Subacromial impingement syndrome “SAIS”

subacromial impingement syndrome

Contents of this article:

Introduction about SAIS
Anatomy and Incidence
Differential diagnosis
Presentation and Examination
Management and Treatment

Introduction of subacromial impingement syndrome :

SAIS is the most common pathology of the shoulder pain which often occurs due to compression of the rotator cuff muscles (RCM) by superior structures such as ”AC joint, acromion, or CA ligament” which lead to inflammation/irritation and development of bursitis , it’s usually occurs in patients < 25 years, specially in active adults or manual professions..


  • Most common cause of shoulder pain.
  • Account about ( 40_60%)of shoulder disorder.

Subacromial impingement syndrome:

It’s an inflammation or irritation of the rotator cuff tendons “ RCT “ which pass through the subacromial space, causing pain, weakness, and restricting range of motion ROM within the shoulder joint.

** When the subacromial bursa is inflamed and impinges on the Rotator cuff tendon, it is called “subacromial impingement syndrome”.

What 4 muscles make up the rotator cuff?

The four muscles and their tendons attachment together make up the Rotator cuff:

  • Supraspinatus.
  • Infraspinatus.
  • Subscapularis.
  • Teres minor.

Anatomy of the Subacromial Space:

Where is the subacromial space located?

** It lies below the coracoacromial arch, and above the humeral head and greater tuberosity of the humerus.

** The coracoacromial arch consists of:

  1. The acromion.
  2. The coracoacromial ligament (anterior to the acromioclavicular joint).
  3. The coracoid process.
subacromial space

What is in the subacromial space?

  1. The rotator cuff tendons RCTs.
  2. The long head of the biceps tendon.
  3. The coraco-acromial ligament.

They are all surrounded by the subacromial bursa “which helps to reduce friction between these structures”.

Pathophysiology of subacromial impingement syndrome

What causes subacromial impingement syndrome?

All these conditions may result due to an attrition between the coracoacromial arch and the supraspinatus tendon or bursa.

  • Rotator cuff tendinosis.
  • Subacromial bursitis.
  • Calcific tendinitis.

It can be divided into intrinsic and extrinsic pathological factors as: 

  • Intrinsic mechanisms: 

“It involves pathologies of the rotator cuff tendons due to tension, which including:

  • Muscle weakness: of the rotator cuff muscles may lead to muscular imbalances, So the humerus shifting proximally towards the body.
  • Overuse of the shoulder joint: due to repetitive microtrauma which may cause soft tissue inflammation of the rotator cuff tendons or the subacromial bursa, then leading to friction between the tendons and the coracoacromial arch.
  • Degenerative tendinopathy: any degenerative changes in the acromion will lead to tearing of the rotator cuff.
  • Extrinsic mechanisms:

“It involves pathology of the rotator cuff tendons due to external compression, like:

  • Anatomical factors: acquired or congenital anatomical differentiation in the shape of the acromion.
  • Scapular musculature: reduction in function of the scapular muscles, specially the serratus anterior and trapezius.“These muscles normally allow the humerus to move past the acromion on overhead extension”.
  • Glenohumeral instability: superior subluxation of the humerus as a result of any abnormality of the glenohumeral joint or weakness in the rotator cuff muscles, and causing an increased contact between the acromion and subacromial tissues.

****Differential Diagnoses:

  1. Muscular tear ( rotator cuff tear, or long head of biceps tear) 
  1. Frozen shoulder syndrome (calcific tendinitis or adhesive capsulitis).
  1. Neurological pain (thoracic outlet syndrome TOS, cervical radiculopathy, brachial plexus injury).
  1. Acromioclavicular pathology ( arthritis, or glenohumeral arthritis).

** Other conditions:

  • hook shaped acromion.
  • scapular dyskinesis.
  • posterior capsular contracture.
  • tuberosity-fracture malunion.
  • instability.

Presentation of  subacromial impingement …

  • Symptoms.
  • Pain,

**Gradual onset.

**Exacerbated by overhead activities and lifting objects away from the body.

**Night pain.

All of the inflammation signs may be present in the shoulder, to indicate this type of bursitis. These may be:

1. Minor sharp pain in the shoulder, even at rest.

2. The shoulder may look swollen in some cases.

3. Reduced shoulder ROM to active or passive ROM.

4. Tenderness in the shoulder. 

5. Warmth feeling to touch around the shoulder. 

6. In some cases, the shoulder may look reddish.

  • Physical Examination: 
  • Strength: usually Normal. 

****Most common specific examination signs for Subacromial impingement syndrome are: 

  1. Neer’s Impingement test: 
  • Patient arm is placed into the patient’s side.
  • Fully internally rotated IR and then passively flexed arm.
  • Test is positive: pain in the anterolateral aspect of the shoulder when flex more than 90. 
  1. Hawkins test: 
  • Patient shoulder and elbow are flexed to 90 degrees.
  •  The examiner stabilizes the humerus and passively internally rotates IR the arm.

Test is positive: pain is in the anterolateral aspect of the shoulder.

subacromial impingement tests
  • Radiography
  • X-Ray: AP view for shoulder joint.
  • MRI:

Used to evaluate the degree of rotator cuff pathology.

subacromial and subdeltoid bursitis are often seen.


  • osteophytes.
  • sclerosis.
  • subacromial bursitis.
  • humeral cystic changes.
  • narrowing of the subacromial space.
subacromial impingement MRI
  • CT arthrography:

accurate image for the rotator cuff tendons and muscle bellies.

  • Ultrasound:

Also accurate image for the rotator cuff tendons and muscle bellies

Management and treatment OF subacromial impingement :

  1. Nonoperative:
  • subacromial injections.   
  • Non steroid anti inflammatory medication.
  • physical therapy.
  1. Operative: 

subacromial acromioplasty or decompression. 

** indications: failed the nonoperative treatment, a minimum of 4-6 months. 

Physiotherapy management:

  1. Pain management.
  2. Patient education: change into the type and amount of exercises performed, athletic activities, and home or work activities. 
  1. ROM exercise: because limited the mobility of the shoulder joint and scapula. This will increase stress to various structures.
  1. Manual exercise: gentle mobilization for muscle and joints. 
  1. stretching and strength exercises: 

Muscle weaknesses or imbalances may cause impingement of the shoulder, as the scapula deviates due to weakness of the muscles, based on the level of the injury, physical therapist will design a safe, personalized, and progressive resistance program.

  1. Functional training: last stage of recovery, to minimize the stress to the shoulder. 


  1. Deltoid dysfunction.
  2. Anterosuperior escape. 


Subacromial bursitis occurs when there is inflammation of the subacromial bursa. When this bursa is inflamed, it becomes swollen and looks larger in size. This makes it impinge on the tendon of the supraspinatus muscle and makes it irritated.




https://www.orthobullets.com/shoulder-and-elbow/3041/subacromial-impingement https://www.sciencedirect.com/science/article/abs/pii/S003194060400197X


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