As the connection that holds a prosthetic leg or arm to an amputee’s body, the prosthetic socket plays an important role in an amputee’s ability to complete everyday tasks. However, depending on the design and material used, the socket can sometimes be more of a hindrance than a help to the amputee.
“If you look at the history of people who have tried to determine what is important to amputees for development and research, improved socket is always at the top of the list and it has been like that for decades,” David Boone, CP, PhD, chief technology officer of Orthocare Innovations, told O&P Business News. “You can go back through 40 or 50 years of research and when you ask patients what we have to work on, what we need to fix, they will say the socket. We have a lot of work to do and we have not gotten there yet, but at least we know that’s what’s important.”
Researchers have responded by examining new materials and different technologies to improve sockets for amputees, including a subischial prosthetic socket, osseointegration, osseosynchronization and computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies.
When designing a new type of socket, it is important for researchers to look at existing research to find out what designs and materials have worked in the past. It is also important to keep the research up-to-date and accurate, as well as to see how new technologies compare.
Maria J. Gerschutz, PhD, applied research engineer at WillowWood, and colleagues recently performed two studies that looked at prosthetic socket materials and strengths. In the first study published in 2011, the researchers “evaluated tensile and impact properties of the current state-of-the-art materials used to fabricate prosthetic check sockets, copolymer sockets and definitive laminated sockets.”
In a more recent study published in 2012, Gerschutz and colleagues analyzed prosthetic sockets from a variety of facilities to compare socket performance.
Using a modified International Organization for Standardization (ISO) standard 10328, the researchers measured static failure loads of prosthetic sockets before comparing them with the criteria set by this standard for other components.
Thickness, material choice and fabrication method influenced check socket strength, while copolymer socket strengths depended on thickness and fabrication methods. Researchers found that the strengths of definitive laminated sockets were influenced by construction material and technique. According to study results, some prosthetic sockets performed more favorably than other sockets.
The two main purposes of the study, according to Gerschutz, were to enhance the understanding of current socket technology and to provide a benchmark for the use of evaluating new or improved socket technology, materials and designs.
“The results from this article provide a foundation for understanding the strength of prosthetic sockets, some insight into possible routes for improving the current care delivered to patients and a comparative basis for future technology,” the researchers concluded. WillowWood is actively exploring new socket technology including the evaluation of a direct manufacturing technology, selective laser sintering, as a potential fabrication process for prosthetic sockets.
Research has not stopped at what types of materials and fabrication process should be used. At Northwestern University, Stefania Fatone, PhD, of Northwestern University, Ryan Caldwell, CP, FAAOP, of Scheck & Siress Prosthetics, and colleagues have been researching a new flexible transfemoral socket design that does not impinge on the pelvis when the hip is moved.
“What we have been looking at specifically are subischial sockets that do not impinge or touch the pelvis for transfemoral amputees and using materials that make the sockets very flexible,” Caldwell told O&P Business News. “What we have been taught as prosthetists is to make sockets out of carbon fiber and other materials that you can literally drive your car over. They are super thin and super strong, but they typically do not work like the human anatomy. So we are trying to make these sockets as strong as possible, but also to be flexible and work with the anatomy.”
Caldwell’s flexible transfemoral subischial prosthetic socket has proximal trim lines, which terminate distal to the pelvis and greater trochanter, increasing range of motion and comfort without compromise to biomechanical stability.
“Our goal in socket design is to provide a system that is able to maintain a comfortable and secure fit throughout the day,” Caldwell said. “The ability to eliminate much of the socket’s rigid component has provided very successful outcomes for both very active and less active prosthesis users.”
Roy Bloebaum, PhD, of the University of Utah School of Medicine, and colleagues have recently been performing research on osseointegration, which is the ability for bone to integrate with the metal of an implant.
“A lot of amputees have trouble sitting or they can’t sit for very long periods because the socket digs into their groin region,” Bloebaum told O&P Business News. “However, if they have an osseointegrated implant, they can sit down with no problem for long periods. There is no socket required so it is much more comfortable.”
Studies performed on osseointegrated implants, used primarily throughout Europe, have shown numerous positive results, such as fewer falls on uneven surfaces.
The major challenge that still confounds researchers is the possibility of infection after osseointegration, but, according to Bloebaum, progress is being made in research as well as clinical settings.
“Osseointegration is under FDA scrutiny and isn’t going to be broadly available for a good 3 to 5 years. It’s time for prosthetists and orthotists to start thinking about what unique things they can do, how they can integrate their knowledge to make osseointegration a more powerful connection to the prosthesis and get better feedback from the patient,” Bloebaum said. “I hope prosthetists will keep an open mind. I hope they realize that they are not going to be out of the socket business anytime soon.”
In September 2012, Randall Alley, BSc, CP, chief executive officer of biodesigns inc., presented biodesign’s first product in its new OsseoSync Technology line, the High-Fidelity Interface System, at the American Orthotic & Prosthetic Association National Assembly.
The HiFi Interface System is designed to replicate the stability achieved through direct connection to the bone osseointegration provides – but without the surgery.
“In traditional sockets a patient’s soft tissue is simply encapsulated in a generic bucket-like design which is highly inefficient. A patient is required to expend a great deal of energy to walk because their bone moves freely within the socket, uncontrolled. The HiFi Interface is able to capture and control the underlying bone through a patented compression and release design,” Alley said. “The benefits — enhanced connectivity, superior performance with faster response times, increased comfort, subischial trim lines, reduced energy expenditure, greater range of motion, M-L and A-P stabilization and improved rotational control.
“It also encourages wearers to walk correctly, minimizing and sometimes eliminating back pain or discomfort.”
The HiFi Interface can be used with all major suspension methods. There are currently more than 50 prosthetists trained by Alley in the United States and abroad in the HiFi technique with more training sessions being scheduled for the year.
Using CAD/CAM software
The industry has begun to move from hand molding sockets to using computers to help in the design and manufacture of sockets.
“Scanning and utilizing computers through CAD/CAM is an area that has really advanced considerably in recent years,” Kevin Carroll, MS, CP, FAAOP, vice president of prosthetics at Hanger, told O&P Business News. “Many of today’s clinicians have grown up in the computer age, and as a result they are very comfortable with utilizing the CAD system. It’s very well accepted today in our clinical practices and patients expect that type of technology when they go into clinics.”
According to Joan Sanders, PhD, professor of bioengineering at the University of Washington and director of its prosthetics science technology lab, there are many advantages to using CAD/CAM that are not found with traditional methods.
“[CAD/CAM is] faster, there are records of the shapes that clinicians have made in case they need to make a replacement and they can see how their patient has changed over time,” Sanders told O&P Business News. “It can be cost effective because physicians do not have to [make the socket] in their own lab. They can send the file to a central fabrication facility and receive the socket back, which saves the cost of having all the equipment in their lab, as well as technicians to do that work.”
However, studies have shown that the software is only used by 24% of practitioners because of inconsistent or poor performance. Sanders and colleagues published a study recently that found CAD/CAM software accuracy can be hit or miss across central fabrication facilities.
“Our study showed that there are some people that make CAD/CAM sockets perfectly, they manufacture it and they are dead on with what the manufacturer designed. Then there are other companies that are off by 3% or 4% volume, which is terrible,” Sanders said.
Sanders and colleagues created an assessment technique in which they measured the shapes of the fabricated models and sockets and compared them with each other and with the electronic file shapes that they were fabricated from. This assessment technique was designed to help facilities test the quality of their models and sockets and identify fabrication problems, and limitations.
“The prosthetics computer-aided socket fabrication industry may benefit from creating and implementing model and socket assessment standards to enhance quality and consistency across the industry,” the researchers concluded in their study published in the Journal of Rehabilitation Research & Development. “Such an effort might improve practitioner confidence in CAM, serve as a basis for enhancement, reduce patient healthcare costs and serve as a means for documenting performance.”
Their continuous research on CAD/CAM software has not been performed in vain.
“The interest by practitioners in CAD/CAM is actually quite high, at least from our perspective,” Sanders said. “There’s a sense that practitioners need to keep listening to see where [the technology is] going and if it is a viable thing they should pursue in the future because of the potential benefits that are rising.”
Looking to the future
As manufacturing technology improves, socket technology can improve as well. Although various studies are being performed to find new and innovative ways to design sockets, some researchers and physicians believe that the research is only focusing on certain aspects of sockets and overlooking ideas that could help lead to better technology.
According to Caldwell, future research should focus less on manufacturing prostheses, and more on why certain parts of the prostheses work the way they do.
“As a field, a lot of what we have done has been manufacturer driven, such as putting all our research funds into manufacturing a part or foot as opposed to looking at design and why things function the way they do,” he said. “We should be looking more at why things work the way they do, as opposed to coming up with a new product.”
Boone believes it is important to look at the structure of the socket and how it compares to the anatomy. A prosthetic socket is usually stiff and hard, while the human socket changes to support the body, which, according to Boone, is how a prosthetic socket should act. He also believes it is important to examine how prosthetic sockets affect gait.
“When we create a prosthetic socket for the lower limb, what we are doing is transferring the loads of movement up through a mechanical structure to the body,” he said. “We need to think of it dynamically that way at each moment those forces are changing. We need to carefully know what they are, measure them and then optimize the socket structure and design to transfer those loads comfortably and efficiently through the limbs so that amputees feel stable, in control, have a good sensation of where their limb is in space and they can do all that with maximum comfort.”
Although these new innovations may take several more years until they are fully developed, prosthetists believe that these new ideas will help move the O&P industry forward and use the technology that is available in a positive way.
“There is a lot happening [in socket technology] and it is exciting,” Carroll said. “We are communicating rapidly with our clinicians, patients and physicians that we work with, so the future is very bright for us all.” — by Casey Murphy
Disclosure: O&P Business News does not endorse any company or products mentioned herein. Not all companies or products relevant to the topic are represented.Disclosure: Bloebaum receives funds from DJO Global, the National Institutes of Health and the Department of Defense. Boone is employed by Orthocare Innovations. Carroll is employed by Hanger. Gerschutz is employed by WillowWood Company and received funds from US Army Medical Research & Material Command and Telemedicine & Advanced Technology Research Center. Caldwell’s work has been funded by the Department of Defense. Sanders has no relevant financial disclosures.