Your knee is made up of many important structures, any of which can be injured. The most common knee injuries include fractures around the knee, dislocation and sprains and tears of soft tissues, like ligaments and tendons. In many cases injuries involve more than one structure in the knee.
What most people call the shoulder is really several joints that combine with tendons and muscles to allow a wide range of motion in the arm–from scratching you back to throwing the perfect pitch.
Mobility has its price, however. It may lead to increasing problems with instability or impingement of soft tissue or bony structures in your shoulder, resulting in pain. You may feel pain only when you move your shoulder, or all of the time. It may be temporary or it may require medical diagnosis and treatment.