Senior cat not sitting down completely

So as the title says, my 18 year old cat does not truly sit. He hovers over the ground as if uncomfortable.

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He has stage 3 CKD. His thyroid levels are normal and his urinalysis just came back clean. I know he has arthritis and there is significant muscle wasting in his hind legs.

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Is this posture common with cats who have advanced CKD? I don't want him to be unc and I'm not taking care of it..

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