Subacromial Impingement

The rotator cuff is the term used to describe the 4 muscles surrounding the shoulder that help raise and lower the arm.  The muscles lie under the roof of the shoulder, known as the acromion and need to glide freely in this space.  The subacromial bursa, a fluid filled sac, is also found in this space to assist the smooth movement  of the rotator cuff.

Subacromial impingement occurs when the rotator cuff muscles are unable to glide easily under the acromion when trying to raise or lower the arm causing pain and loss of function.  

What are the causes?

Muscle problems: The shoulder relies on the rotator cuff muscles working well to keep the humeral head (ball) sitting on the glenoid (socket) throughout all shoulder movements.  If the rotator cuff is not working well or has been injured the humeral head can move upwards and cause the tendons of the rotator cuff to pinch under the  acromion.  Physiotherapy can significantly help if this is the cause of your symptoms.  

Inflammation: Swelling and inflammation can occur in the subacromial bursa causing this to become thickened.  A cortisone injection can help in reducing this inflammation.

Bony/ligament problems: A bony spur can form under the acromion narrowing the space that the rotator cuff glides into.  A ligament at the front of the shoulder (coracoacromial ligament) can shorten in response to inflammation also causing a narrowed space.

What are the symptoms?

Subacromial impingement commonly causes pain around the outer aspect of your shoulder particularly when lifting your arm above shoulder height.  Many patients will also have difficulty lying on their shoulder at night or have pain from the shoulder, which will wake them up.  

How is it diagnosed?

Your surgeon can usually make the diagnosis by asking about the symptoms you have and examining your shoulder.  

X-rays are usually normal with subacromial impingement but can help rule out other possible causes such as arthritis.

An ultrasound or MRI is useful to assess whether the rotator cuff muscles and their corresponding tendons have been damaged or torn.  

How is it treated?

Most patients with subacromial impingement will improve with painkillers and physiotherapy.  Physiotherapy helps improve posture and strengthen the rotator cuff muscles.

An injection into the subacromial space can help if pain is preventing you from doing your physiotherapy exercises.  It can also help reduce the inflammation.

Keyhole surgery is reserved for patients who have not improved with physiotherapy.  The aim of surgery is to increase the space between the rotator cuff muscles and the acromion.  The name of the operation performed is Arthroscopic Subacromial Decompression.