separating conjoined ("Siamese") twins by using 3D Rapid Prototyping Models

Sure, sure, click.

1. Abigail (Abby) and Brittany (Britty) Hensel, circa 2005.

2. The conjoined twins Chang and Eng Bunker, watercolor on ivory, circa 1835.

3. August 15, 2002 -- Maria Teresa and Maria de Jesus Quiej-Alvarez were born on 24 July 2001 in a rural village in Guatemala. Together, they weighed 4.4 pounds at birth and, despite their small size, were healthy in every way -- except for being joined at the head.

Over the past year, the girls have remained healthy and happy but they have been severely restricted by their condition. Recently, a nonprofit organization called Healing the Children arranged for the girls to be flown to Los Angeles where a volunteer team of neurosurgeons and plastic surgeons at the University of California Los Angeles (UCLA) Mattel Childrens’ Hospital successfully separated them in a 22-hour-long operation.

Today, both girls are doing well, and the prognosis for both is excellent. Without rapid prototyping, say the doctors, the operation would have been much more difficult.

Copyright © 2002 CAD/CAM Publishing, Inc. All rights reserved.

4. A traditional 2D X-ray of the Quiej-Alvarez twins' brains. The brains are completely individual and separate, but the brains shared blood vessels, which the surgical team had to separate. The 2D X-ray is of relatively little help in guiding this 3D procedure.

5. The interior of a plastic RP model of one twin's skull/brain after it was separated in a rehearsal of the surgery. The model reveals not just the skull bone, but the maze of blood vessels in 3D precision.

6. An RP 3D solid model of the whole conjoined skull before a surgery rehearsal, in the hands of lead surgeon Henry Kawamoto.

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"Siamese twins" who survived infancy traditionally found work with travelling carnivals as human oddities. In modern times most USA states have outlawed theatrical performances that feature authentic (not faked) human oddities.

There is, surprisingly enough, another side to this humane advancement from our wise and benevolent state legislators.

First, without the travelling carnivals and circuses, there was utterly no ordinary or "respectable" employment conjoined twins would ever be offered, and there was practically no chance they would ever be accepted and respected in any human community. When their employment by carnivals was outlawed, they and other undisguisable human oddities immediately became state-designated welfare lepers for life. Before this Great Ethical Leap Forward, they had had close, warm, respectful acceptance within and by the close-knit carnival/circus community -- they had family, and a self-earning job for life that featured an enormous amount of travel. (In the USA carnivals and circuses spend the winter off-season in a famous town in Florida.)

Second, these ethical, humane laws were regularly used as leverage for local officials to extort cash from travelling carnivals to grant them permission to perform. If the show featured human oddities, the sheriff or mayor could claim that without a bribe to sweeten things, the law forced him to forbid the show from going on.

The term "Siamese twins" comes from the Siam-born Chang and Eng Bunker (1811 - 1874), who were huge money-makers for the inventor of the modern circus and freak show, Phineas T. Barnum.

Barnum also pressured the Connecticut legislature to outlaw all forms of artificial birth control, including condoms, and the ban included married couples. The U.S. Supreme Court declared the law unconstitutional in Griswold, and in so doing declared that, however invisible it may seem to the idle reader, the U.S. Constitution indeed contains a guaranteed right of privacy for every citizen. Whether a husband can legally use a condom in New Haven was small potatoes, but Griswold's discovery (some say invention) of the Constitutional right to privacy later became the basis for the Supreme Court's Roe v. Wade, which legalized abortion for American women, and still does. Before Roe v. Wade, American women who sought abortions and medical practitioners who provided them were prosecuted and punished as criminal felons.

The modern medical/anatomical term for Siamese twins is conjoined twins. During prenatal development, they end up sharing tissues, bone structures, organs and blood vessels. The Bunker twins shared only a small amount of cartilege at the hip, and modern surgery could easily and safely have seperated them.

But other twins are far more intimately conjoined. They regularly survive birth and grow into physically and emotionally healthy adults, but for many, separation surgery is either impossible or far too risky.

Surgeons begin separation by using the most modern body imaging techniques -- CAT (Computerized Axial Tomography) and MRI (Magnetic Resonance Imaging) are the most famous.

Previous imaging technology -- the classic X-ray photograph invented by Roentgen around 1890 -- could "see" inside the body with great detail, but could only produce 2-dimensional (flat) images.

By a mechanical system of precise rotation of the imaging beam and its receiving sensors in a 360-degree arc surrounding the body or skull, and storing the results as numerical computer data, CAT and MRI offer a huge advance over the X-ray, and can display details of every part and at every depth and angle of the body or skull/brain.

But the images must still be displayed in flat 2D form, typically on a computer screen, "one slice at a time" of the body or the brain. Despite enormously clever and revealing image-display software, we are 3D objects, but doctors could only see us as flat 2D objects.

The stored numerical data from CAT and MRI had, however, an amazing new unexpected magic trick up its sleeve: Rapid Prototyping.

The numerical data could be manipulated, by ordinary geometry and trigonometry, in a computer to describe a solid 3D object. The Rapid Prototyping system -- where a computer-controlled laser precisely evaporates the surface of a special laser-sensitive resin -- takes CAT/MRI data and "creates" a tangible, 3D solid object.

As inidicated in the post about the Rapid Prototype Solid of the Zeta Function, the current limitation of RP is maximum size -- right now, somewhat smaller than a toaster oven.

In medicine, this limitation means that RP can't make solid 3D models of the whole adult human body, useful though such models might be.

But RP can make a near-perfect 3D solid true-size model of a human skull and the brain inside it, or other similar-sized parts of the body.

If you wished, CAT/MRI and RP would let you fill your closet not with dozens of shoes, but with dozens of perfect same-size models of your feet, their bones, and their internal larger circulatory vessels. (Your RP feet would be very different from plaster-cast models of your feet, which would only reproduce the exterior skin surface, and none of the internal structures.)

The first successful use of RP for surgically separating conjoined twins -- within the past decade -- seems to have been for infant twins conjoined at the spine, and the infant spine is a perfect size for RP's current size limits.

Separation surgery is an incredibly lengthy, risky and complicated procedure. Until RP, there was no way to practice the procedure without risk to the patients.

By creating RP solid true-size plastic models of the twins' conjoined spine, the surgical team was able to rehearse the procedure a half-dozen times before subjecting the actual patients to the slightest risk. Without such rehearsals, mid-procedure surprises would very likely have doomed the patients. With the benefit of the RP rehearsals, there were almost no serious surprises, and the surgical team proceeded with smooth choreographed efficiency. The twins were separated and are now healthy and much older.

I still can't find an image of their RP spine. But here's another coinjoined twin separation that depended very heavily on surgical team rehearsals on RP solids of the conjoined skull/brain. These kids are separated and doing fine, too.

from Wikipedia:

Conjoined twins are twins whose bodies are joined together at birth. This happens where the zygote of identical twins fails to completely separate. Conjoined twins occur in an estimated one in 200,000 births, with approximately half being stillborn. The overall survival rate for conjoined twins is between 5% and 25%. Conjoined twins are more likely to be female (70-75%).