1. Your insurance will not be interested to deal with the other party's insurance because you only have liability. But you should let your insurance company know asap anyway. You also should contact the other party's insurance company and let them know your leg pain.
2. As you described, it is not your fault. You should go to hospital (maybe ER) asap. Keep a copy of everything.
The best way to deal with this, find a personal injury attorney. He will help you the most.