During his medical career, Dr. Larry Hollier has seen only two babies born with three arms.
In both cases, there was no question about which arm had to be removed.
"The third arm was not as developed, so it was a fairly easy decision to amputate," said Hollier, co-director of the cranial facial surgery program at Texas Children's Hospital in Houston.
However, a baby boy born in China poses a more difficult challenge for doctors. Known as Jie-jie, the 2-month-old was born with one right arm and two left arms -- which do not seem fully functional.
His Shanghai surgeons now must decide which arm to remove, and at this point, they aren't sure which arm will be the one to go.
Although rare, doctors have reported children born with extra extremities, such as arms, legs, fingers, toes. They usually determine which to remove depending on how well it works. Hollier said there are no reliable statistics to say how common extra limbs or extremeties are, especially since malformed fetuses are often aborted either spontaneously or surgically and therefore are not reported accurately.
When deciding which extremity to keep, doctors must carefully analyze the anatomy and physiology through imagery like X-rays and MRIs, which show bone structure and blood flow, as well as electro-diagnostic studies, which monitor nerve impulses from the brain to the muscle, doctors said.
While an extra limb is rare, children with multiple digits and even hands are more common, said Dr. Ann Van Heest, an upper extremity surgeon at Gillete Childrens Speciality Healthcare in Minnessota. She has never seen a case like the baby in China.
Van Heest estimated that one out of 200,000 babies are born with two thumbs on one hand and one out of 2 million have doubling at the wrist, resulting in two hands.
To decide which extremity to remove, doctors usually wait until the child is six to 12 months old to perform any surgery, as they want to observe which extremity the child favors and uses more, Van Heest said.
"For a 2-month-old, I am not sure one would be ready to make that final assessment," she said.
Most cases of multiple limbs result from conjoined twins forming in development. One child does not survive and becomes essentially absorbed into the other, said Dr. Russell Jennings at the Children's Hospital in Boston.
In those cases, the extra limb is not connected to the baby's brain and the decision to amputate is straightforward. The cause of Jie-jie's extra arm seems unclear.
According to the evidence so far, Dr. Steven Stylianos of Miami Children's Hospital said he suspects that the extra limb most likely came about in the conjoined twin process.
Whatever the explanation, Dr. Jorge Lazzareff said he has confidence in the Shanghai doctors' skills. In the last four years, he has traveled to China several times to perform surgery on orphans with birth defects.
"The baby is in good hands, in my experience. They are up to the task," said Lazzareff, director of pediatric neurosurgery at the University of California Los Angeles.
Hollier, at Texas Children's, said that infants tend to adapt to these disabilities. Their minds are at the early stage, so they can adapt to changes in motor development.
"Basically a child never misses a beat," he said.