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Lower extremity prostheses

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Lower-Extremity Prostheses

The level of amputation a person has will, in large measure, determine the type of prosthesis a person will use. Lower-extremity amputation and disarticulation levels include the following (Smith 2004): 1. Foot levels including toe, ray, transmetatarsal, tarsometatarsal (Lisfranc), transtarsal (Chopart) 2. Ankle levels including Symes, Pirogoff, Boyd, and Boyd-Pirogoff 3. Below the knee (transtibial) amputation 4. Knee disarticulation 5. Above the knee (transfemoral) amputation 6. Hip disarticulation 7. Hemipelvectomy

Partial foot amputation/disarticulation prosthses (Fig 1) Partial foot prostheses and prosthoses refer to the shoe fillers and cosmetic coverings used to treat this level of amputation and disarticulation. These include in-shoe devices, devices that terminate around the ankle, and devices that terminate at the calf. They may be made of foam, plastic, or even metal, depending on the specific person’s needs.

The purpose of these is both cosmetic and biomechanical. Biomechanical purposes include resisting foot deformation over time (using fillers and spacers) and improving balance. These will help the foot function better and improve comfort. Cosmetic aids include silicone toe and partial foot caps.

Ankle level amputation/disarticulation The prostheses for this level of amputation and disarticulation are made from a custom shaped hard socket that covers the stump from below the knee to the end of the limb. The socket may be padded with a foam liner, or a gel liner may be rolled on the residual limb. The bottom of the socket is attached to a prosthetic foot. These devices are often called “low profile” or a “Symes” prosthesis.

Below the knee (transtibial) prosthesis (figure 2) While the exact construction of the prosthesis will vary, the parts of a below the knee (transtibial) prosthesis may include a socket, pylon, and foot. The socket is often molded the precise shape of the residual limb. The socket is typically made from hard plastic or resin. Similar to a Symes prostheses, a foam or plastic liner may be placed in the socket or a gel liner may be rolled on the residual limb. The socket is connected to a pylon (which is often an aluminum tube), which is connected to a prosthetic foot. Some people choose to cover the pylon with a custom shaped foam cover, while others prefer to leave it exposed. The materials the foot is made of could be carbon fiber, metal, foam, and wood may be part of their construction. Standard ways to hold the socket to the leg include a tight socket brim, suction, a locking pin, and knee cuffs.

Knee disarticulation and above the knee (transfemoral) The prosthesis for a knee disarticulation or above the knee (transfemoral) amputation includes transtibial prosthesis parts (socket, pylon, and foot) but also includes an artificial knee. There are monocentric and polycentric knees, with multiple possible features including, hydraulic, pneumatic, computerized control. In addition to the knee, other components such as rotator units for the knee and stability belts may make activities of daily living easier. Standard ways to hold the socket to the leg include a tight contoured socket (for knee disarticulation), belts, suction, and locking pins.

Hip disarticulation and hemipelvectomy Hip disarticulation an hemipelvectomy prostheses include all the parts of a transfemoral prosthesis (socket, knee, pylon, and foot) but also includes a hip joint component.

Rehabilitation The optimal experience for someone with an amputation is multi-faceted. A multidiciplinary team- including the patient- is best suited to manage care before surgery, after surgery, during rehabilitation, and through a lifetime. Together they address subjects such as gait assessment, biomechanical analysis, material and technology selection, and activity tolerance. This team may include the patient, the patient’s family, doctors, therapists, and prosthetists (See Lusardi O&P in Rehab). In general, using a prosthesis is easier with better health, a lower amputation level, and a good medical team. However, despite best efforts, prosthetic care does not completely restore normal walking ability (Perry, Gait Analysis).

Limitations of this article While this article identifies major types of prostheses, the specific prosthesis used is customized for each patient. Patient, caregiver, and device factors leads to a specific prosthesis. Patient factors include: goals, abilities, and future abilities. Device factors include cosmesis, cost, function, safety, and comfort. Finally, caregiver factors include the knowledge, determination, skill, and ability to provide the best prosthesis available for a specific individual.

References Lusardi, M., Nielsen, C. Orthotics and Prosthetics in Rehabilitation, 2nd ed. Saunders, Elsevier, 2007.

Perry, J., Burnfield, J. Gait Analysis, Normal and Pathological Function, 2nd ed. Slack Inc., 2010.

Smith, D., Michael, J., Bowker, J. Atlas of Amputations and Limb Deficiencis, Surgical, Prosthetic, and Rehabilitation Principles. 3rd ed. American Academy of Orthopaedic Surgeons, 2004.