Shoulder impingement is a very common cause of shoulder pain, where a tendon (band of tissue) inside your shoulder rubs or catches on nearby tissue and bone as you lift your arm.
It affects the rotator cuff tendon, which is the rubbery tissue that connects the muscles around your shoulder joint to the top of your arm.
Shoulder Impingement Syndrome
Shoulder impingement syndrome, which is sometimes called swimmer’s shoulder or thrower’s shoulder, is caused by the tendons of the rotator cuff muscles becoming impinged as they pass through a narrow bony space called the subacromial space. The subacromial space is so called because it is under the arch of the acromion. With repetitive pinching, the tendons become irritated and inflamed.
This can lead to thickening of the tendon which may cause further problems because there is very little free space, so as the tendons become larger, they are impinged further by the structures of the shoulder joint and the muscles themselves.
Impingement Syndrome in itself is not a diagnosis, it is a clinical sign. There are at least nine different diagnoses which can cause impingement syndrome which include bone spurs, rotator cuff injury, labral injury, shoulder instability, biceps tendinopathy and scapula dysfunction. If left untreated, shoulder impingement can develop into a rotator cuff tear.
The supraspinatus muscle is probably the most commonly involved in impingement syndrome of the shoulder.
Shoulder impingement is classified as internal or external depending on the causes with external impingement being divided into primary which is caused by a bony spur or some direct cause and secondary impingement which occurs as the result of poor stabilisation of the shoulder joint.
An impinging shoulder will often improve in a few weeks or months, especially with the right type of shoulder exercises, but occasionally it can be an on-going problem and a few people may need surgery.
Symptoms of shoulder impingement
Shoulder impingement can start suddenly or come on gradually.
- pain in the top and outer side of your shoulder
- pain that’s worse when you lift your arm, especially when you lift it above your head
- pain or aching at night, which can affect your sleep
- weakness in your arm
Your shoulder won’t usually be stiff. If it is, you might have a frozen shoulder instead.
Your physiotherapist may be able to advise you about simple shoulder exercises you can do. Physiotherapists can also diagnose shoulder impingement and suggest exercises to help improve shoulder posture and further strengthen your muscles to improve your pain and range of movement.
You may need to do these exercises with a physiotherapist at first, but after a while you’ll usually be able to continue doing them at home.
Steroid injections into your shoulder can help relieve pain if rest and exercises on their own don’t help.
But it’s still important to do your shoulder exercises, as injections usually only have an effect for a few weeks and your pain may come back if you stop the exercises.
While the injection can be repeated if needed, having more than two isn’t usually recommended because it might damage the tendon in your shoulder in the long term.
An operation called a subacromial decompression may be an option if other treatments haven’t helped. This involves widening the space around the rotator cuff tendon, so that it doesn’t rub or catch on anything nearby.
The operation is usually done using small surgical instruments passed through small cuts in your shoulder – this is a type of keyhole surgery known as arthroscopy. It’s usually done under general anaesthetic (where you’re asleep).
Most people can go home the same day or the day after surgery and are able to use their shoulder normally again after a few weeks.
Causes of shoulder impingement
When you lift your arm, the rotator cuff tendon passes through a narrow space at the top of your shoulder, known as the subacromial space.
Shoulder impingement occurs when the tendon rubs or catches on the bone at the top of this space, called the acromion.
This can happen if:
- the tendon becomes swollen, thickened or torn – this can be due to an injury, overuse of the shoulder (for example, from sports such as swimming or tennis) or “wear and tear” with age
- the fluid-filled sac (bursa) found between the tendon and acromion becomes irritated and inflamed (bursitis) – this can also be caused by an injury or overuse of the shoulder
- the acromion is curved or hooked, rather than flat – this tends to be something you’re born with
- there are bony growths (spurs) on the acromion – these can develop as you get older