Subacromial pain syndrome (impingement)

   Keywords: Shoulder, assessment, differential diagnosis, treatment, objective measures, corticosteriod injection, NSAIDs, posture re-education, ultrasound.

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Clinically Relevant Anatomy

The four muscles that raise and lower the arm (and their respective tendons) are collectively known as the rotator cuff. The rotator cuff lies under the roof of the shoulder (an extension of the shoulder blade known as the acromion ). The space between the acromion and the rotator cuff tendons is filled by the subacromial bursa . This bursa is a fluid filled sac that allows for smooth gliding of the rotator cuff under the acromion with overhead movements of the shoulder.

The rotator cuff works a depressor and centraliser of the humeral head in the glenohumeral joint.  As the arm is elevated the rotator cuff depresses the humeral head allowing it to glide easily underneath the acromion.


Should any abnormality occur affecting the rotator cuff this would lead to dysfunction of the rotator cuff. Therefore as the arm is elevated, the depressing and centralising effect would be lost and the humeral head would ride upwards closer to the acromion at risk of causing impingement.  Pathologies that could do this are those directly affecting the rotator cuff such as:

Direct Causes:

  1. Rotator cuff strain
  2. Partial or full thickness tear
  3. Calcific tendonitis 
  4. A tendonopathy due to chronic overuse.
Indirect Causes:
  1. Glenohumeral instability
  2. Labral tears, in particular SLAP tears
  3. Abnormal muscle patterning problems of the shoulder.

The acromion differs in individuals normally (morphological variants). These were described by Bigliani as type I, type II or type III.   Type I is flat, type II is curved and type III hooked.  A person with a type II or type III acromion would be at a higher risk of impingement due to the narrowing of the acromiohumeral gap and bursal space.

In addition to the above, with advancing age people tend to develop a bone spur on the front and side of the acromion.  This further reduces the subacromial space increasing the risk of impingement.

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Therefore somebody with a rotator cuff injury who has a type III acromion and is their 50’s has a very high risk of developing significant impingement compared to a patient in their 20’s sustaining a supraspinatus strain who may have a type I acromion and no spurs.

The rotator cuff and acromion will then rub against one another, causing a painful condition known as impingement. Each time the arm is raised there is a bit of rubbing on the tendons and the bursa between the tendons and the acromion, which may cause pain and inflammation.

Impingement may become a serious problem for some people and disturb their normal activities. This is when treatment is needed.

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Underlying Mechanisms (NICE Guidelines, 2004)
  • Bony antomy and pathological factors (as mentioned above)
  • Shoulder Instability – Rotator cuff weakness, Capsulo-ligamentous laxity.
  • Impaired scapulohumeral rhythm and scapula instability.
  • Capsular tightness
  • Postural factors.
  • Soft tissue changes – ie inflammation and thickening of the subacromial bursa.


Characteristics and Clinical presentation

  • Pain the the shoulder region particularly with over head positions.
  • Night pain- which can prevent patient from lying on that side
  • Can be sudden or insidious in onset.


Differential Diagnosis

  • Adhesive capsulitis  (Also presents with night pain, to differentiate from SIS assess if there is a capsular restriction indicative of AC)
  • ACJ ( Pain normally can be localised to the joint)
  • Osteoarthritis (produces aching after activity)
  • SLAP lesions (very similar presentation to SIS)

Examination                                       Shoulder Ax 

Objective measures

Disabilities of the arm, shoulder and hand.  – DASH


Advice for patient

  • Rest. Particularly from aggravating factors such as lifting arm over head.
  • Apply ice or cold therapy to reduce pain (20mins 2-3 x daily).
  • See a doctor or physiotherapist if symptoms persist.
  • NSAID’s may help – recommend that your patients speaks to their doctor for further information on this.


What can the health professional or physiotherapist do?

(see below for NICE Guidelines.)

 Medical/Surgical Management
  • Injections reduces inflammation and control the pain
  • Surgery – Rarely Surgery is required – the goal of any surgery to reduce the effects of impingement, by  increasing the amount of space between the acromion and the rotator cuff tendons, which will then allow for easier movement and less pain and inflammation. The operation performed is arthroscopic Subacromial Decompression (ASD)

What do the NICE guidelines have to say??


Aims of Physio

  1. Minimise pain
  2. Optimise function
  3. Appropriately refer those who are unresponsive to PT

Objectives of physio

  1. To reduce subacromial inflammation and manage pain.
  2. To improve posture
  3. To restore range, strength, stability and scapulohumeral rhythm.
  4. To identify when patients should be referred for an orthopaedic opinion.
Treatment modalities and their evidence.


  • Relative rest and avoidance of aggravating factors can help settle inflammation
  • Absolute rest is rarely necessary and may result in adhesive capsulitis.
  • The potential benefits of short term (7-21 days) of NSAIDs outweigh the risks. This point is controversial check out our news section to see the latest or FOR/AGAINST non steriodals.

Cold therapy

Cold packs may be used to reduce pain and settle irritation post exercises. Applications vary between 30mins(obese) and 10mins(thin).

Heat therapy

Due to insufficient evidence, no recommendations can be made.

 Restoration of range, strength, stability and scapulohumeral rhythm.The Shoulder

  • Passive mobilization of the upper quadrant according to Maitland (1991) principles.
  • Scapula stability when performing strengthening exercise sis paramount.
  • The following exercises have been recommended.
  1. Stabilisation in sitting, stabilization in standing, stabilization in 4 point kneeling, stabilization with a ball.
  2. Medial rot, lateral rot, anterior capsular stretch, posterior capsule stretch.
  3. Flexion, rowing, scaption(in medial rot),Horizontal abduction with lat rot. Push ups, press ups plus  (please see NICE guidelines for more details)


Except in calcific tendinitis, ultarsound is not beneficial in SIS.

Steriod Injection

  • Steriod Injections benefit SIS in the short term.
  • May compromise tensile strength of collagen for up to 14 days. Resistive exercises should be avoided during this time.
  • The same subacrmial space should nt be njected into on more than 3 occasions.
  • Studies into the accuracy of injection placements have shown disappointing results.

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photo credit: CarbonNYC via photopin cc

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