I am not saying that the Carroll quantitative test for upper extremity function is necessarily the test most related to my own Activities of Daily Living (ADL). It is not.
But manufacturers are going above and beyond their call of duty to build "bionic" prostheses that seem to excite their engineers, the media and that by and large miss the point of functional prosthetic support while public money for research is wasted away on similarly useful gadgetry. Can you believe it? With a BeBionic hand you can even grab an apple? How amazing! With the iLimb, you can hold a water bottle! Wild! And the Otto Bock Michelangelo hand can also grab an apple. Oh, well.
So again amputees are mostly on their own as far as the real works are concerned.
On my way trying to get an understanding of the interplay between grip angles and usefulness I am trying to work towards better defining a modern test for relevant dexterity. And for that, it helps to play with a previously established test and then discuss maybe what it does well, what it does not show, and what it can be used for.
Furthermore, current advertising for "bionic" prostheses [Michelangelo, BeBionic, iLimb] usually show activities that any prosthesis can achieve and as such do not prove a particular point.
After reading through Carroll's paper, I decided to implement the following tasks:
Task 1. Lift wood block (~ 8 x 8 x 14cm).
Task 2. Lift wooden triangle (~ 25 x 5,2 x 6,2 cm).
Task 3. Place iron tube (25mm outer diameter, 22mm inner diameter) over iron bar (16mm diameter) located on shelf / box.
Task 4. Place three washers (30 mm outer diameter, 7 mm inner diameter) and then a rubber tube (5 mm inner diameter, about 6 cm long) over a screw or nail sticking out from the shelf / box.
Task 5. Pick up and lift twelve wooden balls (sized 30mm, 15 mm, 10 mm and 5 mm, three of each).
Task 6. Pick up and lift heavy iron.
Task 7. Fill water from pitcher into glass.
Task 8. Fill water from glass into pitcher.
Task 9. Write something.
s= weird shoulder movement
The ratings were given by me so they are necessarily subjective. In particular, I lack objective criteria for what does constitute a 'weird shoulder' movement. But you will be able to do your own rating when you check the videos (below).
|Tasks||Task 1||Task 2||Task 3||Task 4||Task 5||Task 6||Task 7||Task 8||Task 9||A: Task completion points||B: Weird shoulder minus points||Total (A-B)|
|Otto Bock MovoHook||+||+/s||+/(s)||(+)||+||+||-/s||+/s||+||7.5||3.5||4.0|
|Becker hand||+/(s)||+||+||+/(s)||(+) (5mm balls)||+||(+)/s||+/s||+||7.7||3.0||4.7|
|Otto Bock hand||+/(s)||+||+||+/(s)||- (5mm balls) ||+||-/s||+/s||+||7.0||3.0||4.0|
In any real world situation, this never plays out. It just does not.
I will use a different terminal device for various things that I do, and an optimal shoulder motion as well as overall posture are always key targets as well as best function.
So currently, I use a Dorrance / Hosmer Mod.7 or Mod. 555 work hook for a range of manual works including typing. I use a V2P Prehensor for a range of things including house work or garden work. I use Otto Bock's hand to hang out or sit in meetings. I wear a Becker hand for mixed work and play. I wear Otto Bock's all metal Movohook 2Grip work hook for hands-on dirty work as that is the one I can clean best afterwards. For kitchen work, it depends what I do.
The biggest restriction I see would be to only use one terminal device. A nice finger based gripper such as the Becker hand is not nearly as good as any of the hooks for typing, opening of doors, lids, drawers or holding on to other handle bars.
Otto Bock Movohook
Becker Lock Grip hand
Otto Bock hand
 The Becker hand still allowed a visual check of the failure to grasp these tiny balls from within the bowl. The Otto Bock hand then caused the balls to at first stick to the fingers, then the spring closed and ejected the balls which is a more irritating way to fail this task. For the irritating way of non-foreseeably fail this task, I gave 1/2 a point less than the Becker hand for this task.
 Approximated but not perfect.
Far more relevant than meets the eye are these consequences:
- Reducing shoulder and arm twist motion. Some tasks cannot be solved other than by using whole arm, shoulder or even body motion. That also is the reason why a prosthetic hook or hand is an aid, not a replacement. On the other hand, amputees lack degrees of freedom of joints and rather than supplementing joints, cleverly shaped terminal devices do the trick. If you pay attention to the video footage, the test can be rated as to the amount of required shoulder distortion. That is why for daily work, the Becker hand, but particularly the hooks, predominantly the V2P Prehensor and Dorrance hooks, are so very functional. I have major issues with tense muscles, trigger points and pain from unbalanced overuse.
- Small details in hook design play a major role. Both grip and should issues are determined by small design differences in hook design. The Dorrance hook is elegantly shaped and warps around the handle of my water pitcher - the same is not true at all for the Otto Bock hook that, despite being a recent design, can not at all be used to pour water. The V2P Prehensor is very strong and could hold any other pitcher well but here, the shapes are not optimally combined and an awkward shoulder motion results.
- Using convenient products. My water pitcher is a good example of a nice but rather unsuitable product. But my water glass - already bought to be used with prosthetic terminal devices - works well with any of the terminal devices used here. - If I type, I am not always pushing the keys perpendicularly to their spring mechanism. That means my keyboard needs to be forgiving to that. The IBM type M keyboards are very good in that respect, some Apple keyboards are surprisingly bad. - Overall, the result of such a test can also be used not just to select a better terminal device but also to identify areas of improvement for table height, cutlery, kitchen tools, wrist mechanism, keyboard, bathroom utensils et cetera.
- Test for vital activities. Some tasks seem to be uselessly indiscriminate here but still represent vital activities. So, don't throw out test items that represent activities required in daily life. Lifting that iron was a cool thing to do even though in this test setup, this posed no obstacle with any of the devices. Lifting the washers off the table and getting the wooden balls out of the bowl was a bit difficult with all of the terminal devices but these tasks seems to be helpful.
- This particular test misses out on a number of hugely relevant issues. Grabbing thin plastic bags (top: V2P Prehensor, Becker hand), typing on a computer without shoulder distortion (top: Dorrance hook, V2P Prehensor - but also Otto Bock hand or Otto Bock Movohook), filling up car windshield wiper fluid (top: Becker hand) , handling round objects (top: Becker hand) etc. are extremely important in daily life. Also, grip strength (winners: V2P and Dorrance hooks as well as the Becker hand) and ability to carry a heavy item (how much?) can play a role.
- Socket design is hugely relevant. The best terminal device is useless if the socket does not work.
- Even though there are differences, all products used here are at least fairly good. They do have a price, they will fail eventually - and this test is not the end all be all. While "friends don't let friends wear Otto Bock", their products don't fail completely either.
- Cable controlled hooks are simply better. They just are. Who thinks of these as outdated proves that they don't understand working through a day of manual tasks.
The solution to such a problem as here is to have a number of terminal devices. You start by wearing a prosthetic hand until you run into a problem the hand is not useful for. Then you switch it for a hook device. Or vice versa.
So don't blindly go for such test results - see to it that you can do your own test of what is important to you personally.