Subacromial Impingement Syndrome Flashcards
What is subacromial impingement syndrome (SAIS)?
Subacromial impingement syndrome (SAIS) refers to the inflammation and irritation of the rotator cuff tendons as they pass through the subacromial space, resulting in pain, weakness, and reduced range of motion within the shoulder.
SAIS encompasses a range of pathology including rotator cuff tendinosis, subacromial bursitis, and calcific tendinitis. All these conditions result in an attrition between the coracoacromial arch and the supraspinatus tendon or subacromial bursa.
Who is commonly affected by SAIS?
It occurs most commonly in patients under 25 years, typically in active individuals or in manual professions, and accounts for around 60% of all shoulder pain presentations, making it the most common pathology of the shoulder.
Briefly describe the anatomy of the subacromial space
The subacromial space lies below the coracoacromial arch and above the humeral head and greater tuberosity of the humerus. The coracoacromial arch consists (lateral to medial) of the acromion, the coracoacromial ligament (anterior to the acromioclavicular joint), and coracoid process.
Within the subacromal space run the rotator cuff tendons, the long head of biceps tendon, and the coraco-acromial ligament, all surrounded by the subacromial bursa which helps to reduce friction between these structures.
Briefly describe the intrinsic pathophysiology of SAIS
Intrinsic mechanisms involve pathologies of the rotator cuff tendons due to tension, including:
- Muscular weakness: weakness in the rotator cuff muscles can lead to muscular imbalances resulting in the humerus shifting proximally towards the body
- Overuse of the shoulder: repetitive microtrauma can result in soft tissue inflammation of the rotator cuff tendons and the subacromial bursa, leading to friction between the tendons and the coracoacromial arch
- Degenerative tendinopathy: degenerative changes of the acromion can lead to tearing of the rotator cuff, which allows for proximal migration of the humeral head
Briefly descirbe the extrinsic pathophysiology of SAIS
Extrinsic mechanisms involve pathologies of the rotator cuff tendons due to external compression, such as:
- Anatomical factors: congenital or acquired anatomical variations in the shape and gradient of the acromion
- Scapular musculature: a reduction in function of the scapular muscles, particularly the serratus anterior and trapezius, that normally allow the humerus to move past the acromion on overhead extension, may result in a reduction in the size of the subacromial space
- Glenohumeral instability: any abnormality of the glenohumeral joint or weakness in the rotator cuff muscles can lead to superior subluxation of the humerus, causing an increased contact between the acromion and subacromial tissues
What are the clinical features of SAIS?
The most common symptom of SAIS is progressive pain in the anterior superior shoulder. The pain is classically exacerbated by abduction in the affected shoulder and relieved by rest, and may be associated with weakness and stiffness secondary to the pain.
Briefly describe Neers Impingement test
The arm is placed by the patient’s side, fully internally rotated and then passively flexed, and is positive if there is pain in the anterolateral aspect of the shoulder.
Briefly describe Hawkins test
The shoulder and elbow are flexed to 90 degrees, with the examiner then stablising the humerus and passively internally rotates the arm, and the test is positive if pain is in the anterolateral aspect of the shoulder.
What investigations should be ordered for SAIS?
The diagnosis of impingement is a clinical one, however it is often confirmed via additional imaging.
MRI imaging of the affected shoulder is often the mainstay of imaging for SAIS.
What are the features of SAIS on an MRI scan?
Features that can be seen in affected individuals include formation of subacromial osteophytes and sclerosis, subacromial bursitis, humeral cystic changes, and narrowing of the subacromial space.
Briefly describe the conservative management of SAIS
Conservative management is the mainstay of treatment in most cases. Patients should have sufficient analgesia, typically NSAIDs, and regular physiotherapy, including postural, stability, mobility, stretching and strength exercises.
For those who require further intervention, corticosteroid injections in the subacromial space can be trialled. Patients should be educated appropriately with adequate warm-up techniques and monitoring for early signs of worsening impingement.
When is surgical management required in SAIS?
If SAIS persists beyond 6 months without response to conservative management, surgical intervention is recommended.
Briefly describe surgical management of SAIS
Current surgical techniques include:
- Surgical repair of muscular tears, most commonly the supraspinatus and long head of biceps tendon, resulting in an improvement in range of motion
- Surgical removal of the subacromial bursa, a bursectomy, increasing the subacromial space and reducing pain
- Surgical removal of a section of the acromion, an acriomioplasty, increasing the subacromial space and reducing pain
What are the complications of SAIS?
Complications of SAIS include rotator cuff degeneration and tear, adhesive capsulitis, cuff tear arthropathy and complex regional pain syndrome.
If diagnosed and assessed early, SAIS resolves with conservative management in 60 – 90% of patients.
What differential diagnosis are considered for SAIS?
- Muscular tear
- Neurological pain
- Frozen shoulder syndrome
- Acromioclavicular pathology
