I had evaluated, subjectively, the grip performance of various prosthetic options that I have. These have been already analysed in the context of grip taxonomy, where so far, research has largely focused on grip geometry as such, using some idiosyncratic logic that I found not too relevant.

Using a more relevant logic, I approached the question of grip mechanic from a different angle, both verbally and proverbially speaking: from a user angle, both actually geometrically and subjectively speaking.

I realized that most of my frequently used grips and grip situations fall into a far more narrow range of angle distributions than I had ever assumed.

While others keep rambling about compensatory motion [1] where they assume the "cause" to reside inside some extra joint or so, I know, from exposure and from intelligent looking (all that is needed, boys¹) that the orientation of the grip angle and shape in relation to the fixed gripper geometry - including wrist rotation - has to work in conjunction with the average orientation of objects in everyday life, work, tasks and jobs. Not everyone understands adaptive or adaptable grip really well²  when really, modern "bionic" prosthetic hands have an electrically controlled adaptive grip that, by definition of "adaptive" (and not: "adaptable" [1]), closes fingers around any irregularly shaped object - just like, since maybe 1938, the Becker Mechanical hand does. So there is nothing new at all with regard to that. With regard to device-angle constraints, adaptive grip options do not change that really. The typical "tests" (ULPOM, SHAP, etc.[1]) do not produce output that forces the examiner onto the answer of "there, angles, you... you" so one is thrown unto oneself yet again, so to speak, in order to shed light into this aspect.

So I sat down to add "typical object angles" to my already present grip success statistics over a list of my most frequently or typically used grips. Then I did that in theory and then I figured, why not go and video some.

Thereby, a prosthetic hook as gripper device appears to be a lot more advanced, design wise, geometrically, in reducing device materials, bulk and design to approximate a really good overall use performance - also with regard to angular constraints - than the iLimb (which I have here also for as much testing as I like) and with that, many current commercial (or other) multi articulated hands.

In fact, prosthetic hands appear to be by far the older (and thus possibly less reflected) geometric design idea of a prosthetic arm's terminal device than the definitely more modern split hook. I may also go history hunting, but the claim that a split hook is old or outdated, and that therefore by inference a prosthetic hand is automatically new or more modern, as an idea, is wrong, particularly technically speaking. But also historically, to replace a hand with a hand is a straightforward design idea, that does not take any particular imagination, thus it is reportedly old, very old indeed, not new, like some uninformed people try to promote. Conversely, split hooks are so transformative and groundbreakingly new that not even the self-proclaimed transhumanists have understood, or adopted this concept. In a way, a split-hook efficiently unmasks a number of wrong beliefs - just look at their faces, listen to a few sentences of these mouths, and you know more about them than they ever wanted to admit.

The far more elegant reduction, also of angles and controls, to fit into the limited action and option constraints of an arm amputee, is certainly that of a body-powered split hook. It boils down the prosthetic needs to a successful sleek elegant reduction of a functional minimum, making it the ideal choice for anyone that wants a maximum of performance from a minimum of failure, cost, decay, bulk, futile grip attempts and total overhead. The subtle distinction is that a "body-powered split hook" is an entirely different beast than a passive hook, obviously, which probably no one ever noticed, particularly not the people that assumed that a body-powered split hook is best portrayed by installing a "Captain Hook" metaphor.

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@article{kyberd2017assessment,
  title={Assessment of functionality of multifunction prosthetic hands},
  author={Kyberd, Peter J},
  journal={JPO: Journal of Prosthetics and Orthotics},
  volume={29},
  number={3},
  pages={103--111},
  year={2017},
  publisher={LWW}
}