What Are The Possible Injuries That May Happen After Falling Down?

I fell down a flight of concrete steps with metal nosing. I landed on my right lower back with my right arm extended to catch the fall, but continued slipping down each time hitting a step while my arm was extended. I felt as though my arm was ripped off at the right shoulder. The doctor took x-rays and found no broken bones. He believe that I tore my bicep tendon and bruised my back. I am beginning to get range of motion back in my shoulder/arm, but it is still not healed (the accident was three days ago). My back is hurting quite a bit. The doctor prescribed PT for two weeks with a follow-up appt. I wonder why he didn t do a catscan or mri to determine any soft tissue damage? Should I be concerned of other possible injuries?