Normally, the bones, ligaments, and muscles of a joint work together to support the various parts of the joint in their correct positions while also allowing the full range of motion of the joint.
In joint instability, there is lack of support, with the result that the joint may not move correctly or may be dislocated easily.
In shoulder instability, for example, the shoulder joint feels abnormally loose, and there may also be symptoms such as tingling, numbness, or weakness in the arm. In extreme cases, the shoulder may dislocate.
Treatment may involve physical therapy and anti-inflammatory medication or surgery to stabilize or repair the joint. If the joint has dislocated, it will need to be manipulated back into position.