Body Power: Pushing the Functional Envelope

Power has a variety of meanings. It refers to the ability to have influence, authority, or control over people, circumstances, or events; the ability to act or to do something; a force or energy that can be applied to work; and physical or mental strength. When an accident results in upper-limb loss, all of these definitions may come into play, leaving a person feeling powerless and out of control. Upper-limb loss can deprive individuals of much of their ability to participate in areas around which so much of life revolves-family, work, recreation. Even everyday activities such as eating, combing hair, and dressing can become difficult or even impossible. Regardless of the cause, learning to be functionally independent with upper-limb loss is a challenge for the patient and his or her healthcare team. For the prosthetist, restoring quality of life through improving function involves creating a prosthesis with the largest functional envelope possible within the parameters of the amputee's circumstances.

"The functional envelope involving the upper limb consists of multiple spheres of action that are integrated and determined by the shoulder complex, elbow, wrist, and hand," writes Jayne Drummey, CPO, in "Enhancing the Functional Envelope: A Review of Upper-Limb Prosthetic Treatment Modalities" (The Academy TODAY, June 2009).

Bob Radocy tests his COBRA terminal device. Photograph courtesy of TRS.

Amid the dazzling developments in high-tech upper-limb prosthetic technologies, body-powered prostheses may seem like a family sedan in an array of Lamborghinis and Ferraris; however, they remain widely prescribed and are the workhorses of prosthetic options, able to take on heavy-duty industrial and agricultural work and other activities involving water, dirt, grime, excessive vibrations (such as with some power tools) and hard use-factors that are much more likely to damage electronic devices. Innovations in componentry and advances in clinical care are also allowing body-powered, upper-limb prostheses to push the functional envelope.

Innovations Increase Function

Just as the desire to create a mind-controlled, powered upper-limb prosthesis with multiple degrees of freedom has driven innovations in multiarticulating, myoelectric devices-not to mention surgical procedures to improve the link between the device and the user-the need for something better or original has driven creative energies and launched new devices and enterprises in the body-powered space as well. While The O&P EDGE is not able to include an exhaustive list of all recent developments, what follows are several innovations that were developed either wholly or in part by persons with upper-limb amputations or deficiences.

Anchor System Eliminates Harness

Born with a forearm limb deficiency, Debi Latour, MEd, OTR, OTL, Springfield, Massachusetts, had been wearing a body-powered prosthesis with a Figure 8 or Figure 9 harness, when, after years of wear, she started experiencing problems with her contralateral limb. She then put her training as an occupational therapist to work to find a solution: the Ipsilateral Scapular Cutaneous Anchor (the Anchor) system.

Powered mainly through the ipsilateral scapula, the Anchor consists of a cable attached to a plastic patch that adheres to the skin at the scapula. Because the harness is eliminated, benefits of the system include increased comfort, improved cosmesis, and decreased impingement at the axilla, according to the paper, "The Ipsilateral Scapular Cutaneous Anchor: Implications in Consumer Use," which Latour presented at the 2011 Annual Meeting & Scientific Symposium of the American Academy of Orthotists and Prosthetists (the Academy). Other benefits include more symmetrical bilateral muscle development, decreased repetitive motion in the contralateral shoulder, and improved function, especially in bilateral tasks. Consumers have reported high satisfaction rates and more natural, intuitive use. Latour has launched Single-Handed Solutions, Springfield, to market and sell the Anchor system.

Running Shoes Inspire Socket Design

Retired U.S. Marine Corps Capt. Jon Kuniholm, who underwent a right transradial amputation after being wounded in Iraq, is continually seeking improved upper-limb prosthetic socket solutions. Kuniholm cofounded the Open Prosthetics Project, an open-source collaboration among individuals with amputations, researchers, and others. He has developed an initial prototype of a softer, more comfortable socket and launched a company, StumpworX, Durham, North Carolina. The socket is inspired by athletic shoes that provide stiffness where needed and flexibility where more foot movement is required, according to a TIME magazine article, "Breaking the Mold in Prosthetic Arms," by Nate Rawlings, published online March 26, 2013. "The prototype permits more movement," according to Rawlings, "and like running shoes, it allows for changes in the size of the arm." The socket won't cause friction and rubbing on hot days when the residual limb swells during activities, he adds.

Elegant, Simple, Tough

Bill Hottel uses the V2P in an industrial setting. Photograph courtesy of ToughWare Prosthestics.

It's not often that simple, affordable prosthetic technologies created primarily for amputees in developing nations make an impact on U.S. prosthetics. But that has been the case for ToughWare Prosthetics, Westminster, Colorado, especially with its Variable Pinch-force Prehensor™ (V2P) terminal device. In fact, all of the upper-limb specialists interviewed for this article mentioned the V2P. Chris Lake, CPO, LPO, FAAOP, Lake Prosthetics and Research, Euless, Texas, says, "A new device, the V2P from ToughWare, has adjustable grip force-gentle pinch for more delicate items and strong pinch when you need it. It has been very well accepted by bodypower prosthesis users."

The V2P is a voluntary opening (VO) design to help prevent contralateral injuries and overuse syndrome, explains Brad Veatch, PE, founder and owner. "You don't have to use as much force to operate the device and don't need to remove it to add or subtract bands to get the pinch force you need. Some bilateral amputees can change their bands without help-no tool or assistance needed."

The V2P is fabricated in three versions using different materials and methods. Injection molding using EMS-GRIVORY polymer produces a strong, lightweight model that is popular with bilateral amputees. Another version, which Veatch describes as "our standard V2P workhorse," is made of aluminum alloy, and the third version is made with additive manufacturing technology developed by ExOne™, North Huntingdon, Pennsylvania. "Additive manufacturing allows us to create parts with the strength of stainless steel but with internal structures you can't make with machining or casting. It has really opened up new manufacturing options," he says.

Adaptive Devices Increase Function

A user demonstrates the N-Abler II with a mini hacksaw connection. Photograph courtesy of Texas Assistive Devices.

Texas Assistive Devices, Brazoria, and TRS, Boulder, Colorado, have long been the go-to companies for specialized terminal devices and other products to enlarge the functional envelope for body-powered prosthesis users. TRS focuses mainly on sports and recreational devices; Texas Assistive Devices specializes in work-related and activities-of-daily-living componentry. A new product from Texas Assistive Devices is the Quick Disconnect Myo-Electric Wrist Adapter. The device enables myoelectric prosthesis users to switch easily from a myoelectric hand to the N-Abler® II or a conventional terminal device. Both companies were founded or cofounded by individuals with upper-limb amputations who were frustrated with what was available at the time, and rather than accept the status quo, they created their own solutions.

Body-powered prostheses are often preferred for more rugged activities such as gardening or landscaping. Photograph courtesy of Texas Assistive Devices.

A new company, Amputee Mobility Products, Weatherford, Texas, was founded by bilateral upper-limb amputee David Worley, a longtime patient of Lake's. Amputee Mobility Products offers adaptive knives and SpinWare, which features a patented, unidirectional step-rotation design for secure, consistent independent eating.

Why a Body-Powered Prosthesis?

Technological advances have made myoelectric upper-limb prostheses much more appealing; however, body-powered devices offer some distinct advantages, our experts explain. "Electric prostheses can be noisy; body-powered devices make very little noise," Lake notes. "A myoelectric prosthesis is heavier than a body-powered, especially a concern for higher levels of amputation." He adds that comfort level with electronics and "gadget tolerance" can be factors when deciding whether or not a myoelectric prosthesis is a good option.

Jack Uellendahl, CPO, Hanger Clinic, Phoenix, Arizona, who also specializes in upper-limb prosthetics, mentions that there is a greater sense of proprioception with body-powered prostheses. "Electric prostheses don't provide as much feedback," he says.

The steering ring used with the N-Abler II aids with driving. Photograph courtesy of Texas Assistive Devices.

TRS President and CEO Bob Radocy, an advocate for and wearer and manufacturer of voluntary closing (VC) Grip Prehensors and other VC technology, says, "I believe that a young, active person with a unilateral, transradial hand absence equipped with modern VC prehensor technology can outcompete and outperform anyone wearing a bionic or alternative VO system because of the speed, natural reflexive control, and gripping power available when using these systems." He emphasizes, "There is really no competition when these technologies are compared fairly in rigorous tasks requiring bimanual, bilateral control-VC prehensor, body power is simply higher performance!"

For individuals with transhumeral amputations, a body-powered prosthesis, typically worn with a sock, can be easier to don and doff. "Generally, a myoelectric is more difficult since the electrodes have to be in contact with the skin, so a more elaborate donning technique is required," Uellendahl says, adding, "Even though in my practice I fit more myoelectric-control prostheses, when it comes to the transhumeral level, I fit far more with hybrid control-a body-powered elbow with a myoelectric hand."

"Body-powered elbows are more spontaneous and easier to precisely position throughout the range of motion than electric elbows," Lake observes. "When used as a hybrid configuration, the patient is able to have more fluid control of the prosthesis with simultaneous operation of the elbow and terminal device."

Upper-limb specialist Randall Alley, CPO, LPO, CEO and chief prosthetist at biodesigns, Westlake Village, California, notes that clinical preferences for cable-driven technology have typically revolved around factors such as weight, weight distribution, durability for specific activities, and simplicity of operation. However, he notes, "Sometimes body-powered systems are more complex than their externally powered counterparts."

Other advantages to body-powered upper-limb prosthetic systems include a lower initial cost, lower maintenance costs, and easier repairs.

Body Power: Why Not?

No piece of technology is without some drawbacks. Alley points out some of the disadvantages to body-powered prostheses: increased axilla pressure, risk of nerve entrapment syndrome, a more limited functional envelope, a limited gripping surface area, increased gross body motion requirements, and "most of all...the absolute lack of adequate prehensile force in voluntary opening terminal-device designs means that the sound side in a unilateral amputee consistently gets overused, increasing the potential for critical adverse medical conditions."

A book on military medicine, Care of the Combat Amputee (Edited by Walter Reed Army Medical Center Borden Institute, 2010), points out that because of the forces exerted on the residual limb, careful consideration is required for patients with fragile, healing tissues. "If a body-powered prosthesis is fit too early in the rehabilitation process, patients can experience breakdown around the suture line." The tight fit of the control harness can restrict proximal joint range of motion and the effective envelope of the prosthesis, as well as limit the possible grip force of the terminal device.

Another frequently mentioned disadvantage is the appearance of cables, harnesses, and hook-type terminal devices. However, Lake devised an innovative solution for one of these issues. For one of his patients, he created a lightweight, cosmetic body-powered prosthesis by running the cable through the middle of an Ottobock hand so the cable wasn't visible.

Finding the Best Option

"There is no one prosthesis that can meet all the needs of the patient," Lake says. "And no prosthesis matches the anatomy and functionality of the natural hand." Sometimes not enough thorough consideration is given to what really best meets the patient's specific needs, he explains. Based on clinical assessment, the patient's lifestyle and goals, insurance coverage, and other considerations, some patients are clearly myoelectric candidates and others would be better suited for body-powered devices. For some, using both types is optimal, and yet others may elect not to use an upper-limb prosthesis at all. There are also occasional cases in which it simply is not clear what option is best. These patients often try out a test prosthesis that, with the help of specialized couplings and using the same interface, can essentially be several prostheses in one. Patients can use the prosthesis as body-powered, passive functional, electric, and activity-specific at different times, enabling them to determine objectively what works best for them and meets their individual goals. Payers have generally been willing to cover the extra expenses involved, according to Lake; however, he adds that about 90 percent of Lake Prosthetics and Research upper-limb patients' amputations are traumatic and are generally covered by workers compensation insurance. "It's a different type of medical and insurance team working with these patients, but many private insurers will also cover these additional expenses," he says. This way, if the best option turns out to be a body-powered or hybrid system, a costly high-tech device won't end up in a closet.

Patients' Perspectives

"Keep Your Life in Drive"

Price is shown here with a modified vice grip that works in conjunction with his prosthesis. Photograph courtesy of biodesigns.

No one can attest to the fact that there is no "one-size-fits-all" prosthetic solution better than the patients themselves. Bobby Price of Delano, California, for example, is the kind of guy who loves his life, his work, and his family, and he doesn't let much of anything slow him down or dim his upbeat attitude. A mechanic supervisor for a helicopter company that specializes in aerial spraying, Price was servicing equipment on June 23, 2009, when his life changed in an instant. Suddenly, his left hand was sucked into a fan and torn off.

After surgery, Price was back on the job in three weeks. He later received his first prosthesis, a body-powered device, which he describes as "heavy, durable-tough! After I'm gone, it'll still be around forever," he says.

Price later went to biodesigns for devices to better fit his lifestyle and variety of needs. Alley created three: a body-powered prosthesis for work and strenuous recreation; a myoelectric prosthesis for social life and lighter activities; and a body-powered adaptive device for cycling.

Alley describes Price's body-powered prosthesis as "pretty souped-up" with the biodesigns High-Fidelity™ (HiFi) High Performance interface, a TRS Voluntary Closing Grip 3 terminal device, and a Sure-Lok cable-locking device. The Sur- Lok, which was developed by Alley, Radocy, and Veatch, enables locking down the Grip 3 in an infinite number of positions rather than having to maintain constant cable tension while in use. Price's myoelectric prosthesis uses the HiFi interface and a Steeper bebionic hand, and his body-powered, adaptive prosthesis uses the HiFi and TRS Criterium Bicycle Handlebar Adapter.

Price makes all his own adaptive tools as needed for his body-powered prosthesis. Although he has had to overcome a number of challenges, he faces them all with the same attitude: "Keep your life in drive; don't put it in park."

Out-of-the Box Solutions

Avraham Hertz, 73, an Israeli citizen and Israeli defense forces veteran, has been a bilateral upper-limb amputee for more than 54 years. He describes his experience on the Lake Prosthetics and Research website: "I have been using body-powered prostheses with hooks ever since my injury, enabling me to have...fully independent functioning-from dressing and writing to driving and traveling overseas," he says. For the past three years, he has suffered from swelling in both residual limbs and has had to be fitted repeatedly for new prostheses. Hertz adds, "[Lake] goes out of his way and out of the box to find solutions to multiple complex barriers...."

Ten-Year Old Flips for Adaptive Devices

For Sydney Howard, ten, gymnastics is a passion. Despite a congenital left forearm deficiency, this California girl performs hip circles, cartwheels, handsprings, and other gymnastic moves with agility and grace. She enjoys soccer, basketball, and other sports. Adaptive sports terminal devices have enabled her to increase her functional envelope: Sydney uses a TRS Super Sport Mitt for soccer and basketball and the new TRS Swinger for gymnastics along with the Shroom tumbler. Although she has used the Shroom for about six years, she just began using the Swinger in January. Nervous about using the device at first, she is now enthusiastic about its 360-degree performance and a "stance saddle" for above-the-bar forearm stability and support. (Editor's note: Howard's story is featured in the October 2012 issue of The O&P EDGE: "Flying Like a Birdie")

Expanding the Functional Envelope

Photograph courtesy of Texas Assistive Devices.

New developments continue to expand functional possibilities for users of body-powered upper-limb prostheses. For example, researchers at the Rehabilitation Institute of Chicago (RIC), Illinois, and Northwestern University, Chicago, have developed a new VO/VC terminal device that allows users to switch easily between the two modes. The new device may allow body-powered prosthetic hands to become more functional by combining the best features of both modes-the VO's ease of use and the VC's large pinch force-in one device, the researchers point out in a paper presented at the 2013 Academy Annual Meeting & Scientific Symposium.

Body power continues to be a vital part of the prosthetics armentarium. As Leonardo da Vinci said, "Simplicity is the ultimate sophistication."

Miki Fairley is a freelance writer based in southwest Colorado. She can be contacted via e-mail at