A transradial prosthesis is an artificial limb for individuals with an amputation below the elbow. This type of amputation preserves the elbow joint, allowing for a high degree of functional potential. The primary purpose is to restore capability for daily activities and provide a sense of wholeness by restoring the body’s natural silhouette.
Functional Types of Transradial Prostheses
Prostheses for below-elbow amputations are categorized by their function. One category is the passive, or cosmetic, prosthesis, designed primarily for appearance. It restores the visual symmetry of the arms and provides a surface to push or stabilize objects. While they lack active grasping capabilities, they can assist in simple, two-handed tasks by offering opposition.
A second functional type is the body-powered prosthesis, which operates through a mechanical harness and cable system. Controlled by the user’s own body movements, this durable design provides direct tactile feedback through cable tension. This gives users a sense of spatial awareness about the position and grip of the terminal device.
The third category is the myoelectric prosthesis, powered by an external battery. These devices use electrodes to detect electromyographic (EMG) signals from muscle contractions in the residual limb. A processor translates these signals into commands to operate a motor in the terminal device, allowing for control without a harness.
Anatomy of a Transradial Prosthesis
A transradial prosthesis consists of several components, the most fundamental being the socket. This is the custom-molded interface that fits over the user’s residual limb. The quality of the socket’s fit determines comfort, prevents skin issues, and efficiently transmits the forces required to control the prosthesis.
A suspension system is integrated to keep the device securely attached. Suspension can be achieved through anatomical shaping that grips the bony prominences of the elbow, known as supracondylar suspension. Another method involves a soft silicone liner that rolls onto the limb, which may feature a pin that locks into the socket. Suction is another method that provides a secure fit by expelling air.
The “business end” of the prosthesis is the terminal device, which interacts with the environment. The most common options are hooks and hands. Hooks are favored for their precision and durability, while prosthetic hands offer a more natural appearance and are capable of various grip patterns. Specialized terminal devices are also available for specific hobbies or work tasks.
How Transradial Prostheses Are Controlled
The control system for a body-powered prosthesis is entirely mechanical. A harness, often a figure-eight strap configuration, is worn across the back and shoulders, with a cable connecting it to the terminal device. When the user performs a specific body motion, such as moving their arm forward, it pulls on the cable. This tension directly operates the terminal device.
Myoelectric control systems use electrodes embedded into the socket wall, positioned over specific muscles in the forearm. When the user contracts a muscle, it generates a small electrical voltage. The electrodes detect this EMG signal, which is amplified and sent to a microprocessor. The processor interprets the signal as a command; for instance, contracting flexor muscles might signal the hand to close, while contracting extensor muscles signals it to open.
The Journey to Proficiency
Receiving and mastering a transradial prosthesis is a multi-stage process. The journey begins with a consultation with a prosthetist, who evaluates the individual’s residual limb, lifestyle, and functional goals. A precise cast or digital scan of the limb is taken to create a diagnostic test socket to assess fit and comfort before the final prosthesis is fabricated.
Once the definitive prosthesis is ready, the user is scheduled for a delivery and fitting appointment. During this session, the prosthetist makes final adjustments to the socket and ensures the control system is functioning correctly. This is followed by initial training with the prosthetist and an occupational therapist to learn the device’s basic controls.
The final phase is dedicated rehabilitation with an occupational therapist. This therapy is focused on helping the user become proficient with their new limb. Training involves repetitive drills to master control of the terminal device, followed by practicing how to integrate the prosthesis into activities of daily living like eating, dressing, and writing.