The shoulder is a complex area of the body that includes many joints, tendons, ligaments, and muscles. When one small part breaks down or does not function properly, it can affect everything else around the shoulder and cause many different problems. When this happens, your body uses pain to tell you something is not working correctly. Such pain can range from a small, occasional ache to a severe, constant pain that keeps you awake at night.
The most common causes of shoulder pain are impingement syndrome, rotator cuff tendon tears, shoulder arthritis, frozen shoulder, and biceps tendon tears. Some patients have more than one of these problems, so your doctor will need to know the details of your symptoms, perform an examination, and sometimes order special tests in order to make the correct diagnosis. 
Impingement syndrome is the most common cause of shoulder pain. Patients with impingement syndrome experience pain when they raise their hand above their shoulder or out to the side. It can also cause pain and stiffness when a patient reaches behind his back, or tries to reach toward his other shoulder. In severe cases, the shoulder pain is more bothersome at night and can wake the patient up if he rolls onto the painful side. When asked to point to the pain, the patient will either indicate one or two spots on the front of the shoulder, or put his whole hand over the side of the shoulder. Because they feel pain radiating down the arm or up toward the neck, some patients worry that the nerves are also injured, but this is not the case. The nerves are normal, but the pain from the shoulder can spread all the way down the arm.
Every time we move our shoulders, the shoulder muscles pull on the rotator cuff tendons. These tendons can wear out, just like any other part of the body, and when they do, they can start to cause pain. The rotator cuff tendon has a soft tissue bursa (a small pouch) that protects the tendon from injury. If that bursa becomes inflamed or worn out, the tendon can become damaged and cause pain. Pain can also be caused by bone spurs growing over the rotator cuff tendons. This is part of the normal aging process, although it is less common than damage to the bursa. Such bone spurs can rub against the bursa and irritate the rotator cuff tendons. The pain occurs when the arm is raised to shoulder height, because that is the position where the rotator cuff is strained the most.
The first step in treating impingement syndrome is to try to understand its cause. Repetitive physical activities can injure the rotator cuff, and so can recurring shoulder positions in which the arm is held overhead or to the side. These activities and positions must be avoided so that the tendon can rest and heal. The rotator cuff can also wear out when it is placed under abnormal stress. This occurs when the patient neglects to use the other muscles in his shoulder when lifting heavy things. Learning the proper technique for lifting objects, with the correct posture of the back and shoulder blades, will take stress off of the injured rotator cuff tendon and allow it to heal. Once the tendon is no longer irritated and inflamed, the muscles attached to the rotator cuff tendon can be exercised. This is an important step.
A common misperception of physical therapy is that it will not benefit patients who already participate in demanding sports or heavy-duty jobs. “I already lift 50 lbs all day at the construction site. Physical therapy isn’t going to make me stronger than my job already does.” This type of perspective is like that of a pitcher who thinks he can make it to the major leagues just by pitching as many innings as he can. The shoulder depends on a lot of other muscles in the body, including those in the hips, abdomen, and back for core strength. If those muscles are not conditioned, then the shoulder muscles have to work twice as hard to lift the same amount of weight. The shoulder blade is the platform for the rotator cuff muscles. If the should blade is not held in the correct position, then the rotator cuff muscles do not have the leverage needed to move the arm, and the body compensates by using the rotator cuff muscles twice as much. This is easy to do occasionally, but if you have to do it all day on a construction site (or every pitch for 9 innings), your body loses the ability to compensate, and eventually the tendons are injured. So physical therapy is beneficial because it strengthens the muscles that we often neglect during our normal activities and therapy teaches us how to use every muscle properly.
Another treatment option for impingement syndrome is steroid injections into the inflamed rotator cuff bursa. These injections are much less painful than those given in other areas of the body, like the foot or hand. Many patients ask, “Isn’t a steroid injection like putting a Band-AidTM on the problem, rather than fixing it?” The answer is yes, but in this case, a Band-AidTM is exactly what is needed. The steroid temporarily covers up the pain, allowing the patient to fix the problem with physical therapy. Proper sleep is also important when treating an injured rotator cuff, so if steroid injections help a patient sleep, it will be beneficial. Steroids have side effects, which include tendon degeneration, but this usually occurs after multiple injections. One or two injections rarely cause tendon tears in the shoulder.
If rest, activity modification, and physical therapy do not cure the pain from impingement syndrome, then surgery may be needed. The surgery can be performed with an arthroscope, an instrument with a tiny camera on the end that can be inserted through small incisions around the shoulder. This type of surgery makes the recovery relatively easy. Your surgeon will look inside the shoulder joint to make sure all the other structures are normal, then remove the injured rotator cuff bursa and any bone spurs that may be irritating the rotator cuff. The success of the surgery depends on the healing of the rotator cuff, which will take up to 6 months. The rehabilitation process includes a few weeks of rest immediately after the surgery, as well as physical therapy once the pain from the surgery subsides. Those patients who experience temporary pain relief from an injection prior to surgery often have more pain relief after surgery. The surgery will most likely eliminate any constant, aching pain and night pain, but patients may still have brief pain associated with overhead activity.