I can't move my left arm up past my ear. It just won't go -- even when I try to force it. There's absolutely nothing on the X-ray to show what's going on inside there. How is that possible?
Loss of shoulder motion like you are describing might be diagnosed as a frozen shoulder or adhesive capsulitis. There is a specific pattern of motion loss that points to a tightening or stiffening of the joint capsule (soft tissue around the joint holding it in place).
The capsular pattern with a frozen shoulder results in loss of rotation, forward elevation, and abduction (moving the arm away from the body). X-rays are negative unless there is a fracture or tumor. This is because changes in the joint contributing to a frozen shoulder are in the soft tissues, not the bone.
New research shows that frozen shoulders occur when tiny fibroblasts or adhesions develop. Biopsies of the tissue show signs of chronic inflammation. Specific inflammatory cells such as mast cells, T cells, B cells, and macrophages are present. Other studies have shown that vimentin (a cellular protein) is present whenever the anterior shoulder capsule is involved.
Again, these kinds of changes in the collagen structure simply don't show up on X-rays. More advanced imaging may be helpful but is usually expensive and not required to make the medical diagnosis.
Peter C. Lapner, and George S. Athwal, MD, FRCSC. Shoulder: The Stiff Shoulder: How, Why, and When to Treat. In Current Orthopaedic Practice. September/October 2008. Vol. 19. No. 5. Pp. 538-541.