Concepts about what makes a prosthetic socket more comfortable and functional have evolved over the years from the time that the plug socket for transfemoral amputees was developed 50 years ago until the various types of ischial containment sockets reached their current level of popularity. The same is true for sockets for transtibial amputees, who no longer must wear thick wool socks and a thigh corset with their prostheses to walk.
A better understanding of the principles of anatomy and biomechanics, along with better materials and experience, made these improvements possible. Unfortunately, neither knowledge nor training in many of the new concepts, principles, and techniques has been standardized, and not enough research has been done to make authoritative statements on a number of issues. Often the methods of fitting and making a socket are based on such considerations as experience, current trends, or cost, since data providing more scientific criteria are currently not available.
The following articles, written by O&P professionals, are presented to provide a glimpse of the exciting changes that are taking place in the industry. Each article, however, is limited in scope and only reflects the opinions and experiences of the individual author. As is always the case with new ideas, some of the opinions expressed in these articles might be controversial, for there is not yet widespread consensus among the clinical experts on many of these issues.
Every socket philosophy has its proponents, successes, and failures. The truth is that the verdict is still out as to what is the optimal choice for an individual, so this must still be determined subjectively. The Amputee Coalition hopes that by sharing various viewpoints on these emerging ideas, today's amputee consumer will be better prepared to participate in evaluating and refining these new approaches to prosthetic design.
The views expressed in inMotion do not necessarily reflect those of the Amputee Coalition or the National Limb Loss Information Center, nor does inMotion endorse any specific technology, company or device. Consumers are urged to consult with their healthcare providers before making any purchasing decisions involving their care.
The Sabolich Socket
by Scott Sabolich, CP
Above-knee socket design has undergone a complete transformation in the past 20 years, largely caused by the emergence of new urethanes, silicones and thermoplastics, which made it possible to reinvent the shape and fit of the socket.
Before 1980, the standard above-the-knee or transfemoral socket was a quadrilateral socket made of rigid, heavy plastic or wood. It had a distinctly rectangular shape with a narrow anterior/posterior dimension and a hard shelf for the upper leg and buttock to sit on. While some patients ambulated well with the “quad” socket, many others struggled with pain, discomfort and immobility.
The initial version of the CAT-CAM socket was introduced in the mid-1980s and featured primitive ischial containment to lock the residual limb directly into place under the body. Its shape was dramatically different from that of the quad socket. Experience with the CAT-CAM socket and years of research and fitting thousands of patients led to the *Sabolich Socket design. It was lightweight and flexible, featuring bone and muscle contouring to increase rotational stability and suspension, with anatomical ischial containment. It gave prosthetic users a new level of comfort and improved their gate.
The Sabolich Socket has continued to evolve. Continued research and development, new technologies in design and materials, and a better understanding of the underlying anatomy of the residual limb have led to great improvement. We now know that the contours of the socket must be shaped specifically to the individual, just as a key must be shaped specifically to fit a keyhole. There are no two Sabolich Socket designs that are identical. In fact, any two given sockets may look very different from one another while still integrating the same Sabolich design considerations. Variables such as the length of the residual limb, the condition of the muscles, tissue and nerve areas, the anatomical shaping of the musculature and bony structures, and the patient's activity level are all considerations in determining the optimal shape for the socket. Just as an imperfect key will not open a door, a socket shape that is not optimized specifically to the patient will not allow the full measure of comfort and mobility.
The newest generation of the Sabolich Socket designs includes a flexible inner socket interface to increase comfort and range of motion and to provide a more natural feel in walking and sitting. A high-strength, lightweight external laminated frame provides the skeletal support of the socket. It may utilize strait suction suspension, sock fit, wet fit, or a gel liner with a pin or lanyard system. The shaping at the top of the socket curves to meld smoothly with the distinct characteristic of each user's thigh and pelvis. The materials used in each socket and frame are selected to allow for the appropriate biomechanical characteristics of the limb within the socket. It must be flexible in some areas and rigid in others for the limb to have enhanced comfort.
The spectrum of amputees who wear the Sabolich Socket designs include elite athletes, children, daily ambulators, and elderly, single-cadence ambulators. The muscular contouring and improved suspension of this socket are beneficial to the older adult as well as the elite athlete. Amputees are looking for a high level of comfort and mobility, and many can find it with the unique design features of the Sabolich Socket.
Transfemoral socket design will continue to advance as research sheds new light and technology moves ever forward. While the Sabolich design has evolved into its fourth generation, future advancements are inevitable as new materials are created, surgical procedures are enhanced, and our understanding of the biomechanical nature of the limb within the socket continues to grow. Breakthroughs in prosthetics are an essential part of enabling hundreds of thousands of prosthetic users around the world to restore their lives.
*The Sabolich Socket patent was purchased by Hanger Prosthetics and Orthotics, Inc. Scott Sabolich continues to utilize and explore the Sabolich Socket technology with his patients.
About the Author
Scott Sabolich, CP is owner and clinical director of Scott Sabolich Prosthetics & Research Center in Oklahoma City, Oklahoma.
Getting Down to Basics:
Improving Life With An Above-Knee Prosthesis
by Kevin Carroll, MS, CP, FAAOP
Today's prosthetic designs are enabling above-knee prosthetic users to walk, run and participate in activities they used to think were impossible. While the range of sophisticated prosthetic components currently available can play an important role in mobility, other more basic considerations are equally significant. A well-fit, comfortable socket, a pro-active mindset from the user, improved above-knee suspension options, techniques that make it easier to put on the prosthesis, and good grooming habits that keep the residual limb clean and dry are some of the more simple elements that lead to success for the above-knee user.
The fitting process for a transfemoral socket has advanced dramatically over the past 10 years. A greater understanding of the underlying anatomy of the residual limb, combined with the use of test sockets, has led to improvements in the shape of the socket.
Instead of a standard round or squared shape, today's highly contoured sockets are designed to interface very smoothly with the unique requirements of the individual user's body.
For example, those with soft, fatty tissue on their residual limbs need their sockets to have a wider side-to-side fit to accommodate the tissue as it spreads out when they sit. Those with more toned and muscular limbs require a narrower, side-to-side fit to conform to their more firm tissue. Fabricated from thin, flexible plastics, dynamic sockets expand and contract in harmony with the muscles of the residual limb. Ideally, the residual limb should be in direct contact with the socket - no gel liners or socks in between - allowing users to really feel the prosthesis and, thereby, have better control over it. This softer style of socket is also very lightweight; it slips down into a sturdy outer frame that adds stability, yet is also flexible. Perhaps most importantly, dynamic sockets are comfortable to wear, and comfort is the key ingredient. If the socket doesn't fit right and is uncomfortable, the other components of the prosthesis won't matter because the person won't wear it. Above-knee users who are experiencing discomfort with their prosthesis need to understand that the fit of the socket is the essential element. They should not hesitate to ask for a lightweight, dynamic socket.
A lot of energy has gone into making prostheses comfortable for ambulation, but what about when the above-knee user sits down? Does the back of the socket dig into the leg or thigh, or does the tissue feel pinched? Most people spend more time sitting than they do standing or walking, so how the prosthesis feels while they are sitting is a very important consideration. The sitting surface of the socket needs to be completely flexible so that it relaxes under the weight of the residual limb. This is most noticeable when sitting on a hard surface. Since the prosthetist is likely to be focusing on a comfortable socket for walking, consumers must take it upon themselves to try out the sitting surface of their prosthesis and to ask for modifications as necessary.
The other important consideration that relates to sitting down is the suspension of the socket. When standing on a typical above-knee suction socket, there is total contact between the residual limb and the socket. It's when a person sits down or stands back up that gaps may occur between the socket and the residual limb. If the muscles are allowed to go slack within the socket, air may be introduced, causing the socket to lose suction and possibly slip off. One way to help prevent this problem is to tighten the muscles of the residual limb when going through the motions of sitting down or standing up. It is also important to fire the muscles when getting in and out of a car, walking, or playing a sport. Instead of adjusting the socket to compensate for volumetric changes, users can focus on flexing their muscles to control the fit of the socket. Exercising this kind of muscular control means taking a pro-active approach to wearing a prosthesis. The result is improved suspension and a residual limb that is toned and strengthened.
Gel liners are currently a hot topic among prosthetic users. While gel liners can be an essential component for some, the best-case scenario is usually a total contact suction socket without a gel liner. This is the most intimate fit possible - the interface between the human form and the mechanical device. A direct contact suction socket connects the prosthesis with the person's central nervous system by stimulating the nerves in the residual limb. This gives individuals strong proprioception - a sense of where their limb is in space - and increases their control over the prosthesis. Anything that comes between the residual limb and the socket is going to diminish proprioception. A good analogy is that of wearing gloves. When wearing thin, surgical-type gloves, a person still has a strong sense of touch. Switch the gloves to thick, wool mittens, though, and the sense of touch is dramatically reduced.
Some people, however, wear a gel liner with a pin lock system for more secure suspension. The liner is rolled onto the residual limb and has a metal pin extending from the bottom. The pin snaps into a lock in the bottom of the socket. Unfortunately, new users may find it takes practice to learn to position the liner so that it hits the pin lock. There is suction between the skin and the gel liner and, sometimes, between the gel liner and the socket. The benefit of this approach is that it greatly reduces the chances of losing suction on the prosthesis as users stand, sit and move through their day. Also, when the residual limb has a lot of scar tissue, skin grafts or other trauma, it's important to wear a gel liner as a protective layer. Gel liners are also available with a lanyard system instead of a pin. A cord extends from the bottom of the gel liner and threads out through a hole at the end of the socket. The residual limb is simply pulled into the socket with the lanyard cord, and the cord is then clipped to the side of the socket.
Putting on a prosthesis, or donning, is a major frustration for many above-knee users. Pulling the leg on while working the residual limb down into the socket can take a lot of energy. Older adults and people with diabetes are often lacking in upper body strength, and repeated gripping and pulling with their hands can result in injuries like carpal tunnel syndrome. While there are many to don a suction socket, let's examine four of the most popular techniques.
• Using a cotton pull sock, which is pulled over the residual limb. The limb is worked down into the socket with a slight pumping action, and the sock is pulled out through the ion valve. This approach to donning is very common but not particularly easy.
• The “wet fit,” applying lotion or liquid body powder to the residual limb and the inside of the socket. This reduces the frictof the skin against the socket, allowing the limb to slip down into place.
• Using an Ace bandage to aid in donning is another approach. Rather than wrapping the bandage around the limb, try laying it flat along the inside wall of the socket - the side that runs along the inner thigh - with the end of the bandage extending out the suction valve at the bottom of the socket. With a slight pumping motion, work the residual limb into the socket and then gently pull the Ace bandage out the valve. This pulls the tissue at the top of the limb down into the socket, requires mil strength and is even easier if lotion is used along with the bandage.
• Using a nylon slip sock made of parachute material is another simple method. This thin, slippery sock is placed over the residual limb, and after the limb has been worked down into the socket, the nylon slip sock is pulled out through the suction valve. There is no need fotion or powder, making this a very clean and simple donning method.
Some people may have so much soft tissue that they can't pull it all into the socket using the Ace bandage or the nylon slip sock alone. If tissue is lapping out the top of the socket after donning, try a combination of both techniques. First, unroll an Ace bandage and lay it flat along the inside wall of the socket with the end of the bandage extending out the suction valve. Next, place the nylon slip sock over the residual limb and, again, use a slight pumping motion to work the limb down into the socket. Holding onto the top of the Ace bandage with one hand, pull the slip sock out through the valve, and then gently pull out the Ace bandage. This donning technique should be tried by anyone who is struggling to contain soft tissue within the socket.
Good personal hygiene is another basic, yet important, consideration. Antiperspirants can help keep the residual limb dry within the socket and are especially important during the warm summer months. Users can try regular over-the-counter antiperspirants that are fragrance-free or ask their doctor about prescription-strength products. One effective approach is to apply it at night and then wash it off the next morning before donning the prosthesis. This allows a little of the antiperspirant to be absorbed into the system, but prevents it from over-drying or otherwise damaging the skin. Putting antiperspirant on just before donning the prosthesis is not a good idea. If the skin becomes too dry, try using the antiperspirant every other day or less. It is equally important to clean the socket well every night. One of the easiest ways to do this is to wipe it out with packaged baby wipes and let it dry thoroughly. Lotion, powder, antiperspirants and sweat can all build up quickly inside the socket cause bacteria growth, odor, and skin infections.
It's not always the latest gadget or the most expensive component that offers the greatest benefit to above-knee users. Often, it's the more basic ideas that can really improve people's life. Try some of these simpler approaches to using above-knee prosis and see what a difference they can make in your life.
About the Author
Kevin Carroll, MS, CP, FAAOP, has been a practicing prosthetist for 24 years. He is vice-president of prosthetics for Hanger Orthopedic Group, Bethesda, Maryland. As such, he presents scientific symposiums to healthcare professionals across the country and manages one-day of prosthetic clinics for patients who are difficult to fit. Carroll has a bachelors degree in gerontology and specializes in the prosthetic care for older adults. He can be reached at 1-800-522-4428 or at kcarrollcp@aol.com
Suction Suspension
by Phillip Harrison, CP, and Raymond Francis, CP
A key aspect of any socket is how it is attached to the residual limb. Some methods, such as locking pin systems, are relatively recent entries into the field and have become quite popular during the past decade. Other methods, such as straps or cuffs, have long been available. A type of suspension that has been around for years has recently developed into a very effective means of providing a secure and comfortable suspension - namely, suction suspension.
The basic concept behind a suction socket is fairly simple: As the residual limb enters the socket, air in the socket is forced out through an opening at the bottom of the socket. A valve of one kind or another is then used to close the opening, creating a perceived vacuum that holds the socket onto the limb. The socket is then sealed off to prevent additional air from entering. Amputees who wear a well-fitting suction socket often say that it provides better suspension and control than any type of suspension they've ever worn.
The materials and techniques associated with suction sockets have changed quite a bit in recent years. So if you've tried a suction socket in the past but rejected it because it wasn't very user-friendly, perhaps it's time to take a second look.
Improvements in suction suspension
To hold the prosthesis on the residual limb with “suction,” a very close fit between the limb and the socket is necessary. As you might expect, however, such a snug fit can present some challenges when donning the prosthesis. The “old style” suction socket required the amputee to don the socket by lubricating the limb and pushing it into the socket (referred to as a “wet fit”) or by wrapping the limb in an Ace bandage and using the bandage to pull the limb into the socket. Although both methods were effective, neither was particularly convenient.
Fortunately, the thick gel socket interfaces now available are making suction suspension a more viable option for many amputees. The layer of gel evens out the pressure in the socket, making the prosthesis much more comfortable to wear. Also, some of the thick gel liners are covered in an outer layer of fabric, which allows the limb to slide into the socket without the use of messy lubricant.
Benefits of suction suspension
A well-fitting suction socket provides numerous benefits over other methods of suspension. There are no straps, and there is no pin on the bottom of the interface that has to be lined up almost perfectly with any kind of mechanism in the socket. Also, the intimate fit of a suction socket allows minimal movement between the socket and the limb, giving users better control of the prosthesis. Moreover, this lack of displacement between the limb and the socket makes the prosthesis feel as if it weighs less than it does.
Finally, suction suspension is also beneficial to amputees who are sensitive to anything pulling on the distal end of the limb (such as those amputees with scarring or grafting) because suction doesn't pull on that “bad” skin in the manner that some suspension systems do.
Unfortunately, amputees with very short residual limbs may not be able to use a suction socket successfully. The reason is that when these amputees flex the knee, the fit of the socket loosens somewhat, leading to a loss of suction. Another potential drawback is that suction suspension typically requires a seal around the outside of the socket, which adds bulk and a slight amount of weight to the prosthesis.
Components of a suction socket
One of the key components in a suction socket is the valve. Until the past decade, most valves were a type that screwed into the wall of the socket. The amputee had to unscrew the valve, don the prosthesis, screw the valve back in, and then manually bleed the valve to allow any remaining air to escape. Recently, one-way expulsion valves have been introduced that do not have to be removed and reinstalled. Instead, they automatically expel air as the amputee dons the prosthesis, making the donning process much more convenient.
Among the valves available today, some are better at keeping dirt, sock lint, etc., out of the valve than others. If you will be wearing a suction socket, ask your prosthetist to choose a valve that has some kind of filtering device to keep the valve from getting clogged.
The other key component of a suction system is a seal to prevent any additional air from entering the top of the socket after the prosthesis has been donned. For below-knee amputees, the seal is often accomplished by applying a suction sleeve over the socket after the prosthesis is donned. Above-knee amputees typically obtain a seal by folding the top edge of the gel liner back over the top of the socket. To doff the prosthesis, the amputee simply removes the seal to allow air to enter the socket. The prosthesis then slides easily off the leg.
Of course, there are always exceptions to every rule. Some amputees whose residual limbs are in extremely good condition may find that the fit between the limb and the socket provides such a secure seal that they do not need to wear a sleeve over the socket at all.
Caring for your suction socket
If you are wearing a suction socket, it is important to get a good seal across the top of the socket. Whenever you don your prosthesis, you'll need to smooth out any wrinkles in the seal so that air won't seep into the socket through them. You should also inspect the seal on a daily basis for holes or other damage.
If you should ever hear any kind of strange noises coming from your prosthesis (something along the lines of a “phffft, phffft, phffft” with each step), you should contact your prosthetist because you probably have a leak in the system somewhere. It is not normal for a suction system to make noise.
Depending on how intimate a fit you had with your previous prosthesis, it is possible that you may experience some shrinkage of your residual limb after you are fit with a suction socket. You should talk to your prosthetist about this to get an understanding of how much shrinkage is acceptable before you need to go back for adjustments.
For many amputees, the need to wear a seal on the outside of the socket is a small tradeoff for the many benefits afforded by a well-fitting suction socket. Ease of donning, a high level of comfort, new technological innovations that improve the suspension results, and excellent control of the prosthesis, all add up to make suction suspension one of the more effective methods of suspension available to amputees today.
About the Authors
Phillip Harrison, CP, is currently the clinical education prosthetist at Ohio Willow Wood. He takes an active role in education, research and development, and technical support.
Raymond Francis is a certified prosthetist with over 30 years experience. He is the chief prosthetist for Ohio Willow Wood and works extensively on research and product development.
Sockets for Hip-Disarticulation and Hemipelvectomy Amputees
by John Angelico, BS, OTR, CP
According to the 2000 census, the population of the United States is 281 million people. Of this number, 1.5 million are amputees, and less than 1 percent of these individuals, or approximately 10,000 people, are either Hip-Disarticulation (HD) or Hemipelvectomy (HP) amputees.
It is estimated that the energy required to walk at this amputation level is 200 percent greater than for normal ambulation. As a result, many HD and HP amputees choose not to be full-time prosthetic users. Because HD/HP amputees are only a small segment of the amputee population and many of these are not full-time prosthesis users, there have not been as many advances in fitting techniques at this level. In fact, the “Canadian Design” for fitting, introduced in 1954, is still the standard for fitting in the United States today.
Early HD/HP sockets were made of leather and a metal frame. Over time, the leather shaped itself to the residual limb resulting in a more comfortable fit. Its main disadvantage, however, was that it deteriorated quickly from perspiration. Although plastic laminated sockets, used in the 1950s, remedied this durability problem, they also required more skill to create the rigid and flexible areas that were necessary to provide both strength and flexibility for ease in donning.
Great advancements have been made in materials and components for the transfemoral (above-knee) and transtibial (below-knee) amputation levels in the last 10 to 15 years, and skilled prosthetists are using these advancements to enhance the fittings at the HD and HP levels. The industry has begun to use thermoplastic materials such as polypropylene and copolymer to fabricate sockets and has achieved good results.
Flexible plastics are used as the interface between the individual's limb and prosthesis. With the wide variety of such plastics available, the prosthetist can make a socket more or less flexible depending on the client's needs . With HP sockets, the trim lines must extend higher on the torso due to the lack of bony anatomy with which to bear weight. With flexible plastics, the trim lines remain high but are more flexible and thus far more comfortable to the individual. Body heat helps make the plastic more flexible and, like the leather sockets, it reshapes itself to the user's needs. This material is strong, but due to its flexibility it cannot support a person's body weight by itself on a prosthetic hip joint without collapsing. Similar to the leather and metal frame technique, a rigid frame is fabricated over the flexible socket. Materials such as carbon graphite and polypropylene are used to form the main support and structure of the socket, and the rigid frame encompasses the prosthetic hip joint and the socket. The height of the frame is usually lower than the flexible interface to achieve the benefit of the flexible plastic. Depending on the condition of the residual limb, areas of the frame can be cut out to help relieve problem areas in the socket.
Sheets of silicone may be used on the bottom of HD sockets to achieve a more comfortable fit, provide shock absorption, and help decrease shear forces on the residual limb. Inevitably, there is movement within the socket, but the silicone material on the bottom reduces discomfort and abrasions from the shearing movement. The silicone material can also be incorporated anywhere on the socket to protect bony prominences. This technique works best, however, when incorporated into the initial fabrication of the socket. Retrofitting the socket at an area of increased pressure by adding silicone may only cause further irritation and skin breakdown.
The biggest advance in the fitting of HD prostheses has been in designing sockets that capture as much of the underlying skeletal anatomy as possible. Careful casting and a good knowledge of anatomy help prosthetists utilize these contours to improve weight-bearing surfaces and control movement within the socket. Much attention is now paid to containing the ischium in the socket. This idea was initially used in transfemoral sockets where containing the ischium and stabilizing the femur result in a better fit. This may help the individual achieve a more natural gait and may also reduce energy consumption. By containing the ischium within an HD prosthesis, excessive movement of the pelvis is minimized. This gives the individual more control of the socket, helps reduce abrasions and breakdown, and may reduce the energy required to walk - an obvious benefit for those using HD or HP prostheses.
Many new components have been introduced in the prosthetic industry over the past few years, and their proper selection plays a crucial part in a successful fitting. Computerized knees and polycentric knees with stance flexion features make ambulation easier, safer, and more natural. Torsion adaptors reduce shear forces inside the socket while thigh turntables allow individuals to sit more comfortably. Hip flexion bias systems assist in getting the thigh section out so that the next step can be taken more quickly, thus reducing energy consumption. Special prosthetic feet can help increase the stability of the knee joint or improve the dynamics of gait. Lightweight componentry such as aluminum, titanium, and carbon reduce the overall weight of the prosthesis. With all of the different components available, users and their prosthetists can find the ones that best suit their individual needs.
Because fewer individuals use HD or HP prostheses, it is difficult for all prosthetists to become skilled at fitting these types of amputations. Although advances in this area of amputation have been slow, a skilled, experienced, and creative prosthetist will be able to adapt knowledge from other levels of amputations into HD or HP sockets.
About the Author
John A. Angelico, BS, OTR, CP, is a member of the Amputee Coalition Professional Advisory Committee and a partner at Scheck & Siress in Oak Park, Illinois, specializing in lower-extremity prosthetics. He may be contacted at johnangelico@msn.com
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