Medical devices sustain and improve the quality of life for millions of Americans. But as the over $100 billion-a-year industry pushes thousands of devices to market every year, reports of faulty devices, repeat surgeries, and recalls have increased. The FDA and the industry maintain that a speedy approval process gives patients faster access to life-saving devices. But critics say that unlike drugs, a substantial number of risky devices are cleared without clinical testing, and receive almost no oversight once on the market. We've taken a closer look at four types of implantable medical devices that have drawn the most criticism.