A prosthetic hand is an artificial device designed to replace a missing hand or a portion of a hand. Its fundamental purpose is to restore both function and appearance for individuals who have experienced limb loss due to injury, illness, or a congenital condition. These devices range from simple replacements to highly advanced systems. A certified prosthetist assists in selecting the appropriate hand prosthesis, ensuring a proper fit, and providing training for its use.
Types of Prosthetic Hands
Prosthetic hands are categorized into types, each offering distinct features. The choice depends on individual needs, lifestyle, and the nature of limb loss. Categories include cosmetic/passive, body-powered, and myoelectric devices.
Cosmetic, or passive, prostheses focus primarily on appearance rather than active function. They are designed to closely resemble a natural hand, often custom-painted to match skin tone and include details like freckles or fingerprints. While they lack active movement, they can serve as a stabilizer or carrying surface for simple tasks, such as assisting with writing.
Body-powered prostheses operate through the user’s own body movements, utilizing a mechanical cable and harness system. These devices are known for their durability and can be suitable for practical, heavy-duty tasks, as they are not electronic and can withstand getting wet or dirty. They can provide a sense of feedback through the cable system, allowing users to feel the device’s operation.
Myoelectric prostheses are advanced, controlled electronically by muscle signals from the residual limb. These devices, sometimes called “bionic hands,” incorporate electrodes that detect electrical impulses from muscle contractions. These signals are translated into movements, often powered by rechargeable batteries. Myoelectric hands offer precise control, enabling multiple grip patterns and individual finger movements, making them suitable for intricate tasks.
How Prosthetic Hands Operate
Prosthetic hands operate through various control mechanisms and integrated components, enabling movement and interaction with objects.
Body-powered Operation
Body-powered prostheses use a mechanical control system. A harness, typically worn around the shoulder, connects to a cable that runs to the terminal device, which is the hand itself. By moving specific body parts, such as shrugging the shoulder or moving the upper arm, the user creates tension in the cable, which then mechanically opens or closes the hand. Depending on the design, one action (opening or closing) is actively controlled by the user, while the other might be managed by a spring mechanism.
Myoelectric Operation
Myoelectric prostheses operate using electromyographic (EMG) signals. Sensors embedded within the socket, which is the part that fits over the residual limb, detect tiny electrical impulses produced by muscle contractions. These signals are amplified and sent to a controller within the prosthesis, which then activates small motors to perform movements like grasping or releasing. Advanced myoelectric hands can interpret complex muscle patterns to allow for a wider range of movements, including individual finger control and various grip patterns.
General Components
The general components of a prosthetic hand include the socket, which provides a secure and comfortable attachment to the residual limb, often through suction or harness systems. The terminal device, or the hand itself, is the functional end of the prosthesis, designed for grasping and holding. For myoelectric systems, additional components include sensors that detect muscle activity, motors that drive the hand’s movements, and power sources, typically rechargeable batteries, that supply energy to the electronic system.