Shoulder impingement syndrome is a common condition and is responsible for a significant proportion of shoulder related doctor visits.
 Impingement can be a primary condition but is also a common secondary complication of other injuries.

Impingement causes pain by the compression of soft tissue structures in the shoulder. Because we continually use both our arms we find it difficult to rest following injury or the initial onset of the pain.
This makes it a difficult condition to treat and many cases become chronic.
Early diagnosis and intervention make Shoulder Impingement Syndrome much easier to treat and non-invasive interventions more successful.

 Impingement is caused by the compression of soft tissues under a bony arch known as the Acromion. The Acromion is located at the point of the shoulder and is a projection coming off the scapula or shoulder blade.
The soft tissues in question pass between the acromion and the head of the humerus - better known to most as the ball part of the shoulder's ball and socket joint.

The gap between these two bones is called the sub-acromial space. The shoulder's rotator cuff muscles and a bursa (a kind of fluid filled sac that helps tendons glide smoothly) occupy this space.
Impingement occurs when these structures become aggravated, often through trauma but sometimes with no identifiable cause. Once annoyed they become inflamed, swelling in an already tight space.
This makes them more likely to be compressed again with any arm movement and a vicious cycle is formed. As you continue to use your arm you continually feed into the inflammation cycle and the condition perpetuates.

 Impingment usually causes pain to a large area of the shoulder rather than a specific point. People typically complain of a generalized tooth ache like pain over the side and front of their shoulder. As the pain gets worse it can travel further down the arm towards the elbow.

With the pain of impingement, it is often difficult to find a position of comfort. Even supporting the arm across the body like it's in a sling often doesn't help.

One of the classic signs of shoulder impingement is called the "Painful Arc". This is assessed by raising the arm up straight out the side. The test is positive when the movement starts as pain free when moving off the thigh, becomes painful through the middle section before again being pain free when the arm is in the upper range and straight up. In severe cases the pain is too great to get past the painful section of the arc.

Because Shoulder Impingement Syndrome can often start as a very minor complaint, it is normal for people to put up with it for a considerable amount of time before consulting their doctor. By this time, it is limiting most activities involving that arm and become more difficult to treat.

Due to normal anatomical difference in our body shape, some people are more susceptible to impingement than others. This can lead to impingement being present in both arms at some stage of their life.

The first line of treatment for shoulder impingement should always be physical therapy. It is non-invasive and has a very low risk of complications. A large number of cases can be resolved with the use of physical therapy alone, particularly when treatment starts promptly.

For cases that don't respond to physical therapy, the next step is usually an injection into the sub-acromial space. A doctor injects a corticosteroid (often combined with a local anesthetic) into the offending area. This acts as a strong local anti-inflammatory, reducing the swelling in the space that is leading to continuing aggravation. For lucky people, this will resolve the problem completely. For most, it will reduce their pain and provide a window of opportunity for them to make progress with their physical therapy.

When both injections and physical therapy fail to resolve the problem, the final step is key-hole surgery. A surgeon places an arthroscope into the joint to assess the problem and shaves the bottom of the acromion off. This creates more space and prevents the soft tissues from continually being aggravated. This type of surgery is usually done on a Day Case basis and is known as an Acromioplasty.