Stiff shoulder. The medical term is adhesive capsulitis. The capsule covers the joint, and in this condition the capsule "tightens" up and restricts motion. It can be caused by trauma, is associated with Insulin dependent diabetics, and often occurs without any reason (idiopathic). Diagnosis is typically through clinical exam. Often gets better with time, but therapy, injections, and surgery may be required.
Stiff joint. A frozen shoulder or adhesive capsulitis, is when the shoulder joint becomes contracted. The thin capsular tissue gets fibrotic, thickened and prevents motion. People with diabetes are more likely to get a frozen shoulder, but anyone with shoulder inflammation can have this happen. Loss of motion and pain are the most common symptoms. Injections, therapy and sometimes surgery are treatments.