Printed parts represent only a small fraction of the overall market for orthopedic implants, but for two important reasons that share could grow quickly in the coming years. First, an aging population is getting more joint replacement operations. The number of annual hip replacements in the U.S. doubled between 2000 and 2010. Second, in recent years engineers have gotten much better at using additive manufacturing technology--as 3-D printing is also called--to make titanium implants.

Leading orthopedic implant makers are investing substantially in the development of the technology; earlier this year Stryker announced plans to build a $400 million additive manufacturing facility. Companies hope to cut costs by simplifying the production process for these implants, which are often geometrically complicated assemblies of multiple metal pieces. Building them layer by layer allows companies to consolidate many pieces into one, and save material that would be wasted in traditional subtractive manufacturing processes like forging and casting (see "10 Breakthrough Technologies 2013: Additive Manufacturing").

But perhaps the biggest potential benefit is the ability to design implants that are specific to an individual patient's body, by using data from magnetic resonance imaging or computerized tomography scans. That's especially true for parts of the skeleton that have complicated geometries that can be very unique to an individual, like the pelvis, says Jason Koh, an orthopedic surgeon at NorthShore University Health System and director of the NorthShore Orthopaedic Institute. Koh says customized total joint replacements could also have substantial benefits for patients.