They removed one of his two left arms that had been laid across Liu Junjie's chest. The second left arm is further up his shoulder.
'We found the nerves and blood vessels for the arm were formed just as they would be for a normal arm,' said Dr Chen Bochang, chief surgeon at Shanghai Children's Medical Centre.
The baby's parents are poor farmers from rural Anhui province. Although the surgery went off successfully the baby would still require long-term physiotherapy to gain complete function in the remaining hand that has no palm and has flexion abilities in both direction.
'We're hoping to exchange information with doctors who've dealt with similar cases anywhere in the world,' said Chen. 'This is so rare that we have virtually no information to go on.'
Junjie's case was especially remarkable because both left arms were almost equally well developed. The choice between the two left arms was made for the one closest to the chest, as it did not fully extend.