How Can One Diagnose A Suspected Rotator Cuff Tear In The Right Arm?

Hi, doctor, I fell out of bed and landed on my elbows and knees - most of the force seemed to be on my right elbow. I had severe pain in both shoulders and knees so I went to the ER. There were several x-rays taken. No bones were broken. I have had therapy on my shoulders. The physical therapist is suspicious of a bone spur and of a possible rotator cuff tear. I am unable to extend my right arm as in shaking hands. However, if I raise my right arm a few inches I can then use my left arm to raise my right arm further. The condition has slightly improved but I do have pain when raising or lowering the right arm. It seems as though something is restricting the movement in both directions. It also feels as though I have no muscle power as I extend my arm. The therapist is considering asking my doctor to order an MRI to look for tearing or bone chip or anything else. Where can I find more information about rotator cuff - descriptions, pictures, animations, etc.? Also, do you have any other suggestions? Thank you, XXXX at YYYY@YYYY thank you