The issues that challenge prosthetic liner and sleeve manufacturers are age-old: durability, residual-limb volume fluctuations, temperature and moisture control, and skin health. The solutions that are in development, however, are entering a whole new world. Innovations range from elegantly simple advances to amazingly sophisticated breakthroughs involving embedded computerized sensor systems. As elevated vacuum prosthetic technology grows in popularity, liners and sleeves will undoubtedly play a significant role. New, "smart" materials that can repair themselves or change their shape, thickness, softness, or durometer in response to changes in the socket environment to maintain fit and comfort may also step forward.
Some of the developments under way are so new, in fact, that several major manufacturers were unable to divulge many details at the time of this writing.
Although it is not possible to include all liner and sleeve manufacturers or research projects, this article reviews some of the newer liners, sleeves, and related products that are available on the market, previews what's coming soon, and provides a glimpse of what's on the horizon.
Addressing Liner Slippage
Ottobock's Anatomic 3D PUR Liner, introduced in 2011, combines several innovations to solve common problems such as liner slippage when skin moisture builds up. The liner uses a textured inner surface to maintain good skin contact despite moisture. Moisture collects in the "valleys" of the textured material while the "peaks" maintain good contact, explains Scott Weber, senior market manager for Ottobock, Minneapolis, Minnesota.
The nonstick outer surface, a Parylene coating bonded to the urethane using a chemical vapor deposition (CVD) process, allows easier donning and doffing. The liner's Anatomic Specific Geometry (ASG) design strategy addresses the problem of comfort and range of motion during knee flexion by having thicker gel walls in areas needing more protection and thinner gel walls in areas requiring greater flexibility; the liner also provides 20 degrees of pre-flexion for ease of bending and reduced wrinkles in the popliteal area. The liner is also available with SKINGUARD® antibacterial additive, Weber says.
Aligning the Liner Pin
The Ottobock MagnoFlex® Shuttle Lock helps solve the difficulty that individuals with amputations, especially those with vision or dexterity problems, sometimes have in aligning the locking liner pin with the socket hole. The device was shown at the 2012 National Assembly of the American Orthotic & Prosthetic Association (AOPA) and is expected to be released in the United States this year, according to Weber. The MagnoFlex features a flexible pin and a magnet in the shuttle lock. "As the amputee is settling into the socket, if the pin doesn't hit exactly in the middle, the magnet will help guide the tip toward the center, and the pin can flex and slide to align the liner…properly with the socket," Weber explains.
The Aura and Echo Locking Seals from Evolution Industries, Orlando, Florida, are designed to work with expulsion or vacuum systems. The Aura, released in late 2011, is designed for soft tissue density, and the Echo, introduced in July 2012, is designed for medium to firm tissue density. "Using the locking seals with an elevated vacuum system provides a very secure system that doesn't require a knee sleeve," says Craig MacKenzie, CP, RTP(c). "The durability of most knee sleeves is terrible; bump against something and you can get a hole in them. But with Össur's off-the-shelf seal-in liners [Evolution Industries is an Össur company] or the customizable Aura and Echo, the seal is internal to the socket and can't be damaged."
MacKenzie continues, "With the Aura and Echo, we can put the seal anywhere you want. For instance, for a really long [residual] limb, such as with a Symes patient, we can put the seal 13 inches from the distal limb and use all that surface area for sealing and suspension."
Taming Volume Changes
Technology and design developments from Össur, headquartered in Reykjavik, Iceland, tackle longstanding prosthetic fit and comfort problems, including daily residual-limb volume fluctuations, skin sensitivity, and sufficient liner and sleeve flexibility for comfort and range of motion.
The new Iceross® Seal-In® V transtibial liner, introduced in January, combines the best features of its previous iterations, the single-seal Iceross Seal- In liner and the five-seal Iceross Seal-In X5, according to Diane-Marie "Mardi" Herte, Americas product manager, prosthetics, Össur Americas, Foothill Ranch, California. The latest version incorporates volume adaptive blades (hence, the "V" in the product name) behind the seal, which can accommodate up to an eight-ply volume change. "The volume adaptive blades adjust to limb shape as it fluctuates in volume throughout the day," Herte explains. "In the morning, when the amputee's residual-limb volume fills the socket, the volume adaptive blades lie flat. However, as the volume shrinks with activity during the day, the blades stand up and push, maintaining contact to ensure that the seal is adhering to the socket wall to provide a secure and safe suspension."
Both the Seal-In V and Össur's Iceross Comfort® Wave S Liner, introduced in the fall of 2012, offer the Wave design innovation: horizontal "waves" that allow more stretch over the patella while reducing bunching in the popliteal area for pressure relief and easier knee flexion.
The Iceross Comfort Wave S liner is designed for patients with thinner or more sensitive skin such as geriatric or dysvascular patients. The liner doesn't include skincare ingredients, "since some patients prefer different options," Herte explains. "However, the silicone formulation provides a smoother surface that is only a tad tacky with its silky inner surface for skin comfort and integrity."
Controlling Temperature, Enabling Self-Repair
Stan Patterson, CP, owner and president of Prosthetic & Orthotic Associates of Central Florida (POA), Orlando, is sharing in a $4 million U.S. Department of Veterans Affairs (VA)-funded project along with several universities and other entities. The project primarily targets ways to improve prosthetic socket comfort and function for individuals with transfemoral amputations.
Patterson is part of a team that is investigating various types of sensors and nanotechnologies to create a liner that is capable of controlling temperature inside the socket, as well as a computerized feedback system to help amputees know as they don the prosthesis whether they need to remove or add socks. (Editor's note: For more information, read "Outcome Measures: Are We There Yet?" and "Walk This Way" in this issue.)
"Being able to control the temperature within the socket environment can eliminate a lot of issues," Patterson says. "Besides discomfort, hot temperatures can cause the skin to sweat and macerate, leading to skin breakdown and possible infection. On the flip side, controlling socket temperature to provide more warmth in cold weather can prevent further circulation impairment for dysvascular amputees. We know that if we can keep the temperature close to the 98.6-degree body temperature, the skin is much less susceptible to breakdown."
Patterson's prosthetic team has patented and is utilizing a silicone liner that features a pleated, accordion-type design in the popliteal area that prevents material from bunching as the knee is flexed and eliminates tension from the distal part of the tibia. Patterson is also developing a sleeve that amputees can repair themselves. "Sleeves are something that just drove me nuts!" he exclaims. "Just like many other facilities, for every sleeve we get reimbursed for, we probably have two that we don't get paid for. Extremely active patients can go through two or three sleeves a month…. Are we going to say, 'Well, our prosthetic care has helped you get to this level of activity; now stop being so active and tearing up those sleeves?'"
Users can repair holes, "not big slashes," Patterson points out, in the sleeve by mixing a formula that enables the gel material to be added into the hole and then curing the material by heating the liner in a microwave oven for four to five minutes.
"As an industry, we've made great strides with prosthetic feet, knees, and other componentry, but when we look at sockets and interfaces, we haven't done a good job of utilizing the technologies and materials that are out there," Patterson observes. "As they say, 'If the socket don't fit, you want to quit.'"
Shear within a prosthetic socket can be a big problem for prosthesis users. "If the shear is not addressed, it can cause skin breakdown, which can limit overall function," says Charles Kuffel, CPO, FAAOP, owner of Arise Orthotics & Prosthetics, Blaine, Minnesota. "Some of the areas of most concern include the patella during knee flexion, the fibular head during ambulation, and the distal anterior tibia."
Most interface liners are fabricated in a linear fashion but undergo multiple plane disfigurations during dynamic prosthetic use, he explains. This pushing and pulling between the skin, liner, and socket can create areas of shear. Although lubricated gels, socks, and sheaths can be helpful when used beneath the liner, they don't always provide adequate relief from shear. They can also cause distal migration of the liner and possible loss of suspension.
Tamarack Habilitation Technologies, Blaine, recently developed GlideWear™, a low-friction interface technology that is successfully being used on wheelchair cushions to reduce shear and tissue breakdown beneath the ischial tuberosities. Prosthesis users are using a scaled-down version of this technology, the GlideWear patch, to reduce shear on affected areas of the residual limb. Placed between the skin and prosthetic liner, the GlideWear patch is used to spot-reduce shear by creating a gliding motion between the two layers of fabric that otherwise cause the skin to absorb the motion and disrupt skin integrity, explains Kuffel, who is helping Tamarack test the technology. The patch has been used on all areas of the residual limb that are prone to skin breakdown with positive patient responses and outcomes, he says, adding, "The use of the GlideWear patch by prosthesis wearers has also resulted in reduced incidences of follow-up for socket modifications and adjustments."
According to Kuffel, studies of the patch and its effectiveness are currently under way.
Columbia, South Carolina-based SCRA Applied R&D and Porticos, Research Triangle Park, North Carolina, have developed an affordable socket-cooling sleeve that uses a water-bottle-size canister of liquid carbon dioxide (CO2), such as that used in paintball guns.
The cooling sleeve is being tested at the Georgia Institute of Technology (Georgia Tech), Atlanta. "We are excited about this concept although there is a way to go before commercialization," says Rob Kistenberg, MPH, CP, LP, FAAOP, co-director and prosthetics coordinator for the master of science in prosthetics and orthotics (MSPO) program at Georgia Tech. "We have tested it on one patient; for mild exercise it eliminated almost 90 percent of the total temperature rise." Although the test patient used his usual pin-and-shuttle suspension system, the researchers are conceptualizing ways to use the sleeve with other types of suspension, plus it's applicable to other amputation levels, Kistenberg says.
"At this point, what we've got is a proof of concept," says Christopher Norfolk, PhD, SCRA Applied R&D program manager. "We've found that the system can be effective, comfortable for patients, and that liner materials are not an impermeable barrier to the cooling effect.... Having gotten this far, we've got a lot of variables that have to be tweaked." Questions involve what CO2 usage rate would provide an effective cooling system while maximizing the supply's lifecycle and how the system can best be integrated with the prosthesis, Norfolk says. The partnership is currently investigating multiple options to commercialize the technology.
WillowWood, Mt. Sterling, Ohio, has recently embarked on a two-year project for the VA to create more comfortable sockets for individuals with transfemoral amputations, according to Jim Colvin, MSBME, director of research and development.
The R&D team is focusing on improvements in subatmospheric technology. Challenges include developing a way to better seal the socket to create vacuum and placing the vacuum system so that it occupies a minimum amount of space below the socket. "For transtibial amputees, we can use a sealing sleeve that comes up above the socket to create a tight seal, but this is not a good option for high-level amputations such as transfemoral," Colvin says. Because the socket volume is greater for transfemoral amputees, with more air to evacuate, the vacuum system needs to be adjusted to accommodate that greater volume, he adds.
WillowWood's research team is looking at various socket and liner materials as well, Colvin says, "but we're just at the beginning of the process, so we have a long way to go before we get that nailed down. We're looking at anything that would improve comfort and durability. Having materials that can adjust their properties based on activities or environmental conditions is certainly of interest to us." The project team is looking at selective laser sintering (SLS) direct manufacturing as well; the company already has the equipment. "There are [direct manufacturing] materials that lend themselves to a more comfortable socket; we are definitely interested in that technology."
Improving the Liner Selection Process
With a plethora of prosthetic liner choices available, how can clinicians decide which one would best meet the needs of a specific patient?
Help is at hand, not only for clinicians but also for researchers, developers, and manufacturers. The Prosthetic Liner Prescription Assistant (PLPA) is a web-based suite of testing instruments and systems for data acquisition developed by a team at the University of Washington (UW), Seattle. The goal is to improve the prescription and design of interface liner materials for patients with limb amputation to help create mechanically stable prostheses that resist soft tissue injury during ambulation. "The…PLPA should quickly and easily allow practitioners to evaluate materials for use with their patients and assist them in making informed decisions based on the best available scientific evidence and mechanical testing data," according to an online project description.
Characteristics tested include cushioning, prosthetic suspension, skin adherence, volume change accommodation, breathability, thermal conductivity, and durability. The O&P industry has been very interested and supportive of the project, according to project head Joan E. Sanders, PhD, professor in the UW Department of Bioengineering. As of this writing, several manufacturers had already submitted products for testing, including ALPS, St. Petersburg, Florida; Össur; Ottobock; and WillowWood.
"This all started when we began…talking to practitioners," Sanders says. "So many of them only used products they had experience in prescribing—perhaps only two or three liners and that was it. Practitioners often didn't want to try a new liner because they weren't familiar with it and how it would work for their patients. We're trying to fill that void so that practitioners can see what these new materials are really like and they can compare different materials and characteristics. For instance, if a clinician likes everything about a certain liner except it's not tacky enough, he or she can go online and search for another liner with the same features, except it's tackier."
As of this writing, the PLPA is expected to go live mid-February. Access to the online information is free, product testing is available at low cost, and manufacturers can build their own in-house testing suites from online information. "We'd like to see the industry on the same page so that accurate comparisons of liner characteristics can be made," Sanders says.
Sockets, liners, and sleeves are fundamental components of prosthetic solutions that provide comfort, fit, and function. With new materials and designs currently on the scene and even more advances in the works, these foundational products are on the cusp of transformational change.
Miki Fairley is a freelance writer based in southwest Colorado. She can be contacted via e-mail at
Editor's note: The content of this article is for informational purposes only and does not indicate sponsorship on the part of the participating companies or endorsement from The O&P EDGE. Space does not allow us to include descriptions of all prosthetic and liner sleeves on the market or in development today. If you know of an emerging technology that you would like to be considered for publication in The O&P EDGE, contact