Exposed on a vertical face, rock climbers rely on their instincts, experience, and equipment.
However, since C.J. Howard, a northern California-based rock-climbing enthusiast, is a lower-leg amputee, he also relies on a customized prosthetic foot that he designed with climbing partner and environmental/aerospace engineer Mandy Ott.
An athlete all his life, Howard was a distance runner for the University of California, Irvine cross-country team before a diagnosis of osteosarcoma and amputation of his left leg just below the knee. He was fitted with prosthesis, and went on to set amputee world records in several events.
When Ott introduced him to climbing in 2008, Howard started out with his standard artificial foot fitted to a climbing shoe. However, the prosthesis’ generic shape did not work well with his specialized footwear. Ott got out her laptop, opened an engineering CAD program and, on the spot, created what Howard described: an aggressive climbing shoe with a downturned toe – like a banana.
How best to manufacture the new prosthesis? Ott immediately thought of an additive manufacturing process called direct metal laser sintering (DMLS) that she had encountered in her work at a major aerospace company. The technology is often used to build one-of-a-kind prototypes and end-use parts with a turnaround time of just a few hours. “I never even thought about fabricating it using traditional machining techniques,” Ott says. “That would have left seams in the foot or protruding nuts and bolts that would not work well for climbing.”
Ott contacted Morris Technologies, an Ohio firm that specializes in additive manufacturing and is the largest deployer of DMLS in the world.
“They completed the prosthesis just before Christmas,” Ott says, “When C.J. opened his surprise present and saw the new foot, he had a grin on his face that was priceless.”
Building the Prosthesis, One Step at a Time
Fabricating the approximately 6”x3”x2”, smooth-edged foot out of commercial-grade titanium (Ti64) took about forty hours on a system manufactured by German-based EOS GmbH, developer of DMLS technology. Unlike traditional metal forming techniques – such as milling, drilling, sanding, and polishing - that remove, or subtract, material from a solid block, the DMLS process builds (or “grows”) an object, layer-by-layer, out of laser-sintered metal powder. Ott’s digital CAD model of the prosthesis served as the 3D blueprint to guide the process.
The finished 5 lbd foot was a single-piece construction, hollow (to minimize weight) and with no seams or fasteners. A separate vendor coated it with a rubber used for climbing shoe soles. The accompanying leg – a solid titanium rod – connects to a socket and Howard’s upper leg.
While this prosthesis was the first one Morris Technologies had produced, Tim Warden, vice president of sales and marketing at the company, sees laser sintering as ideal for this kind of application.
“A prosthesis should be customized to an individual’s anatomy,” Warden says.
As designs go, Howard’s climbing prosthesis was fairly simple. Specialized prostheses (replacements) and orthoses (braces) for competitive disabled athletes who run, ski, and cycle can be more complex. Warden points out that the DMLS process is also perfect for producing medical products with even more critical geometries. This could include orthopedic implants for hips, knees, shoulders, ankles, and even spines, as well as patient-specific surgical instruments. A growing list of materials – including biocompatible plastics and metals – is enabling Morris engineers to consider laser sintering for a number of cutting-edge medical applications.
Morris also uses the process for a wide variety of other applications from aerospace to automotive to industrial. “We select DMLS over traditional manufacturing methods in instances where it can reduce both product development lead time and cost,” Warden says.
Best Route is not One-Size-Fits-All Climbing Foot
Climbing as much as three times a week when he can get away, C.J. has now had a number of opportunities to try out his new prosthesis in the field. His northern California test sites have included the granite of Tahoe’s Lover’s Leap, the single-pitch trade routes of Phantom Spires, sport climbing at Luther Spires, and the crevice and chimney systems of nearby Sugarloaf. He has also climbed with it on dome and crack routes in Yosemite.
“Now that I’ve used this prosthesis, I know what types of climbing it works really well on and what types it doesn’t,” Howard says.” He and Ott can imagine at least two more artificial foot designs that could be used by disabled climbers. “I want to design one shaped like a triangle for pure crack climbing and another with less downturn for more slabby conditions,” Howard says. “It’s like changing tires on a race car. You would just switch your leg for different climbs.”