New Central Fabrication Technology Steps Onstage
August 2012 Issue
"There's a way to do it better-find it." -Thomas Edison (1847-1931)
When one of the world's fastest amputees, Jerome Singleton, Irmo, South Carolina, competes in the upcoming 2012 Paralympics in London, United Kingdom, his prosthesis will feature an extrastrong, extra-light socket fabricated using an innovative braided carbon-fiber technology.
The carbon-fiber braiding technology was developed in 2008 with U.S. Department of Defense (DoD) funding through public-private collaboration under the auspices of the Columbia, South Carolina-based SCRA Applied R&D sector Prosthetics and Orthotics Manufacturing Initiative (POMI). The sockets produced with this technology are up to 50 percent lighter, cost 40 percent less to manufacture, are produced quicker, and have longer lifecycles than traditionally fabricated sockets, according to SCRA.
Project collaborators include Friddle's Orthopedic Appliances, Honea Path, South Carolina; Mentis Sciences, Manchester, New Hampshire; SensorTech Corporation, Greenville, South Carolina; Georgia Institute of Technology (Georgia Tech), Atlanta; Clemson University, South Carolina; and other federal and state government agencies, private companies, and charitable organizations.
Dennis Clark, CPO, founder and president of O&P1, Waterloo, Iowa, who uses this new technology, provides some examples of how light the sockets can be. "We made a prosthetic forearm socket with a wrist connection- no terminal device-and the wrist connection was more than 50 percent of the weight of the socket." Clark says. "And the socket is incredibly strong!" In another example, he says that the new sockets reduced the overall weight of the prostheses used by a young soldier with bilateral transtibial amputations by 2.6 pounds-1.3 pounds apiece. "That's a significant reduction in weight and increase in functionality for someone walking a tremendous number of steps per day; you're saving them from lifting an additional ton or more each day." The soldier also reported improved proprioception. "He could feel the ground, the gas pedal, the brake pedal better," Clark says. "He still used the same prostheses as he had before; the only change was the sockets."
Led by SCRA Program Manager Chris Norfolk, PhD, on behalf of the Office of the Secretary of Defense, POMI was initiated to aid in the care of wounded warriors returning to combat; however, the technology is now being used in the private sector by Spyder Technologies, a company incorporated in 2011 by Clark and Frank Friddle Jr., CO, owner and president of Friddle's Orthopedic Appliances.
The custom sockets are manufactured exclusively at their respective central fabrication facilities, Clark says, adding that the system has been used to manufacture sockets for hip disarticulation, transfemoral, transtibial, transradial, and transhumeral levels.
"Practitioners can use any socket design they choose," Clark says. "What the individual practitioners do in their clinical practice- in terms of shape, liner, whatever they normally do-they can still do it. We have the standard, techniques, and technology in place where customers know exactly what they are getting. The technology produces consistent, clinically engineered results; we have a quality-assured standards checklist that is identical in both locations."
Exceeding the ISO Strength Standard
Mentis Sciences developed the carbon-fiber braiding machine that Friddle's received and began using in March 2010; O&P1 began using the technology about six months later. Clark says the sockets produced using this technology exceed the International Organization for Standardization (ISO) strength standards by twice as much or more.
"We have been developing the process and have had all the different socket variations we fabricate tested for strength against the ISO standard," Clark says. "Each socket is clinically engineered based on the patient's K-level and weight up to 500 pounds. Thus we know that each person's prosthetic socket is appropriate for his or her K-level and weight, and that it exceeds the ISO standard for strength."
Clark notes that the issue of socket strength standards has been addressed in Thranhardt lectures and papers presented at the Annual Meeting & Scientific Symposium of the American Academy of Orthotists and Prosthetists (the Academy) and the American Orthotic & Prosthetic Association (AOPA) National Assembly. He cites a paper presented at the 2012 Academy meeting, "Industry Wide Evaluation of Prosthetic Socket Strength," by Maria J. Gerschutz, PhD, et al., which describes the testing of 98 sockets against the ISO strength standard. (Author's note: An abstract of Gerschutz's 2012 Academy presentation can be viewed at www.oandp.com/link/163. For expanded reading on this subject, see "Strength Evaluation of Prosthetic Check Sockets, Copolymer Sockets, and Definitive Laminated Sockets," Journal of Rehabilitation Research & Development vol. 49 no. 3 (2012), Maria J. Gerschutz, PhD, et al., which can be accessed at www.oandp.com/link/164)
The sockets tested in the study were provided by three central fabrication facilities, three private practice facilities, and three military/U.S. Department of Veterans Affairs (VA) hospital facilities. Thirty-four diagnostic sockets, 31 copolymer sockets, and 33 definitive laminated sockets were included. "A majority of the sockets, regardless of type, failed to pass the same strength standard other prosthetic components are required to pass [for the given geometry tested in the study]," the authors noted. "Socket strengths also varied significantly. Potential sources of variability for diagnostic and copolymer sockets included thickness and fabrication method. Diagnostic sockets also varied by material type. In contrast, definitive laminated sockets were influenced more by construction material and technique." The study suggests several areas for improvement in socket fabrication: (1) the development of industry-wide best practices; (2) the optimization of practices to reduce variability; and (3) the evaluation of new materials and practices with improved strength properties.
Clark says, "That is exactly what Spyder Technologies is working toward. When we work with patients, they want to know what they are getting, and when we work with payers, they want to know what they're buying." Because the sockets have been tested against ISO standards, Clark says they are "able to guarantee the strength and durability of our product for patients, providers, and payers alike."
Friddle adds that there is no additional cost over traditionally fabricated carbon-fiber sockets to manufacture sockets using the carbon-fiber braiding system.
Creating Carbon-Fiber Braided Sockets
To create the sockets, carbon fibers are braided individually to the patient's shape rather than the socket being laminated with manufactured carbon stockinette, Clark explains. "The practitioner sends us an aligned diagnostic socket, and we send back a finished socket or completely finished prosthesis with the socket fabricated with Spyder technology. The definitive sockets are braided automatically on a machine developed by Mentis Sciences. The technician is able control the braid while it is being woven directly on the positive plaster mold or foam carving. Similar to traditional methods, resin is bagged and infused using vacuum pressure." (Editor's note: To view the braider in operation, visit www.oandp1.com/ and click on the Spyder Technologies video).
According to SCRA, the braider is capable of achieving fiber densities that are unobtainable using traditional fabrication methods and materials, producing substantially lighter sockets. "The braider is capable of triaxial braiding, which aligns fibers directly along the socket's main axis," SCRA noted in its POMI Przirembel Prize Application. "Studies of socket failure indicate that fibers aligned in this direction are important for overall socket strength. Further, the braiding of the metallic attachment point into the composite structure results in superior strength. The braider allows for the selective reinforcement of the structure at highly loaded areas, allowing tailoring of properties." Friddle adds, "Being able to control fiber orientation and density at any transverse level of the socket is the key to the entire process."
Shape-memory composite materials used in the application are "activated" by heat and can easily be influenced to assume other shapes, including changes that positively affect socket fit. This ability allows for easier adaptation to changes in socket volume and other anticipated changes, thus increasing the life of the socket, according to SCRA. "These materials are supplied as both resins and foam inserts, which can be positioned in areas anticipated to require change in the future."
The braiding machine was exhibited at the Academy Meeting in March and will also be on display during the AOPA National Assembly in September, Clark says.
"The patient feedback we have received from the new technology has been nothing less than phenomenal," Friddle says. "We are seeing more advantages than we had originally anticipated."
"Innovation is the process of turning ideas into manufacturable and marketable form," observed noted software engineer Watts Humphrey (1927-2010). The O&P industry, including central fabrication, seems well on the way to following Humphrey's dictum. One wonders what other new technologies and adaptations of existing technologies to O&P are in planning or rehearsal, just waiting their turn to step onto the stage.
Miki Fairley is a freelance writer based in southwest Colorado. She can be reached at