WELL, THIS IS THE 21ST CENTURY, YOU KNOW: 3-D Printing Prosthetic Hands That Are Anything but Ordinary. “The Rivermans, of Forest Grove, Ore., could not afford a high-tech prosthetic hand for their son, and in any event they are rarely made for children. Then help arrived in the guise of a stranger with a three-dimensional printer. . . . The proliferation of 3-D printers has had an unexpected benefit: The devices, it turns out, are perfect for creating cheap prosthetics. Surprising numbers of children need them: One in 1,000 infants is born with missing fingers, and others lose fingers and hands to injury. Each year, about 9,000 children receive amputations as a result of lawn mower accidents alone. State-of-the-art prosthetic replacements are complicated medical devices, powered by batteries and electronic motors, and they can cost thousands of dollars. Even if children are able to manage the equipment, they grow too quickly to make the investment practical. So most do without, fighting to do with one hand what most of us do with two.”