The shoulder is the most free-moving joint in the body. It is composed of three bones: the humerus (upper arm), the scapula (shoulder blade), and the clavicle (collar bone). The humerus and scapula form a ball and socket joint, but the socket is very shallow in the shoulder. There is a bony prominence at the top of the shoulder blade called the acromion.
The rotator cuff is made up of four muscles whose tendons come together as a “cuff” to attach on the head of the humerus. The muscles of the rotator cuff are attached to the shoulder blade, and their tendons are attached to the head of the humerus. This serves as an attachment for the upper arm to the shoulder blade and gives stability to the joint and helps keep the ball centered in the socket during motion. They also help coordinate the complex motions of the shoulder with the larger, stronger muscles such as the deltoid and the pectoralis muscles.
There is a fluid sac (bursa) that lies between the rotator cuff and the bone on top of the shoulder (acromion). This provides lubrication and helps the shoulder move freely.
Description of Shoulder Impingement
When you raise your arm above your shoulder, the rotator cuff muscles and tendons pass through a narrow space in order to slide under the acromion. Usually there is enough space for easy movement, but sometimes there may be too much narrowing of the space, causing the acromion to rub against the tendon and the bursa, causing irritation and pain.
Causes of Shoulder Impingement
Activities that can lead to shoulder impingement include:
- Playing overhead sports, such as volleyball and tennis
- Throwing overuse, as in baseball
- Repetitive lifting
- Overhead jobs such as painting or construction
Symptoms of Shoulder Impingement
Shoulder impingement is often characterized by mild early symptoms that worsen over time. Some of the symptoms are:
- Pain radiating from the front of the shoulder to the side of the arm
- Pain when raising the arm above the shoulder
- Pain when moving the arm to the back, such as when reaching for a back pocket
- Pain that worsens during overhead motions or throwing
- Loss of range-of-motion
The physician will take your history and discuss your symptoms before performing a physical exam. The exam will include checking for tenderness, measuring range of motion, and testing arm strength. An x-ray will generally be ordered to help look for bone spurs or acromion abnormalities that may be causing the impingement. If the doctor suspects the rotator cuff may be torn, an MRI may also be ordered.
Most shoulder impingements are treated non-surgically. Rest and avoidance of overhead activities may be suggested for a period of time, followed by physical therapy. Typically physical therapy will focus first on stretching exercises to improve range of motion, and then follow with strengthening. Ice and non-steroidal anti-inflammatory medications may also be recommended.
If symptoms persist and physical therapy does not relieve the pain, a cortisone injection into the bursa may be recommended.
If non-surgical treatments have been exhausted and you still experience pain, surgery may be an option. A procedure called a subacromial decompression is standard treatment, in which the front edge of the acromion along with any bone spurs and a portion of the bursa will be removed arthroscopically.
The risks of arthroscopic surgery for impingement are fairly low. Infection is always a risk with any surgery, and there is a chance that the decompression will not alleviate all of your shoulder pain. Post-operative shoulder stiffness is always a concern with shoulder surgery, but this complication is less likely after decompression than with most other shoulder procedures.
After surgery, rehabilitation exercises will begin as soon as you can comfortably move the arm. Exercises will focus both on regaining full range of motion and strengthening the arm. Full activity, including most sporting activity, can be resumed by 6-8 weeks at the latest.
- What causes the narrowing in the shoulder that leads to shoulder impingement?
The narrowing can be a result of a person’s anatomy – some people are born with an acromion that is shaped differently and has a downslope or a hook on the front. These people are more prone to impingement symptoms. Sometimes, the impingement is caused from an abnormality in the way that the shoulder moves, as in an incorrect or abnormal throwing motion, or in cases of muscle weakness around the shoulder and shoulder blade.
- What can happen if I don’t do anything about my shoulder impingement?
Obviously the symptoms can persist or worsen over time if impingement goes untreated. Also, long-standing impingement can lead to wear and partial or full thickness tearing of the rotator cuff tendons.
- Can impingement get better on its own?
The symptoms of impingement can improve with rest and changes in activity. The underlying anatomic problems that cause the impingement will still be present and the symptoms may always recur.
If you have more questions, please call my office at 502-394-6341.