Chick's leg too straight

I am sure there is a technical term for this, but since I've never had it happen before, I have not paid any attention.

In the last couple months I have hatched different batches of chicks and two of the batches have produced a chick with a poker straight leg.

Instead of the leg angling slightly backwards towards the butt, the leg comes out from the body and meet the ground dead straight. In the older chick, this is now causing mobility problems. Seemingly the problems are showing in the hip joints. The chick, several months old, lays down a lot and once down has trouble getting back up. His movements are awkward and uncoordinated. I keep hoping he'll grow out of it.

The new chick is just a few days old, and shows no mobility problems yet, but the leg lacks all angulation.

What is this? Does it correct?

I had this in a chick for the first time this year. The chick's legs just got more and more extreme. Balance was an issue and the chick was always sitting. It eventually died. Not sure why it happened, but progression of the issue was interesting.