The custom prosthetics and orthotics market is shaping up to be the next place where 3-D printing is headed. Companies like Stratasys (NASDAQ:SSYS) and 3D Systems (NYSE:DDD) have increased their exposure to this multi-billion-dollar industry. In this video, Fool.com contributor Steve Heller sits down with The Motley Fool's Erin Miller to discuss why this is another area where 3-D printing is changing the landscape and how it could lead to billions in new revenues.