It could quite well be, that movement of an endplate might cause pain, but the only guaranteed way is by x-ray.
Yes you're absolutely right, bending and twisting apart from not being helpful and overstretching minor muscles blood vessels and ligaments that are trying to heal, could quite well move a plate if it is not well secured and hammered in (Charitee). Also if you notice in my previous reply to you, at six weeks, there is good substantial bony growth round the prosthesis and from that point on everything should be secure providing the positioning is correct in the first place. The positioning and experience of the surgeon in my humble opinion is 99.9% of a successful surgery.
Best,
Alastair