Hi

from my understanding there is still alot of debate with regards to warm ups/stretching and injury prevention although most will agree it aids performance. The general consensus is that it is also better to do dynamic stretching before sport/exercise and static after but this is going off the point a little.

Are you able to do non weight bearing or low impact exercise such as cycling, cross trainer or swimming? If you can you could use these as a way of warming up instead of running.