it made the transition to sitting so much easier for him, and I think that is why he did it. We'd just about given up on him crawling anyway and were just working on walking, so we were thrilled with any kind. I thought he would progress to full quadraped, but he never did. He is three now, and sometimes he will still crawl to get something if it's close and he doesn't want to stand up and walk over to it - he's always gauging what is easiest LOL Sometimes he crawls on both knees, and sometimes he still crawls with that knee up

It did make the one leg stronger, but, he still learned to walk just fine

We tried and tried to get him to crawl on both knees and he fought it, so we got to the point that we just let him crawl how he wanted.
So - not much advice, but I think it is quite common for kids w/T21 to tweak their crawls - so you are not alone

and