3D printed casts are not your average cast—though they are used for your average broken bone. Anyone who's had a cast and is familiar with the itching and the...less than ideal...smell that can happen underneath the plaster while the bone heals will likely be quick to notice how light, airy, and accessible these new versions look compared with the classic plaster. Given how far technology has come, I'd say we were due for an update. In fact, you can read a 510(k) premarket notification for a plaster cast here: it's from 1977.
Traditional plaster casts certainly do the job: they're effective and customizable. But they're also cumbersome, prone to itching, smelling, and sores on the covered area, and they cannot get wet. Breakthroughs in technology in the last few years have brought improved customizable tech to an area of medicine that is long overdue for an upgrade. 3D printed casts are lightweight, waterproof, airy, and, frankly, cool-looking.
Or as this article in New Atlas put it, a 3D printed cast "...takes the form of an open plastic framework as opposed to an enclosed plaster (or fiberglass) casing. This allows it to hold broken bones in place, while still letting the injured appendage "breathe". Additionally, unlike the case with plaster, its plastic construction won't absorb sweat or other fluids. As a result, skin ulcers and infections are less likely to occur and itches can be more easily scratched."
One potential downside to 3D printing casts is that they can take a few hours to produce. Ideally broken appendages should be cast as quickly as possible, but perhaps with continuing advances in technology the timeframe will come down.
You can check out some other really cool-looking designs here. Jake Evill's Cortex design was featured on NPR, Mashable, and elsewhere when it first came out in 2013. As NPR put it in their headline, these are "3-D Casts So Cool You'll Almost Want to Break a Bone".