Subacromial Pain Syndrome

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Clinically Relevant Anatomy

Subacromial Impingement is defined as the compression of the subacromial structures (rotator cuff tendons, long head of the biceps, glenohumeral joint capsule, and subacromial bursa) during elevation of the arm. These structures are compressed against the coracoacromial arch, creating sensations of pain. The margin between the superior portion of the humeral head and the inferior

Subacromial Structures

surface of the acromion is known as the subacromial space. In healthy individuals, this space is approximately 10mm, but as this space narrows the likelihood of tissue irritation increases. This margin holds the supraspinatus muscle belly and tendon, long head of the biceps brachii, and subacromial bursa. Subacromial structures can be pinched either due to pathologic factors (muscle imbalance, overuse) or anatomic factors. The shape of the acromion can play a role. There are three types of acromial shapes:

1. Type I Acromion: Flat shape (Least likely to contribute to impingement)
2. Type II Acromion: Curved shape
3. Type III Acromion: Hooked shape (Most likely to contribute to impingement)

Bony spurs on the underside of the acromion process can also cause irritation of the subacromial structures. 

Mechanism of Injury / Pathological Process

Impingement is often a condition than can have a variety of causes acting together to create symptoms. Subacromial impingement occurs when the arm is elevated, narrowing the subacromial space and compressing the structures that reside in that margin. With repeated elevation, these structures sustain microtrauma that can cause them to become inflammed. Subacromial impingement can be caused by a variety of factors:

• Rotator cuff weakness, causing the humeral head to drift superiorally
• Chronic rotator cuff irritation due to overuse
• Posterior GH capsule tightness
• Anatomical variations such as narrow SA space, Type II or III Acromion, or bony spurs
• Poor posture (forward shoulder posture can cause functional narrowing of subacromial space)

Clinical Presentation

Individuals with subacromial impingement will usually complain of pain with active elevation of the shoulder. Activities performed with the involved arm below shoulder level are often not painful because the subacromial structure are not impinged when the shoulder is in anatomic position. These individuals often do not remember a traumatic incident as the onset is more of a gradual, degenerative condition rather than due to a strong external force.

Diagnostic Procedures

Also see Impingement Cluster page

An accurate history is often one of the best indicators in diagnosing subacromial impingement. However, many diagnostic procedures can be used to validate this diagnosis. The following are a few special tests for the presence of subacromial impingement:

• Hawkins-Kennedy
• Neer
• Painful Arc[1][2][3]

Outcome Measures

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Management / Interventions

Treatment of subacromial impingement can be managed either operatively or non-operatively.

Operative treatment usually includes repair of any tissues that have been damaged due to repetitive trauma. Such structures often involve the supraspinatus muscle and/or tendon, proximal biceps tendon, or joint capsule. Removal of the subacromial bursa is a procedure known as a bursectomy. A procedure known as a subacromial decompression (SAD) is often performed to increase the available space in the subacromail space by removing bony spurs, removing the coracoacromial ligament, and even occasionally removing the most inferior portion of the acromion (acromioplasty).

Non-operative treatment is typically attempted first, assuming there is no significant biceps or rotator cuff tear that will require surgery.

Differential Diagnosis

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Key Evidence

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Resources

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References

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