Upper Limb Prosthetics

Which Type of Prosthesis is Best?
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One of the many things I like about upper-limb prosthetics is that every person is unique, and the entire prosthesis, not just the socket, is designed differently each time.  There is no standard approach.  Every prosthesis is a solution to a different problem or challenge… or many.  So as for “what kind is best?” there really isn’t an answer to that question.  There is only what is best for you. 

There are many things a prosthetist must consider to determine the best prosthetic system for you.  We must
figure out what options are possible for you to use, and work within those parameters to create a prosthesis that will fill your needs.

The prosthetist must consider:

What do you want to use the prosthesis for?
What is your job? 
What duties do you have to perform to excel at your job?
What is your home environment like? 
What must you do around the house and yard?
Are you living independently?  Do you have support at home?
What are your hobbies? 
What activities make you happy? 
What do you need to be able to do to live your life the way you want?
Are you going to be getting the prosthesis wet and dirty?
What objects are you going to need to manipulate?
How durable does the prosthesis need to be? 
How much weight will it need to carry and in what positions?
How many hours a day are you going to be wearing the prosthesis?  Minimum needed?  And the maximum desired?
How active are you?
How much pressure can you tolerate?
How heavy of a prosthesis could you comfortably wear?
Do you sweat a lot?
Will you get hot in a gel liner?
Will you be able to put it on by yourself?  How hard will it be?
What have you used in the past and what was your experience?

The prosthetist will look at the physical characteristics of your residual limb:
What is the level of your amputation? 
How long ago was it?
What shape is it?
Is it painful? Do you have adherent scar tissue or neuromas
Do you have scarring?
How sensitive is your skin? 
Do you have nerve damage limiting sensation or muscle strength?
Are there other injuries?
Do you have limited joint movement?
How many viable myosites do you have?  How strong are the signals?  How well can you control them?

The prosthetist must consider the larger issues related to your general health.  The type and degree of motion you have in your residual limb and the rest of your body is very important.
Did you lose your dominant hand?
Do you have full use and function of your other hand?
Do you have good vision?
How is your general health?
Do you walk with a cane?
How is your fitness level and stamina?
Do you have the strength to tote around a heavy, externally powered device?

And the prosthetist must find out from you if you have the time and motivation needed to learn how to use an externally powered device.
Will you have access to occupational therapy? How much?
How much do you care about how the prosthesis looks?
Are there financial limitations?

And that's not even everything--because they do really have to factor in everything.

Considerations:  amputation level



Partial Hand
Partial hand amputations account for the vast majority of upper extremity loss.  Traditionally, partial hand prostheses consisted of cosmetic restorations and functional extensions allowing use of the remaining fingers.

These designs are still commonly used, but there are also a few types of externally powered partial hand/fingers available on the market today, as well.

Wrist disarticulation/through the wrist:
Wrist disarticulation level amputations present both benefits and challenges to a prosthetist.  You usually still have all your forearm muscles.  This allows you to still rotate your hand palm up to palm down (which we call pronation and supination), and the functional benefit of this ability is considerable.  However the extra length of the residual limb creates problems with regard to componentry:  there isn’t a lot of room for much stuff.  To address this issue, many manufacturers make specially designed, reduced length components for wrist disarticulation or long transradial patients.

 

 

Transradial/through the forearm.
The the shorter the residual limb, the less ability there is to turn the arm palm up/palm down, and a prosthetic wrist that allows rotation of the Terminal Device (TD) becomes more necessary.  In general, the prosthesis also becomes more difficult to suspend (keep on) and a prosthetist’s experience plays a key role in their ability to make a functional prosthesis for the user.

 

 

Elbow disarticulation/through the elbow:
Elbow disarticulation level amputations preserve the muscles of the upper arm, allowing full ability for rotation of the elbow relative to the shoulder (with elbow bent at 90 degrees, hand out in front vs. hand out to the side).  The long length of the residual limb allows for easier operation of prosthesis.  In addition, the remaining bony anatomy on the end makes suspension easier so that the socket does not need to encase the shoulder, allowing full range of motion.  There is still the room-for-prosthetic-components problem, athough, just as for wrist disarticulation, there are some special options.

 

Transhumeral/through the upper arm
This level of amputation has three major challenges:  1) keeping the prosthesis on while still leaving you comfortable and still able to move,  2) preventing the prosthesis from rotating around your residual limb and 3) generating force and movement that can operate a prosthesis. 
Generally, the shorter the residual limb, the less remaining musculature there is to either a) move the limb to operate a body-powered prosthesis, or b) generate muscle signals to operate an externally powered device. 

Shoulder disarticulation and higher:
Shoulder disarticulation prostheses must be attached to the body via interfaces and harnessing that involve a good part of the upper torso.  Since there is no shoulder, generating movements to operate a body-powered prosthesis is challenging.  In addition, with no remaining arm musculature, there are few muscles from which to obtain a good signal for myo operation.  But there are still options available.  It just takes extra knowledge, time, and creativity on the part of the prosthetist to create a solution that works for you.

 

Some notes on prosthetic options:


In the beginning, patients may shy away from the idea of a prosthetic hook.  And it's understandable really--why wouldn't you want a hand?  But many quickly discover why the traditional split hook has remained so popular.

1. It usually has comparatively less material than a hand shape and may be lighter.  Over the course of
the day, weight may become a considerable impediment to comfort.  In addition, because it consists of less material, it can be made out of steel, titanium, or aluminum, which increases its durability.

2. Because you cannot feel through your prosthetic hand, you rely exclusively on visual cues to determine whether you have picked up something.  Unfortunately, prosthetic hands generally obscure your view of things you are trying to pick up, touch, or move, making it hard to do fine motor tasks.

 

 

For a video about using a body powered hook, click below. 
http://www.youtube.com/watch?v=b3HNq1tCd4E&feature=related

There is a similar pros vs. cons dilemma with regard to body powered vs externally powered/myoelectric prostheses.

 

 

Externally powered devices are cool, to be sure.  But they are also expensive, heavy, and breakable.  The ability of any patient to operate such a device depends on the number and quality of inputs (myo signal/electrodes or other), placement of electrodes or other input devices, intimate, consistent fit of the socket, and training in how to use it.

 

Generally, the more moving parts something has, the more things there are to break or go wrong.  You need to charge it and be careful about getting it wet and dirty.  But technology is improving all the time...
Still, some find they prefer the predictability, reliability, durability and low maintenance of a body powered device whose movement and grip force they can directly control with more deliberate movements.  But for others the harnessing required can cause discomfort, pain, sometimes physical damage from the long term force exerted around the shoulder and axilla (armpit) on the other side. 

Body powered hook vs. myo
http://www.youtube.com/watch?v=bCSVkkhSy3M&feature=related

To watch a video of one person's experience with body powered vs myoelectric above elbow prosthesis:
 
http://www.youtube.com/watch?v=UZ2sg92XC0M&feature=related

Article with table comparing different options: link

Be sure to check out the Videos page to get a better idea of the benefits and challenges of different systems.


That said, there are not really 'good' and ‘bad’ prosthetic options.  There are simply better and worse choices for each individual patient based on their needs.  It is best to go to your provider with an open mind and listen to their opinion.  Listen, but be honest about how you feel and what you want.  In the end, you are the one that has to wear it.  It does you no good if it sits in the closet.  Learn all you can.  Advocate for yourself.  Insist on dialogue.  A good prosthetist will be your partner through the process.  Our goal is to provide you with a prosthesis to help you do what you want to do and to live the life you want to live.