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I would like to know how my forearm bones move inside my forearm when I'm twisting my hand. (Also, it would help to see the hand bones action too). "twisting hand" means to me the motion in which the rest of the body is in place except the hand which turns from upside up to downside.

I have the intuition that the bones inside my forearm move between themselves to make my hand twist, but am not sure if that is true.

I would like pictures of the forearm bones before and after twisting. Animations would also be great of course.

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  • $\begingroup$ I replaced the "I want" and similar expression (that give of answering to the request of a dictator) by "I would like" and other more appropriate expression. In the same logic, in your comment under the current answer i would remove the I will accept your answer if you clarify that [..] part of it. Of course, I don't think you feel like giving orders. It is only a matter of expression. You might as well not be a native english speaker. (I am not either). $\endgroup$
    – Remi.b
    Sep 17, 2016 at 19:17
  • $\begingroup$ @Remi.b yes, thank you for editing, I was experimenting with language. He fulfilled my request and now I gave him his prize. And yes, I'm not native english speaker. $\endgroup$
    – Santropedro
    Sep 17, 2016 at 20:01

1 Answer 1

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Here is a basic image. Palm up is called supination and is the resting (anatomical) position. The radius and ulna sit parallel. When the forearm is in pronation, the radius crosses the ulna.

You can feel this yourself. Put your fingers on the ulna and move the palm into pronation and supination. You will not feel the ulna rotate. Only the radius pivots during this movement. The wrist is not involved in this movement.

pronation

The ulna is unable to rotate at all, because its olecranon process is locked into a groove on the distal end of the humerus. If you put you fingers on your bony "elbow" (olecranon process) and pronate/supinate your hand (without flexing/extending your elbow), you will not feel you ulna moving.

ulna

ulna2

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  • $\begingroup$ Suppose I rotate my forearm as described, from pronation to supination. My ulna rotates around itself? I see the radius moves, but I want to know if the ulna rotates around itself. I will accept your answer if you clarify that in your answer. $\endgroup$
    – Santropedro
    Sep 17, 2016 at 1:32
  • $\begingroup$ Thank you very much, this is indeed the info I needed! Please feel useful :). $\endgroup$
    – Santropedro
    Sep 17, 2016 at 20:03

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