What is Impingement?

Impingement is a common condition that causes a painful shoulder. The shoulder joint is a ball and socket joint at the top end of the arm. Above this is the collarbone that forms a joint with a flat bone known as the acromion (part of the shoulder blade). This joint is the acromioclavicular joint (AC joint). The space below the acromion and the AC joint is known as the subacromial space. It is normally occupied by a group of four tendons (Rotator cuff) that are responsible for most movements of the shoulder joint. Above the tendons is a small sac of fluid called a bursa that decreases friction.

 

3D Image Showing Impingement

In a normal shoulder there is adequate room in the subacromial space so that lifting the arm upwards above shoulder level or backwards causes no problem. Sometimes the space between these two bony structures decreases e.g. if the bony arch curves as one grows old, if there are arthritic changes with spur formation in the AC joint or if spurs develop at the front end of the acromion. Now if the arm is lifted away from the body upwards at some point the rotator cuff becomes pinched between the shoulder and the acromion causing pain. This is known as impingement.

3D Animation Showing Impingement

 

What Causes Impingement?

 

Impingement is most common in middle-aged people. It can occur spontaneously with no apparent cause or due to the result of minor injury. Often you may not recall the injury that occurred. This could be as innocuous as pulling some weeds out, reaching out behind in the car to pick up something or putting your shoulder into an awkward position. It can also be brought on by over using the shoulder with repetitive activities particularly above the head like painting for an extended length of time, carrying heavy weights. It is also found it young athletes particularly these who use their arms for overhead activities like swimming, tennis, squash etc.

 
What Are The Symptoms?

 

The first sign of impingement is pain over the front, outer aspect of the shoulder. It is common to notice that there are no symptoms when the arm is at the side of the body and with activities below shoulder level like using a keyboard. The pain usually occurs when the arm is moved above the shoulder level. Examples include brushing hair, reaching behind, reaching up to a shelf above eye level etc. Often this progresses and may cause further restriction in movement. Sleeping can be particularly uncomfortable and it is not uncommon to be woken up especially when trying to sleep on the affected side. As the condition progresses the strength in the arm can decrease.

The pain starts over the outer aspect of the shoulder but moves into the upper arm. It is not uncommon to have more pain in the upper arm muscles rather than the shoulder itself.

 

How is Impingement Diagnosed?

 

Impingement X-ray

 

A good history often points the surgeon in the right direction. There are a number of tests that can reproduce the symptoms of impingement to confirm the diagnosis. Often a test is performed in the clinic by injecting a local anaesthetic into the area between the acromion and the rotator cuff. Relief of pain and improved movement after this injection confirms the diagnosis. Occasionally it also necessary to perform MRI scans with a dye to ensure that there are no other problems in the shoulder and also to investigate whether the rotator cuff tendons are torn  

What is the Treatment?

3D Animation Showing Treatment For Impingement

 

In the early stages of impingement ice, rest and avoidance of overhead activities can be beneficial. Anti-inflammatory medication helps during the acute phase as can targeted exercises by the physiotherapist. The physiotherapist's aim is to build the rotator cuff muscles, which then push the ball and socket joint downwards creating, in effect, more space. It is always important to try these conservative measures before considering surgery.

Surgical Video Showing Impingement Treatment

 

 
If conservative measures fail then surgery is indicated. The aim of keyhole surgery is to remove the cause of impingement. A small half centimeter hole is made at the back of the shoulder to introduce a telescope into the subacromial space. Initially any scar tissue that has formed here because of the inflammation and part the bursa is removed. This is carried out using an instrument known as a vaporiser, which burns the tissue away. Following this a shaver is introduced to take away excess bone at the acromion and the acromio clavicular joint. This increases the space and removes the causes of impingement.