Transhumeral Amputation & Elbow 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 elbow disarticulation procedure is the surgical separation of the lower arm from the upper arm at the elbow joint. In this procedure the radius and ulna (lower arm bones) are separated from the humerus (upper arm bone). The lower arm and hand are then removed from the body. No bones are cut during this surgery.
Electric elbows available today contain an electronically controlled lock that can be locked or unlocked with myoelectric signals from the amputee’s body, as well as with a switch. This happens inconspicuously in fractions of a second and offers reliable loading in any position. Flexion of the elbow can be controlled by an electric motor and allows for quick, exact positioning of the hand with little energy expenditure.
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).
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.
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).
Forearm Lift Assist
The forearm lift assist can be added to any mechanical elbow to reduce the force necessary to flex the elbow.
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.
Internal/External Locking Elbow
The locking elbow is used by transhumeral (above elbow) amputees. This elbow allows the amputee eleven locking positions of flexion controlled by the cable system of the prosthesis. The locking elbow has manual friction positioning for internal and external rotation.
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.
Nudge Control Unit
The nudge control unit is a paddle-shaped device that is used by upper extremity amputees. It is often activated by the patient’s chin. It is typically prescribed when other body movements are not available. The nudge control can be used to provide small amounts of cable excursion, to lock and unlock a prosthetic elbow, or to control a wrist unit.
Outside Locking Hinges
Outside locking hinges are used by elbow disarticulation amputees. These hinges allow the amputee seven different locking positions that are controlled by the cable system of the prosthesis.
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.
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 sensing 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 to 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.
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.
A transhumeral amputation is a surgical procedure in which the humerus (upper arm bone) is cut and a portion of it, along with the rest of arm, is 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 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 boney 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.