My damage was in the ankle, so YMMV. But a few suggestions:
1. Definitely ask your PT. (Physical Therapist)
2. Do EVERYTHING the PT says. Religiously. I lost some range of motion, and I think it was from not pushing it early on.
3. I had tremendous results from riding a bicycle. Low impact, high blood flow, natural increase in range of motion. And outdoors in the fresh air. Stick to flat, easy rides in low gears at first. (I actually started out on a trainer in my garage for a few weeks prior to being weight-bearing).