Prosthesis

A prosthesis is an artificial device designed to replace a missing body part. People may require a prosthetic implant due to physical trauma, disease, or a congenital disorder, which is a condition present at birth. These devices serve two primary purposes: restoring normal bodily functions or providing a cosmetic appearance. When a person undergoes an amputation, they are referred to as an amputee. Managing this transition requires an inter-disciplinary team of specialists. This team includes physiatrists, prosthetists, nurses, physical therapists, and occupational therapists.

Modern prostheses are created through precise engineering. Creators may use computer-aided design, or CAD. This software interface uses 2-D and 3-D graphics to help designers analyze and optimize the creation. Clinical prosthetists are the professionals responsible for manufacturing and fitting these devices. For lower limb prostheses, they must also assess the user's gait and prosthetic alignment. Once fitted, a rehabilitation physiotherapist, known in America as a physical therapist, helps the user learn to move. They may use verbal instructions, touch, or tactile cues. Training sometimes occurs on a treadmill to help the user experience the challenges of walking.

Upper-extremity prostheses are categorized by how they are powered. Passive devices are the most basic type. These can be static, meaning they have no moving parts, or adjustable. Passive hands are often used for cosmetic reasons, while passive tools serve specific vocational tasks. Approximately one-third of upper limb amputees worldwide use a passive prosthetic hand. Body-powered devices use a harness and cable attached to the opposite shoulder. Recent research has even explored using a user's breathing to power a prosthetic hand.

A more advanced category is the myoelectric device. These arms include a battery system to provide energy for sensing and actuation. Actuation refers to the movement of the limb, often using motors or pneumatic systems. These devices function by detecting minute electrical currents from contracted muscles. Techniques like Electromyography help capture these signals. The device then converts these signals into specific gripping patterns or postures. This allows the artificial hand to execute movements based on the user's muscle activity.

Lower-extremity prostheses replace limbs at various levels, such as the hip, knee, or ankle. They are often divided into two main subcategories: trans-tibial and trans-femoral. A trans-tibial prosthesis replaces a leg missing below the knee. A transfemoral prosthesis replaces a leg missing above the knee. Walking with a transfemoral prosthesis is significantly more difficult. A transfemoral amputee must use approximately 80% more energy to walk than a person with two natural legs. This difficulty arises from the complex movements required by the knee.

To assist with movement, engineers use many advanced materials and technologies. Modern designs often incorporate carbon fiber reinforced polymers, which are lightweight and strong. Other materials include aluminum, polyethylene, polypropylene, and acrylics. For transfemoral users, newer designs use hydraulics, mechanical linkages, and computer microprocessors. These technologies help provide better control.

Prostheses can also be used for parts of the face, known as craniofacial prostheses. These include extra-oral types like nasal or orbital prostheses, and intra-oral types like dental implants.

The history of prosthetics stretches back to the ancient Near East, around 3000 BCE. The earliest evidence of eye prosthetics comes from ancient Iran, where an eye made of gold-covered bitumen paste was found. In ancient Egypt, researchers discovered a mummy with a prosthetic big toe dating from 950 to 710 BCE. This toe was made of wood and leather. In 2011, engineers found that this ancient device actually allowed the wearer to walk in sandals.

Other historical examples include the iron hand of Götz von Berlichingen in the 16th century.

Prosthetics connect to many different fields of science and medicine. They relate to materials science through the development of lightweight composites. They connect to neurology through myoelectric sensing of electrical muscle signals. Even organ replacement falls under this umbrella, with artificial hearts and kidneys serving as internal prostheses.

This field continues to evolve as technology improves the ability of humans to regain mobility and independence.