Suspension

Under normal circumstances suspension of a limb is carried out by ligaments, which attach bone to bone, and by tendons, which attach muscles to bone within the limb. Clearly after a leg or arm amputation the prosthetic limb has to be fitted and attached in such a way that it does not fall off. Suspension of the prosthesis is therefore crucial to the amputee’s confidence.

Numerous ways have been devised in which to suspend a prosthetic device. Before 1958, the thigh corset combined with a waist belt was undoubtedly the most common form of transtibial prosthetic suspension. Modern materials have meant the introduction of silicone sleeves which fit snugly to the stump and are connected to the lower part of the prosthesis with a pin system. Ossur. An Icelandic company, has recently introduced a “seal-in-liner”, which incorporates a very strong vacuum between the stump and the prosthetic limb. The prosthesis is removed after releasing the vacuum with a button.

WillowWood, an Ohio company, manufactures a series of, Alpha® Liners, which are thermoplastic elastomer liners which gently cling to skin, protecting it from abrasion and breakdown. The gel in these liners contains mineral oil and vitamin E, making them skin-friendly and comfortable to wear. There are Alpha® Liners designed for both above and below knee amputations. In a similar way to Ossur’s liners, the vacuum seal is released by means of a one-way valve.

Knees

The prosthetic knee joint is one of the most critical components of the prosthesis. Replacing the amazingly complex human knee has been an ongoing challenge since the beginning of modern prosthetics. A prosthetic knee has to mimic the function of a normal knee while providing stability and safety at a reasonable weight and cost. A prosthetic knee that produces the most functional outcomes is needed. Developing such a knee requires familiarity with normal gait, because that is the basis for understanding an above-knee amputee’s gait.

The normal gait cycle is divided into two major phases: stance phase and swing phase. The stance phase describes the period when   the foot is on the ground. It is not a period of inaction, but rather the time when weight is applied to the leg. The swing phase describes the period when that foot is in the air and swinging forward. The stance phase takes up approximately 62 percent and the swing phase takes up approximately 38 percent of the gait cycle. The quadriceps (muscles in the front of the thigh) and hamstrings (muscles at the back of the thigh) provide significant control of the knee joint in the stance and swing phases of gait. They both move the knee and lock it so that it doesn’t bend when it shouldn’t. In addition, the ligaments and bony anatomy of the knee joint provide a strong foundation for both static and dynamic function.

The ankle joint assists gait by providing a second hinge during both gait phases. Hip and ankle joint muscles also provide the control and stability of the leg during walking, but the knee is the most critical component.

The above-knee amputee faces a considerable challenge since he/she has lost both the knee and ankle joints. The challenge for the prosthetist is to replace what has been lost and provide the best function for the patient based on his/her goals and lifestyle.

Prosthetic knees can be classified into two distinct types: those that use mechanical control of the knee joint (non-microprocessor) and those that use some form of computer chips (microprocessor) to control the swing and/or stance phases of gait.

The non-microprocessor knee:

Hundreds of non-microprocessor knees are available worldwide. They all use a mechanical hinge; the speed and ease of the hinge’s swing is controlled by one of the following mechanisms:

• Free swing
• Manual lock
• Constant friction
• Weight-activated friction
• Geometrically locking
• Hydraulics

The hinge swings, then locks manually when pressure is placed on the leg during stance phase. Mechanicalknee users must exert muscular and mechanical control to alter speed and step length and provide stability in the weight-bearing phase of gait. The prosthetist or the user can manually adjust some mechanical knee joints to set the controls in the swing and stance phases based on the patient’s needs.

These adjustments can only be made when the person is in a static (still) position.

The microprocessor knee:

Since the early 1990s, microprocessor-controlled prosthetic knees have been available in the United States. The microprocessor controls the speed and ease with which the knee swings throughout the swing phase. It also controls the degree of stability the knee joint maintains during stance phase.

Microprocessor-controlled prosthetic knees are equipped with sensors that continuously detect the position of the knee throughout the stance and swing phases of gait. These sensors provide input to the prosthetic knee so that the knee “knows” which gait phase it’s in.

This allows it to adapt to different walking speeds, terrains and environmental conditions as the user walks. In addition to these features, a microprocessorknee has been shown to improve the stability in the stance phase of gait because it senses that the user is not walking and thus resists if the knee tries to collapse.

This feature provides improved safety when standing and more confidence when walking. The knee’s ability to control the swing phase during walking and to provide resistance in the stance phase reduces the amount of energy it takes to walk and provides additional safety for walking.

Microprocessor knees use a variety of systems within the knee mechanism to provide resistance, including pneumatics, hydraulics and magnetic systems. Each type of microprocessor knee uses software that controls and modifies the function of the knee.

Microprocessor- knee manufacturers train and certify prosthetists in the setup and alignment of the knee as well as in the software used to adapt the knee to each patient’s weight, functional status, and goals.

Comparing the two:

There are many significant differences between a microprocessor and a non–microprocessor knee. The mechanical knee is generally more durable and requires less maintenance than a microprocessor knee. The cost of the non-microprocessor knee is significantly less than a microprocessor knee.

The mechanical knee has no battery, so it does not require daily charging. Mechanical knees have fewer issues with water compared to microprocessor knees. In general, an above-knee amputee who uses a non-microprocessor knee must give more thought to controlling the knee in both the stance and swing phases of walking. That is, walking is less natural and requires more attention and energy. If an amputee with an adjustable knee wants to change the settings for running or for a different terrain, they must stop walking and adjust the settings before walking or running again.

Most users who have tried both types of knees report that the non-microprocessor knee shows significantly less stability in the stance phase of gait and on stairs, ramps and uneven terrain compared to a microprocessor knee.

Many, but not all, patients who have gone from a mechanical to a microprocessor knee report that they feel safer and stumble or fall much less; have a smoother and more natural gait; can descend stairs and ramps with greater ease and stability; expend less energy when walking; and don’t have to think and focus on how to walk as much as they did with a non-microprocessor knee.

The microprocessor knee adjusts automatically for people who walk with a variable cadence and walk in changing conditions.

Although a microprocessor knee can be used for many higher-level activities, a non-microprocessor knee would be the type of knee chosen for many recreational and competitive sports. When considering the addition of a custom cosmetic skin cover, a mechanical knee may offer simpler solutions due to the charging and maintenance needs of the microprocessor knee.

Compared to a non-microprocessor knee, the microprocessor knee’s high-tech solutions come with a considerable increase in cost. Also, the knee’s battery must be charged on a regular basis and the knee must be kept from getting wet or immersed in water for long periods.

In addition, with the current multiple forms of medical aids and insurance for prosthetics in South  Africa, reimbursement for microprocessor knees varies widely, from full payment to complete denial. (Denial would be based on the insurance company determining that the knee is “not medically necessary” and/or “experimental” or “investigational.”)

Who should get which kind of knee? To determine which type of knee is appropriate for a given patient, a complete evaluation and profiling of that patient must be done. The type of prosthetic knee suitable for a person can only be determined through a complete understanding of that patient.

The evaluation and profiling of the patient should include the following considerations: age, medical history, length of residual limb, muscle strength, activity level, home environment and occupational needs. The patient’s functional goals and aesthetic concerns must be considered, too.

Major advances in the application of technology have improved the function of the lower-extremity amputee. Prosthetic knee joints with microprocessors have had a significant impact on the functional outcomes for the above-knee amputee. Indeed, they provide increased function and safety for many people.

Socket Design

If it doesn't fit correctly, you can experience pain, sores and blisters, and the prosthesis will feel heavy and cumbersome. Also, your mobility may be compromised, or the prosthesis may even end up at the back of your closet.

Socket design technology has come a long way since the days of hard plastic and wooden sockets. With the emergence of contoured sockets that fit every aspect of the residual limb, amputees are more comfortable and mobile than ever before. This type of socket evenly distributes weight across the entire surface of the residual limb, eliminating pressure points. Flexible, lightweight materials enable the socket to bend and expand along with the patient's residual limb.

Art Form

Fitting a socket is an art form that continues to evolve. The prosthetist's goal used to be to create a socket from softer materials; now the goal is to make the prosthesis as stable as possible while maintaining comfort. However, although today's materials are much lighter, it's difficult to create an inanimate prosthetic socket to comfortably contain a part of the body that is living and constantly changing.

When creating a socket, prosthetists often feel as if they're expected to stabilise something that seems like a stick (bone) surrounded by Jell-O (residual tissue). On top of that, they're expected to make the casing feel soft and flexible, yet stable and secure. Each socket is as unique as the person who wears it. A residual limb never keeps the same shape or consistency. To resolve this problem, prosthetists create the shape and size of the socket for the limb within a reasonable range, allowing for volume fluctuations. The wearer’s responsibility is to keep his or her weight within a range of 2 percent (plus or minus) of their body weight.

Weight Distribution

Where weight is carried within the socket can be a critical issue. With a tighter socket, weight is borne around the thigh of an above-knee amputee. If the above-knee socket is looser, more weight will be loaded on the bony structure of the pelvis area or the distal (lower) end of a below-knee limb. The goal is to balance both of these issues within a range that's comfortable for the amputee. Some amputees cannot bear weight on the distal end of their residual limb. If you're experiencing pain or redness in certain areas of your residual limb, your prosthetist can help by making slight adjustments to the socket itself or by adding socks or padding.

The use of socks and padding can be explained with this nautical analogy. Think of the residual limb as the rudder of a ship. The water can be thought of as socks. If the water level gets too low, the rudder will drag at the bottom; as water is added, the ship will rise, freeing the rudder.

Alignment

Since your body continually changes, your prosthesis also requires regular adjustments to maintain alignment. It's a mechanical device, just like your car, and must be taken care of in order for it to work properly. Ideally, the alignment of a prosthesis should be checked every six to twelve months. The slightest change in weight or muscle mass can change the alignment and cause problems with your residual limb. Back, hip, and knee problems can also be caused by an ill-fitting socket.

For a new amputee, the residual limb changes so rapidly in a temporary prosthesis that the alignment may require weekly updating.

Socket Care

One of the most important things you can do to care for your socket is to clean it thoroughly every day. Socks and liners should also be cleaned and rinsed well before donning. This can't be stressed enough. Dirty sockets, socks and liners can harbour bacteria, causing odour and skin problems, such as a rash, fungus and redness. Follow the manufacturer's directions for care and cleaning. If you have any questions, you should discuss the care of your prosthesis and hygiene with your prosthetist

Socket Replacement

A new amputee with a temporary prosthesis can expect that it will need to be replaced at least once before receiving a definitive prosthesis. The residual limb will shrink drastically over the first few months of wearing the prosthesis, but it may take up to two years to stabilise. Sometimes this volume loss may be handled by adding socks, but at some point the socket can become unstable, signalling the need for a new socket. The prosthesis may require several socket changes before the limb matures.

Once the prosthetist has determined that the limb has stabilised, he or she will cast for a definitive socket. Although this is often called a permanent socket, it will need to be replaced. Just as cars wear out, so will a socket and a prosthesis. When in doubt about whether a new socket is required, contact your physician, physical therapist or prosthetist. A socket normally requires replacement when:

• The socket is worn out or cracked. A typical socket lasts two to four years, depending on your activity level.
• The socket is discoloured.
• The socket no longer fits. If the wearer has gained more than 2 percent of body weight, the socket will be uncomfortable and donning will be difficult. More than 2 percent of body weight loss may cause the socket to rotate or cause the limb to piston within the socket.
• There is a change in the size or shape of your residual limb.
• You've had revision surgery.

Attitude Is Everything

Amputees can surprise everyone, even their caregivers. After an amputation, an amputee may be seen as too elderly, too frail, or too seriously injured to manage walking with a prosthesis. But determination and desire can enable many people to achieve success against the odds. They don't see giving up and remaining in a wheelchair or on crutches as an option.

Learning how to wear a prosthesis and finding a socket design that works best for you can be a daunting task. Keep a list of questions for your prosthetist between appointments or call and ask. The Amputee Coalition of America is a great source for prosthetic information and can guide you in your search for answers. A support group can also provide some advice and help you realise that you're not alone.

A new amputee with a temporary prosthesis can expect that it will need to be replaced at least once before receiving a definitive prosthesis. The residual limb will shrink drastically over the first few months of wearing the prosthesis, but it may take up to two years to stabilise. Sometimes this volume loss may be handled by adding socks, but there comes a point when the socket can become unstable with too many piles of socks, signalling the need for a new socket. The prosthesis may require several socket changes before the limb matures.

Once the prosthetist has determined that the limb has stabilised, he or she will cast for a definitive socket. Although this is often called a permanent socket, it will need to be replaced. Just as cars wear out, so will a socket and a prosthesis. When in doubt about whether a new socket is required, contact your physician, physical therapist or prosthetist. A socket normally requires replacement when: