LOWER LIMB PROSTHETICS

LOWER LIMB PROSTHETICS

PROSTHESIS AND ORTHOSIS

A prosthesis is a device designed to replace, as much as possible, the function or appearance of a missing limb or body part.

An orthosis, in contrast, is a device designed to support, supplement, or augment the function of an existing limb or body part.

CHARACTERISTICS OF A SUCCESSFUL PROSTHESIS

Ideally, a prosthesis must be comfortable to wear, easy to put on and remove, light weight, durable, and cosmetically pleasing.

Furthermore, a prosthesis must function well mechanically and require only reasonable maintenance.

Finally, prosthetic use largely depends on the motivation of the individual, as none of the above characteristics matter if the patient will not wear the prosthesis.

CONSIDERATIONS WHEN CHOOSING A PROSTHESIS

• Amputation level

• Contour of the residual limb

• Expected function of the prosthesis

• Cognitive function of the patient

• Vocation of the patient - For example, whether the patient is employed at a desk job or at manual labor

• Avocational interests of the patient (ie, hobbies)

• Cosmetic importance of the prosthesis

• Financial resources of the patient

REASONS FOR LOWER EXTREMITY AMPUTATION

Most lower extremity amputations occur in individuals older than 60 years and result from disease complications.

Complications of diabetes and peripheral vascular occlusive disease are the leading causes of amputation (65%), followed, among disease-related causes, by complications of thromboembolic disease and vasculitis.

Trauma is the second most common cause of lower extremity amputation (25%) and typically occurs in the young male population.

Tumors and congenital malformations less commonly (5% each) result in lower extremity amputation.

TERMINOLOGY AND TYPES OF AMPUTATIONS

• Transphalangeal amputation - Excision of part of 1 or more toes

• Toe disarticulation amputation - Resection through the metatarsophalangeal joint or joints

• Ray amputation - Resection of the toe and part or all of the corresponding metatarsal

• Transmetatarsal amputation - Resection through all metatarsals

  • This amputation is designed to provide a functional, weight-bearing foot with an adequate forefoot lever arm to permit reasonably normal walking without major prosthetic restoration. 

• Lisfranc amputation - Resection through the metatarsal and tarsal joints

  • Because the insertions of the dorsiflexors of the ankle are sacrificed with this amputation, to provide for a balanced ankle and avoid development of an equinovarus deformity the distal tendons of the peroneus brevis and the anterior tibialis must be reattached proximally in the residual foot to the cuboid and to the neck of the talus, respectively.

  • The shape and shortened length of the residual foot increases the difficulty of fitting it with a partial foot prosthesis that can provide adequate suspension and/or a forefoot lever for ambulation. Successful prosthetic restoration often requires a prosthetic or orthotic design that is more substantial and extends proximal to the ankle.

• Chopart amputation - Resection through the calcaneocuboid and talonavicular joints

  • To prevent equinovarus deformity, the peroneus brevis tendon must be transferred to the cuboid and the anterior tibialis tendon must be transferred to the neck of the talus.

  • The shape and length of the residual limb make the limb even more difficult to fit with a partial foot prosthesis than it would be after the Lisfranc amputation.

• Syme amputation - Ankle disarticulation with or without removal of the medial/lateral malleoli and distal tibia/fibula flares

  • The advantage of this amputation is that it provides a residual limb with an end-bearing surface.

  • The length of the residual limb limits the prosthetic foot options compared with a more proximal transtibial (below-knee) amputation.

  • This amputation leads to a poorer cosmetic prosthetic result because of the need for the prosthesis to accommodate the bulbous distal shape of the residual limb (which is produced by the malleoli). This is especially true for slim patients.

  • Careful surgical technique is required to prevent heel pad migration from the distal end of the residual limb. If this occurs, the weight-bearing advantage of this amputation level could be compromised.

• Transtibial amputation - Below-knee amputation (BKA); resection through the tibia and fibula

  • The ideal length is from the proximal one third to the middle of the limb. 

• Knee disarticulation amputation – Through-the-knee amputation; resection through the knee joint

  • The advantage of this amputation is that can provide a broad, end-bearing surface for the residual limb and a maximal lever arm for powering and controlling a prosthesis

  • The disadvantage of this amputation is that it does not provide an ideal length for prosthetic restoration, because it limits the amount of space available for the knee joint components in the prosthesis. This limits the options for prosthetic knees that can be used to maintain the symmetry of the knee-joint centers.

• Transfemoral amputation - Above-knee amputation (AKA)

  • The ideal length is about 8 cm proximal to the knee joint, so that the femoral condyles are excised with adequate room to accommodate prosthetic knee options

• Hip disarticulation amputation - Resection through the hip joint; pelvis intact

• Hemipelvectomy amputation – Resection of all or part of the hemipelvis and of the entire lower extremity

MYOPLASTY AND MYODESIS

There are 2 approaches to managing the muscle in the limb during amputation: myodesis and myoplasty.

Myodesis: The muscles and fasciae are sutured directly to the distal residual bone through drill holes. The objective of this technique is to provide a structurally stable residual limb, with the insertions of the residual muscles securely attached to maintain their function; this ultimately results in better prosthetic control and function. 

Myodesis is not always performed, because when attempted by even the most experienced surgical hands it often fails. Myodesis is contraindicated in patients with severe peripheral vascular disease, because the blood supply to the muscle may be compromised. 

Myoplasty: Requires the surgeon to suture the opposing muscles in the residual limb to each other and to the periosteum or to the distal end of the cut bone. Sufficient muscle stretch must be provided to maintain active muscle control of the residual limb following amputation, but without producing so much muscle tension that the blood supply is compromised.

A well-performed myoplasty can provide some distal soft-tissue padding over the residual bone and result in a stable, functional residual limb. On occasion, some myoplasties will not securely anchor to the distal residual limb, resulting in a movable soft-tissue sling, with a bursa developing between the soft tissues and the underlying bone. Some of these bursa can become symptomatic and painful.

END-BEARING (WEIGHT-BEARING) AMPUTATIONS

Amputations that provide an end-bearing residual limb are advantageous for prosthetic restoration. These amputations theoretically permit the weight-bearing forces within the prosthesis to be concentrated in a circumscribed area of the residual limb, or specifically, the residual limb's weight-tolerant, distal end. 

This can simplify prosthetic socket fitting considerations and minimize many of the prosthetic fitting complications, most of which are related to residual limb socket interface issues. Because of their shape and length, some end-bearing residual limbs limit the prosthetic options that are available for prosthetic restoration.

End-bearing lower extremity amputations include the following:

• Partial foot amputations - These are more weight bearing than end bearing.

  • Transmetatarsal amputation

  • Lisfranc amputation

  • Chopart amputation

• Syme amputation

• Ertl transtibial osteomyoplasty amputation procedure - An osteoperiosteal tube joins the ends of the bones, which ossify to form a sturdy, weight-bearing bone bridge.

  • Shrinkers for limb shaping are not advisable after this procedure because they will compress the fusion site.

  • Preparatory prosthetic fitting is delayed until the bony bridge has completed fusion.

• Knee disarticulation

DETERMINANTS OF A SUCCESSFUL OUTCOME WITH PROSTHETIC USE

To insure a successful prosthetic outcome, it is necessary to determine the goals of each individual amputee.  This should include the patient's expectations for functional activities with the prosthesis. 

The physical, as well as psychologic or emotional, status of the patient (including any pre-existing or limiting comorbidities) are important considerations.  

These could include such issues as strength, endurance, joint contracture, ambulatory status, hemiparesis from a prior stroke, and retinopathy resulting from diabetes. The patient may have been nonambulatory for months and therefore be deconditioned. 

A program of preprosthetic training would improve the needed upper extremity strength and overall endurance required for prosthetic training.

Some patients may not want to ambulate with a prosthesis but may instead wish to use a prosthesis only for Cosmesis and improved self-esteem. 

Ideally,these discussions should begin preoperatively and should  involve  the surgeon, the physiatrist, the physical therapist, the prosthetist, the patient, and, whenever possible, a peer counselor (if the patient is open to this).

Once it is decided the patient wishes to proceed with prosthetic restoration, several factors related to the prosthesis itself will impact on whether the outcome is successful. 

The prosthesis must be comfortable to wear, easy to put on and remove, light weight and durable, and cosmetically pleasing. Furthermore, the prosthesis must function well mechanically and require reasonably low maintenance.

Successful prosthetic intervention should be judged by patient-specific functional outcomes. A nonambulatory patient may report an improved quality of life with a prosthesis used for transfers (movement from one position or surface to another) as opposed to one employed for ambulation.

FACTORS TO CONSIDER WHEN CHOOSING PROSTHETIC COMPONENTS

Consider the following factors when choosing prosthetic components for successful prosthetic restoration:

• Amputation level and residual limb strength

• Contour of the residual limb

• Health status 

  • Physical status (ie, balance, strength) and fitness level

  • Activity tolerance from underlying medical comorbidities (ie, atherosclerotic heart disease, ischemia)

  • Effects of peripheral vascular disease and diabetic nephropathy, which may cause unstable residual limb volume

  • Impaired cognition or other neurologic deficits (ie, stroke)

  • Sensorimotor deficits caused by peripheral nerve dysfunction

  • Visual impairments resulting from diabetic retinopathy, or other ophthalmic disorders

• Expected function and needs of the prosthesis 

  • Patient's vocation (for example, desk job vs manual labor)

  • Patient's avocational interests (ie, hobbies)

  • The cosmetic importance of the prosthesis

• The patient's financial resources (ie, medical insurance, worker's compensation)

THE PROCESS AND TIMELINE FOR AMPUTATION AND PROSTHESIS FITTING

PRE-AMPUTATION PHASE

Most lower extremity amputations are performed as a result of disease and are, to some extent, preplanned. This allows the rehabilitation team to meet with the patient prior to surgery. 

The team typically consists of a physiatrist (a physician who specializes in physical medicine and rehabilitation), an occupational therapist, a physical therapist, a prosthetist, a psychologist or social worker, and when appropriate, a case manager.

Many patients with amputations have reported that meeting with the rehabilitation team has proved to be a critical and helpful component in making informed decisions and in adjusting to life as an amputee.

During this time, an assessment of the patient's postoperative needs and desires can be addressed, and range-of-motion (ROM) exercises and strengthening can be initiated, as can training for the activities of daily living (ADL).

The prosthesis-related implications of the amputation level should be addressed because a longer residual limb does not always best fulfill a patient's prosthetic needs.

A tibia that is longer than two thirds of the residual length limits the choice of prosthetic components and may not be as functional for more active patients.

Example, in patients with active lifestyles, a transtibial length is more accommodating for sports than a Syme level length is, owing to the available selection of prosthetic components.

Cosmesis also can be affected by extreme length deviations. In the case of a short residual limb, auxiliary suspension aids may be required that are bulky or difficult to hide.

Peer support visits by a successful amputee with a similar level of amputation have a tremendous benefit for the new amputee. Potential amputees often feel a reduction in anxiety and fear after speaking with another amputee. Many amputee peer counselors are happy to answer questions and offer support to potential patients. 

Psychology should be involved at this phase if possible (i.e. elective procedure) or immediately postoperatively. Adjustment and grief reactions are common for new amputees. The patient may struggle with self-image and cosmetic concerns early, as well as later, in the prosthetic restoration process. 

A simple and organized psychological framework proposed by Van Dorsten delineates the process well.  The stages address survival, recovery and reintegration. The amputee will have many questions and concerns during each stage. As mentioned, peer support visits by another successful amputee can be of great benefit to the new amputee. 

Initially, the rehabilitation team should suggest this option to the patient or remind him or her that it is available, but it is important to allow the patient to indicate whether he or she is ready for peer support.  

The frequency of psychological visits depends on many factors, such as premorbid coping skills, family support, pain intensity, and medical-surgical complications. 

The patient will need to be followed throughout the course of immediate post amputation, prosthetic training, and functional reintegration back into societal routine.

LIMB SALVAGE VERSUS AMPUTATION

In some instances, patients may have the option to make an informed decision regarding an elective amputation. This obviously is a difficult decision to make. Trauma, infection, and dysvascularity are the main indications for an elective amputation.

Trauma often involves non healing fractures or vascular, thermal (burn- or cold-related), or nerve injury. All may result in a limb length that is less functional than a prosthesis.

A limb should be salvaged only if it has sufficient sensation to be capable of protective sensory feedback. Amputation is indicated if a vascular injury cannot be reconstructed.  

In patients who have an infection, a guillotine (open) amputation is performed to prevent further dissemination. The limb is allowed to drain and is later revised to a closed amputation.

SURGICAL PROCEDURE

During amputation surgery, several actions can be taken to maximize the function of the residual limb.

These include the following:

• Shortening and beveling the bone end to allow adequate soft tissue coverage

• Sharply transecting the nerve under tension to allow retraction and to decrease the likelihood of neuroma formation

• Securing the muscles with a myodesis or myoplasty to create a structurally stable and functional limb

• Positioning the wound edges to avoid bony prominences at the far distal end of the residual limb

• Keeping the bony lever arm as long as possible but covering it with adequate muscle and soft tissue to avoid fitting problems later

The above principles apply to transtibial and transfemoral procedures.  In contrast to transtibial amputations, in which a long

posterior flap is employed, transfemoral procedures utilize a fishmouth technique in which equal anterior and posterior flaps are used for closure and avoidance of split-thickness skin grafts.

There is general agreement in the literature that mortality is lower following transtibial amputations than after transfemoral amputations, because the transtibial procedures have higher healing rates. 

Transtibial amputation also results in better tissue viability and provides a better weight-bearing surface. Moreover, following this procedure, ambulation requires less energy expenditure.

A temporary prosthesis can be fitted in surgery so that the patient can visualize a limb in place. This is called an immediate postoperative prosthesis (IPOP).

The use of IPOPs is not a widespread practice, but there are several small groups looking into this area again.  IPOPs are usually fitted in healthy, young patients with traumatic amputations, in which case rehabilitation physicians work integrally with orthopedic specialists and prosthetists for successful outcomes. 

It is an option that the surgeon and the physiatrist must agree on together. 

ACUTE POSTSURGICAL PHASE

The major issues in this phase are adequate wound healing, pain management, the administration of soft and rigid dressings for limb shaping, and physical and occupational therapy to train the patient to perform ADL and ROM exercises and to improve strength and mobility.

Prevention of contractures is important because they affect the fitting and function of the prosthesis. During this time, a program to prepare the residual limb for the prosthesis should be initiated.

A skin desensitization program consists of the following:

• Gentle tapping and massage (with a washcloth) on the distal portion of the residual limb

• Scar mobilization and massage to prevent excessive scar formation from causing the soft tissues and skin to adhere to underlying bone

• Edema control, initially with ace wraps and, when the drainage subsides, with a residual limb (stump) shrinker

• The application of pressure to the distal aspect of the residual limb to prepare the limb for weight acceptance

A rigid, removable dressing may be used over the residual limb during this phase. The rigid dressing serves the following functions:

• Aids in edema control and leads to rapid residual limb shrinkage

• Promotes healing by providing protection and preventing edema

• Desensitizes the limb

• Prevents residual limb trauma

  • Reduces wound pain 

PROSTHETIC FITTING AND TESTING

When the suture line has completely healed, fitting for the prosthesis can begin. Each prosthesis must be individually fitted to the patient.

Prostheses are either preparatory or definitive.  

The preparatory prosthesis is fitted while the residual limb is still remolding.

This allows the patient to commence the rehabilitation program, which includes the following activities:

• Training in the donning and removal of the prosthesis

• Transfer training

• Building of wear tolerance

• Attainment of balance

• Ambulation with the prosthesis several weeks prior to final residual limb volume stabilization

Use of a preparatory prosthesis often results in a better fit of the final prosthesis because the preparatory socket can be used to mold the residual limb into the desired shape and stable volume. Because of the materials from which they are constructed, most preparatory prostheses are easily modified.

The definitive prosthetic socket is most often of a laminated design and provides durability.

If the patient is being fitted for a definitive prosthesis without having had a preparatory prosthesis, there should be a delay in fitting for the socket until the residual limb is fully mature or until general volume stabilization of the residual limb occurs (which in some cases can take several months).

Minor cosmetic modifications aside, most prostheses can be expected to last at least 3-5 years with standard daily use. The socket may need more frequent replacement because of volume or weight changes, but the other components should be reusable. 

Children may need much more frequent modifications or adjustments as they grow.

A patient must meet the following minimal requirements to be functionally successful with a lower extremity prosthesis:

• Sufficient trunk control

• Good upper body strength

• Adequate knee stability and control

• Static and dynamic balance

• Adequate posture

Once these basic requirements are met, stability, ease of movement, energy efficiency, and the appearance of a natural gait are the goals to be achieved with prosthetic training and use.

Determination of functional level for Medicare patients influences which components are used.

The Centers for Medicare and Medicaid Services (CMS) have identified the following specific levels of prosthetic function (K-levels) and requires that these be listed on prosthetic prescriptions or certificates of medical necessity when determining eligibility for a specific prosthetic:

v  Level 0 - The patient does not have the ability or potential ability to ambulate or transfer safely with or without assistance, and a prosthesis does not enhance quality of life or mobility.

v  Level 1 - The patient has the ability or potential ability to use a prosthesis for transfers or ambulating on level surfaces at a fixed cadence. This is typical of the limited and unlimited household ambulator.

v  Level 2 - The patient has the ability or potential ability to ambulate well enough to traverse environmental barriers, such as curbs, stairs, or uneven surfaces. This is typical of the limited community ambulator.

v  Level 3 - The patient has the ability or potential ability to ambulate with variable cadence. This is typical of the community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activities that demand prosthetic use beyond simple locomotion.

v  Level 4 - The patient is capable or potentially capable of prosthetic ambulation that exceeds basic ambulating skills and that exhibits high impact, stress, or energy levels. This is typical of the prosthetic demands of a child, an active adult, or an athlete.

LOWER EXTREMITY PROSTHESIS COMPONENTS

The major components of a lower extremity prosthesis are the socket (with or without a socket liner), a suspension system, interposed joint components (as needed), a shank (pylon), and a prosthetic foot.

The prosthetic foot is typically a component that functions and looks like a foot but that may take other forms or functions for water or other sports activities.

THE SOCKET

The socket serves as the interface between the residual limb and the prosthesis. It must not only protect the residual limb but must also appropriately transmit the forces associated with standing and ambulation.

The preparatory (temporary) socket will likely need to be adjusted several times as the volume of the residual limb stabilizes. The preparatory socket can be created by using a plaster mold of the residual limb as a template.

Some prosthetic manufacturing facilities use computer-assisted technology to map the residual limb, manufacturing a socket directly from that data.

The most common socket used in a transtibial amputation is a patellar tendon-bearing (PTB) socket. This socket emphasizes increased contact or weight bearing in the area of the patellar tendon, inferior to the patella, but that is not to say that there is not significant contact or weight bearing elsewhere on the residual limb.

The concept of total contact is important because prior to the total-contact PTB socket, transtibial sockets often had an open-ended, plug-fit design, which lead to numerous skin problems, chronic choke syndrome, ulceration, and other problems. 

Total-surface–bearing (TSB) transtibial socket designs are moving away for the concept of emphasizing patellar tendon weight bearing, but even these require selective loading and selective relief over certain areas of the residual limb. Neither socket will work well for every amputee. The prosthetist still needs to work with an individual patient to fit a socket that meets that particular patient's needs. 

With the PTB design, weight is distributed over many different areas, such as the anterior and posterior compartments and the medial tibial flair. One may see the term "total contact socket," which denotes the PTB design. 

The PTB socket has variations, including the PTB-supracondylar (PTB-SC) socket and PTB-suprapatellar-supracondylar (PTB-SCSP) socket. 

A PTB-SC has high medial and lateral sidewalls that extend above and over the femoral condyles, providing enhanced mediolateral stability and self-suspension for the prosthesis. 

The PTB-SCSP socket furthers the PTB-SC concept by also extending the anterior aspect so that the patella is enclosed within the socket. 

The PTB-SCSP socket gives additional stiffness to the mediolateral walls and applies force proximal to the patella during stance, in this way providing sensory feedback to limit genu recurvatum. 

The PTB-SC and PTB-SCSP sockets are used primarily for amputees with short residual limbs in order to improve varus/valgus control and to provide greater surface area for weight distribution.

Another option is a joint-and-corset system, which is especially good for heavy-duty use. This system may be used to increase the weight-bearing surface area onto the thigh or to off-load the transtibial residual limb, transferring the weight to the thigh.

The joint-and-corset system is also used when there is a need to provide great mediolateral stability for the knee of a transtibial amputee. Another option is a rigid frame with a flexible liner; the outer rigid frame has windows that provide additional pressure relief.

An alternative socket design for transtibial amputees is the TSB socket that is used with an elastomeric liner system. The TSB socket is made from a cast of the residual limb that has minimal modifications. 

When used with gel liners, the TSB socket is believed to distribute pressures more uniformly within the socket. It should be kept in mind, however, that the gel liners themselves have their own set of problems, including increased motion and, particularly, rotatory instability that leads to skin irritation and breakdown. 

The relative advantages and disadvantages of the TSB socket versus PTB socket are unique to each individual. When a comfortable fit with one socket style cannot be achieved, empirically switching to the other may be successful.

The most commonly fabricated socket for transfemoral amputations is the ischial containment socket. There are a number of subtle variations in this socket design.

The socket has a wide anteroposterior dimension and a narrow mediolateral dimension. This design replaced the quadrilateral socket design, which had a wide mediolateral dimension and a narrower anteroposterior dimension. 

The ischial containment socket was initially designed to provide compression of soft tissues and limited abduction of the femur within the socket during the stance phase. It has been subsequently been demonstrated that resecuring the transected adductor muscles distally is more important and effective in controlling the lateral movement of the femur in the socket, resulting in improved prosthetic ambulation.

THE SUSPENSION MECHANISM

Every prosthesis requires some type of suspension system to keep it from falling off the residual limb. 

Suspension can be achieved by a variety methods, including the following:

• Self-suspension of the socket - This makes use of the anatomic shape of the residual limb (Syme or knee disarticulation).

• Suction suspension - Methods of creating suction suspension include the use of an appropriate suction socket design, of a gel suspension liner.

• Suspension device or harness - Such equipment includes belts, cuffs, wedges, straps, and sleeves.

A combination of these techniques also can be used. 

Standard suction is a common suspension choice for transfemoral prostheses; it employs a total-contact, form-fitting, rigid or semirigid socket with a 1-way air valve in the distal end that allows air to be expelled after the socket is donned. 

The socket's intimate fit creates a seal between the skin of the residual limb and the socket. When air is driven out of the end of the socket, a small negative pressure—strong enough to suspend the socket on the residual limb—develops inside the socket.

This form of suspension allows excellent proprioceptive feedback and is lightweight. One disadvantage of the suction socket is its inability to tolerate much weight or volume fluctuation up or down before it requires replacement.

A total elastic suspension (TES) belt and a Silesian belt are used for auxiliary above-knee suspension or as the sole means of suspension, especially in the pediatric patient.

Left, above-knee prosthesis with an ischial containment socket, a total elastic suspension (TES) belt, a single-axis knee with extension assist, endoskeletal components, and an energy-storing foot (lateral view with flexed knee).

The Silesian belt fastens to the socket laterally, above the greater trochanter, and wraps around the opposite iliac crest. Because it does not control rotation very well, people using this type of suspension belt often have difficulty with internal rotation, especially if the residual limb is fleshy. 

The TES belt is made from the same neoprene material that is used for transtibial suspension sleeves. It slips over the outside of the prosthetic socket and surrounds the waist above the iliac crest to provide suspension. 

The TES belt is more commonly used today than is the Silesian belt and aids in rotational control. Disadvantages include some inevitable pistoning of the prosthesis, reduced comfort because of bandage pressure, heat intolerance, and the possibility that the belt will cause dermatitis and chafing.

A single-axis hip joint is integrated into the lateral socket wall and pelvic band to control rotation and is used for weak hip adductors or short residual limbs.

Patients with a transfemoral or transtibial amputation may utilize the gel liner suction system, which uses a gel elastomeric liner. The liner rolls onto the residual limb and is then inserted and locked into the socket. 

A pin may or may not be used. This suspension system can provide improved cosmesis, cushions the residual limb, can reduce shear between the residual limb and the socket, and minimizes pistoning of the residual limb in the socket.

Heat buildup, skin problems, and decreased proprioception can be drawbacks to this suspension system.

The supracondylar cuff is a long-standing suspension design for a transtibial prosthesis. It consists of an adjustable strap encircling the distal thigh above the femoral condyles and is good for heavy laborers who may have difficulty with heat buildup from some of the more enclosing suspension systems.

Suspension sleeves made of neoprene, rubber, latex, or other elastic materials may be used as the primary suspension system or in combination with another suspension system as an auxiliary mechanism.

The sleeve fits snugly over the outside of the proximal prosthesis and extends up onto the thigh, over the prosthetic sock.

Another transtibial suspension option is suction. As with standard transfemoral suction suspension, it uses an airtight sleeve and a 1-way air valve located in the bottom of the socket to create a partial vacuum within the socket. 

This vacuum helps suspend the prosthesis during swing phase. The vacuum needed to hold the residual limb can be generated when air is expelled from the socket through the valve during stance, with a resultant negative pressure inside the socket during swing. The vacuum can also be generated through the use of a small vacuum pump built into the prosthesis.

This vacuum-assisted suspension system (VASS) works by use of a vertical shock pylon that acts as a vacuum pump and continually withdraws air from the sealed socket during ambulation.

KNEE JOINT

The prosthetic knee must fill the following 3 functions:

• Provide support during the stance phase of ambulation

• Produce smooth control during the swing phase

• Maintain unrestricted motion for sitting and kneeling

The prosthetic knee can have a single axis with a simple hinge and a single pivot point, or it may have a polycentric axis with multiple centers of rotation.

• The 4-bar linkage design and shifting center of rotation provide knee stability. Cosmesis is excellent, especially during sitting; therefore, this design is used for knee disarticulations and short residual limbs.

• Polycentric knees are heavy, costly, and require high maintenance.

• The weight-activated, or safety, knee cannot be flexed during weight bearing, which provides stability during stance phase. The safety knee can accommodate up to 20º of knee flexion, produces friction, and prevents buckling. It allows ambulation on uneven surfaces. A delay in swing phase is noted because complete unloading of the knee must occur for knee flexion to transpire. The safety knee is a common initial prosthetic knee for geriatric patients, persons with extreme debility, and patients with poor hip control. It is contraindicated in patients with bilateral transfemoral amputations.

• The hydraulic knee (pneumatic or oil) allows for cadence variance. The design uses a piston in a fluid-filled cylinder that accommodates the swing phase of the patient's gait. The knee is heavy, costly, and requires high maintenance.

• The manual-locking knee provides the most stability, but the gait is awkward and energy consuming. However, it is ideal for a hemiparetic residual limb.

Prosthetic science is advancing the types of knees now available.

The hydraulic-based Otto Bock C-Leg (Otto Bock Health Care, Minneapolis, Minn) provides several benefits over purely mechanical knee systems. 

These microprocessor-controlled knees improve upon the timing of the hydraulic and pneumatic knees. The patient can ambulate at greater speeds with optimal, biomechanically correct symmetry while expending less energy.

Most importantly, the user can safely walk step over step up and down stairs. The built-in battery lasts anywhere from 25-40 hours, which means that it can support a full day of activity. The recharge can be performed overnight or while traveling in a car (via a cigarette lighter adapter).

The magnetorheological-fluid–based Rheo Knee (Ossur, Reykjavic, Iceland; Ossur North America, Aliso Viejo, Calif) is capable of "learning" how the patient walks.

Electronic sensors on the artificial joint measure the joint's angle and the loads it is bearing, 1,000 times per second while a computer chip controls the viscosity of magnetic fluid inside the knee.

Tiny metal particles suspended in the fluid form small chains when the magnetic field is turned on, causing the fluid to become thicker. That, in turn, affects the stiffness of the joint, which is modified constantly while the knee is in use, allowing for a smooth swing of the leg. However, the cost of technologically advanced knees is prohibitory for most amputees.

TYPES OF PROSTHETIC KNEES AND USAGE 

*Unable to adjust to variation in cadence speed

THE PYLON AND ANKLE

The pylon is a simple tube or shell that attaches the socket to the terminal device. Pylons have progressed from simple, static shells to dynamic devices that allow axial rotation and that absorb, store, and release energy.

The pylon can be an exoskeleton (soft foam contoured to match the other limb and covered with a hard, laminated shell) or an endoskeleton (an internal, metal frame with cosmetic soft covering). The ankle function usually is incorporated into the terminal device.

A separate ankle joint can be beneficial in heavy-duty industrial work or in sports such as mountain climbing, swimming, and rowing. However, the additional weight of a separate joint requires more energy expenditure and greater limb strength to control the additional motion.

PROSTHETIC FEET

The 5 basic functions of the prosthetic foot are as follows:

• Provide a stable, weight-bearing surface

• Absorb shock

• Replace lost muscle function

• Replicate the anatomic joint

• Restore cosmetic appearance

Prosthetic feet are broadly classified as energy-returning feet or non–energy-returning feet.

Non–energy-returning feet include the solid-ankle, cushioned-heel (SACH) foot and the single-axis foot. The SACH foot mimics ankle plantar flexion, which allows for a smooth gait. The prosthetic is a low-cost, low-maintenance foot for a sedentary patient who has had a BKA or an AKA.

The rigid forefoot provides an anterior lever arm and proprioception. The single-axis foot adds passive plantar flexion and dorsiflexion, which increase stability during the stance phase. They are most commonly used for patients with a transfemoral amputation if knee stability is desired.

Energy-returning feet are probably improperly named because, in fact, they do not return energy. They do, however, assist the body's natural biomechanics and allow for greater cadence or less oxygen consumption.

The multiaxis foot and the dynamic-response foot are members of this family. The multiaxis foot adds inversion, eversion, and rotation to plantar flexion and dorsiflexion; it handles uneven terrain well and is a good choice for the individual with a minimal-to-moderate activity level.

The dynamic-response foot is the top-of-the-line foot and is commonly used by young, active persons and by athletic individuals. The forefoot acts like a spring, compressing in the stance phase and rebounding at toe-off. Geriatric patients benefit from the light weight of these feet.

TYPES OF PROSTHETIC FEET AND USAGE  

TYPES OF PROSTHETIC FEET AND USAGE  

PROSTHETIC TRAINING

The patient should initially be taught the basics of prosthetics care, including how to put on and remove the prosthesis, how to inspect the residual limb for signs of skin breakdown (a task that should be performed daily), and how to perform safe transfers. 

Focus should then be shifted to weight bearing with the prosthesis. This begins with the patient standing in parallel bars, where balance is emphasized.

Progressive ambulation starts with use of the parallel bars before moving to the employment of assistive devices, as appropriate. Finally, ambulation should be addressed on level surfaces, with the patient using a walker or other assistive device, again as appropriate.

Once the patient has mastered these skills, training on stairs, uneven surfaces, and ramps/inclines should begin. The end goal is for the patient to be able to safely ambulate on all usual surfaces without adaptive equipment.

When initially fabricated, the prosthesis is set up for static (or bench) alignment. When the prosthesis is fitted on the patient, dynamic alignment is performed by a prosthetist to fine tune the alignment to the patient's gait pattern.

This process takes into account the different components that were used to fabricate the patient's prosthetic leg. Incorrect alignment of the prosthesis can result in observable gait abnormalities. 

Gait deviations caused by weakness or restrictions in ROM also can occur. The following table shows common gait deviations in patients with a transtibial or transfemoral amputation.

TRANSTIBIAL AMPUTEE GAIT 

*Causes of excessive heel lever - Foot dorsiflexed too much, foot too far posterior, heel cushion too hard, or shoe heel too hard

†Causes of inadequate heel lever - Foot plantarflexed too much, foot too far anterior, or heel cushion too soft

‡Causes of inadequate toe lever - Foot dorsiflexed too much, foot too far posterior, or foot keel too soft/flexible

§Causes of excessive toe lever - Foot plantarflexed too much, foot too far anterior, or foot keel too stiff

TRANSFEMORAL AMPUTEE GAIT 

*Causes of excessive heel lever - Foot dorsiflexed too much, foot too far posterior, heel cushion too hard, shoe heel too hard

COMMON PROBLEMS

WEIGHT BEARING

An individual with a lower extremity amputation must bear his or her full body weight on soft tissues that are not designed for that function.

Therefore, the socket must be designed to distribute these forces over as large a surface area as possible and as evenly as possible over pressure-tolerant areas.

For a transtibial limb, the following areas are important:

• Pressure-tolerant areas

  • Patellar tendon

  • Pretibial muscles

  • Posterior aspect of the residual limb over the upper portion of the gastroc-soleus muscles

  • Lateral shaft of fibula

  • Medial tibial flare

• Pressure-sensitive (relief) areas

  • Tibial crest, tubercle, and condyles

  • Fibular head

  • Distal tibia and fibula

  • Hamstring tendons

The same considerations must be taken into account for a transfemoral limb. Weight bearing is concentrated in the medial aspect of the ischium and the ischial ramus. 

The ischial tuberosity is contained inside the socket, providing a bony lock between the ischium and the greater trochanter. The femoral shaft will distribute some force, and relief is provided to bony prominences. 

Sources of pain in the residual limb that are difficult to manage may include the following:

• Bony osteophytes or spurs from trauma or from periosteum that was incorrectly stripped during surgery

• A hypermobile fibula that is longer than the tibia

• An unbalanced myodesis for transfemoral amputation, which can cause the femur to extrude through the muscle and skin

• The failure of a myoplasty or myodesis

There is an increased chance that the presence of osteoarthritis in a patient's sound limbs and/ or back will become a factor over time. There are greater stressors on the remaining joints after an amputation, and the patient tries to adapt to this. 

Poor socket fit or suspension may be another source of pain. The presence of ongoing pain, skin breakdown, a change in the ability to put on and remove the prosthesis, and a change in the number of sock plies indicate that the prosthesis needs to be modified.

Erythema normally appears within a few minutes after the prosthesis is removed and should fade quickly. Erythema that is present upon removal of the prosthesis or that does not completely resolve within 20 minutes is particularly worrisome.

CONTRACTURES

Hip and knee flexion contractures affect prosthetic fitting and function. A knee flexion contracture of 10º or less can be treated conservatively with stretching, ambulation, and ultrasound, if desired.

A knee flexion contracture of 25º or more may require hamstring lengthening with posterior knee capsule release or a bent-knee prosthesis. The ability to accommodate a hip flexion contracture depends on residual limb length. A long transfemoral residual limb with a contracture of 15º or more leads to compensatory lumbar lordosis.

A short transfemoral limb can accommodate up to 25º of hip flexion contracture with resultant loss of hip extension power. For the patient with a transfemoral amputation, a hip contracture results in knee instability and may require the use of a lockable knee.

Knee and hip contractures also decrease cosmesis and efficiency of ambulation. 

PHANTOM SENSATION AND PHANTOM PAIN

In addition to the usual postoperative pain, most individuals who have undergone an amputation experience phantom sensation.

Phantom sensation is the perceived sense that the amputated limb or part of the amputated limb is still present. Phantom sensation is not painful, and the patient usually needs only to be reassured that this sensation is common and not an indication of a mental disturbance. 

The phenomenon of telescoping—the sensation that the amputated limb has shrunk (eg, the toes are at the ankle, the foot is at the knee)—can accompany phantom sensation. Telescoping is normal and usually fades without sequelae.

Phantom pain is the sensation of pain originating in the amputated part.

Phantom pain may or may not be dermatomal in nature. Individuals describe a burning, stinging, or cramping pain or report the feeling that the missing body part is "positioned awkwardly or painfully."

The pain usually develops in the first month after amputation. It is most likely to appear in individuals who experienced a lot of pain before amputation. Phantom pain is constant and most intense right after the amputation. The pain becomes more intermittent over time before ultimately resolving, although some patients still experience phantom pain years after the amputation.

Patients who have undergone amputation commonly report intermittent phantom pain symptoms, but these individuals are able to ignore the pain and require no medication for treatment. Phantom pain usually is worse at night, after the extremity has been in a dependent position, and can be exacerbated by anxiety and stress.

Unlike postsurgical pain, which responds well to opioid medications, such as acetaminophen plus oxycodone (Percocet) and acetaminophen plus hydrocodone (Lortab), phantom pain is best treated with low doses of tricyclic antidepressants (ie, nortriptyline or amitriptyline, 10-25 mgPO qhs) that can improve sleep. 

Phantom pain may respond well to medications such as carbamazepine (Tegretol), amitriptyline (Elavil), pregabalin (Lyrica), and gabapentin (Neurontin; titrate to at least 300 mg tid; serum gabapentin levels can be monitored); these stabilize the nerve's ability to depolarize and can decrease dysesthetic symptoms.

Transcutaneous electrical nerve stimulation, topical anesthetics (ie, capsaicin cream), and anxiolytics may be useful against phantom limb pain. Decreasing residual limb edema is helpful, and the use of prostheses has been found to result in fewer reports of phantom limb pain.

Theories exist as to why patients experience phantom limb pain and phantom sensation. For example, it may be that the remaining nerves continue to generate impulses spontaneously or as a result of irritation.

A second theory is that the spinal cord nerves begin excessive spontaneous firing in the absence of expected sensory input from the limb. Still another theory is that altered signal transmission and modulation occur within the somatosensory cortex. Other possible

causes include abnormal sympathetic function and psychological factors.

CHOKE SYNDROME

When the proximal part of the socket fits too snugly on the residual limb, venous outflow can be obstructed. When this is problem is combined with an empty space more distally in the socket, swelling can occur until that empty space is filled.

In an acute choke situation, the skin is red and indurated and may have an orange-peel appearance, with prominent skin pores. If the constriction is not resolved, then chronic skin changes can occur with hemosiderin deposits (verrucose hyperplasia), and venous stasis ulcers can develop.

Choke syndrome and verrucose hyperplasia are treated by restoring total contact and eliminating the void between residual limb and socket.

This is achieved by relieving a tight proximal constriction, adding distal padding inside the socket, improving suspension to eliminate pistoning or a loss of suspension that may be creating the void, using compression on the residual limb when the patient is out of the prosthesis, or constructing a new socket.

DERMATOLOGIC PROBLEMS

Common skin management issues include the development of contact dermatitis or sebaceous cysts, excessive sweating, and scar management.

• Contact dermatitis frequently appears as a macular, papular, erythematous rash that is often pruritic. The liner, socks, and suspension mechanism are the usual culprits for contact dermatitis. The socket is a less likely cause. Treatment consists of identification and removal of the offending item and symptomatic treatment with topical diphenhydramine (Benadryl) or cortisone creams.

• Cysts and sweating can be signs of excessive shear forces and components that are improperly fitted. Sweating can also result from the loss of surface area (following amputation and the covering of the skin surface area with a prosthesis) needed for thermoregulation.

• Skin maceration is caused by excess moisture next to the skin. Treatment may include frequently changing prosthetic socks, applying cornstarch or talc power to the limb, and using specially formulated antiperspirants.

• Tinea infections are caused by excessive moisture, with or without poor hygiene.

• Folliculitis is an infection of the hair follicles. It is caused by poor hygiene, sweating, and poor socket fit. Treatment includes use of antiseptic cleaner and topical ointments. Socket modification may be required to avoid high-pressure areas.

• An epidermoid cyst is a sebaceous gland that is plugged with keratin. Treatment includes the use of topical or oral antibiotics, as well as incision and drainage or excision.

• Scar management is focused on massaging and lubricating the scar to obtain a well-healed result without the appearance of "dog ears" or adhesions. Skin adherence may result from scar tissue.

ENERGY CONSUMPTION IN LOWER EXTREMITY PROSTHESES

The increased energy requirements of prosthetic ambulation can limit the use of a prosthesis.

An individual who has a lower extremity amputation and requires a walker or crutches to ambulate (with or without a prosthesis) uses 65% more energy than does someone with a normal gait.

Energy consumption (percentage above normal, according to amputation level) for ambulation with a prosthesis is as follows:

• Below-knee, unilateral amputation - 10-20%

• Below-knee, bilateral amputation - 20-40%

• Above-knee, unilateral amputation - 60-70%

• Above-knee, bilateral amputation - >200%

BKA actually requires less energy consumption than does ambulation with crutches. However, ambulating with an AKA requires more energy than ambulating with crutches does, which makes the cardiopulmonary status of the patient more significant.