Tyler and Tyson were two twins sharing chest, abdomen and a liver creating difficulties for their surgical separation. However, using 3D Printing technology, surgeons at Children's National Medical Center in Washington created models and were able to visualize the whole operation before the actual surgery, thereby leading a successful surgery.

Source: http://health.usnews.com/health-news/hospital-of-tomorrow/articles/2015/09/16/3-d-printing-to-the-rescue