What is shoulder impingement syndrome?
Impingement syndrome is pain and inflammation that occurs when the rotator cuff tendons rub against the roof of the shoulder, the acromion, when you lift the arm.
What part of the shoulder is affected?
The shoulder is made up of three bones: the scapula (shoulder blade), the humerus (upper arm bone), and the clavicle (collarbone). The rotator cuff surrounds the shoulder joint and is formed by the tendons of four muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis. Tendons attach muscles to bones. Muscles move the bones by pulling on the tendons. The rotator cuff helps raise and rotate the arm. As the arm is raised, the rotator cuff also keeps the humerus tightly in the socket of the scapula, the glenoid. The upper part of the scapula that makes up the roof of the shoulder is called the acromion.
A bursa is located between the acromion and the rotator cuff tendons. A bursa is a lubricated sac of tissue that cuts down on the friction between two moving parts. Bursae are located all over the body where tissues must rub against each other. In this case, the bursa protects the acromion and the rotator cuff from grinding against each other.
What causes impingement syndrome?
Usually, there is enough room between the acromion and the rotator cuff so that the tendons slide easily underneath the acromion as the arm is raised. But each time you raise your arm, there is a bit of rubbing or pinching on the tendons and the bursa. This rubbing or pinching action is called impingement. Impingement occurs to some degree in everyone's shoulder. Day-to-day activities that involve using the arm above shoulder level cause some impingement. Usually it doesn't lead to any prolonged pain. But continuously working with the arms raised overhead, repeated throwing activities, or other repetitive actions of the shoulder can cause impingement to become a problem. Impingement becomes a problem when it causes irritation or damage to the rotator cuff tendons. Raising the arm tends to force the humerus against the edge of the acromion. With overuse, this can cause irritation and swelling of the bursa. If any other condition decreases the amount of space between the acromion and the rotator cuff tendons, the impingement may get worse. For example, bone spurs can reduce the space available for the bursa and tendons to move under the acromion.
What are the symptoms?
In the early stages impingement syndrome causes a generalized shoulder and pain when raising the arm out to the side or in front of the body. Most patients complain that the pain makes it difficult for them to sleep, especially when they roll onto the affected shoulder. As the condition worsens, the discomfort increases. Sometimes a catching sensation is felt when you lower your arm. Weakness and inability to raise the arm may indicate that the rotator cuff tendons are actually torn.
How is it diagnosed?
The diagnosis of bursitis or tendonitis caused by impingement is usually made on the basis of your medical history and physical examination. Your doctor will ask you detailed questions about your activities and your job, because impingement is frequently related to repeated overhead activities. Your doctor may order X-rays to look for an abnormal acromion or bone spurs around the AC joint. An ultrasound or magnetic resonance imaging (MRI) scan may be performed if your doctor suspects a tear of the rotator cuff tendons.
In some cases, it is unclear whether the pain is coming from the shoulder or a pinched nerve in the neck. An injection of a local anesthetic (such as lidocaine) into the bursa can confirm that the pain is in fact coming from the shoulder. If the pain goes away immediately after the injection, then the bursa is the most likely source of the pain.
What is the treatment?
Many cases of impingement can be treated successfully without needing surgery. You may be prescribed anti-inflammatory medications such as aspirin or ibuprofen. Resting the sore joint and putting ice on it can also ease pain and inflammation. If the pain doesn't go away, an injection of cortisone into the joint may help. Cortisone is a strong medication that decreases inflammation and reduces pain. Your doctor may also refer you for physiotherapy. Your therapist will use various treatments to calm inflammation, including heat and ice. Therapists use hands-on treatments and stretching to help restore full shoulder range of motion. Improving strength and coordination in the rotator cuff and shoulder blade muscles lets the humerus move in the socket without pinching the tendons or bursa under the acromion.
If you are still having problems after trying nonsurgical treatments, your doctor may recommend surgery. Subacromial decompression is a procedure that increases the space between the acromion and the rotator cuff tendons, relieving the pressure off the tissues under the acromion. The surgeon must first remove any bone spurs under the acromion that are rubbing on the rotator cuff tendons and the bursa. Usually the surgeon also removes a small part of the acromion to give the tendons even more space. Surgically cutting and shaping the acromion is called acromioplasty. Today, it is more common to do this procedure using the arthroscope. An arthroscope is a slender tool with a tiny TV camera on the end. It lets the surgeon work in the joint through a very small incision. This may result in less damage to the normal tissues surrounding the joint, leading to faster healing and recovery.
Impingement may not be the only problem in an aging or overused shoulder. It is very common to also see degeneration from arthritis in the AC joint. If there is reason to believe that the AC joint is arthritic, the end of the clavicle may be removed during impingement surgery. This leaves a space between the acromion (the piece of the scapula that meets your shoulder) and the cut end of the clavicle, where the joint used to be. As your body heals, the joint is replaced by scar tissue.