Subacromial Impingement Syndrome

Disclaimer: Please read the Disclaimer at the bottom of this page.
Copyright © Educom Pty Ltd: All material on this website (including the text, graphics, videos and downloadable files) is owned by or licensed to Educom Pty Ltd and is subject to copyright and other intellectual property rights under international conventions

Subacromial Impingement Syndrome

Subacromial Impingement Syndrome is commonly seen in individuals who perform repetitive overhead activities in their occupations or in sports (e.g., swimming, throwing, and tennis). The subacromial space contains the tendons of the long head of the biceps and the supraspinatus muscles as well as the subacromial bursa. Any of these structures may suffer impingement.

Several aetiologies have been proposed for Subacromial Impingement Syndrome. These include:

• Muscle weakness leading to proximal displacement of the humeral head
• Repetitive microtrauma to the tendons or bursa resulting from overuse with the shoulder in the elevated position
• Degenerative tendinopathy
• Abnormal acromial morphology with enlargement, downward slope, or prominence of the undersurface
• Glenohumeral instability leading to the disturbance of shoulder mechanics
• Acromioclavicular degenerative joint disease leading to osteophytic encroachment of the subacromial space
• A thickening or degeneration of the coracoacromial ligament
• The presence of an unfused distal acromial epiphysis (Os Acromiale)
• Osseous deformity following fracture of the acromion or greater tubercle

The pathophysiology of subacromial impingement can be classified into two groups: primary impingement and secondary impingement.

Primary Impingement

Primary impingement is mainly caused by subacromial architecture. As described above, impingement occurs when the rotator cuff tendons, particularly the supraspinatus tendon, or other structures including the subacromial bursa and the long head of the biceps tendon, are compressed between the humeral head and the undersurface of the acromion or the coracoacromial ligament.

Primary impingement can occur due to:

• The shape of the acromion
• Osteophytic change of the acromioclavicular joint
• A thickening and stiffness of the lateral band of the coracoacromial ligament

Types of Acromion Process

A patient may have an abnormality of the acromion process that could lead to irritation of the supraspinatus tendon as it moves back and forth underneath it. According to the Bigliani Classification, there are three variations in the morphological shape of the acromion process:

• Type I – The acromion is flat.
• Type II – The acromion is curved.
• Type III – The acromion is ‘hooked’ (this is associated with a greater incidence of subacromial impingement syndrome).

Osteophytic Change of Acromioclavicular Joint

An osteophyte formation at the acromioclavicular joint can also impinge the underlying soft tissues. A spur on the underside of the acromion process may result in direct irritation of the supraspinatus tendon each time it moves back and forth.

Secondary Impingement

Secondary impingement is mostly a result of dysfunctional shoulder biomechanics such as:

• Glenohumeral joint instability
• A disturbed scapulothoracic rhythm

Both can lead to an increased superior translation of the humeral head resulting in subacromial impingement.

Progressive Stages of Subacromial Impingement Syndrome

There are three stages in the progression of Subacromial Impingement Syndrome:

• Stage 1 is characterised by oedema and haemorrhage and is more common in patients aged 25 years or younger.
• Stage 2 is characterised by tendinopathy and occurs more often in patients between the ages of 25 and 40.
• Stage 3 is characterised by a rotator cuff tear, particularly in the supraspinatus or biceps tendons. This stage is generally seen in patients older than 40 years.

• Most commonly seen in individuals over 40 years of age.
• Typically, the pain arises insidiously over a period of weeks or months, but the onset may be sudden if induced by trauma.
• Pain is localised to the anterolateral acromion but may radiate to the lateral shoulder and upper arm.
• Pain that is provoked or aggravated by overhead activities.
• Pain at night from lying on the involved side or sleeping with the involved arm overhead.
• The patient may report a generalised loss of shoulder strength.

• Inspection may reveal shoulder muscle atrophy.
• A positive painful arc with provocation of pain in an arc between 60 and 120 degrees of shoulder abduction.
• The Apley’s Scratch tests may also provoke or aggravate pain.
• Tenderness on palpation at the anterolateral corner of the acromion. Other structures may be tender including the supraspinatus muscle and the acromioclavicular joint (depending on the underlying cause).
• Muscle weakness is variable but most likely involves the rotator cuff and scapular stabiliser muscles.
• Positive Neer Impingement, Hawkins-Kennedy, and Yocum tests.
• A positive Empty Can test if supraspinatus pathology is involved.
• The Scapulohumeral Rhythm may be disturbed and the Scapular Assistance test may be positive.

Subacromial Impingement Syndrome is essentially a clinical diagnosis. However, plain radiography can detect the presence of an Os Acromiale, abnormal acromial morphology, acromioclavicular joint osteoarthritis, or a reduction in the subacromial space. It may also reveal calcific tendinopathy of the supraspinatus tendon.

Diagnostic ultrasonography can be used to demonstrate tendinopathy, tendon tears, or bursitis.

Magnetic Resonance Imaging may be used to rule out other shoulder pathologies including labral tears.

The following are examples of red flags for patients presenting with shoulder pain:

• History of a significant injury
• Severe pain
• Unrelenting pain
• Nocturnal pain
• Unexplained weight loss
• Fever
• Deformity
• Significant swelling
• Presence of upper extremity tingling, numbness, burning, or other neurological impairment
• Significant loss of range of motion
• Severe tenderness on palpation or severe pain with any examination procedure

If any red flags are identified during history taking and clinical examination, referral for urgent medical evaluation and further investigation is warranted.

Ice or Heat?

Some practitioners advocate using moist heat in the subacute or chronic phase of subacromial impingement. However, we have found that patients often benefit from the continued application of ice to reduce discomfort and manage inflammation. The application of ice helps to decrease the patient’s pain which then allows them to tolerate some movement. This helps the patient to maintain range of motion, stimulates circulatory perfusion, and prevents potential atrophy, all of which help to speed up recovery.

Heat therapy may not be the best option for shoulder impingement. Shoulder impingement often involves inflammation in the rotator cuff tendons or the bursa. Applying heat can potentially increase blood flow to the area and worsen the inflammation, leading to more pain and discomfort. Whilst heat therapy may provide temporary pain relief, by relaxing muscles and increasing blood flow, it does not address the underlying cause of the impingement. Therefore the use of heat therapy may delay recovery.

Shoulder Pain Caused by Myofascial Pain Syndrome

In patients presenting with anterior shoulder pain, a complete clinical examination should include an evaluation of the following muscles to check for the presence of myofascial pain syndrome as the concomitant or primary cause of the patient’s pain:

• Infraspinatus (commonly involved but often overlooked)
• Pectoralis minor
• Pectoralis major (depending on the location of the trigger point, pain may refer just to the anterior shoulder, or only to the chest and the medial elbow)
• Supraspinatus
• Deltoid
• Biceps brachii

• The trigger points associated with myofascial pain syndrome may be located anywhere within a muscle and its fascia. Therefore, the entire muscle should be examined thoroughly. However, based on our clinical experience, the common locations for trigger points are presented in the images below.