The rate of lower limb amputations secondary to vascular injuries is increasing, and the need for physiatric providers to improve the quality of life of these patients remains paramount. Physiatrists need to maintain knowledge about the changing technologies in prosthetics, understand gait and its analysis, and know the complications encountered by prosthetic users. By improving function of these patients, their quality of life can be altered in a positive way.
Epidemiology
The number of patients with limb loss has continued to increase because of several factors, thereby requiring more rehabilitation intervention. An aging population, an increase in the number of dysvascular cases for amputation, and an increase in the frequency of osteomyelitis contribute to these increases. Studies predict a doubling of the elderly dysvascular amputation population by 2030 and a doubling of the overall amputation population prevalence by 2050. The majority (82%) of people with lower limb amputations undergo amputation as a result of disease processes, such as diabetes mellitus (DM) or peripheral vascular disease. Other causes include trauma (16%), malignancy (1%), or congenital abnormality (1%). DM increases the risk for amputation to a greater degree than either smoking or hypertension. DM is reported to contribute to 67% of all amputations, and cigarette use is associated with a reamputation risk 25 times greater than that of nonsmokers. Individuals with amputation at an earlier age require a longer continuum of care.
The most frequent amputation level in the lower extremity varies according to the etiology. Toe amputations are the most common level overall when considering both major and minor amputations. With advances in limb salvage techniques, the number of partial foot amputation procedures has shown a significant increase over the past 10-15 years. The transtibial level is the most common major amputation level in the lower extremity, with transfemoral being the second most common.
Amputation Terminology
The International Organization for Standardization (ISO) terminology for the description of both acquired amputations and congenital limb deficiencies has been widely accepted and increasingly used.
Rehabilitation Implications of Amputation Level and Surgical Technique
The main goal of surgery is to remove diseased or damaged tissue to allow healing. Without healing, prosthetic training cannot begin. The large numbers of muscles within the leg complicate surgery (eSlide 10.1) . The amputation level and surgical healing affect outcomes following amputation. In general, preservation of limb length with accommodations for future prosthetic fitting improves outcomes. Presurgical planning allows for consultation with the physiatrist and aids in discussion about the amputation level and future prosthetic fitting. Myodesis (suturing muscle attachment to bone) and myoplasty (suturing muscle fibers to fascia) are commonly performed surgical closures.
Postoperative healing, daily skin care, and residual limb shaping are of increased importance after amputation. Shrinkers or figure-of-8 wraps should be used to maintain limb shape when not wearing the prosthesis. To prevent loss of the contralateral limb, daily skin care and inspection should also be performed on this limb. Inadequate socket pressure on the distal end of the residual limb leads to verrucous hyperplasia. Shrinker socks and modification of the socket to apply appropriate pressure on the distal end help resolve this problem. Hyperhidrosis is a common symptom in amputee patients. Topical antiperspirants and botulinum toxin type B have been used in this population.
Heterotopic ossification can occur secondary to osteoblast activity. This can lead to range of movement (ROM) issues, problems with ambulation, or neurologic or vascular compromise. Diagnosis can be made on the basis of increased alkaline phosphatase levels and radiographs when suspicion of heterotopic ossification is high.
Pain Management
Residual limb pain (RLP), phantom limb pain (PLP), and phantom limb sensation (PLS) are frequent findings after an acquired limb amputation. RLP is confined to the affected limb; PLP is pain in an area that is no longer present. PLS is prevalent in the immediate postoperative period and improves with prosthetic use and desensitization strategies. PLP varies and is described as dull, squeezing, cramping, electric shock-like, shooting, or sharp. Medications for PLP include N -methyl- d -aspartate receptor antagonists, opioids, anticonvulsants, antidepressants, local anesthetics, and calcitonin. Mirror therapy and transcutaneous electrical nerve stimulation have also been used for PLP.
Psychological Support
Undergoing amputation is a traumatic physical and psychological experience. Amputees may go through several stages of recovery: shock and confusion, mourning, and ultimately, adjustment and self-worth. Family support, goal-directedness, patient attitude, and spirituality are indicative of positive psychological predictors. Return-to-work is correlated with better prosthetic fitting, fewer medical conditions, amputation level, and premorbid career.
Prosthetic Fitting Timeline and Rehabilitation Considerations
Preprosthetic fitting begins before surgery and continues until prosthetic training is initiated. Positioning and shaping of the limb and ROM exercises are important aspects of this phase. Wound healing, pain management, and edema control limit progression to prosthetic fitting in this phase. Preambulatory therapy and awareness of a changed center of mass after amputation are characteristics of therapy concerns during this phase.
During initial prosthetic training, standing, balancing, and simple stepping exercises predominate. Pregait activities, involving dynamic weight-shifting exercises, occur after mastery of the basics. Gait deviations are frequently seen, which require modifications from prosthetists during this phase. Fit, sock management, and donning and doffing of the prosthetic safely and effectively improve long-term use. Limb size and shape change during this phase as fluid shifts occur. Residual limb changes occur during this time, necessitating socket modifications. Skin redness or irritation indicates prosthetic fit issues. Time in the prosthesis should be gradually increased.
Functional Classification and Prosthetic Prescription
The Centers for Medicare and Medicaid Services have published a functional classification system that guides prosthetic limb prescription. Five levels (termed K-levels) assist providers in selecting appropriate devices, based on anticipated goals and medical comorbidities. With the prosthetic prescription, the emphasis should be on identifying the class of prosthetic components best suited to achieve the patient’s functional goals. Design of the prosthesis is a team decision that includes input from the patient, physiatrist, physical therapist, and prosthetist.
Socket Designs
Prosthetic sockets serve as the connection between the limb and patient, and they occasionally provide support. Transtibial sockets (patellar tendon bearing, patellar tendon bearing with supracondylar suspension, or full contact) and transfemoral sockets (quadrilateral and ischial containment) accommodate patients with differing residual limb lengths. Each socket type provides different benefits to the user. In patients with transtibial amputations, the patellar tendon-bearing socket is most frequently used and provides pressure relief in soft tissue areas that are able to resist forces during walking. The ischial containment socket for transfemoral amputees has gained popularity over the quadrilateral socket because it incorporates a more anatomic approach to fitting by “containing” the ischium within the trim line.
Prosthetic Limb Suspension
Suspension holds the socket and prosthesis onto the residual limb. Suspension is extremely important when considering the safety and use of prosthesis. Suction systems create a negative pressure within the socket to maintain suspension. Complications arise when the distal contact between the residual limb and prosthesis is lost. Pin-locking suspensions require a gel liner worn by the patient, with a threaded pin that engages the prosthesis. This can be used in transtibial or transfemoral amputees. The audible click heard when engaging the prosthesis provides feedback to ensure proper suspension. Lanyard suspensions are also used in transfemoral amputees to aid in prosthetic wearing. Higher-level amputations, such as shorter transfemoral amputations with short residual limbs, may require Silesian belt suspensions or a combination approach with a mixture of suspension types. Patients with short transtibial amputations may need supracondylar suspension or cuff suspension mechanisms.
Recently developed prosthetic liners provide protection against shearing forces with softer materials such as Pelite, gel, urethane, and silicone. Unfortunately, there are some issues with durability and wear and tear, and thus occasional replacing is required.
Prosthetic Limb Frame Options (Endoskeletal or Exoskeletal)
Prosthetic frame options include endoskeletal or exoskeletal designs. Exoskeletal sockets use rigid exterior lamination, which helps with heavier patients or cosmesis under clothing. Endoskeletal devices, on the other hand, are more commonly used and require a pylon system to connect the socket to the foot, as in the case of a transtibial amputee. This also allows for customization of prosthetic height.
Prosthetic Feet
Prosthetic feet are available in many different materials and designs. Each has some benefit or potential drawback, depending on the function of the individual wearing the prosthesis. Solid ankle cushion heel (SACH; eSlide 10.2 ) feet are used for K1 level amputees; they have no moving parts, allowing for a lightweight, durable, and inexpensive design. A stationary attachment flexible endoskeleton (SAFE) prosthetic foot is similar to the SACH foot in that it has no joint articulations and is durable and inexpensive. The SAFE foot is primarily indicated for K1 and low-level K2 ambulators. Neither the SACH nor SAFE foot is an articulated design.
Articulated feet provide an advantage of increased movement in higher-functioning prosthetic users. Single axis feet (for K1 and K2 level ambulators; eSlide 10.3 ) allow controlled dorsiflexion and plantar flexion, with bumpers to limit any excessive motion. Multiaxial feet (K2 and K3) allow movement in multiple planes as the foot interacts with the ground (eSlide 10.4) . Some feet allow energy storage and return in the gait cycle, improving efficiency. Energy-storing feet allow active patients to have spring-like ground effects that propel them into the next push-off phase in gait or provide cushioning (e-Slides 10.5 and 10.6) . This type of foot is indicated for K3 and K4 level ambulators. Microprocessor-controlled feet are commercially available and provide improvements when walking over varying ground, but they are not always covered by insurance companies, which limit their accessibility (eSlide 10.7) . Specialized feet are available for higher-level prosthetic users (eSlide 10.8) .
Prosthetic Knees
Prosthetic knees used by transfemoral amputees are classified with respect to use and functional levels. Prosthetic users with increased functional abilities may use increasingly complex knee units that respond quickly to changes in gait, stride length, or cadence. Manual locking knees are for K1 level patients; they are either hinged and freely mobile or locked in place (such as in extension while standing). These are inexpensive and durable knees but provide poor gait mechanics compared with higher-level knee units. Single axis knee units (for K1 level ambulators) have a spring-assisted extension for quicker swing of the foot through the gait cycle. However, proximal muscle control is needed to prevent falling. Weight-activated stance control knee units (indicated for K1 and K2 level ambulators) are single axis knee units, but the knee locks when weight is applied through the prosthesis in the stance phase. When the weight is shifted off the prosthesis, the locking mechanism disengages, allowing for flexion in the swing phase. Polycentric knee units provide stability because of their construction and points of rotation, which are aligned to improve stability and knee flexion compared with single axis knee units (eSlide 10.9) . Hydraulic knee units improve the ability to control the distal prosthetic limb using either fluid-filled or air-filled devices. These knees are indicated for K3 level ambulators as they allow for varied cadences and are adjustable. Microprocessor knee units provide increased feedback with a processor analyzing information at 50-1000 times per second to account for knee resistance forces (eSlide 10.10) . One limitation is the inability to use these in areas that are at a risk of being exposed to water. They are for high-functioning K2 or K3 level amputees.
Additional Componentry Considerations
Torque absorbers are needed to automatically return the prosthetic to its original position. This is worthwhile in K3 level patients who would be able to torque a knee unit when walking or performing tasks. Diagnostic test sockets are frequently ordered before constructing a final socket to ensure fit before costly materials are used. Prosthetic socks, ranging from 1-ply to 5-ply, allow a user to adjust the fit quickly and precisely. When a patient starts to wear 10-ply socks, the general rule is to consider replacing the socket. Certain cosmetic covers can be added to allow the affected limb to appear more similar to the contralateral side.
Prosthetic Prescription for Partial Foot Amputations
There are many levels of partial foot amputations, which are treated in different ways. Any prosthetic design should reduce shear forces and pressure points. With an ankle disarticulation (Syme) amputation, patients can actually bear weight on the residual limb; however, the limb length does not allow for most energy-storing feet to be used. The liner is typically a gel liner with padding such as Pelite. Prosthetic foot options include a low-profile Syme SACH foot or a carbon composite foot. The carbon foot allows some energy storage and also provides better accommodation over uneven surfaces.
Prosthetic Prescription Algorithms for Transtibial Amputees
The choice of components for transtibial prosthetic prescriptions depends on the individual’s current or potential functional abilities and the patient’s goals for prosthetic use. The following recommendations for each functional level are for general consideration; it is important to develop a prescription that is individualized to a specific individual. The essential elements for transtibial prosthesis that need to be included for every functional level are socket, interface, suspension, pylon or frame, and type of foot and ankle. Items included in all prescriptions for prosthesis are a clear diagnostic socket and socks (single-ply and multiple-ply, six of each). The patient can select a custom-shaped cover, a prosthetic skin, or both to help address cosmetic concerns.
Functional Level One (K1)
Patients in this functional category have the ability to use a prosthesis for transfers or to ambulate over level surfaces for short household distances. Safety is the greatest priority for this population. The socket design should be a total contact style, with special considerations for comfort during sitting. The type of interface and suspension system used should consider the patient’s ability to don and doff the prosthesis and manage his or her hygiene independently. The frame should be lightweight and endoskeletal (with or without alignment ability) in design. Recommended foot and ankle components include a nonarticulated foot, such as the SACH or SAFE foot, or a simple articulated foot, such as the single axis foot. Also included in this prescription will be a clear diagnostic socket, prosthetic socks, and a cosmetic cover.
Functional Level Two (K2)
Patients in this functional category have the ability to perform limited community distance ambulation and traverse some environmental barriers. The major changes in the prosthetic prescription will be that the components should be alignable and the prosthetic foot should be a multiaxial or flexible keel-type foot to allow for accommodation over uneven terrain. Suspension for this group can use a pin lock, sleeve or suction suspension with a sleeve, and one-way expulsion valve in the socket.
Functional Level Three (K3)
Functional K3-level amputees are community distance ambulators who have the ability to traverse most environmental barriers and ambulate with variable cadence. Special consideration for this group will be the type of prosthetic foot. This will be some type of energy-storing (dynamic response) foot, and depending on the activities they are performing, it can include a dynamic pylon or feature that allows greater accommodation over uneven terrain. Foot and ankle components that incorporate hydraulic units, with or without microprocessor control, can also be considered in this population. A foot and ankle component with both microprocessor control and internal power may also be indicated for these patients. An additional consideration for prosthetic suspension is the use of an elevated vacuum technology.
Functional Level Four (K4)
Patients in this classification level have the ability or potential ability for ambulation that exceeds normal requirements. This may include sports or recreational activities that require high impact, high stress, or high energy levels, which are typical of the prosthetic demands of a child, high-activity adult, or athlete. At this level, specialty components are running feet, waterproof foot and ankle components, and components with heel height adjustability. Suspension is also a key for this group to avoid catastrophic disruption of the prosthetic connection during activity. This may include use of a backup or secondary suspension method. Special considerations are also needed for the pediatric population because of growth and the wearing out of components secondary to high usage.
Knee Disarticulation
A knee disarticulation amputation level leaves the femur intact and creates a distal weight-bearing surface with retained thigh musculature. This long lever provides potentially better control of the prosthetic limb and maintains the distal growth plate of the femur, which is important for individuals who are skeletally immature at the time of amputation. The disadvantages of this amputation level are the discrepancies between the height of the prosthetic knee center and contralateral anatomic knee, as well as the worse cosmetic appearance. As with the ankle disarticulation level, the prosthesis proximal trim line will depend on the patient’s ability to bear weight on the distal end of the residual limb. If full weight bearing occurs, then the proximal trim can be lowered to the subischial level. If there is no distal end weight bearing, then the residual limb is treated as a transfemoral amputation with use of a more traditional ischial containment socket.
Prescription Criteria
Socket design for this level typically includes an anatomically shaped socket with a flexible inner socket. The proximal trim lines of the socket will be determined based on distal weight-bearing tolerance as noted earlier. Interface and suspension options are generally the same as those for the transfemoral level, but there is also the possibility of creating suspension of the prosthesis with use of femoral condyles. Polycentric knee units are commonly recommended to reduce the difference in knee centers between the prosthetic limb side and the intact limb side. Depending on the functional goals of the patient, additional features, such as a hydraulic mechanism, may be indicated and beneficial.
Prosthetic Prescription Algorithms for Transfemoral Amputees
The prosthetic prescription for transfemoral amputees is based on current and potential functional abilities when considering medical comorbidities and social situations. Table 10.1 summarizes traditional prosthetic prescription parts for each K-level. In patients with transfemoral amputations, considerations about the knee unit and alternative methods of suspension are needed for safety purposes.
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