I think (but haven't checked recently) that there is some research indicated that people who do most of their running on treadmills tend to end up with different types of injuries than those running on the open road. Repetitive stress type injuries are more common if your feet and leg placement are identical step after step, while sprains and twists happen more with uneven terrain. Extending from that, I would think that your alignment on the treadmill has been pretty good, and that this has helped you to protect and strengthen important parts of your legs and back and core.

I hope that whatever you have been doing continues to work for you.