Lower Limb Prosthetics

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1. OVERVIEW AND DESCRIPTION

Definitions

A prosthesis is an artificial substitute for a missing body part.

A lower limb prosthesis refers to a prosthesis that replaces any part of the lower limb to restore the functional and/or cosmetic purpose of the lower limb. This may include artificial components that replace the hip, thigh, knee, ankle and foot.

(Photo credit Hanger Clinic)

2. RELEVANCE TO CLINICAL PRACTICE

1. Post Amputation Process and Prosthetic Evaluation

   Pre- prosthetic training

   After the patient has an amputation in the lower extremity, they will remain in the acute care hospital until they are medically stable. After that time they may be either transferred to a skilled nursing facility (SNF), acute inpatient rehabilitation facility or discharged home with homecare services. The patients that are discharged to acute rehabilitation facilities often have better functional outcomes than those patients with any other discharge destination.(1) During the initial time after the acute care hospital the focus is to determine if the patient is a candidate for a prosthesis based on their functional level, potential for progress and to prepare the residual limb for a prosthesis if the patient is a candidate. This includes training in mobility and activities of daily living (ADLs) without the prosthesis, education in skin care, muscle strengthening, pain reduction and management and also shaping and shrinking of the residual limb. Specifically, early range of motion and desensitization of the scar from the amputation are important. There are many different options for discharge after the acute hospital care stay, however, receiving inpatient rehabilitation care immediately after acute care was associated with reduced mortality, fewer subsequent amputations, greater acquisition of prosthetic devices, and greater medical stability than for patients who were sent home or to an SNF.(1) Acute inpatient rehabilitation facilities stabilize chronic problems such as renal failure and diabetes and optimize surgical wound management which may lead to improved outcomes.

   Prosthetic Evaluation

   Initial evaluation to determine if a patient is a candidate for a lower limb prosthesis should include the following assessment of the patient’s history:

   1. The patient’s prior level of function and activity level, including level of independence in ADLs, and any assistive devices previously utilized for ambulation
   2. The patient’s geographical location and proximity to medical care and prosthetic lab
   3. Etiology of and time since amputation
   4. General medical condition, including comorbidities such as heart and lung disease, diabetes, vascular disease, and polyneuropathy
   5. Employment
   6. Recreational pursuits and sports participation
   7. Goals of patient and family
   8. Family and caregiver support

   The patient must also be physically and mentally evaluated to determine the appropriate prosthetic prescription, complete assessment includes:

   1. Assessment of cognitive function necessary to care for and don/doff the prosthesis, as well as the ability to learn techniques and strategies in therapy.
   2. Function of the upper limbs
   3. Function of the opposite lower limb
   4. Residual limb strength, shape, length, and condition. This assessment should include skin condition, sensation, and circulation of the amputation site.
   5. Stability of joints and ligaments of the residual limb
   6. Presence or absence of any joint contractures in any of the limbs
   7. Weight of the patient (as some prosthetic components have weight limits)

   Based on the above gathered information, physical examination, and potential for progress, the amputee patient is classified to a particular functional level. The K levels were adopted by the federal government to clarify which lower limb prosthetic components (knee, foot, and ankle) should be used for patients depending on their functional levels. The higher the K level the more potential for prosthetic ambulation.

   K level Description K0 Does not have the ability or potential to ambulate or transfer safely with or without assistance, and a prosthesis does not enhance quality of life or mobility. K1 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. K2 Has the ability or potential for ambulation with low-level environmental barriers such as curbs, stairs, and uneven surfaces. Typical of the limited community ambulator. K3 Has the ability or potential for ambulation with variable cadence. Typical of the community ambulator who can traverse most environmental barriers and has vocational, therapeutic, or exercise activity that demands prosthetic utilization beyond simple locomotion. K4 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.

2. Prosthetic Prescription

The initial prosthetic fitting

When preparing a patient’s residual limb for a prosthesis the process includes healing, shrinking and shaping the residual limb appropriately with the use of ace wraps and eventually an elastic shrinker. During this period often the patient’s residual limbs are protected in a rigid protective device.

(Photo credit Hanger Clinic)

The goal of the shrinking and shaping process varies depending on the type of amputation. When there is a plateau in the day to day change in shape of the residual limb the patient with a lower-limb amputation is prescribed and measured for their initial prosthesis. In the past, this was referred to as preparatory or temporary prosthesis, although with the advancement of prosthetic technology this prosthesis is still custom made and can be used for quite some time. It is designed to be strong and can be adjusted for alignment, fit, componentry, etc. With this prosthesis, the patient typically will work with physical and occupational therapists with the goal of achieving independence in ambulation and ADL’s with the prosthesis. While the patient uses this initial prosthesis, the residual limb is expected to continue to shrink, but at a slower pace, and sometimes the shape will change as well.  The prosthetic socket often needs to be replaced as the residual limb shrinks, usually within the first 6 months to a year after amputation.  When needed, a “definitive” prosthesis is prescribed. This term was often used in the past to describe when the socket, alignment and componentry were no longer requiring change, so that a cosmetic cover could be applied.  Most patients at this time choose not to cover their prostheses but to leave the componentry visible.  The general public’s acceptance has grown, and this is much more practical for prosthetic management, as continued changes are often necessary. Currently, the semantics of “temporary” and “definitive” prosthesis have fallen by the way-side, as most patients will use their initially prescribed prosthesis until a new one is needed.

The prosthesis prescription

The level of amputation determines which components of the lower extremity prosthesis will need to be prescribed. The two most common lower extremity amputations are the transfemoral (above the knee- AK) and the transtibial (below the knee- BK). The major components of a lower limb prosthesis include the socket, interface (where the liner contacts the skin), suspension, pylon/frame, knee unit (if applicable), foot/ankle complex, hip joint (if applicable).

Prosthetic interface:  The interface is where the prosthesis contacts the residual limb; this can be made of either a soft or hard material. Some common interface options are: pelite liners, urethane liners, thermogel/gel liners, silicone liners, or a hard interface directly with the socket.

Pylon/frame: The prosthetic frame is the method of connecting the prosthetic components together. There are two main types: exoskeletal or endoskeletal. The exoskeletal construction is infrequently used in current practice. This design uses a rigid exterior lamination from the socket down and has a light-weight filler inside. The endoskeletal construction is the most commonly used type of prosthetic frame. This construction uses pipes called pylons to connect the prosthetic components. The pylons can be constructed from aluminum, titanium, stainless steel or any hybrid of these materials.

Hip disarticulation and hemipelvectomy prostheses

The socket encases bilateral iliac crests in the hip disarticulation patient and utilizes abdominal compression in the hemipelvectomy patient. These prostheses must include a hip joint, which may be a ball-and-socket joint or single-axis.

Transfemoral Prostheses

Transfemoral Socket Designs

1. Quadrilateral socket is an older socket design that is relatively narrow anterior-to-posterior, with a posterior shelf to enable weight bearing on the ischium.

(Photo credit Hanger Clinic)

2. Ischial containment socket is more ovoid in shape, with a smaller mediolateral dimension. The posterior and medial walls encase the ischial tuberosity. When compared with the quadrilateral design, the ischial containment socket may distribute pressures more evenly. There are also several variations of this socket, including a flexible inner socket within a rigid frame. One example is the comfortflex socket from Hanger Clinic.

3. Sub-ischial socket the trimline of this socket falls distal to the ischial tuberosity and relies completely on the thigh musculature for weight bearing.

Transfemoral Suspension

1. Suction is a common choice for transfemoral suspension, utilizing a one-way valve and liner with concentric rings.

2. Elevated Vacuum Suspension is a derivative of the suction suspension; air is actively drawn from within the socket environment.

3. Distal suspension with a pin or lanyard is another option.

4. A pelvic band or silesian belt may be used as the primary suspension or as auxiliary suspension in some patients.

Prosthetic Knees

1. Manual-locking knees can be locked for patients who require the most stability and must be unlocked for the patient to sit.
2. Single-axis knees have a single axis of rotation, and stability is achieved through alignment and the patient’s voluntary control.
3. Weight activated stance control (safety knees) these typically used for K1 through K2 functional levels. These are single axis knees with a weight activated locking mechanism.
4. Polycentric knees consist typically of 4 bars that pivot during flexion, which allows for a changing axis as the patient progresses through the gait cycle. This allows a great deal of knee stability and reduces the protrusion of the knee unit when the patient sits. This is advantageous with a knee disarticulation amputation or a particularly long AK residual limb.
5. Hydraulics or pneumatic knees to provide resistance to swing and/or stance phase. These can be adjusted for the patient’s unique needs.
6. Microprocessor-controlled knee units utilize a microprocessor to control the pneumatics or hydraulics throughout the gait cycle. The microprocessors gather information on the position in the gait cycle and process electronically to adjust the resistance of the knee. Some allow the individual to change the mode of the knee to suit the intended activity. These knees are appropriate for active individuals at the K3 or K4 vel. However, some patients at K2 level may benefit from a microprocessor stance-controlled knee to improve their function and balance These can be combined with any number of other components to make the most functional prosthetic for the amputee patient.
7. Microprocessor knees with internal power this knee provides active knee flexion and extension, which is useful with sit to stand activities and with ascending stairs.

(Photo credits Hanger Clinic)

Knee disarticulation prostheses

This level of amputation preserves the femoral condyles, which allows for supracondylar suspension and a long lever arm. However, the functional length of the thigh becomes much longer when the socket and prosthetic knee are added. This can be partially compensated for by utilizing a low-profile polycentric knee.

Transtibial Prostheses

Transtibial Socket Designs

1. Patellar tendon-bearing socket has an inward contour that uses the patellar ligament as a partial weight-bearing surface. Despite the name, this socket design aims for a total-contact fit and involves weight-bearing throughout the pressure-tolerant areas of the residual limb, including the medial tibial flare and the popliteal fossa region. Raising the proximal trim line of the medial-lateral dimension to above the condyles, additional support for the residual limb is provided with added suspension this raised trim line is classified as a supracondylar/suprapatellar socket.

2. Total surface-bearing socket is designed to distribute pressure more equally across the entire surface of the residual limb, including carrying some of the load on pressure-sensitive areas.

Transtibial Suspension

1. Supracondylar cuff or strap may be helpful for patients with very short residual limbs or may be used as auxiliary suspension in some patients.

2. As noted above, a supracondylar/suprapatellar socket provides supracondylar suspension by encompassing the medial and lateral femoral epicondyles within the socket.

3. Supracondylar Pelite liner with compressible or removable wall: pelite is a type of expanded cross-linked sponge foam which is shaped to fit to residual limb to provide cushioning inside the socket.

4. Auxiliary suspension sleeve, provides additional support to the primary suspension and holds the prosthesis on with material such as neoprene or gel type sleeves.

5. Liner with pin-locking mechanism, a silicone liner with a distal pin system is donned over the residual limb. The pin system consists of a metal or plastic disc with a metal pin in the center. The pin then locks into the bottom of the prosthetic socket.

6. Suction with or without liner, utilizes a one-way valve and slight negative pressure to hold the prosthesis on the residual limb. Another option is a special liner with several concentric rings to create the seal; this eliminates the need for an additional suspension sleeve.

7. Electric vacuum pumps: Suction creates a very secure fit but can be compromised by small holes in the suspension sleeve; the suspension sleeve also increases bulk behind the knee, especially in positions of knee flexion.

8. Thigh corset with side joints may be considered in long-time prosthesis wearers who prefer this style, or those with poor mediolateral stability due to derangement of the knee ligaments. This is an older mode of suspension. It is sometimes considered where additional off-loading of the residual limb is needed such as in a patient with a hypersensitive residual limb, or a residual limb that does not tolerate full weight bearing

Symes and ankle disarticulation prostheses

This amputation level has the advantage of a long lever arm and allows some distal weight-bearing without a prosthesis. The distal residual limb is bulbous due to the presence of the malleoli. Because of the increased length of the residual limb, fitting a prosthetic foot can be challenging. Fortunately, there are several options of low profile feet.

Prosthetic Foot/Ankle

1. SACH (solid-ankle cushion heel) foot does not have an articulated ankle but allows for simulation of plantar flexion when the heel cushion is compressed during initial contact. This foot is inexpensive, stable, durable, and low-maintenance. A major disadvantage is that it does not accommodate for walking on uneven surfaces. Prescribed for individual in the K1 functional level.
2. SAFE foot similar to the SACH foot, it has no joint articulations and is durable and inexpensive, but it allows some inversion and eversion motion, and provides more ability to accommodate to uneven terrain.
3. Single-axis foot has an articulated ankle with one axis of rotation. It allows the prosthetic foot to reach foot-flat easily in early stance phase, which enhances knee stability. Indicated for K1 and K2 ambulators.
4. Multi-axis foot allows movement in multiple planes and allows the user to accommodate for uneven surfaces. Indicated for K2 and K3 levels.
5. Dynamic response/ Energy storing feet have a flexible keel that “stores” potential energy during early stance phase (during weight bearing) which is then “released” through recoil of the material in late stance and early swing phase. This energy transfer imitates the function of the gastrocnemius-soleus group. These feet are appropriate for active community ambulators who change their cadence, and for athletes (K3 and K4).
6. Microprocessor feet these feet are capable of internal power generation. Some of these feet provide active power generation to produce ankle dorsiflexion, while others power both active dorsiflexion and plantar flexion.(2) Appropriate for level K3 and above.
7. Specialty feet can be made to accommodate the lifestyle of the amputee. Some examples: a foot that is adjustable for varying heights of shoe heels, shower foot, swim feet, running blades, golf prostheses, rock -climbing and ski legs to name just a few.(3)

Partial foot prostheses

The various levels of foot amputations may require toe fillers and shoe modifications. Many studies have demonstrated that these can assist in gait mechanics and prevent skin break down and peak plantar pressures specifically studies have recommended: the full length shoe, total contact insert, and Rigid Rocker Bottom sole for most patients with Diabetes Mellitus and Transmetatarsal amputations.(4) One group also described the benefits of a transmetatarsal prosthesis with a carbon fiber plate that improved functional outcomes as well.(5)

Additional componentry considerations

Vertical shock pylons decrease the impact of initial contact.(6)  Torsional adapters allow motion in the transverse plane to simulate tibial rotation.(7)

3. CUTTING EDGE/UNIQUE CONCEPTS/EMERGING ISSUES

Prosthetic Technology and Considerations

The Genium

(Photo credit Hanger Clinic)

by Otto Bock has several features that have biomechanical advantages over the older microprocessor knee designs, including the ability to ascend stairs step over step. A military-grade version of this knee joint, the X3 is ideal for physically demanding occupations, an active family life, swimming, sports activities, and situations where you encounter water, dust, sand, dirt or grime.

Microprocessor feet are becoming more widely used, as well as those that are powered.

Osseointegration is the practice of placing a titanium implant directly into the long bone of the residual limb after amputation, extending outside of the skin. The prosthetic limb can attach directly to it, eliminating the socket-skin interface. This is still in the development stage in the United States and mostly performed in the United Kingdom, Germany, and Canada.

Sports prostheses can include specialized components for running, cycling, swimming, and many other activities. Prescription and fabrication of these prostheses requires close collaboration between the physiatrist, prosthetist, and patient, in order to meet the demands of the athletic activity and the patient’s desired outcome.

Future directions

3D printing and Lower extremity prosthetics

3D printing for prosthetic fitting and fabrication began with Ivan Owen, a Bellingham, Washington puppet-maker and Richard Van As, a South African carpenter that had lost some of his fingers. The two developed the first 3D printed prosthetic hand. Initially, 3D printing began with upper extremity prostheses, recently this has progressed to lower extremity prostheses. Currently, some components of the lower extremity prostheses are able to be 3D printed. SHC Design is a Japanese company with a focus on manufacturing prostheses using 3D printing technologies.(8) Another company Art4Leg is designed to work with an amputee’s current, standard prosthetic leg and designs custom artistic covers for lower extremity prostheses.(8)

Bionic prostheses

Össur’s commercially available Bionic prostheses are smart limbs capable of real-time learning and automatically adjusting to their user’s walking style (gait), speed and terrain.(9) Walking with a Bionic prosthesis, however, still typically requires some conscious, intentional thought from the user. Recently, two amputees were the first people in the world able to control their Bionic prosthetic legs with cortical control. This was accomplished via tiny implanted myoelectric sensors (IMES) that have been surgically placed in their residual muscle tissue.(9) The IMES, instantaneously triggers the desired movement, via a receiver located inside the prosthesis. This process occurs subconsciously, continuously and in real-time.(9)

Cambridge Bioaugmentation Systems (CBAS) and their prosthetic interface

The Prosthetic Interface Device (PID) is like a “USB connector for the body”.(10) This integrates with a residual limb through direct implantation into the bone (osseointegration) and electronic connection with the nerves. The hope from this company for this device is to allow full functionality through conscious control of the prosthetic limb and allows sensation to be fed back to the brain.(10)

4. GAPS IN KNOWLEDGE/EVIDENCE BASE

It is important for physicians caring for patients with amputations to understand the evidence base for their prescriptions and determine the best prosthesis for each patient. Many decisions are made based on expert opinion and the best practice of the experienced prosthetic team. It will be important for physicians to be involved in continued research to demonstrate the advantages and disadvantages of various prosthetic components, especially from a functional and clinical perspective.

There is much about the prosthetic componentry that has been elucidated, but more that still remains to be discovered, such a building a more affordable prostheses, more comfortable, and more durable. One study described comfort and durability being most important to patients with amputations. (11) These are areas that can continued to be improved. Also, from a monetary standpoint many prostheses that are currently available are a significant sum of money, further research needs to be done as to how to create more affordable options. As technology advances it is key that the practitioner utilize an evidence-based approach to best care for their patients with amputations, depending on the etiology of the amputation there different health concerns that need to be addressed (e.g. in patients with amputations caused by diabetic ulcers, wound healing may be more of a concern than a patient with a traumatic amputation). In conjunction with new materials for prosthetics being available there have also been additional methods of gait training.(12) Overall, the practitioner and the patient remain a team, with the common goal of achieving the best overall outcomes.

REFERENCES

1. Dillingham TR, Pezzin LE. Rehabilitation setting and associated mortality and medical stability among persons with amputations. Arch Phys Med Rehabil. 2008;89(6):1038-45.
2. Hahn A, Sreckovic I, Reiter S, Mileusnic M. First results concerning the safety, walking, and satisfaction with an innovative, microprocessor-controlled four-axes prosthetic foot. Prosthet Orthot Int. 2018;42(3):350-6.
3. Prosthetics L. Specialty Lower-Limb Prostheses – Special-Purpose Prosthetic Legs Enhance Life For Amputees 07 Feb 2017 [Available from: https://www.llop.com/specialty-lower-limb-prostheses/.
4. Mueller MJ, Sinacore DR. Rehabilitation factors following transmetatarsal amputation. Phys Ther. 1994;74(11):1027-33.
5. Tang SF, Chen CP, Chen MJ, Chen WP, Leong CP, Chu NK. Transmetatarsal amputation prosthesis with carbon-fiber plate: enhanced gait function. Am J Phys Med Rehabil. 2004;83(2):124-30.
6. Berge JS, Czerniecki JM, Klute GK. Efficacy of shock-absorbing versus rigid pylons for impact reduction in transtibial amputees based on laboratory, field, and outcome metrics. J Rehabil Res Dev. 2005;42(6):795-808.
7. Heitzmann DW, Pieschel K, Alimusaj M, Block J, Putz C, Wolf SI. Functional effects of a prosthetic torsion adapter in trans-tibial amputees during unplanned spin and step turns. Prosthet Orthot Int. 2016;40(5):558-65.
8. Greguric L. 3D Printed Prosthetic Leg – 5 Most Promising Projects in 2019. 2019 February 14 [Available from: https://all3dp.com/2/3d-printed-prosthetic-leg-most-promising-projects.
9. Össur. Össur Introduces First Mind-Controlled Bionic Prosthetic Lower Limbs for Amputees 2019 [Available from: https://www.ossur.com/corporate/about-ossur/ossur-news/1246-ossur-introduces-first-mind-controlled-bionic-prosthetic-lower-limbs-for-amputees.
10. CBAS. PID – USB CONNECTOR FOR THE BODY 2018 [Available from: https://cbas.global/our-work/.
11. Mohd Hawari N, Jawaid M, Md Tahir P, Azmeer RA. Case study: survey of patient satisfaction with prosthesis quality and design among below-knee prosthetic leg socket users. Disabil Rehabil Assist Technol. 2017;12(8):868-74.
12. Highsmith MJ, Andrews CR, Millman C, Fuller A, Kahle JT, Klenow TD, et al. Gait Training Interventions for Lower Extremity Amputees: A Systematic Literature Review. Technol Innov. 2016;18(2-3):99-113.

Original Version of the Topic

Bradeigh S. Godfrey, MD. Lower Limb Prosthetics. 9/20/2013

Author Disclosure

Karen M. Pechman, MD
Nothing to Disclose

Tiffany M. Lau, MD
Nothing to Disclose