The O&P Edge - March 2008
'Hanging Tight': Elevated Vacuum Suspension Systems Step Forward
By Miki Fairley
"It feels like I got my leg back!"
This is how amputee Andy May described the first time he ran with a prosthesis incorporating the new LimbLogic™ VS prosthetic vacuum suspension system from Ohio Willow Wood, Mount Sterling, Ohio.
Although every type of prosthetic suspension system has advantages and disadvantages, with no one system being right for everyone, elevated vacuum suspension offers significant benefits. "Time after time, patients have commented that now the prosthesis feels like a part of them," says Jeff Denune, CP, LP, Ohio Willow Wood clinical director of prosthetics. With their previous prostheses, amputees would experience pistoning or other movement within the sockets, which made them continuously aware of them. "It's sort of like dentures," he explains. "When you wear them, you always know they're in there."
Steve Smith, BSc, director of technical service for Smith Global, Laurie, Missouri, agrees. "Amputees feel more as though the prosthesis is an extension of their body, with more proprioception and stability.
One of the most important benefits of elevated vacuum suspension is that it maintains limb volume throughout the day. With other suspension systems, amputees' residual limbs lose volume as they go about daily activities. This loosens the socket, which makes controlling the prosthesis more difficult, reduces proprioception, and increases the potential for skin damage. The amputee may add more sock layers as the day goes on, but this is a time-consuming inconvenience for busy people.
Carl Caspers, CPO, pioneered the concept. His company, TEC Interface Systems, St. Cloud, Minnesota, developed the Harmony® VASS™ (Vacuum-Assisted Socket System) in cooperation with research by the St. Cloud University Human Performance Laboratory. TEC was acquired by Otto Bock HealthCare, Minneapolis, Minnesota, in 2003.
In addition to Otto Bock's Harmony and the LimbLogic VS, current elevated vacuum systems on the market include the eVAC® from Smith Global, with other companies poised to enter the marketplace.
Exciting Impact on Transfemoral Socket Design
Elevated vacuum suspension—also known as subatmospheric technology—also is having successful transfemoral and upper-limb applications. But it's the impact on transfemoral socket design that has Denune excited. With the elevated vacuum suspension system it has been possible to design transfemoral sockets with lower trimlines, greatly increasing amputees' comfort and range of motion. Denune first revealed the brimless socket design at the 2007 Annual Meeting of the American Academy of Orthotists and Prosthetists (the Academy) in 2007. "We've been getting phone calls from all over the world; clinicians are saying they've been able to cut the brim down. The floodgates have opened."
With other transfemoral designs, whether ischial containment, narrow M-L, or others, the "sitting bone," or ischium, sits in the socket, which creates discomfort for the amputee.
"Traditionally, transfemoral sockets have been made with walking in mind, and all of the design changes have focused on holding the prosthesis securely while the person is standing up and in motion," Doug Smith, MD, medical director for the Amputee Coalition of America (ACA), explains in the article "Great Prosthetic Components Are Good, but a Good Socket Is Great" (inMotion, September/October 2004). However, the optimal shape for walking is not the best shape for sitting, Smith notes. A transfemoral socket molds up to or around the ischium to transfer weight when the person is upright; however, the socket can dig uncomfortably into the groin and buttocks when the person is seated. "Technically, it's hard to design one socket that's optimal for both sitting and standing," says Smith.
A landmark socket design, the M.A.S. socket by Marlo Ortiz, unveiled in 1999, allows far more comfort, range of motion, and cosmesis than previous designs. However, Denune notes that the socket is somewhat difficult and complex to fit and depends on a skeletal lock for control.
Commenting on one of Ohio Willow Wood's test patients, Denune says, "He's able to do things that [are] just amazing to see. He feels secure on his limb. It doesn't move in the socket, and we're able to cut the trimlines down very low."
Elevated Vacuum vs. Suction Suspension
Both elevated vacuum suspension and suction suspension use a difference in atmospheric pressure to attach the socket to the residual limb, according to Ohio Willow Wood. As air is expelled from the socket, the limb is pulled toward the socket wall and held in place by the force of the negative air pressure as the vacuum effect is created. Suction suspension normally uses a passive expulsion valve to allow air to exit from the socket but only creates a negative pressure differential when the limb begins to move. Vacuum suspension uses an active pump to create a negative pressure differential that doesn't depend upon the limb position.
"In a suction socket you still have some movement, but with elevated vacuum you eliminate almost all pistoning," says Denune.
"A suction suspension system with a one-way valve is a very good system, but the socket has to move away from the limb to start creating a vacuum," explains Scott Weber, MS, Otto Bock's U.S. marketing manager for prosthetic feet and socket technologies. "However, when you use an elevated vacuum pump system, you've already pulled the air out, and the system is locked down before you begin."
Suction suspension basically is just a sealed chamber, Caspers explains. Suspension is created during the swing phase of gait, which creates a negative pressure. "To weight bear, you have to reseat the limb into the socket, creating forces on the limb. But with elevated vacuum, you're under vacuum continuously, so there is no pressure on you as the limb is held to the socket wall."
According to Jim Colvin, Ohio Willow Wood director of engineering, the primary advantages of elevated vacuum suspension over suction suspension include more secure suspension, more even load distribution, more stable residual limb volume, and potentially improved circulation.
Both suction socket suspension and elevated vacuum suspension provide significant benefits over the commonly used pin locking system. A major disadvantage of pin suspension is the "milking" or pistoning effect of pressures on the distal part of the limb in gait.
Prosthetists try to fit transtibial amputees with sockets providing a firm connection to the residual limb without causing skin disorders and pain. However, the challenges lie in the large loads placed on the previously non-weight bearing tissues of the residual limb, which were never designed for these pressures, notes Tracy L. Beil, MS, and Glenn M. Street, PhD, St. Cloud University in the article "Comparison of Interface Pressures with Pin and Suction Suspension Systems" ( Journal of Rehabilitation and Research, November/December 2004).
"Evidence suggests that skin adapts to these stresses but also that skin health is clearly compromised," according to Beil and Street. Ulcers, epidermoid cysts, Kaposi-like sarcoma, and verrucous hyperplasia are skin conditions attributed to external pressures applied to the residual limb. "Sustaining proper circulation and fluid exchange in the soft tissues is imperative for maintaining a healthy residual limb. Pressures applied to the limb by socket systems, chiefly during ambulation, complicate this task," they note.
Some clinicians question the use of pin liner/shuttle lock suspension because of observed daily and chronic changes to the residual limb, Beil and Street continue. The symptoms most commonly seen in amputees using a locking pin system for suspension are daily reddening and swelling of the distal residual limb. Long-term changes include general thickening and discoloration of the distal tissues, which can sometimes develop into verrucous hyperplasia. "Prosthetists attribute these symptoms to the liner being stretched during swing phase, thus squeezing the limb proximally and creating a heavy localized suction distally," Beil and Street note.
However, pin locking suspension systems are not without some benefits. The chief advantage cited is that pin locking sockets can provide a strong sense of secure prosthesis attachment for amputees. To reduce the "milking" effect, some pin liners incorporate various stiffening materials to help stabilize the liner. Also, many locks are available with a one-way air expulsion valve to help provide suspension and simultaneously reduce the pistoning effect.
May Improve Limb Health, Help Heal Wounds
"There is considerable anecdotal evidence from amputees that shows [elevated] vacuum suspension improves limb health," says Street ("Vacuum Suspension and Its Effect on the Limb," Orthopädie Technik, English Ed., the German Federation of Guilds in Orthopaedic Engineering, Bundesinnungsverband für Orthopädie-Technik).
Anecdotal evidence indicates improvement in amputees' residual limb health and may even help in wound healing as well as preventing sores and other skin and tissue problems. Research is under way to explore this benefit from the technology.
"Elevated vacuum is not just about suspension; it also reduces the forces and thus many of the issues amputees cope with," says Caspers. "It allows the socket to act as a vascular pump and actually improve the blood supply in the limb." Improved circulation promotes healing and overall tissue health. Other prosthetists have told Caspers that they have put patients with open wounds or significant other skin and tissue damage in the Harmony system, and afterward the wounds have healed. "I've even had a couple of patients who were scheduled for re-amputation surgery because of wounds and other issues. I put them in the Harmony, and they healed without surgery," Caspers says.
"We believe enhanced vacuum increases blood circulation in the limb, and we've recently begun a study to confirm this," says Smith.
Not every amputee is a good candidate for an elevated vacuum system. Careful evaluation is needed, notes Denune. Both prosthetist and amputee education is important to use an elevated vacuum system effectively and to avoid problems.
"For instance, if the amputee doesn't don the socket correctly and turns on the vacuum, it can pull him into the socket with enough force to cause a blood blister or other damage," says Denune. Caspers and Smith also mention the need for amputees to thoroughly understand how to use and maintain the vacuum systems. To this end, manufacturers offer training and technical/clinical support to prosthetists in providing their systems to patients.
Total surface weight-bearing (TSB) socket designs are essential, according to the manufacturers. In addition, Medicare and many private insurers provide coverage for elevated vacuum systems.
Amputees Report Better Function, Increased Comfort
For amputees who are using elevated vacuum suspension, the innovation has been a welcome one. Stacie Broseus, who uses a LimbLogic VS and DuraLite™ foot, can ride her horses, do her barn chores, give riding lessons, and run her boarding stable business with no impairment. She also finds that she finishes her barn chores 45 minutes faster than with her previous prosthesis.
Andy May likes his elevated vacuum suspension system for running, which requires the most support. "In the past, my leg would start to piston inside the socket, making my run a lot slower," he says. "The vacuum keeps my residual limb solidly and comfortably in place."
Another amputee, quoted by Street in the Orthopädie Technik article, comments on how well the Harmony prosthesis stays "glued" to his leg, making the prosthesis feel much lighter and allowing him to wear work boots comfortably again. "Managing my horse farm with tennis shoes was often a challenge, particularly in the muddy months," he says.
Creativity, competition, and research continue to drive prosthetic progress, giving prosthetists more choices in finding what works best for each individual patient. When it comes to elevated vacuum systems, more improvements and new products are on the way. Stay tuned.
For information, visit www.owwco.com;www.ottobockus.com;www.smith-global.com
Miki Fairley is a contributing editor for The O&P EDGE and a freelance writer based in southwest Colorado. She can be contacted via e-mail at email@example.com
Original Article URL: http://www.oandp.com/edge/issues/articles/2008-03_03.asp (Reprinted with Permission of Miki Fairley)