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 your back to throwing a Frisbee to reaching overhead to put something on shelf.

The shoulder’s great mobility has its price, however. It may lead to increasing problems with instability or impingement of the 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. The pain may be temporary or it may continue and require medical diagnosis and treatment.

Shoulder Anatomy

Your shoulder is made up of three bones: your upper arm bone (humerus), your shoulder blade (scapula), and your collarbone (clavicle).

The head of your upper arm bone fits into a rounded socket in your shoulder blade. This socket is called the glenoid. A combination of muscles and tendons keeps your arm bone centered in your shoulder socket. These tissues are called the rotator cuff. They cover the head of your upper arm bone and attach it to your shoulder blade.

Causes of Shoulder Pain

Most shoulder problems fall into four main categories:

• Tendon inflammation (bursitis or tendinitis) or tendon tear

• Instability

• Arthritis

• Fracture (broken bone)

Other much less common causes of shoulder pain are tumors, infection, and nerve-related problems. Sometimes a pinched nerve in the neck can cause shoulder pain and weakness and this can mimic a shoulder problem.

Bursae

Bursae are small, fluid-filled sacs that are located in joints throughout the body, including the shoulder. They act as cushions between bones and the overlying soft tissues, and help reduce friction between the gliding muscles, tendons and the bone.

Sometimes, excessive use of the shoulder leads to inflammation and swelling of the bursa between the rotator cuff and part of the shoulder blade known as the acromion. The result is a condition known as subacromial bursitis.

Bursitis often occurs in association with rotator cuff tendinitis. The many tissues in the shoulder can become inflamed and painful. Many daily activities, such as combing your hair, getting dressed or reaching into the back seat of the car may become difficult.

Tendinitis

A tendon is a rope with many fine strands that connects muscle to bone. Most tendinitis is a result of inflammation in the tendon.

Generally, tendinitis is one of two types:

• Acute- Excessive ball throwing or other overhead activities during work or sport can lead to acute tendinitis.

• Chronic- Degenerative diseases like arthritis or repetitive wear and tear due to age, can lead to chronic tendinitis.

The most commonly affected tendons in the shoulder are the four rotator cuff tendons and one of the biceps tendons. The rotator cuff is made up of four small muscles and their tendons that cover the head of your upper arm bone and keep it in the shoulder socket. Your rotator cuff helps provide shoulder motion and stability.

Tendon Tears

Splitting and tearing of tendons may result from acute injury or degenerative changes in the tendons due to advancing age, long-term overuse and wear and tear, or a sudden injury. These tears may be partial or may completely separate the tendon from its attachment to bone. In most cases of complete tears, the tendon is pulled away from its attachment to the bone. Rotator cuff and biceps tendon injuries are among the most common of these injuries.

Not all rotator cuff tears are painful that is why a detailed evaluation by a shoulder specialist is important.

Impingement

Shoulder impingement occurs when the top of the shoulder blade (acromion) puts pressure on the underlying soft tissues when the arm is lifted away from the body. As the arm is lifted, the acromion rubs, or “impinges” on, the rotator cuff tendons and bursa. This can lead to bursitis and tendinitis, causing pain and limiting movement.

Instability

Shoulder instability occurs when the head of the upper arm bone is forced out of the shoulder socket. This can happen as a result of a sudden injury or from overuse.

Shoulder dislocations can be partial, with the ball of the upper arm coming just partially out of the socket. This is called a subluxation. A complete dislocation means the ball comes all the way out of the socket.

Once the ligaments, tendons, and muscles around the shoulder become loose or torn, dislocations can occur repeatedly. Recurring dislocations, which may be partial or complete, cause pain and unsteadiness when you raise your arm or move it away from your body. Repeated episodes of subluxations or dislocations lead to an increased risk of developing arthritis in the joint.

Arthritis

Shoulder pain can also result from arthritis. There are many types of arthritis. The most common type of arthritis in the shoulder is osteoarthritis, also known as “wear and tear” arthritis. Symptoms such as swelling, pain, and stiffness, typically begin during middle age. Osteoarthritis develops slowly and the pain can worsen over time.

Osteoarthritis, may be related to sports or work injuries or chronic wear and tear. Other types of arthritis can be related to rotator cuff tears, infection, or an inflammation of the joint lining.

Often people will avoid shoulder movements in an attempt to lessen arthritis pain. This sometimes leads to a tightening or stiffening of the soft tissue parts of the joint, resulting in a painful restriction of motion.

Fracture

Fractures are broken bones. Shoulder fractures commonly involve the clavicle (collarbone), humerus (upper arm bone), and scapula (shoulder blade).

Shoulder fractures in older patients are often the result of a fall. In younger patients, shoulder fractures are often caused by a motor vehicle accident or contact sports injury.

Fractures often cause severe pain, swelling, and bruising about the shoulder.