However, this exquisite flexibility makes the shoulder joint susceptible to instability and injury. Although the ligaments, tendons, muscles and cartilage that form a capsule around the joint to maintain stability, trauma or overuse of the shoulder can cause these tissues to stretch or tear. Without the strong support of these tissues the shoulder joint will feel “loose” and may pop out of socket with certain activities. Generally, an unsupported instable shoulder will be weak and painful.