Is MRI Required For A Misplaced Ligament?

I fell on my left foot 4 months ago. One of my ligaments got misplaced and the doctor "massaged" it back into place. It came out again 2 more times since, and now another doctor has given me an aircast to wear for four months. She did an xray and said nothing was fractured, but shouldnt they be doing an MRI? My foot is swollen at the end of each day and it hurts to rotate it. Any suggestions or thoughts?