Prosthetics are artificial devices used as replacement body parts. They come in many forms, including limbs or parts of limbs, breasts, hips, teeth, testicles and eyes. Depending on the type, the prosthetic may be functional, such as a flexing knee or a hearing aid, or aesthetic, such as a glass eye.

Terminology associated with prosthetics can be confusing. The word prosthetics may refer to the replacement body part or the medical science of designing, constructing, fitting and maintaining the devices. Prosthesis is another word for the device used by the patient. A prosthetist is a medical specialist who designs and fits prosthetics.

Much of the need for prosthetics is due to amputation of a limb as a result of vascular disease, injury, cancer or birth defects. About 185,000 limb amputations a year are performed in the United States, according to the Amputee Coalition of America. An estimated 1.9 million Americans are living with an amputated limb.

Lower limb amputations are more common than amputations involving the arms, hands or fingers. More than half of all lower limb amputations in the United States are related to diabetes, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Not every amputee is a good candidate for prosthetics. For example, those who are frail or have loss of vision due to diseases such as diabetic retinopathy, glaucoma or cataracts may be at risk for falls and injuries.

For patients who are candidates, there is great variety in the prosthetic legs available, but they generally consist of the same components. These include:

• Sock or liner. Much like socks worn over the feet, the prosthetic fabric sock, gel liner or foam liner is worn over the residual limb or “stump.” This sock or liner protects the patient’s limb and provides a cushion between the limb and the prosthetic device.
  
  
• Socket. Part of the prosthetic that fits over the residual limb and sock. It is typically made of plastic or laminated polyester. The socket may be lined with material to help reduce irritation of the limb and provide a better fit.
  
  
• Suspension mechanism. Device or set of devices that attaches the socket to the limb. The suspension mechanism may consist of straps, suction or other means of holding the prosthetic in place.
  
  
• Prosthetic leg. The rigid component of the device meant to replace the patient’s lost limb. It provides much of the height of the device. The leg attaches directly from the socket to the ankle in patients with below-the-knee (transtibial) amputations. For those with above-the-knee (transfemoral) amputations, a prosthetic knee is added to provide flexibility.
  
  
• Articulating joint. Artificial joint (e.g., knee) that allows flexibility in movement such as is required for sitting, walking or kneeling. The degree of flexibility and other features of the knee will vary based on the patient’s needs. This may include a patient’s activity level, lifestyle, age and general health. Prosthetic knees may be mechanical or computerized.
  
  
• Pylon. A tube that connects the socket at the top of the prosthetic leg to the feet. This allows rotation of the leg and helps with the absorption, storage and release of energy.
  
  
• Terminal device. In prosthetic legs, the terminal device is the foot and ankle. Artificial feet help with balance and the flexible ankles allow walking. Much like the prosthetic knee, there are many foot and ankle prosthetics available to fit the patient’s needs. Factors to be considered are a patient’s age, weight, foot size, activity level and occupational needs. The amputation level (where the limb was severed) may also affect the type of terminal device required.