How to Make a Customized (and Removable) Wrist Cast

3D Printing & Imaging Craft & Design
How to Make a Customized (and Removable) Wrist Cast

When you break a bone or even just injure the soft tissue in a joint, you have to immobilize it. While the optimal solution might be weeks of lying completely still (yeah, right) we all know that casts or splints are the way to go.


Thousands of years ago, ancient cultures (Egyptians, Greeks, Hindus) used wooden splints wrapped with linen to secure broken bones. Hardened casts started popping up in different forms around 30 AD, incorporating anything from wax and resin, to seashells and egg whites, to flour and animal fat in an effort stiffen the bandages and set the bone more reliably. The process evolved over centuries until we arrived at the plaster bricks we put on our broken bones today, which offer superior support and customized fit to provide the best environment for healing. But casts can invite a host of nasty skin issues, itchiness, staph infections, and dermatitis into your life. Not fun. A splint, on the other hand, is removable and less itchy. However, in order to secure the fracture, its straps must be very tight, meaning a lot of throbbing, aches, and general pressure.MAKEZINE_4-3DThurs_Badge

But leave it to a mathematician with a broken wrist and 3D Systems technology to experiment with a wrist cast/splint (a “clint” or a “splast”). His mission: to quickly blend optimal support with comfort and removability.

Yates, our resident mathematician-cum-cast researcher, injured his wrist after the front wheel of his bicycle locked up on a slick downhill turn. Faced with the possibility of an uncomfortable cast, Yates went through several design iterations of his custom cast and settled on one just in time for his orthopedist appointment. Here’s how he did it.

Wrist Cast 1
Original arm scan.

Cleaned-up wrist surface model.
Cleaned-up wrist surface model.

Step 1: Scan the injured arm. With Geomagic Fuse (a plug-in for Geomagic Studio scan data processing software) and a Microsoft Kinect scanner, Yates captured a 750K-polygon 3D model of his arm in about 30 seconds. The scan was accurate to within 2 or 3 mm, so we’re all set on the fit.

Step 2: Clean the scan. After scanning, we’re left with a few holes in the model. Things like arm hairs don’t scan very well. Missing data between the fingers complicates things a bit as well. But after a few automatic fills, the model is good to go. Yates also trimmed off the ends to get a nice model of the section of arm his cast would cover.

Wrist Cast 3
Closed inner wrist model.

Full wrist shell.
Full wrist shell.

Step 3: Construct the shell. Yates created what would become the shell around his arm by scaling up the arm model just slightly and creating thickness using Geomagic Studio’s offset tool. He cut off the ends of this shell and subtracted the inner hand model, leaving a representation of the custom-fitting outer cast.

Wrist Cast 5
Three sections for stabilization.

Wrist Cast 6
Finished cast model with registration pins.

Step 4: Finish the cast. At this point, Yates essentially had a model of a traditional plaster cast, but that was definitely more material than he needed. So he cut three rings – one from the hand, one from the bottom and one in the middle – then he attached several custom-fit stabilizing diagonal strips to keep the structure rigid in every direction. Lastly, he separated the splint into two halves with registration pegs for easy removal and reattachment.

Finished Wrist Cast
3D printed cast on Yates’ wrist.

There you have it. Yates 3D printed both halves of the comfortable, breathable, removable, supportive, customized, and itch-free cast. He reports that it relieved a great deal of pain that accompanied typing and using the mouse. Even the doctor said it did a good job of immobilizing the joint, and he was surprised at how light it was.

One of the amazing things about 3D design and 3D printing technology is that everyone can use the tools and that design complexity is free. That’s pretty cool, because your imagination isn’t limited by complexity either. So you can pack your designs and projects with every cluster of the beauty and intricacy that you visualize, knowing that 3D printing can make it. Everything that inspires you can come together. No limits. No compromises.

You want to see how this unlimited complexity manifests itself in the medical design field? Go no further than the groundbreaking work being done by Bespoke Innovations. They blend wonderful design, 3D imaging and printing technologies, and gorgeous fashion to create personalized, functional prosthetic limb fairings. Their pieces are great examples of how engineering transcends humanity, even adding lifestyle and emotional integrity into life saving applications.

-The 3D Alchemist

(Written with Josh O’Dell)

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Ping Fu

VP & Chief Entrepreneur Officer, 3D Systems

Honored in 2005 by Inc. Magazine as Entrepreneur of the Year, Ping Fu describes herself as an artist and scientist whose chosen expression is business. In 1997, Ping co-founded Geomagic, a 3D imaging software company, which was acquired by 3D Systems in February 2013. Before co-founding Geomagic, Ping was involved in the NCSA Mosaic software that led to Netscape and Internet Explorer. Ping serves on the National Advisory Council on Innovation and Entrepreneurship at the Department of Commerce and on the board of directors at the Long Now Foundation. Ping’s book “Bend, Not Break” was published by Portfolio Penguin in January 2013.

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