The most movable joint in the body, the shoulder is also one of the most potentially unstable joints. As a result, it is the site of many common problems. They include sprains, strains, dislocations, separations, tendinitis, bursitis, torn rotator cuffs, frozen shoulder, fractures, and arthritis.s the name implies, movement of the shoulder is severely restricted in people with a âfrozen shoulder.â This condition, which doctors call adhesive capsulitis, is frequently caused by injury that leads to lack of use due to pain.