Written By: Chloe Wilson BSc (Hons) Physiotherapy
Shoulder impingement syndrome develops when the shoulder tendons get intermittently trapped and squashed underneath one of the shoulder bones, the acromion.
This impingement damages the soft tissues and can lead to pain, inflammation and reduced movement of the arm, particularly with activities when the arm is above the head.
Most commonly, shoulder impingement syndrome develops gradually over time through wear and tear on the shoulder, but it does sometimes develop following an injury. It affects the rotator cuff muscles, the four main muscles that control the movement and stability of the shoulder.
Here, we will look at the common causes and symptoms of rotator cuff impingement, how it is diagnosed and the best treatment options available to decrease pain and improve movement and strength.
To understand the causes of shoulder impingement syndrome, we need to know a little about the anatomy of the shoulder. The shoulder is made up of three bones, the arm bone (humerus), the shoulder blade (scapula) and the collar bone (clavicle).
Rotator cuff impingement develops when there is a problem at the acromion, the top front part of the scapula. The acromion forms a sort of bridge or roof over the top of the shoulder that the rotator cuff muscle tendons pass through.
As the arm moves up and down, the rotator cuff tendon slides backwards and forwards through this gap underneath, which is known as the subacromial space. Sitting between the subacromial space and the rotator cuff tendons is the subacromial bursa, a small fluid filled sac that protects the tendons and prevents friction against the bone.
The space underneath the acromion is fairly small, and the gap gets narrower as you lift your arm up because of how the bones and tendons move.
Shoulder impingement syndrome refers to a number of problems that can develop in this area, the common characteristic being that the subacromial space narrows more than usual leading to pinching or friction on the soft tissues.
Shoulder impingement syndrome commonly affects people who engage in activities requiring repetitive overhead arm movements or heavy lifting such as swimming, throwing, weightlifting and racket sports, or occupations such as building, decorating and electrical work. It is also often associated with aging.
The common causes of rotator cuff impingement fall into two categories, primary impingement from bony abnormalities, and secondary impingement from instability:
Primary impingement occurs when there are changes in the shape or angle of the acromion that reduce the size of the subacromial space. These can fall into two categories:
Wear and tear of the acromion can result in bone spurs developing. Rather than the acromion being smooth, small outgrowths of bone stick out and rub on the rotator cuff tendons, leading to shoulder impingement syndrome. This may happen through repetitive movements or as part of the normal aging process.
In some people, their acromion forms at a slightly different angle affecting the shape of the acromial arch which can reduce the space in the subacromial space. This also increases the friction on the rotator cuff tendons leading to shoulder impingement syndrome.
Secondary impingement develops due to dynamic instability of the shoulder. This is when there is a combination of weakness and/or tightness in the muscles of the shoulder complex affecting its position. Weakness in the muscles that stabilise the shoulder blade, such as serratus anterior, or tightness in muscles at the front of the shoulder, such as pectoralis minor, can alter the position of the acromion, reducing the subacromial space. This leads to repetitive friction on the soft tissues which in turn causes inflammation.
The two most common types of secondary impingement are:
Repetitive friction on the rotator cuff and biceps tendons leads to inflammation, known as tendonitis. This swelling further reduces the subacromial space and as pressure build up on the tendon, it reduces the blood flow causing further damage.
The tendons most commonly affected here are supraspinatus and long head of biceps as they runs directly through the subacromial space. Inflammation in these tendons is known as supraspinatus tendonitis aka painful arc syndrome and biceps tendonitis.
Tendonitis can occur from a one-off injury, repetitive movements or overuse. In some cases, calcium deposits can build up in the tendon. If left untreated, the tendon may even tear – see the rotator cuff tear section for more information.
Excessive friction on the subacromial bursa leads to inflammation, known as subacromial bursitis. Again, this reduces the subacromial space leading to shoulder impingement syndrome. You can find out more in the shoulder bursitis section.
Symptoms start off fairly mild but get gradually worse as the condition progresses. Common symptoms of rotator cuff impingement include:
Your doctor can usually diagnosis shoulder impingement syndrome from your history and for examining you. They will look for the presence of a painful arc, or increased pain with movements overhead and will test the strength of your shoulder muscles.
They may also carry out special tests to confirm shoulder impingement syndrome such as the Empty Can test or Hawkins Kennedy test.
In some cases, your doctor may send you for further tests. X-rays may be done to check for the presence of bone spurs and to rule out other conditions. An ultrasound scan may be done to assess the soft tissues for any damage such as bursitis, rotator cuff tears or calcium deposits in the tendon.
Successful treatment of shoulder impingement syndrome relies on correctly identifying the cause of the impingement e.g. you would treat impingement from bone spurs differently from impingement due to muscle imbalance. Without this, treatment will be ineffective and even if the pain does settle, it is likely to return.
Most cases of shoulder impingement syndrome can be treated conservatively, but in some cases, particularly if the bone is affected, surgery may be required.
Non-surgical treatment aims to reduce pain and inflammation, and restore full motion and strength. Treatment for shoulder impingement syndrome may consist of:
In some cases of shoulder impingement syndrome, such as if there are bony spurs or if other treatment has failed, subacromial decompression surgery will be advised. Surgery aims to enlarge the subacromial space to make more space for the rotator cuff tendons.
Surgery for shoulder impingement syndrome is usually carried out arthroscopically, aka keyhole surgery. Two or three small holes are made around the shoulder. A camera is inserted to allow the surgeon to see the structures via a video screen and small surgical instruments are inserted into the joint.
In most cases the surgeon will remove part of the acromion bone and sometimes part of the subacromial bursa. This is known as a subacromial decompression or acromioplasty. If he finds any other issues such as arthritis or a rotator cuff tear, he will address those as well.
After surgery, you may be given a sling to wear initially. You will work with a physical therapist on a rehab programme to regain full strength, motion and stability in the shoulder - visit the rotator cuff exercises section to find out more. It usually takes around 3-5 months to recover from surgery.
Find out what happens during surgery and all about the rehab and recovery process in the subacromial decompression section.
There are also a number of other possible causes of shoulder pain. If shoulder impingement syndrome is not sounding like your problem, visit the shoulder injuries guide.
Page Last Updated: 24/11/2020
Next Review Due: 24/11/2020