Subacromial Impingement Syndrome

What is Subacromial Impingement Syndrome (SAIS)?

SAIS is the inflammation and irritation of your rotator cuff tendons. This occurs when the tendons rub against the outer end of the shoulder blade (the acromion) while passing through the subacromial space during shoulder movement. 

The rotator cuff is a group of four muscles that come together as tendons to form a "cuff". These muscles originate from the scapula (shoulder blade) and hold your upper arm bone (humerus) in place in your shoulder. The rotator cuff stabilizes the shoulder and allows for its extensive range of motion. 

Shoulder blades are the two triangular bones on the back of your shoulder that provide attachments for the bone and muscles of the upper arm (humerus).

Subacromial space is the space between the acromion and the top surface of the humeral head. The space houses several soft tissues such as the rotator cuff, bicep tendon and bursa.

Causes of SAIS

Causes of SAIS can be intrinsic or extrinsic in nature:

• Overuse of the shoulder 
• Bone spurs on the shoulder bones
• Injury to the shoulder
• Weak muscles of the rotator cuff
• Anatomical factors: Inherited or acquired differences in acromion shape or gradient  

Who is at Risk of SAIS?

You are at higher risk of SAIS if you are under 25 years and a:

• Swimmer requiring overuse of the shoulder 
• Sportsperson (baseball or tennis player)
• Manual professional (Eg. construction worker)
• Heavy objects lifter or painter

You are also more likely to experience SAIS if you:

• Are older and/or have shoulder injuries such as a dislocation 
• Have an abnormal or unusual shaped shoulder acromion

Symptoms

Symptoms of SAIS can vary from person to person. However, the typical sign is sudden but progressive pain in the shoulder when you lift your arm overhead or backward. 

Other symptoms include:

• Minor but constant pain in the arm that gets worse when you lift your arm 
• Pain in the top or at the outer side of the shoulder that runs to the side of the arm
• Pain that gets worse at night and affects your sleep 
• Persistent feeling of weakness in the arm or shoulder 
• Reduced range of motion within the shoulder

Complications of SAIS

• Rotator cuff degeneration and tear
• Adhesive capsulitis (frozen shoulder)
• Cuff tear arthropathy (severe shoulder arthritis)

Diagnosis

Shoulder pain that is constantly affecting your normal activities and not going away even after a few weeks is an indication that the condition needs a thorough diagnosis. 

The diagnosis begins with a physical examination of the affected shoulder, which involves moving the shoulder in certain ways. 

Subsequently, you will be asked some questions about:

• Any previous injuries or operations to your shoulder
• Your nature of work, sports activities and exercise habits

An X-ray may also be ordered to check for bone spurs or to rule out other conditions such as arthritis.

In cases where the condition looks serious, the following tests may be necessary:

• MRI scan or imaging 
• Neer impingement test
• Hawkins test

Treatment

The treatment of SAIS depends on the cause and severity of the condition. In most cases, certain home remedies are enough to treat SAIS. 

Some of the common home treatments your doctor will recommend include:

• Placing ice packs on the affected shoulder
• Avoiding strenuous movements of the shoulder
• Resting the shoulder till the pain goes away

If there is no improvement in the condition within a few months, the doctor may use:

• Physical therapy involving gentle exercises to rebuild shoulder and arm muscle 
• Medications including nonsteroidal anti-inflammatory drugs 
• Steroid injections (if the condition does not respond with the above two treatments) 

In the event of all the treatments failing to improve the condition, a minimally invasive arthroscopy or an open surgery (in severe cases) can be considered.

Prognosis

Recovery from SAIS may take 3 to 12 months depending on the severity of the condition.