Causes of Shoulder Pain            The shoulder is a very complex structure of muscles, tendons and bones and many reasons exist for shoulder pain. What most patients refer to as arthritis is usually not arthritis at all. The pain usually originates in the soft tissues about the shoulder and is not truly coming from changes in the shoulder joint ball and socket structure. While this does occur, that is true arthritis changes in the joint, it is very unusual compared with the knee and the hip.     Some common causes of shoulder pain are tendinitis, bursitis, injury, and unstable shoulder. The more uncommon causes of shoulder pain are infection, pinched nerve, and tumors.     Pain in the shoulder will come and go at various times and does not require treatment if it disappears in a short time.     If it remains, medical diagnosis and treatment are needed. Many patients ignore temporary minimal shoulder symptoms with few bad effects. However, if an injury has occurred and the pain is intense, medical treatment should be sought. If the pain is not severe it may be fine to wait a few days to see if time will cause the symptoms to disappear.     Tendinitis:   A large number of shoulder problems are the result of the wearing process that takes place in the tissues of the shoulder. Tissue planes can actually split and tear causing damage to the rotator cuff tendons. The rotator cuff is a collection of muscles and their tendons, which provide motion and stability to the shoulder.     Bursitis:   A bursa is a very thin tissue sack around joints, which lessens friction caused by movement of muscles and tendons. Bursitis is closely allied to tendinitis, it maybe be difficult to distinguish from tendinitis. It is very frequently also present with tendinitis.     If the shoulder joint begins to stiffen as a result of more serious degrees of tendinitis and bursitis, a condition called frozen shoulder may occur. It is also referred to as adhesive capsulitis.     Instability:   The shoulder joint is a shallow ball and socket arrangement, which is much different from the hip joint, which is the other ball and socket joint in the body. Because of the shallowness the shoulder joint is prone to sometimes partially or completely slip out of position. This condition can be acute or chronic and usually results in pain often severe and in a feeling of unsteadiness in the joint itself.     Diagnosis of shoulder pain:   There are many means to diagnose shoulder pain including medical history, physical examination, plain x-rays, arthrogram, CT scan, MRI study, and electro-myogram (EMG). Arthroscopy is a surgical procedure in which the joint can be examined by a lighted telescope.