The shoulder is the most flexible joint in the human body. It allows you to place and rotate your arm in many positions in front, above, to the side, and behind your body. This flexibility also makes your shoulder susceptible to instability and injury. According to the American Academy of Orthopaedic Surgeons (AAOS), in 2003 some 13.7 million people went to the doctor's office for a shoulder problem.
The shoulder, like the hip, is a ball-and-socket joint. It is made up of three bones: the upper arm bone (humerus), the shoulder blade (scapula) and the collarbone (clavicle). The ball at the top end of the arm bone fits into the small socket of the shoulder blade to form the shoulder joint.
The socket of the shoulder joint is extremely shallow, making it unstable. To compensate for this shallow socket, the shoulder joint has a soft rim of cartilage (the labrum) that surrounds the socket to help make the head of the upper arm bone fit better and stabilize the joint.
Common Shoulder Injuries
Shoulder injuries are frequently caused by athletic activities that involve excessive, repetitive, overhead motion, such as swimming, tennis, pitching, and weightlifting. Injuries can also occur during day-to-day activities like washing walls, hanging curtains, and gardening.
Most problems in the shoulder involve the muscles, ligaments, and tendons, rather than the bones.
Some people have a tendency to ignore the pain and "play through" a shoulder injury, which aggravates the condition and may cause more problems. Patients may also underestimate the extent of their injury because steady pain, weakness in the arm, or limitation of joint motion can become second nature. Early, correct diagnosis and treatment of shoulder problems can make a significant difference in the long run.