies undergo any diagnostic procedure likely to improve the chances of successful surgery.

But first the doctors had to decide what they wanted. Most around the table seemed confident that the CAT and MRI scans would provide enough information. Someone asked whether there had been any twins like the Buckles set that hadn't gotten cardiac catheterization before separation. No, a cardiologist answered, but those teams didn't have the spectacular diagnostic imaging we have now.

Did the procedure give any information that changed those teams' plans? My sense, Hartman said, is that it didn't.

Sitting near the other end of the table was Gregory B. DiRusso, the pediatric heart surgeon who will have to deal with the problem if it turns out the Buckles twins have a serious heart connection. He wanted to narrow the universe of possible surprises.

"We would have to take two hearts and separate them in two human beings, and a coronary artery that gets divided can result in one of those hearts never working," he said in a slow and didactic voice. "I can't make it more simple than that. That should make it clear what the importance is from my perspective."

With DiRusso's preference expressed in no uncertain terms, the catheterization suddenly seemed much more likely.

Eight days later, the babies got the procedure. It was done by Michael Slack, the main interventional cardiologist at Children's.

Cardiac catheterizations are about the only thing Slack does. With wires and tubes, he finds tiny blood vessels deep inside babies, largely by feel. He then takes fleeting movies of their beating hearts with X-rays produced by a fluoroscope. His days are spent wrapped in lead-lined garments and staring through leaded-glass spectacles. Jade and Erin were the fourth set of conjoined twins he had catheterized.

The good news: The twins shared no blood vessels of the heart. But the films showed with dramatic clarity a different problem, one the doctors knew about already. The girls' hearts weren't face-to-face and symmetrical, like a Rorschach image. Instead, Erin's heart lay almost horizontal, with its tip entirely in Jade's half of their shared chest. As it beat rhythmically in the film, it looked like a droopy-nosed Dr. Seuss character sniffing out the sister's heart.

Gary Hartman would have to find it a home back in Erin's chest.

Planting

For two months, Michael Boyajian had debated with himself about where to place the tissue expanders in the Buckles twins. His decision, however, was "ultimately made at the table," he said, still gowned and scrubbed, after finishing the operation on the Saturday in early May.

Boyajian basically had two choices.

The girls each have two nipples, one on each side of the fused part of their chests. He could insert the tissue expanders under the skin either between the nipples and the point where the chests are fused, or beyond the nipples, more toward the sides of their bodies.

If he did it the first way, the extra skin that grew would be closer to the large wound that would need covering after the infants were separated. Each nipple would not be pulled as far from its original position as would happen if the extra skin was more to the side -- which is where it would be if the procedure was done the second way. The first way also wouldn't be likely to disturb blood vessels going to the dormant bud of each breast.

But the second way would be easier.

With Mark Venturi, a 31-year-old plastic surgery resident at Georgetown University, across the table from him, Boyajian studied a rectangular, slightly yellow valley of skin. It was all that was visible of the twins' draped, anesthetized bodies as they lay on one side on the operating table.

Boyajian, 54, measured various parts of the skin with a sterile plastic ruler. He drew a perimeter in dotted blue lines with a sterile felt tip pen. He gently tested the tension of the skin.

"Here's where the plastic surgeons mark 10 times and cut once," said Stephen Morrow, the Navy surgeon, observing away from the table.

Boyajian chose the first, harder way, explaining later that it simply "gives us the best opportunity for a good result."

After injecting the skin with epinephrine, which constricts arteries and veins, he made a three-inch, nearly bloodless incision, the first of many in the twins' young lives. He gently undermined the skin with a pair of blunt-tipped scissors. He put a wand with a tiny light bulb on its tip into the wound. A dull orange glow moved slowly under the skin as he probed the perimeter of the cavity he was forming.

When it was the right size and shape, he put in the tissue expanders -- two reservoirs about the size of matchbooks, made of plastic, silicone and metal -- and sewed the skin shut. At each step of the way, Venturi helped.

The first side took 72 minutes. The surgeons stepped back as the twins were turned and their other side was prepared for the expanders.

"This side will be quicker now that they know what they're doing," Morrow whispered puckishly.

The second side took 50 minutes.

In the ensuing weeks, the tissue expanders would be periodically injected with water, making them increase in volume and stretch the skin. With time, more skin would grow. It was a process that couldn't be hurried.

But that was all right with Gary Hartman and his team, because there was still more to learn and do before the surgery.

Conjoined twins Jade and Erin Buckles at their home in Woodbridge.

An anesthesiologist monitors the twins as they undergo a CAT scan, one of many forms of diagnostic imaging available to them at Children's.

The medical team studies the scan monitors. Even with tests, "there are going to be unknowns," said Hartman.Melissa and Kevin Buckles stand by as their daughters are prepared for the catheterization. The parents said they were willing to have the girls undergo any diagnostic procedure likely to improve chances of successful surgery.