My x-ray shows no fractures. so why am i unable to straighten my arm?

Immobilization: The loss of full range of motion of a joint typically is caused by not moving the joint (for example, if a joint has been immobilized in a cast) for a long time, or by pathology within the joint (i.e., a loose body) causing pain or physically blocking the motion of the joint. See your doctor to get more details. Often physical therapy can restore motion to the joint.