Powered O&P

Many people — both in the O&P profession and outside it — still see electronic orthotic and prosthetic devices as the future. O&P Business News spoke with a number of professionals who say these devices are, in fact, the now and that the technology that powers them is improving every day.

High technology

The technology behind powered orthotic and prosthetic devices centers around restoring muscle action in the human body.

“That is what we want to achieve with the bionic technology that we are developing today,” said Ian Fothergill, BSc O&P, MBAPO, from Ossur Americas in Aliso Viejo, Calif.

To accomplish this, however, requires more than just a battery.

Parents walking with child
Image reprinted with permission of Otto Bock HealthCare.

Andy Sykes, CEng, BSc, electronic design engineer for Endolite, Blatchford’s North American division headquartered in Centerville, Ohio, describes the difference between actively powered and passively powered prostheses as the ability for the device to move when not attached to the amputee. Either way, these powered devices aid amputees in completing tasks such as walking easier than they could complete them before.

“If an amputee is walking at a speed much slower than the leg’s optimum, he actually has to hold his hip back to stop the leg from kicking through too quickly. Conversely, if he is walking much more quickly than the limb is set up for, he has to throw the hip forward,” Sykes said. “[He] gets a more ungainly walking action when walking at nonoptimal speeds, which in turn requires more energy to drive that limb.”

By using a pneumatically controlled system, however, the device is able to adjust the resistance, regulating how far and the rate at which the leg bends during swing phase. When the amputee flexes his leg, it builds up pressure in the air springs, which assists the limb’s swing as it is going back into extension. This level of assistance creates a much more natural gait pattern with variable walking speed, he said.

Lower extremity

Lower extremity devices have the dual responsibility of supporting amputees and providing their ability to walk. Electronic prosthetic devices offer both with a more natural — and more effortless — gait.

The first area that manufacturers consider when building a powered prostheses is sensored technology. Sensors in the device need to determine the patient’s intention and control its movement so that it synchronizes with the patient’s sound leg, or so that both devices are matched, in the case of bilateral amputees.

Additionally, the sensors must recognize the difference between intended and unwanted movement, like trips and falls. To do this, the technology accounts for reciprocal patterns in the amputee’s gait and ascertains his or her next step based on the last step. All of this information is computed in the device’s microprocessor.

Fothergill described the Power Knee’s technology: the device has multiple microprocessors, which assess and interpret the intention of movement and provide an output to the device’s motor. The motor then drives the prosthesis to the required position.

In addition to the microprocessor, or multiple microprocessors, Ossur’s devices include basic artificial intelligence that learns gait patterns. The idea behind artificial intelligence is to have a device that essentially could program itself.

Powered devices
Powered devices aid amputees in completing tasks such as walking easier than they could complete them before.
Images reprinted with permission of Endolite.

Ossur is not the only company to enter this stage. Endolite, the first company to introduce commercial electronically controlled knee mechanisms with its Intelligent Prosthesis, has since developed an even smarter product. In addition to the product line’s electromechanical technology, the Smart IP and Smart Adaptive also offer this automatic programming, which programs the device itself while the amputee performs a certain set of movements.

The final aspect of powered technology is the source used to power the device. Passively powered devices use the patient’s body power and stimulation of muscles to perform the desired function. Actively powered devices, on the other hand — Ossur’s Power Knee — carry an external power source, such as an electric motor.

“To date, we have been somewhat limited … but what we are hoping is that, as this technology advances, we will get motors that are quieter, more efficient, perhaps even based more like linear muscles,” Fothergill said.

Ongoing research in the field of artificial muscles is working on several materials that react like human muscles. Those performing this research, as well as those who would benefit from the result, anticipate increased power and decreased size as the technology advances. (For more information about artificial muscles, see “Strength in Innovation,” in the July 1, 2007 issue of O&P Business News.)

In 1997 Otto Bock HealthCare introduced the C-Leg, the first microprocessor controlled knee to control both swing and stance phase, said Gregory Schneider, CP, a research and development prosthetist at Otto Bock.

This device, Schneider explained, uses a hydraulic cylinder and onboard microprocessor that alters the resistance to knee flexion and extension through a series of valves and motors. By constantly monitoring the gait cycle, gathering information from strain gauges in the distal end of the pylon, and reading the angle of knee flexion through a sensor at the knee, the microprocessor determines when to change the resistance.

Upper extremity

To perform the specific tasks required of upper extremity prosthetic devices, manufacturers often turn to powered technology.

Otto Bock introduced its first externally powered MyoBock hand in 1967. The technology takes advantage of electric motors, batteries and microprocessor control systems to both open and close the hand, with inputs from either EMG signals or a variety of switch options, Schneider told O&P Business News.

Through the use of electromyography (EMG) signals, amputees control their prostheses with their residual muscles. The EMG signals from the biceps and triceps, for example, can be used to control elbow flexion and extension, Schneider said.

For Touch Bionics, upper extremity technology revolves around three main facets: the mechanics and infrastructure of the device; the microprocessor and software that run the device; and the device’s cosmesis, whether high-tech or natural, Phil Newman, director of marketing for Touch Bionics, said.

Last year the company launched the i-LIMB Hand, the world’s first fully articulating and commercially available bionic hand. For this prosthesis, Touch Bionics took the technology used in myoelectric devices and stretched it. While the prosthesis operates using the two input signals familiar with other myoelectric systems, the i-LIMB Hand also offers individually powered and individually articulating fingers, as well as a thumb that rotates into different positions. The individual finger articulation and digit stall system provide patients with the ability to close their hands around whatever objects they want to hold, Newman said.

These issues — and therefore the technology to solve them — are unique to the field of upper extremity prosthetics. Any specific tasks amputees complete require complex device functions by the manufacturers.

Orthotic devices

Bioness is one company that has introduced the world to powered devices for patients in need of orthotic intervention due to a number of conditions
Bioness is one company that has introduced the world to powered devices for patients in need of orthotic intervention due to a number of conditions.
Image reprinted with permission of Bioness.

Most of the hype of powered devices goes to prostheses, but electronic orthotic devices also serve a significant amount of the O&P patient population.

Bioness in Valencia, Calif. is one company that has introduced the world to powered devices for patients in need of orthotic intervention due to stroke, Multiple Sclerosis, spinal cord injuries, traumatic injuries and other conditions.

Keith McBride, MPT, DPT, director of clinical support and education for Bioness, works with electrical stimulation powered devices for orthoses.

“The most common devices currently deployed now in orthotists’ offices are for foot drop stimulation,” McBride said.

These devices are used to excite paralyzed muscles in people with upper motor neuron diseases or pathologies, to activate the muscles that control the ability to lift the foot and clear the toes while walking, he said.

“This would be as an alternative to the conventional treatment of foot drop by an orthotist with an ankle foot orthosis.”

Max benefits

Patients should consider carefully with their physicians and practitioners the value of using powered devices. Most practitioners, however, cannot deny the obvious benefits to both patients and practitioners.

Some upper extremity amputees enjoy the freedom of switching from harness systems to externally powered prostheses. They can increase their range of abilities as well, Schneider said, and most important, amputees are able to increase their grip force with externally powered prostheses, without having to increase the power they exert.

With this freedom also lifts many issues that arise in the amputees’ sound limb stemming from the auxiliary pressure of the harness.

For lower extremity amputees using electronic prostheses, perhaps the most significant benefits are the stability and security provided by microprocessor stance control, Schneider said.

“The stance control of the C-Leg product line provides absolute stability at heel strike since the stumble recovery is always ready,” he said. “In clinical studies the C-Leg has been shown to reduce stumbles and falls in amputees.”

Sykes had a similar conclusion.

“I think Greg Schneider would probably agree that [the C-Leg’s] main strength is in providing enhanced stability, whereas I would say that [Endolite’s] Adaptive device is much better at providing a more biomimetic gait,” he said.

Of all the electronic devices available, Sykes said that some are better at enhancing stability over the range of gaits — such as stair descent, ramp descent and level walking — and others offer a stronger focus on improved gait. The ultimate goal for amputees is one device that completes both tasks.

On the other hand, any device that provides too much assistance or requires too much energy output serve more to harm the amputee than to benefit.

For orthotic patients, powered devices offer not only the electrical stimulation to the ankle and foot, but the ability to teach patients how to walk again.

“Although there has been some advacement, an ankle foot orthosis tends to be more of a compensatory measure, meaning its benefit is fairly static in nature. Functional electronic stimulation can provide the same immediate benefit, but it also can facilitate recovery, on the local level by strengthening the muscle and on a more central level by helping the patient relearn a more normalized gait pattern,” McBride said. “Since the appropriate patients will walk physiologically closer to normal, while receiving the established effects of electrical stimulation, over time can continue to make gains in their ability to walk, specifically in their gait speed, stability and symmetry.”

The powered orthosis approach can generate motor recovery in orthotic patients, and that is what separates it from the AFO, he said.

Near future

Woman walking with powered prosthetic device
Ossur is already working toward the next generation of the Power Knee, the Proprio Foot and the Rheo Knee.
Image reprinted with permission of Ossur.

Research and development teams all over the world — from military programs to private universities — are hard at work testing out new technology that will push the limits of powered O&P devices. To truly take advantage of this new technology, however, patients, practitioners and other health care professionals must accept the unknown.

For many of the devices currently available, manufacturers have glimpsed that new territory. Ossur, Fothergill said, is already working toward the next generation of the Power Knee, the Proprio Foot and the Rheo Knee.

Researchers at Endolite are focused on emulating amputees’ sound legs, both in passive and active technology, Sykes told O&P Business News.

“We have started to demonstrate that with one of our new products, the Echelon, which is essentially a hydraulic ankle that allows for ankle movement,” he said. “That has lots of major benefits. It is a self-aligning ankle, which enhances the alignment and the performance of the knee as well, be it a mechanical knee or an electromechanical knee.”

Otto Bock’s upper extremity team also has been developing its technology to present updated devices to the O&P community. The Michelangelo Hand, for one, will offer multiple grip patterns and improved compliance of the hand, Schneider said, allowing amputees to use their hands more naturally and with better grip of objects.

The DynamicArm TMR will use current technology in conjunction with targeted muscle reinnervation (TMR), a surgical technique pioneered by Todd Kuiken, MD, PhD at the Rehabilitation Institute of Chicago. This technique, which improves myoelectric control for amputees by increasing the number of EMG inputs available to the prosthesis, will offer amputees better control of the DynamicArm externally powered prosthesis. Schneider expects this device will be released before the end of the year.

Touch Bionics readied itself for the next generation of input signals prior to coming to market last year. A device like the i-LIMB Hand, with multiple output patterns, will have an advantage on other devices with only two input control signals, Newman said. In the meantime, Touch Bionics also has been developing that technology in the background.

“The job will never be done in upper limb because everybody is trying to push the boundaries of the next step,” Newman said.

Orthotic devices will reach a ceiling with surface stimulation, however, McBride said. At that point, the next step for technology will be implantable functional electrical stimulation.

i-LIMB Hand
The i-LIMB Hand’s individual finger articulation and digit stall system provide patients with the ability to close their hands around whatever objects they want to hold.
Image reprinted with permission of Touch Bionics.

Bioness is working on the Bion, “a self-contained battery-powered stimulator that can be placed near a patient’s nerve through an outpatient procedure, and then be activated automatically or externally through sensing technology,” McBride said. “The goal will be to simplify this to almost an invisible foot drop stimulation system.”

He said that the Bion currently is in clinical trials.

McBride’s advice to orthotists: “Approach the technology with an open mind and look at it as a benefit not only to your practice but to your patients,” he said.

Additionally, practitioners and patients should be open to less common uses for these powered devices.

“The survival of advanced prosthetics will rely, I believe, on the whole industry getting behind one concept: that these devices are not for the high-functioning athletes and those that have the ability, but those who are critical and who are losing the ability to mobilize themselves,” Fothergill said.

He would like to send the message that these advanced devices should be considered for the elder population for whom an amputation should improve the quality of their lives, instead of sentencing them to an early retirement.

This objective brings to light the work of proving medical necessity for such advanced devices in an advancing-age population. There are a number of studies available that show that physically active patients are healthier, which ultimately means less money spent on their health care. Practitioners should make the effort to learn about new technologies and the ways new devices can benefit their patients — those of all ages.

For more information:

Editor’s Note:
This article includes a small representative sample of motored O&P devices. O&P Business News does not intend to promote any particular devices, nor to achieve an industry-wide consensus on the issue.

Stephanie Z. Pavlou is a staff writer for O&P Business News.

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