I dislocated my left knee a few days ago , went to orthopedic doctor and they said it was back in place on its own .cannot straighten or bend it or put pressure on it . my left foot is cold constantly and wont warm up. should i be concerned ?

Did they evaluate your foot for vascular flow? Even if a dislocation is back in place, there could be damage to tendons and vascular structures. A thorough examination of the knee by an orthopedic physician should have determined stability and vascular and ligamentous integrity at a minimum. If this was not part of your exam. You may need to be re examined

I agree, that you are describing a potential vascular injury. That needs to be evaluated urgently. It is rare, but can be serious.