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I am creating a humanoid species for my setting and I thought of the idea of ​​making it that can rotate its joints with a 360 angle and can bend its limbs in any direction. Sort of like owl's 270 degree neck rotation but in every joint in the body (knees, wrists, hips, ankles etc). Moving my own joints, I came to the conclusion that the shoulder is the type if joint that mostly resembles the one I am describing, despite not being able to do full 360 rotations.

Would this be possible? And how could it be?

Maybe there are some joints in particular that simply cannot be fully rotatable and/or foldable?

Thank you in advance.

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    $\begingroup$ i remember theres some human with abnormality or disease that make them can rotate 360 degree, one that i manage to found from google is rubber boy so maybe try check that. $\endgroup$
    – Li Jun
    Feb 14, 2020 at 12:30
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    $\begingroup$ With a single joint? An owl’s neck is multiple vertebrae that each do a bit of the turn, and if you try to you (as a human being) can get your hand to do a continuous 360 spin if you utilise your wrist, elbow and shoulder concurrently. $\endgroup$
    – Joe Bloggs
    Feb 14, 2020 at 12:45
  • $\begingroup$ Thumb twiddling. $\endgroup$
    – AlexP
    Feb 14, 2020 at 12:55
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    $\begingroup$ @LiJun Ehlers Danlos (en.m.wikipedia.org/wiki/Ehlers%E2%80%93Danlos_syndromes). The difference between the question and Ehlers Danlos is that one asks for actively making the joints move by itself while Ehlers Danlos only allows you to manipulate it indirectly. Its rather weird to see someone rotate his arm by hand twice though. The disadvantages will be the same though: instability of the joints, less strength. Shoulders take a massive part of your body to allow for its range of movement and still some stability. $\endgroup$
    – Demigan
    Mar 19, 2020 at 17:19

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Well the best course of action is looking at owls themselves

Owls have large spaces in their 14 neck vertebrae (twice as ours) to allow for the blood vessels to move while they twist their head. They also have blood "pockets" on the lower portion of their beak, allowing for oxygenation even when their head are bending the max 270 degrees. Next is their feet: owls are zygodactyl meaning they have 2 toes on the front and 2 on the back, however, due to having extremely flexible ligaments, many owls can move one of their back toes 180 degrees.

Now why did I waste all of this time talking about owls? Because that also would apply to your species.

To have good rotation on your head, you'll need more vertebrae and need additional space to fit in blood vessels along with the trachea. For the overall toes and fingers, elastic and flexible ligaments that allow for movement. The elbows will face decent structural changes in both bone and muscle alike to be nearly symmetrical from front to back, and I'm sure the patella must be absent in these.

Now: here's why I think it's not a great idea to do this in all joints: it compromises stability and there's decent issues with certain joints.

Let's start with the hip movement at the spine level: is it possible? Yes, but it puts sone strain on the organs in the area, squeezes them, so why strain your guts like that unless it's extremely necessary? Next: elbows and knees. As far as I know, no animal can bend these 180,it's just not worth it, running becomes a mess, and there might be higher risks of fracture, as stepping wrongly might cause your joint to bend the opposite way, making balance a tricky activity, since you'd rely more on your muscles than on your bones to stand.

So summing up, some things might be great to swivel/ move better, such as the neck, fingers, toes and ankles (better at climbing), maybe the legs at the hip joint. Other than that, as far as I know, you might bring them more harm than good. For additional reference, look up contortionists, they're a much better example of a flexible humanoid that's stable.

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Tentacles instead of limbs.

Ever seen the kind of multiple-segmented, shower-pipe like limbs of cartoon robots? Well, your race uses a biological version of this, having a lot of ball joints within their limbs that allow full rotation and extreme folding. Their blood vessels are also loose and flexible, possibly concentric and running down the center of their ring-shaped limb bones.

Then you can get the most prehensile limbs you would ever want. Real life octopuses are a great example of this.

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