The next two weeks I want to write about shoulder pain. Most people experience shoulder pain at some point in their lifetimes. Doctors typically see it in athletes, people who overuse their shoulders as well as others who may have fallen on their shoulder or outstretched arm.

To understand shoulder pain, it's important to know the basic anatomy of the shoulder joint itself. The joint is one of the most complex in the body. Most joints permit only a fairly limited range of motion. The anatomy of the shoulder joint, in contrast, allows for a vast range of movements. It has to be relatively unstable compared to other joints in order to be so flexible.

The easiest way to describe the shoulder joint is to picture a basketball sitting on a dinner plate. The basketball represents the head of the humerus, the bone in the upper arm. The plate represents the glenoid fossa, the part of the shoulder blade (scapula) that articulates with the head of the humerus. If you picture the ball on the plate, you can understand how unstable this joint is - the ball can roll off the plate or slide around.

There are anatomic structures that help limit this inherent instability. One is the glenoid labrum, a rim of cartilage that runs around the edge of the glenoid fossa. It serves to shape the fossa into more of a shallow bowl rather than a flat plate. The other structure is the rotator cuff, a combination of four tendons that attach around the head of the humerus to hold it in place. These four tendons are connected to four muscles that rotate the humerus and help initiate arm movements. There are also fluid-filled bursa sacs around the joint that help cushion the movements of the tendons.

Now that you're an expert in anatomy, let's examine what can go wrong. I don't want to cover fractures since they are usually pretty obvious. I don't have enough space in this column to cover all shoulder injuries so I'll need to finish up next week.

I'd like to start with rotator cuff injuries. These are injuries to the tendons and/or muscles that form the rotator cuff. These structures can be inflamed, stretched, partially torn, or completely torn. The injury may involve one or more tendons.

Rotator cuff injuries usually happen when someone falls on an outstretched arm. This can result in too much stress being placed on the cuff tendons or their muscles. Cuff injuries can also occur when someone falls on an elbow and jams the head of the humerus causing it to slip out of its normal position in the glenoid fossa. Finally, overusing one's arm, such as when throwing forcefully, can injure then tendons.

Symptoms of rotator cuff injuries typically depend on the severity of the trauma and can be quite subtle. The shoulder may simply be achy. Some may notice severe pain when moving the shoulder in a particular direction, especially raising it in a forward or sideways direction. Others may note severe weakness. Since the tendons are responsible for initiating arm movements, patients with torn tendons may note they have trouble initiating movements, especially to the front or side.

Treatment of rotator cuff injuries is dependent on the type of injury as well as the age and activity level of the patient. The goal is to stabilize the joint as much as possible by rehabilitating the shoulder muscles to return the patient to maximum function. Young patients and athletes typically receive aggressive treatment including physical therapy and, if they have a torn tendon, often surgery. Elderly or more inactive patients often do fine with physical therapy alone to strengthen the cuff muscles in the shoulder.

Next week I'll cover shoulder dislocations, impingement, and bursitis.

Dr. John Roberts is a family physician. He is also one of the owners of The Paper of Montgomery County. Send him your question today by e-mail at