Frank Szmulowicz, Ph. D. Jul 19, 2018:

I do not know what this means in the medical setting, but in a mechanical setting, this is a colloquial way of saying that something has hit a snag, was caught on something (zachaczyć się), experienced some obstacle to free movement (natknięcie się) that has to be overcome. I can see how there may be a point in the motion of the hips where there may be such a catch.