This activity reviews orthopedic prosthetics that are currently used in practice. It discusses both lower limb and upper limb prostheses and the different devices that make up their componentry. Also discussed are the complications associated with prosthetic devices and emerging advances in technology. This activity also highlights the critical role of the interprofessional team in caring for patients with prostheses.
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Limb amputation is not uncommon in orthopedic practice. [1] As of , nearly 2 million people in the United States were living with limb loss. That's approximately 1 amputee in every 150 people, and that number is projected to double or triple by . Every clinician will treat a patient with limb amputation at some point in their practice. It is important to understand the factors necessary to care for these patients and their required energy expenditure.
Lower Limb Prosthetics
Lower extremity amputations are not uncommon in the United States. Approximately 110,000 people are subject to some level of major (excluding toes) lower limb amputation each year.[2] Up to 70% of lower limb amputations result from a disease state, most of which are due to vascular disease and diabetes. The remaining lower limb amputations are the result of trauma, congenital abnormality, and tumor. Furthermore, the majority of these amputations are transtibial or at a distal site; transfemoral are less common. Interestingly enough, of the 85% of amputees fitted for a prosthesis, only 5% use the prosthetic limb for more than half of their daily walking.[3]
The Center for Medicare and Medicaid Services (CMS) has created a classification system to help guide practitioners and prosthetists to select the appropriate componentry based on their potential to be successful with the prosthesis. This is called the K-Classification System for Functional Ambulation and is often referred to as a patient&#;s &#;K-level.&#;[4] This is especially important to consider in patients with CMS payer status not to place an undue burden on families if the particular prosthesis recommended is not covered by insurance.
The K-Classification for Functional Ambulation[4]
Level 0: Does not have the ability or potential to ambulate or transfer safely with or without assistance, and a prosthesis does not enhance their quality of life or mobility.
Level 1: Has the ability or potential to use a prosthesis for transfers or ambulation on level surfaces at fixed cadence&#;typical of the limited and unlimited household ambulator.
Level 2: Has the ability or potential for ambulation with the ability to traverse low-level environmental barriers such as curbs, stairs, or uneven surfaces&#;typical of the limited community ambulator.
Level 3: Has the ability or potential for ambulation with variable cadence. Typical of the community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic utilization beyond simple locomotion.
Level 4: Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels&#;typical of the prosthetic demands of the child, active adult, or athlete.
The goals of a lower limb prosthesis include it be comfortable, lightweight, durable, aesthetically pleasing, low maintenance, and provide an appropriate degree of mechanical function for the amputee&#;s K-level. The major components of a lower extremity prosthesis include the socket, suspension mechanism, knee joint (if needed), pylon, and the terminal device.
The socket is the portion of the prosthesis that encompasses the residual limb. The initial socket may be a temporary one, sometimes referred to as a preparatory socket. It can be formed with the use of a plaster molding of the residual limb as a template. It is used in the acute setting after amputation as swelling continues to decrease and the surgical incision heals.
The prosthetic socket serves several important roles. It protects the residual limb but also allows for weight-bearing and load distribution. The most commonly used socket today is a patellar tendon-bearing (PTB) prosthesis. This socket is used specifically for transtibial amputations. More modern designs have incorporated hydrostatic loading to more evenly distribute the load through the residual limb, also known as a total-surface bearing.[5] These designs help prevent skin breakdown and are more comfortable for the amputee.
The suspension mechanism attaches the prosthesis to the residual limb. This can be accomplished with the use of belts, wedges, locks, and/or suction. Some suspension designs are created using a hybrid of the aforementioned elements. The two types of standard suspension mechanisms are locking and suction, each of which utilizes a silicone-based sock applied over the residual limb, which is then inserted into the socket. The locking system utilizes a pin or strap adhered to the silicone sock and a distal mechanism that fastens to the pin or strap respectively. A suction suspension system utilizes a similar silicone sock with a one-way expulsion valve and sealing sleeve on the socket to create an air-tight seal, stabilizing the limb from the proximal seal downward.
An articulating knee joint is sometimes appropriate for the prosthesis. These may consist of a single axis simple hinge joint or a polycentric axis with multiple centers of rotation. The simplest and most commonly used mechanism is the single axis hinge joint, of which the primary function is to provide articulation, allow knee flexion in swing-phase, and resist knee flexion during weight-bearing.[6] A polycentric knee joint incorporates four and six-bar mechanisms to enhance stance-phase stability and swing-phase kinematics. Although highly successful in developed countries, the cost and complexity associated with polycentric knee joints make them limited in developing countries.
Even more expensive modern designs have made use of microprocessor-controlled hydraulic knee joints that provide more reliable control when ambulating at different speeds, going up and downstairs, and walking on uneven surfaces.
The pylon or &#;shell&#; portion of a prosthetic is what attaches the socket to the terminal device. It can also be referred to as the containment socket. Recent advances in prosthetic technology have paved the way for dynamic pylons that permit axial rotation and absorb energy from the residual limb. These can be endoskeletal or exoskeletal, whichever is more functionally appropriate and aesthetically pleasing for the amputee.
The terminal device is the last piece of the prosthetic puzzle. This is typically a traditional looking foot, but more customized devices exist for high-level athletes. Ankle function is typically built into the terminal device, however, separate ankle joints may be beneficial in some patient populations. The drawback to these higher-functioning prostheses with ankle joints is the added weight to the distal end of the prosthesis. This added weight requires more energy expenditure and limb strength to control the additional degree of freedom.
The prosthetic foot serves to provide a stable surface, absorb shock, replace lost muscle function, replicate the anatomic joint, and restore aesthetics. Terminal devices can be broken down into non-energy-storing feet and energy-storing feet.
Non-energy-storing feet include a single-axis foot and solid ankle cushioned heel (SACH). The SACH has been extremely popular since its inception and uses a compressible material in the heel to mimic ankle plantarflexion, permitting a smooth gait. It is a great option for the K-1 level ambulator or a sedentary patient with a transfemoral or transtibial amputation.[2] The single-axis foot adds passive plantarflexion and dorsiflexion, increasing stance phase stability.
Energy-storing feet include the multiaxis foot and the dynamic response foot. The multiaxis foot adds inversion, eversion, and rotation to the traditional abilities of the single-axis foot. The increased degrees of freedom of the multiaxis foot make it a great option for the K-2 and K-3 level ambulators who can perform even light to moderate level activity.
The dynamic response energy-storing foot is considered top-of-the-line when it comes to lower extremity terminal prosthetic devices and is reserved for younger, more athletic populations. This device uses a flexible keel that deforms under pressure and returns to its original shape when the load is removed.[7] This allows for higher-level functions such as running and competitive sports participation. These terminal devices are suitable for the K-3 and K-4 level ambulatory.
Upper Limb Prosthetics
Upper extremity amputations are certainly rarer than lower extremity amputations. As of , approximately 41,000 people in the United States were living with major (excluding hand and finger, etc.) upper extremity amputations.[1] This number is expected to triple by the year , following the same trend as lower extremity amputations. Approximately 80% of major upper extremity amputations are the result of traumatic injury.[1] The remainder is secondary to vascular disease, tumor, and infection.
Transradial amputations are the most common amputation performed proximal to the wrist.[8] At this level, preservation of a least 5cm is important for prosthesis fitting.[9] Prosthetic fitting for upper extremity amputations can begin much quicker than for lower extremity amputations due to less concern for wound breakdown, with some centers fitting immediately postoperatively.[10] Early fitting in upper extremity prostheses can protect the stump site, help control pain and edema, and lead to improved outcomes.
Orthopedic surgeons and prosthetists should consider amputation level, expected functional outcomes, financial resources, aesthetic importance, and job requirements of the amputee when fitting for a prosthesis. Like lower extremity prostheses, there are a variety of upper extremity prostheses available to patients. These include cosmetic, body-powered, myoelectric, and hybrid prostheses.[11]
Cosmetic prostheses are generally the most lightweight prostheses available and require the least amount of harnessing.[9] That being said, they provide the least amount of function for the amputee. Body-powered prostheses come at a moderate cost and weight but are the most durable on the market. They provide the most sensory feedback but are less aesthetically pleasing and require more gross limb movement. Myoelectric prostheses function by transmitting electrical activity from muscle contraction to surface electrodes on the residual limb. These electrical signals are then sent to the motor to initiate the function of the terminal device. These devices tend to be the most expensive prostheses available. They are heavier, provide less sensory feedback, and require the most training for amputees. However, they do provide more functional use and are more aesthetically pleasing. Hybrid prostheses use a combination of myoelectrical devices and cables to perform a multitude of functions. Transhumeral amputees generally use these devices.
The goals of upper extremity prostheses are similar to lower extremity prostheses. The major components of upper extremity prostheses include the terminal devices, wrist units, elbow units, and shoulder units.
Terminal devices can be passive or active. Passive devices are cheaper more aesthetically pleasing than active devices but provide less function. Newer materials can produce prostheses that are nearly indistinguishable from a native hand. Active terminal devices are more expensive but allow for more function. They are generally divided into hooks and prosthetic hands with myoelectric devices and cables. There are 5 types of grips available that can be selected based upon desired prosthetic function. These include precision grips (pincer function), tripod grips (3-jaw pinch), lateral pinch grips (key pinch), hook power grips (carrying a briefcase), and spherical grips (turning a doorknob). Hand-like devices are a good choice for patients that work in an office setting, while non-hand prehension, or grasping) devices are better for laborers&#;another factor to consider is whether a voluntary opening or a voluntary closing mechanism would best suit the patient.
Wrist components often come in several flavors. A quick-disconnect unit allows for a simple exchange of different types of terminal devices. This allows patients to perform a multitude of functions. A locking wrist unit is one that prevents rotation during lifting and grasping. Wrist flexion units allow for flexion and extension.
Elbow units are generally either rigid or flexible. A rigid elbow hinge unit can be used when an amputee can still perform elbow flexion but lacks pronosupination. These devices can provide increased stability, especially in patients with a short transradial amputation stump. A flexible elbow hinge can be selected for patients who retain sufficient pronosupination in addition to flexion and extension. These devices are desirable for patients with a wrist disarticulation or long transradial amputation stump and provide more function for the patient.
For patients with amputations at the level of the shoulder, prosthesis fitting becomes much more difficult. The increased weight and energy expenditure of prostheses at this level lead many patients to choose a prosthetic that is purely aesthetic in nature. Cosmetic prostheses in this patient population improve self-image, confidence, and the fit of clothing.
Although there are a variety of prosthetic suspension systems in Kansas City, the main goal for all are clear&#;maximizing comfort while promoting mobility. When a suspension system works well to connect your residual limb to your prosthesis, there&#;s a balance that allows you to maneuver through daily life. However, when suspension is off, it can cause discomfort and even pain.
As prosthetic experts, our providers at Horizon Orthotic & Prosthetic Experience recognize the value in choosing a suspension system that works best for our patients&#; needs. The key in doing so is through education and ensuring our patients are aware of which options are available.
Read on to gain more insight on different types of prosthetic suspension systems and why they are important.
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Simply speaking, a prosthetic suspension system keeps the residual limb connected to the prosthesis. This connection is crucial to the overall prosthetic design, and the better that connection is, the greater the comfort, control, and proprioception will be. The goal is to create the feeling that the device is more of an extension to your body rather than a hard-to-use hindrance.
Different systems control different forces that act against the residual limb. These forces include:
Rotation: When you put weight on your foot, your limb may rotate inside the prosthesis, which isn&#;t ideal. The right suspension method will limit that amount of rotation to reduce excess movement that could cause irritation.
Shear: Shear forces push unaligned forces in the opposite direction. For your limb, that means your skin pulls as your limb moves back and forth inside your device when walking. This is also called pistoning.
Along with those forces, you also should consider proprioception. Proprioception is your body&#;s ability to sense itself, including its parts, how they&#;re moving, and location. This process involves sensory nerves in the muscle sending signals to the brain.
For amputees, however, they have to depend on their suspension connection to create that awareness. As you may suspect, a poor suspension system will lead to poor proprioception, which can negatively affect mobility.
Choosing the right suspension method considers:
Your prosthetist can help you determine which suspension will benefit you most, but oftentimes finding one that works for you will take a bit of trial and error. That is why it is very important to remain patient as you go through the fitting process. Remember, the goal is to get you up and going again, and the only way to do so is by ensuring that your suspension works for your lifestyle.
Increased functionality: When your suspension system properly keeps your limb and prosthetic device secure, you increase your mobility. This allows you to return to your daily tasks such as cleaning and walking your dog without assistance.
More energy: Overtime, you may notice you have more energy. The suspension system is designed to make your life easier. Especially if you&#;re used to crutches or maneuvering on a wheelchair alone, having a prosthetic device can take away that extra work.
A better outlook on life: Getting a prosthesis with the right suspension system helps you get back to your everyday life. Most people tend to be happier and more positive when they can return to doing the things they love.
Not every person will benefit from the same suspension method. For example, someone who plans to be more active won&#;t benefit from a system a less active person may use. There are four common suspension systems you may find in the Kansas City area and beyond:
A suction suspension system implements a soft liner in conjunction with a one-way expulsion valve and suspension sleeve. The liner goes over the residual limb before placing it into the socket. As you apply weight, the valve releases air to keep your limb firm inside the prosthetic. Suction allows for even distribution of pressure to reduce friction and shear.
The sleeves are made of different materials, including:
In addition, suspension sleeves also prevent air infiltration and relieves excess perspiration. If there are changes in volume, you can easily manage this by adding or taking off sock plies.
A self-suspended system depends on the socket to secure the prosthetic device to your limb. These sockets are designed with a brim that firmly attaches to the residual limb. The brim extends and narrows and narrows over a joint to grab hold of the area, therefore creating a snug and secure effect.
For example, the bone in your upper arm (the humerus) has round knob-like bumps that protrude from the bone. A self-suspended socket will then extend past those knobby structures and tighten around the joint. As a result, the socket won&#;t come off easily whenever you move.
An elevated vacuum system is a bit more complex than a suction system, but they are still user friendly. This system involves three components:
Pumps come in two different types: mechanical or electrical.
Electrical pumps: Electrical pumps maintain a desired socket pressure range. When the socket goes below a certain threshold, the pump activates to release air. This allows you to start walking right away, even if you&#;ve been sitting for a prolonged period. Keep in mind that you must charge your electrical pumps each night for them to work properly.
Mechanical pumps: Mechanical pumps compress air with each step. Unlike electrical pumps, you may have to take a few steps before it loosens, but you won&#;t have to charge them.
The components of an elevated vacuum suspension come together to create a more comfortable environment for your residual limb. It works both above-knee prosthetics and below-knee prosthetics.
The locking pin suspension system uses a liner/cushion interface along with a pin to keep the prosthesis in place. The liner rolls directly onto the limb to create a base. For suspension, the pin is threaded through the far end of the liner/cushion. In this method, the liner/cushion also acts as a socket interface to protect your residual limb. You would also wear a prosthetic sock to balance volume fluctuations. To remove the device, there&#;s a release button to disengage the locking pin.
The sealing liner suspension system uses a liner with a gasket ring around the outer portion of the liner. This ring gets lubricated with a standard hand sanitizer or alcohol spray to allow it to slide into the socket. A one-way expulsion valve allows air to evacuate but not come back in. This creates suction suspension without the need of an extra suspension sleeve /cushion interface along with a pin to keep the prosthesis in place.
With the new technology available in the prosthetic industry, belts and straps have become a more old-fashioned method for suspension. This fairly inexpensive suspension system uses belts, straps, and cuffs to hold the prosthesis in place. Though not used as often, belts and straps can be a great alternative if the previous methods don&#;t work. They are also used for people who have a short residual limb or need an auxiliary suspension while going through rough terrain.
If you have a suspension system that doesn&#;t work for your body, you may notice side effects that takeaway your ability to walk. For many, this could lead them to stop wearing their prosthetic device, which could lead to frustration. Here are a few signs that your suspension method may need to be assessed or changed.
A prosthetic suspension system is supposed to reduce skin irritation and help the socket do its job. If you&#;re finding that your skin is red, blistered, or ulcers are forming, you should return to your prosthetist. That way he or she can examine your prosthetic device and reevaluate other methods.
For lower-limb amputees, balance between your healthy limb and the prosthesis is key for optimal mobility. If you are having trouble balancing, it usually means there&#;s an alignment issue that&#;s affecting proprioception. As time passes, your residual limb will go through changes, and you&#;ll need to get a new socket and or change the suspension method to maintain control over your prosthetic device.
Walking with a prosthesis that isn&#;t properly suspended can cause long-term structural changes to your spine due to improper gait patterns. As a result, you may notice low back pain and it could even lead to further spinal injuries if you don&#;t resolve the issue.
In order for the suspension system to work, your residual limb must fit. There is no way around that fact. Since prosthetists perform in-depth fittings, this problem usually arises after months or years of use. Sometimes weight changes or swelling can change how your prosthesis fits, therefore affecting its suspension system.
For swelling, first make sure you&#;re wearing your shrinker sock every night to see if the problem resolves itself. If swelling is not the cause, you should talk to your provider. The solution could be as simple as getting a new socket or you may have to switch out your suspension. At times, both in conjunction may be the best option.
If you&#;re looking for more information about prosthetic systems, our team at Horizon Orthotic & Prosthetic Experience can offer you the expertise you need. We have six different locations in the Kansas City metro area and other Missouri cities to help you achieve your goals. Plus, we create customized prosthetics that are made with the patient&#;s specific needs in mind.
At the end of the day, we give our patients HOPE by providing them with the tools to have their dream lifestyle.
Contact us for more information or if you&#;re seeking a prosthetic device for you or a loved one.
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