Shoulder impingement describes pain caused by friction from two bony surfaces within the shoulder joint. The shoulder is a ball and socket joint made up of the humerus (ball) and the acetabulum (socket). At the side of the shoulder there is a bony arch called the acromium, this is part of the shoulder blade and forms a joint to the front with the collar bone (clavicle) called the acromioclavicular joint. In between the side of the humeral head and the acromium is a gap called the sub acromial space. Within this space lies soft tissue that helps protect and move the joint.
This includes one of the rotator cuff muscles, Supraspinatus, which is responsible for maintaining shoulder joint stability, and the sub acromial bursa. This fluid filled sac (bursa) helps prevent friction occurring between the humeral head and the acromium. In a normal shoulder there is enough space for the arm to lift and allow for movements of the soft tissue within the sub acromial space without friction or pain.
The acromioclavicular joint between the acromium and the collar bone can also cause irritation often after a traumatic injury such as falling onto the side of the arm, or be due to repetitive movements of the shoulder.
Sub acromial impingement is more common than acromioclavicular impingement and is often caused by age. As we get older the supraspinatus tendon can start to deteriorate causing fraying. This can be caused by overuse or natural “wear and tear”. Other causes include inflammation of the bursa (bursitis), calcification of the shoulder joint or bony spurs appearing at the ends of the bone due to osteoarthritis.
Signs and symptoms
Often movements with the elbow by your side such as using a keyboard are painless. However when lifting the arm above shoulder height, it is common to feel pain at the front and to the side of the shoulder. These movements include brushing your hair, putting on a shirt, etc. The pain can be felt down the arm into the bicep region. Sleeping at night can be uncomfortable, especially when lying on the painful side as this compresses the humeral head into the subacromial space. If this condition worsens then the shoulder can become weakened too.
How physiotherapy can help
It is important that your therapist is able to diagnose the correct cause of the impingement. This may require imaging tests such as X-ray or MRI to determine the cause. A good Physiotherapist will take a comprehensive approach to your treatment. This may include postural advice, muscle strength and stability, joint mobilisation, soft tissue massage, electrotherapy or acupuncture.
Should your symptoms persist there are surgical options to consider, these include a keyhole procedure called a decompression in which the sub acromial space is increased in size by removing some of the extra bone that has formed.