Transradial Amputation & Wrist Disarticulate
A cosmetic glove provides the external appearance of the mechanical or passive prosthetic hand. It can be pre-manufactured or custom made. Cosmetic gloves come in a variety of shapes and colors and can be made of vinyl, PVC or silicone.
An electric hand is driven by the electrical impulses transmitted every time an arm muscle contracts or by a switch control on the harness of the prosthesis. Grip speed and grip force of the hand are controlled proportionally to the strength of the muscle signal or pull. In addition, some electric hands feature sensors in the fingertips that prevent objects from slipping; these sensors recognize when an object begins to slip and automatically increase the grip force as needed.
Figure 8 Harness
The figure 8 harness is used with transradial (lower arm) or transhumeral (upper arm) prostheses. On a transradial (lower arm) prosthesis, it functions to suspend the prosthesis and to anchor the cable control for opening and closing the terminal device (hand or hook). On a transhumeral (upper arm) prosthesis, it functions to suspend the prosthesis and to anchor two cable controls: one to control the flexion and extension of the prosthetic elbow and the other to control opening and closing the terminal device (hand or hook).
Figure 9 Harness
The figure 9 harness is used for transradial (lower arm) prostheses when the socket is self-suspending. This harness serves as an anchor for the control cable to the terminal device (hand or hook).
Flail Arm Hinges
The flail arm hinge is used by amputees who do not have good muscular control of the residual limb. These hinges contain a spring loaded counter balance. This allows a small movement of the residual limb to create a large movement in the prosthesis.
Flexible hinges are used by short transradial (below elbow) amputees to translate forearm rotation to the terminal device. The hinges are made of leather, metal, or nylon webbing and are attached to the tricep cuff and the prosthetic socket.
The flexion wrist allows an amputee to preposition the terminal device in 30 or 50 degrees of flexion. This becomes important when performing activities at the body’s midline, such as eating and shaving. Most unilateral amputees (missing part of one upper limb) do not require this; however, it is critical for bilateral amputees (missing part of both upper limbs).
The friction wrist is the most basic wrist design. With this style, the amputee manually pronates (turns the palm down) and supinates (turns the palm up) the hand into position.
A prosthetic hook is the most functional terminal device available, but it is also the least cosmetic (attractive). A prosthetic hook is useful for activities that require dexterity and fine motor skill, such as picking up coins or papers. In addition, the hook is useful for operating tools and holding brooms and shovels. There are several sizes and designs available.
A mechanical hand is a more cosmetic (attractive) terminal device than a hook; however, using a mechanical hand compromises dexterity because typically only the thumb and first two fingers are movable. There are a variety of sizes and styles of mechanical hands available. Often amputees will choose a mechanical hand when appearance is an important consideration for them. Once the hand has been selected, it is covered with a cosmetic glove that resembles the shape and color of the amputee’s sound side hand.
A passive hand is used for opposition and cosmesis (looks). The hand does not open or close, but the amputee can use it to stabilize an object, or to hold objects next to his or her body.
Polycentric hinges are used by short transradial (below elbow) amputees. They are used primarily by amputees who have trouble with soft tissue bunching up and getting pinched just above the brim of the socket when flexing the elbow.
A powered wrist rotator is used for electrical pronation (turning the palm down) and supination (turning the palm up) of myoelectric hands. Wrist rotation is controlled by electrodes in the socket that sense muscle signals initiated by the amputee.
Quick Disconnect Wrist
The quick disconnect wrist is designed to be used by amputees who frequently change their terminal devices (hand or hook). This unit allows the amputee to remove or change the terminal device, manually position the terminal device in varying degrees of rotation, and lock the terminal device in position.
Shoulder Saddle and Chest Strap
A shoulder saddle is a custom made leather pad that is used to help disperse excess pressure. It is attached to a chest strap instead of an axilla loop (under the arm) to prevent excess pressure on the brachial plexus (nerves). It is often used by amputees who carry heavy objects with their prostheses.
Silicone Insert Suspension
The silicone insert is used for comfort, skin protection, and/or suspension of the prosthesis on the patient’s limb. The insert is worn inside the socket of the prosthesis next to the patient’s skin. When this suspension is used, a suspension locking mechanism is necessary to attach the prosthesis to the patient’s limb.
Single Axis Hinges
Single axis hinges are used by transradial (below elbow) amputees to provide rotational stability with flexion and extension.
A suspension sleeve is used for transradial (below elbow) amputees. It is made of elastic fabric, silicone, or a combination of the two that extends from the socket of the prosthesis onto the patient’s upper arm. The sleeve can be used alone or in conjunction with another form of suspension to keep the prosthesis attached to the patient’s body.
Step-up hinges are used by very short transradial (below elbow) amputees. Because the trim line of the socket must be high, the patient looses flexion at the elbow. In order for step-up hinges to work, the forearm section and the socket of the prosthesis are separate. As the amputee flexes the residual limb, the forearm section moves twice as far, thus creating a greater range of motion for the terminal device.
Supracondylar suspension is a socket design used in transradial (below elbow) prostheses. The socket extends proximal to (above) the humeral condyles (wide bony parts of the elbow) and creates suspension for the prosthesis without additional straps.
Suspension Locking Mechanism: Attachment Pin & Lock Body for Upper Extremity
Suspension locking mechanism is a term used to describe the way the prosthesis will be attached to the patient’s residual limb. The two most commonly used types of suspension locking mechanism are the attachment pin and lock body, and the lanyard strap. The attachment pin and lock body method is often used by transradial (below elbow) amputees. A pin is attached to the distal (bottom) end of a silicone or urethane insert. As the patient dons (puts on) the prosthesis, the pin is inserted into a lock in the bottom of the prosthetic socket. The prosthesis is removed from the patient’s body by pushing a button on the outside of the socket to release the lock.
Suspension Locking Mechanism: Lanyard Strap for Upper Extremity
Suspension locking mechanism is a term used to describe the way the prosthesis will be attached to the patient’s residual limb. The two most commonly used types of suspension locking mechanism are the attachment pin and lock body, and the lanyard strap. The lanyard strap method is often used with transhumeral (above elbow) prostheses. The lanyard is attached to the distal (bottom) end of a silicone or urethane insert. As the patient dons (puts on) the prosthesis, the lanyard is fed through a hole in the bottom of the prosthetic socket, through a buckle on the anterior (front) surface, and secured in place with Velcro.
Thermoplastic Preparatory Prosthesis
The thermoplastic preparatory prosthesis is most often prescribed for transradial (below elbow) amputees. It is a temporary prosthesis used by active patients until their limb has healed well enough to be molded for a permanent prosthesis. Usually the patient’s limb is measured and molded while he/she is an in-patient in the hospital, and the prosthesis is fit within 48 hours. This prosthesis will have a terminal device, such as a passive cosmetic hand or a hook. The prosthesis is often held on with a suspension sleeve. This prosthesis is passive and is used for opposition and cosmesis (looks).
A transradial amputation is a surgical procedure in which the radius and ulna (bones of the lower arm) are cut, and the lower portion of these bones and the hand are removed from the body.
Upper Extremity Control Systems
Single Cable Control System
The single cable control system is used with the transradial (below elbow) prosthesis. This cable is anchored to a harness worn by the amputee and is attached to the terminal device (hand or hook). The amputee can open and close the terminal device (hand or hook) by applying tension on the cable through glenohumeral flexion (bringing the arm forward and up) or scapular abduction (moving the arm out to the side) of the shoulder.
Dual Cable Control System
The dual cable control system is used by transhumeral (above elbow) amputees. This system allows the amputee to control flexion (bending) of the elbow, as well as opening and closing of the terminal device.
Heavy duty means selecting more durable components and materials in the fabrication of a prosthesis. Using heavy duty components will increase the durability and weight of the prosthesis.
Teflon Lined Cable
Teflon lining is placed inside the housing of cable control systems to reduce friction when operating a prosthetic elbow or terminal device.
Myoelectric prostheses are electrically powered prostheses driven by the electrical impulses transmitted every time an arm muscle contracts. Grip speed and grip force of the hand are controlled proportionally to the strength of the muscle signal. In addition, some myoelectric hands feature sensors in the fingertips that prevent objects from slipping by recognizing when an object begins to move and automatically increasing the grip force as needed.
Hybrid Control System
A hybrid control system utilizes body power and external power to control the prosthesis.
Upper Extremity Rigid Removable Dressing
The rigid removable dressing can be used for transhumeral (above elbow) or transradial (below elbow) amputations. It can be made of thermoplastic (white plastic) or fiberglass and is often held in place with compression socks. The incision line is covered with non-stick gauze. Then a nylon sheath is applied to hold the gauze in place and protect the patient’s skin. Two mild compression socks are added to control edema (swelling) before the cast is applied.
Upper Extremity Socket Designs
Supracondylar Suspension Socket Design
Supracondylar suspension of the transradial (below elbow) prosthesis is achieved by extending the prosthetic socket proximal to (above) the epicondyles of the humerus (upper arm bone) and the olecranon (pointy part of the elbow).
Suprastyloid Suspension Socket Design
Suprastyloid suspension of the transradial (below elbow) prosthesis is achieved by creating purchase on the styloids (wide bony parts) of the wrist. This is done by using a soft insert or by creating an opening in the wall of the socket.
Single or Double Wall Socket Design
Single or double wall socket design describes the way an upper extremity prosthesis is fabricated. Sometimes it is necessary to have double wall construction to accommodate components or to make the prosthesis more cosmetic.
Flexible Inner Socket with Rigid External Frame
The flexible socket design is used by transhumeral (above elbow) and transradial (below elbow) amputees. The flexible socket creates total contact on the residual limb, while the rigid frame provides support over the pressure tolerant areas. This design provides decreased weight and better heat dissipation, but can be less cosmetic (attractive) and more difficult and time consuming to fabricate.
Voluntary Closing Terminal Device
The voluntary closing terminal device is held open by a rubber band or spring. It closes when the amputee actively closes it with the cable control of the prosthesis.
Voluntary Opening Terminal Device
The voluntary opening terminal device is held closed by a rubber band or spring. It opens when the amputee actively opens it with the cable control of the prosthesis.
A wrist disarticulation procedure is the surgical separation of the wrist and hand from the arm. In this surgery the radius and ulna (lower arm bones) are separated from the carpal (wrist) bones. The hand and wrist are then removed from the body. No bones are cut during this surgery