Upper Extremity Prostheses
There are many factors that determine how much of the limb is amputated. Generally, the longer the remaining limb and the more joints that are kept intact, the easier it is to be fit with and use a prosthesis.
The major categories of upper-limb amputations are:
- Partial-Hand Amputations-Finger, thumb or portion of the hand below the wrist
- Wrist Disarticulation – Limb is amputated at the level of the wrist
- Transradial (below elbow amputations) – Amputation occurring in the forearm, from the elbow to the wrist
- Transhumeral (above elbow amputations) – Amputation occurring in the upper arm from the elbow to the shoulder
- Shoulder Disarticulation – Amputation at the level of the shoulder, with the shoulder blade remaining. The collarbone may or may not be removed
- Forequarter Amputation – Amputation at the level of the shoulder in which both the shoulder blade and collar bone are removed
There are four main types of prosthesis for the upper limb. People with upper limb amputations have a number of choices to make regarding rehabilitation and your health care team can help you make those choices. The four major design options for fitting of an Upper Extremity prosthesis are:
- Passive or Cosmetic prosthesis
- Conventional Prosthesis – cable operated with a harness system
- Myo-electric Prosthesis – operated by electrical impulses produced by tightening (contracting) muscles
- Adaptive / Activity Specific
There are advantages and disadvantages to each type and design – our UE prosthetic specialist and your health care team will discuss these options with you. The type of prosthesis you will be prescribed will depend on your specific needs, strength, work and recreational pursuits and lifestyle. Prosthetists at TSOP often utilize more than one kind of control system, and can design a ‘hybrid’ type of device for a single patient. For example, we can use myo-electrodes to control the function of the hand and a separate/independent positional servo transducer to control the elbow position. Thus allowing the patient to control both the hand and elbow simultaneously. In the past, you had to do one thing at a time or sequentially. You flexed the elbow, stopped flexing the elbow, switched to the hand, opened the hand, closed the hand, and then extended the elbow. With the multiple input concept, you can do more than one thing at a time and, therefore, have smoother, simultaneous movements.
Passive or Cosmetic prosthesis
Passive prostheses are generally considered to be devices that are worn purely for cosmetic purposes. A Passive or Cosmetic upper extremity prosthetic device is similar in appearance to the non-affected arm or hand and replaces what was lost. It provides simple aid in balancing and carrying. The advantages of this type of prosthesis is that they can be cosmetically appealing, lightweight, simple to use, there is little maintenance, and can provide opposition. They also aid in making the patient feel whole, and not appearing different from the general population. The prosthesis can help fill out the arm of a shirt or jacket and generally make the patient feel more balanced.
Conventional Prosthesis – cable operated with a harness system:
A Body Powered or Conventional upper extremity prosthetic device is operated by a harness system. The harness system is controlled by specific body movements, to pull the cable and make the terminal device (a hand, hook or prehensor) open or close much in the way a bicycle handbrake system works. The advantages of a conventional prosthesis include: the heavy duty construction of the device affords it a long life with little maintenance, it offers proprioceptive feedback to the patient, they are generally less expensive and lighter in weight than myoelectric devices, and there is an initial reduced cost over other options. Mechanical body-powered terminal devices are voluntary-opening or voluntary-closing. Voluntary-opening means that users must open the terminal device by applying force through their cable system. The terminal device then closes on its own with the aid of rubber bands, which limit the grip strength of the device to the strength of the rubber bands. With a voluntary closing terminal device, force must be applied to close it instead of to open it, making the grip strength dependent not on the strength of rubber bands but on the strength of the person using it. Voluntary-opening devices that are closed with the aid of rubber bands offer only visual feedback to the user for control since the bands do the work of closing once an object is grasped, thus taking the body out of the feedback loop. Because they close by the user’s own strength, voluntary-closing devices provide a tension feedback to the body similar to that “felt” when using bicycle handbrakes. Since users can “feel” the force they are applying, they can also control their grip incrementally, applying more or less force as needed.
Typical Advantages of Body-Powered Devices
- Lower Initial Cost
- Easier to repair
- Offer better tension feedback to the body
Typical Disadvantages of Body-Powered Devices
- The wearing and use of the harness can be bulky and cause sound sided muscle discomfort
- The range of motion for functional use is limited by the position of the cable, (i.e. hard to operate the device over your head)
- Mechanical appearance
- Difficult to use for some people because they depend on the user’s physical ability
A Myo-electric upper extremity prosthetic device is powered by a battery system and is controlled by EMG signals generated during muscle contractions. The advantages of a myoelectric prosthesis is that there is an unlimited functional envelope; it offers functional cosmetic restoration; it can increase a person’s grip force to 20-32+ lbs; and the use of a harness system is reduced or eliminated, which offers comfort and increased range of motion. A major improvement in electric prostheses is the use of multiple methods of control to operate them. Electric prostheses are not all myo-electrically controlled, as some people think. It can be explained that myo-electric means that you pick up an EMG/myo signal off the surface of the skin from the muscle that you intend to use to control the speed and direction of the prosthesis. But not all electric systems are myo-electric systems. Some devicesuse pressure, a switch and a harness, a positional servo device or a strain gauge. Each patient is unique and the prosthetist at TSOP will spend time to ascertain which system is the best for each individual patient.
Typical Advantages of Electric Devices
- Do not require a harness or cable and can, therefore, be built to look more like a real arm
- Has a larger functional envelope for range of motion
- Battery-powered so body strength and body movement are not as important for their operation
- Provide a strong grip force
Typical Disadvantages of Electric Devices
- Higher initial cost
- Heavier (Improved batteries have, however, helped reduce their weight and increase their capacity and voltage.)
- Higher repair cost
- Dependence on battery life
Advances in Myo-electric hands
The invention and use of multi-articulated hands, with multiple user adjustable grip patterns has changed the landscape for our upper extremity patient population. There are now several types of multi articulated hands available. The Prosthetic team at TSOP have taken advanced training in all of the newest technologically advanced devices. We have fit multiple patients with the Bebionic and I-Limb technologies. These devices are amazing in function and what they are able to give back to our patients in terms of their everyday lives. They all have user adjustable settings and once dispensed, we train you in being able to use your own laptop, i-pod or i-phone in order to self adjust and maximize the function of your hand. Call TSOP to arrange a demo fitting to see if the use of a Bebionic or I –Limb is appropriate for you
Adaptive / Activity Specific
A Recreational or Adaptive upper extremity prosthetic device is customized for a specific function or recreational activity. There are various adaptive devices available for activities such as holding a camera, gardening, skiing, golf, fishing, construction work, shooting pool, playing guitar, etc… We are able to adapt your prosthesis in any way you can conceive of in order to give you back the function and activities you want to participate in.