There are many prosthetic leg options to choose from, and the best fit will be dictated by an individual’s level of injury, physical factors, complications, as well as their lifestyle and vocational or recreational goals.
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Every amputation is different, and it is critical that persons who have sustained an amputation work with a certified prosthetist and physiotherapist to determine which kind of prosthesis will be the best option for them.
In this article, we will highlight prosthetic leg options and physiotherapy for through-knee or above knee amputation.
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Prosthetic legs allow an individual who has sustained an amputation to walk with a more normal and energy efficient gait pattern and will often allow them to walk without the need for assistive devices such as crutches or walkers. In addition to enabling a more normal gait pattern, they allow the user to accommodate for sitting/standing, stairs/ramps as well as uneven terrain and different walking speeds.
A prosthetic leg includes several components including the socket, which is molded to the individual’s residual limb, the suspension system, which is how the prosthesis stays attached to the individual, and the prosthetic leg itself, which includes different options for knee and ankle joints.
Individuals can be fitted for a prosthesis once the wound from the amputation is stable and well-healed, which can be within a few weeks after the surgery. This may be delayed if they have complications related to the amputation.
After an above-knee or through-knee amputation, the residual limb shrinks, as the individual loses muscle mass in their thigh. Users will need to be fitted for multiple sockets over time to accommodate for the decreasing size of their residual limb.
Amputation refers to the removal of a limb due to injury, disease, or surgery. It can be utilized as a surgical procedure to manage discomfort or a disease condition in the affected limb. Individuals can also undergo traumatic amputations resulting from motor vehicle accidents or workplace accidents.
There are several complications related to amputation such as infection, phantom limb pain (residual limb pain), slow wound healing, vascular issues and necrosis, neuromas, edema, and skin breakdown. Phantom pain is a common occurrence after an amputation and is perceived in the limb that has been removed from the body. It is typically characterized as a sharp or burning pain that occurs due to a miscommunication of nerve signals from the brain to the spinal cord.
Prosthetic knees allow a person who has sustained an amputation at or above the knee to regain use of the knee and ankle joints and participate more easily in their daily activities.
Prosthetic knees are divided into two categories, mechanical or computerized. Mechanical knees are further divided into single-axis, multi-axis, and polycentric knees. Each prosthesis has its own unique features which are chosen based on the user’s requirements.
This is the simplest type of prosthetic knee joint that allows for rotation around a single axis during flexion and extension of the knee. Individuals who use this type of knee require good muscle strength, as this type of prosthesis can be difficult to control. These are sometimes recommended when there are limited economic resources, as it is the most cost-effective option.
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Unlike a single-axis knee, a polycentric knee allows multiple points of rotation around several axes. Polycentric joints can have either 4 or 7 bars, meaning that you can either have 4 points of rotation or 7 points of rotation. This type of joint provides good stability when there is involuntary flexion during the heel strike phase of walking because the center of rotation is located more proximally and posterior when the knee is fully extended. This knee is typically recommended for active people, or people who are more likely to walk independently, without a gait aid.
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This type of joint locks while the user is weight-bearing on it. They will need to manually disengage the lock to be able to sit down.
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This knee provides a constant friction force while weight is on the limb. This helps to prevent it from buckling when standing on that leg, while still allowing it to swing freely when unweighted.
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Pneumatic/hydraulic components (pistons with cylinders containing air or fluid) can be added to either single-axis or polycentric mechanical knees, as well as computerized knees. This is to help increase mobility and control with the leg and allow the user to vary speeds. When walking faster it will limit the air flow and fluid to reduce the flexion of the knee to allow a faster walking pace. The opposite will happen with a slower gait. Typically, hydraulic knees work well for more active individuals.
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Mechanism and Indications
These knees have microprocessors to allow feedback from within the knee or foot joint. Information from the sensors adjusts the range and speed of knee flexion and extension, according to the user’s requirements. Knee extension is powered, and resistance is provided through knee flexion, allowing the individual to more easily get in and out of a sitting position, and navigate stairs using a reciprocal gait pattern. It also allows for a symmetrical weight distribution and a natural gait pattern.
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The nature of rehabilitation after a leg amputation at or above the knee will depend on the client’s goals and physical presentation but will often include:
When an individual has undergone an amputation at or above the knee, learning to use a prosthetic leg is often a crucial step in the rehabilitation process. A well-fitting prosthesis can help individuals regain mobility and return to their daily activities. This allows the freedom and independence to get back to doing the activities that are important to them.
For patients who have lost a leg, regaining mobility is a top priority. However, development of more true-to-nature prosthetic limbs and joints has come an amazingly long way from the often thought of peg leg and hook hand. Over the past several years, medical prosthetic technology has advanced drastically, allowing for patients to regain the normalcy in their life that they would not have had access to in the past.
Otto Bock Healthcare GmbH, Duderstadt, Germany, a company with 90 years of orthopedic experience, has developed a more natural-feeling prosthetic knee joint to not only allow more comfortable and natural ambulation, but also provide a long-lasting, durable solution so patients can spend less time at the orthopedic mechanic, and more time living life as usual.
Otto Bock has developed their 3R60 and 3R78 prosthetic knee joints with their patented “EBS,” or “Ergonomically Balanced Stride”, system, which allows for an individually adjustable stance, reducing the strain on the hips and spine of the wearer. Suitable for patients up to 275 pounds, higher than with many traditional prosthetics, the joint is able to be adapted to patient weight and activity for additional comfort and stability, especially on uneven terrain, and four modular connectors make it an appropriate prosthetic for various levels of injury. The joint system uses special engineered components and features to mimic the motion enabled by a biological knee joint, unlike monocentric, single-jointed traditional prosthetics. (See Figures 1a and b)
In the joint itself, needle and bronze bearings, as well as PTFE guide tape, were replaced with plastic components from igus®. These plastic components are extremely light, do not require external lubrication, and also possess very low coefficients of friction, with excellent wear-resistance. According to Otto Bock, these plastic components allowed for the further development of their EBS joint systems to where they are today. The EBS joint system is lightweight and shock absorbing, allowing for more comfortable walking, and is extremely low maintenance thanks to low-wear, media-resistant, and corrosion-free components, meaning fewer trips to the orthopedic mechanic. The plastic bearings used in the joint were selected for special characteristics specific to the demands in a prosthetic knee joint. There are bearings made of different varieties of plastic material, including iglide® Q, which was selected because it is extremely resilient under high loads and exceptionally shock absorbing, making it an excellent buffer for impact loads. The material is also resistant to many chemicals, including solvents, oils, and weak acids. The bearings also have a low moisture absorption rate, letting the user walk in all weather without increased friction. The shock absorbing qualities of the plastic material, coupled with swing phase hydraulics, act as a substitute for cartilage in a biological knee, cushioning the force of two to four times the patient’s body weight that occurs with each step.
In prosthetic knee joints that utilize metal bearing systems, dirt, dust, pet hair, and other common debris is attracted to the external lubrication, therefore impeding the friction surface which can lead the knee to seize up and the patient to stumble or fall. The specialized plastic bearings in the EBS system are self-lubricating, using microscopic particles of solid lubricant included throughout the plastic material. Without external bearing lubricant, dirt and debris from everyday wear is not attracted to the joint, and any dirt is simply embedded into the plastic material with no noticeable increase in friction.
Patients using the EBS prosthetic joint are able to walk more naturally and comfortably than those with traditional prosthetics. The EBS joint gives a higher ground clearance in the swing phase of a patient walking due to the polycentric nature of the system. Polycentric knees, with more than one axis of motion, are more stable than single axis systems, which are essentially a hinge. The polycentric system gives a much more “knee-like” feel, and with added hydraulic power in polycentric joints like the 3R60, patients are able to have more variability in the walking speed and function, but at a price.
Typically, polycentric knee joints are heavier and more expensive than single-axis joints, even more so with added weight and cost of added hydraulics. Otto Bock’s joint systems, however, have compensated for the added price and weight by substituting plastic components that are very light weight and low cost, too. At only 1.8 pounds, the joint offers a joint flexion angle of 175 degrees, limited only by shaft connections/forms or optional cosmetic cover. The mini hydraulic system utilizes piston rings with separately adjustable flexion and extension to control the behavior of the joint during the swing phase of the walking motion. A rubber bumper is compressed during stance phase flexion, generating the corresponding movement resistance, which is adjustable per patient requirements. The hydraulic components absorb subsequent stance phase extension. The five-axis polycentric design structure of the EBS joint allows for separation between the swing and stance phases. In the stance phase, flexion is made possible by interplay between the lower front axis as the joint’s center of rotation with the EBS’s pivoting mount and the posterior link of the polycentric structure. The EBS pivoting mount also visualizes the degree to which the EBS function is used.
Piston rings are applied in the mini hydraulic unit in the top and bottom pistons located in the pneumatic cylinders. The piston rings replaced PTFE guide tape, used to create bands. When producing the knee joints, each piece of PTFE tape, supplied as a large coil, had to be cut to the appropriate size for the particular joint, then packed and stored in strips, inevitably with some error in sizing. If the strip was too long, it had to be cut again. Cropping on the cutting edge could leave the band too short, keeping it from properly fitting into the driving band groove. Instead of the lengthy and error-prone process of sizing, cutting, and fitting the PTFE tape, the piston rings simply snap onto the piston, greatly reducing the production costs and lowering the total cost of the joint. When tested within Otto Bock EBS joints, barely any perceptible wear was reported on the piston rings, even under maximum stresses, and according to the company, increased the quality, functionality, and durability of their overall system.
This article was written by Ellen Rathburn, Technical Copywriter for igus, Inc. East Providence, RI. For more information on Otto Bock, visit http://info.hotims.com/-189 . For more information on igus, visit http://info.hotims.com/-163 .