Shoulder Impingement Syndrome

Shoulder impingement syndrome develops when the shoulder tendons get intermittently trapped and squashed underneath one of the shoulder bones, the acromion. This 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.

What Is Impingement?

omplex.  Shoulder impingement syndrome develops when there is a narrowing of the subacromial space

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.

Causes of Shoulder Impingement Syndrome

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:

1)  Primary Impingement

X-ray showing subacromial calcium deposits, which decrease the subacromial space, increasing the risk of shoulder impingement syndrome

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:

a)  Degeneration: 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 aging process

b)  Congenital Abnormalities: 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

2)  Secondary Impingement

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:

Supraspinatus tendonitis is a common cause of shoulder impingement syndrome.  The tendon slides through the subacromial space, making it prone to excessive friction which results in inflammation

a)  Tendonitis: Repetitive friction on the rotator cuff 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 tendon most commonly affected here is supraspinatus.  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.

b)  Bursitis: 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.

Shoulder Impingement Symptoms

Symptoms start off fairly mild but get gradually worse as the condition progresses.  Common symptoms of rotator cuff impingement include:

Shoulder impingement syndrome often presents with a painful arc of movement

1)  Pain: across the shoulder and sometimes extending down to the elbow.  People often describe it like a toothache or a sharp pain.  To start with, it will only be painful during activities but as the condition progresses, you may develop pain even when resting.  Pain tends to be worst when the arm is behind the back, e.g. fastening a bra, or above the head e.g. reaching into high cupboards or hanging up washing

2)  Painful Arc:  Movements below shoulder height tend not to be painful, but as you raise the arm up above the shoulder, pain develops.  Depending on the cause of the impingement, the pain may actually decrease again once the arm is up straight due to the change in position of the bones in the shoulder.  In these cases, the most painful part of the movement tends to be from around 70 degrees abduction up to 120degrees, known as a painful arc.  This is a classic feature of supraspinatus tendonitis

3)  Weakness: the shoulder muscles may start to weaken.  This tends to be most noticeable with overhead activities

4)  Difficulty Sleeping: It may become painful to lie on the affected shoulder

5)  Problems with Lifting: Lifting heavy objects, especially overhead may become difficult and painful

6)  Loss of Movement: shoulder motion may become restricted

Diagnosing Rotator Cuff Impingement

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.  They will also 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.

Treatment Options

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.

A) Non-Surgical Treatment

Non-surgical treatment aims to reduce pain and inflammation, and restore full motion and strength.  Treatment may consist of:

1) Rest: avoiding activities that aggravate your symptoms for a period such as any movements placing your arm above your head or behind your back.  This is necessary to allow the inflammation to settle

2) Medication: anti-inflammatory medication such as ibuprofen helps to reduce swelling and pain

Physical Therapy for rotator cuff impingement

3) Physical Therapy: a physical therapist will work on a rehab programme with you.  They will first assess your shoulder to identify any areas of weakness, tightness, stiffness and instability that have caused the shoulder impingement syndrome.  You will be given a combination or strengthening, stretching and stability exercises to do over the course of a few weeks/months.  Visit the rotator cuff exercises section for loads of great exercises that can help

4) Cold Therapy: using an ice-pack regularly can help reduce pain and inflammation.  Ice packs should be wrapped in a towel and placed over the shoulder for ten minutes, three to four times daily.  For more information see the ice therapy section on our sister site

5) Injections: corticosteroid injections can help to reduce inflammation in the tendons or bursa.  A mixture of steroid and local anaesthetic is injected into the area.  Care needs to be taken initially as the injection temporarily weakens the tendon increasing the risk of rupture.  Injections should not be used as a stand-alone treatment, they should be followed by a course of physical therapy to ensure the problem doesn’t return.  You can find out more about steroid injections on our sister site

B) Surgery

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.  Most commonly 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.

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