Subacromial impingement syndrome


Represents a spectrum of pathology ranging from subacromial bursitis to rotator cuff tendinopathy, calcific tendinitis, and full-thickness rotator cuff tears, and subacromial bursitis.

Management includes physical therapy, injections, and, for some patients, surgery, but no randomized controlled trials provide possible evidence for differences in outcome of different treatment strategies.

SAIS is the most common disorder of shoulder, accounting for 44–65% of all complaints of shoulder pain.

Consequences of SAIS are functional loss and disability.

Subacromial space is defined by the humeral head inferiorly, the anterior edge and under surface of the anterior third of the acromion, coracoacromial ligament and the acromioclav-icular joint superiorly.

The height of space between acromion and humeral head ranges from 1.0 to 1.5 centimeters.

Interposed between these two osseous structures are the rotator cuff tendons, the long head of the biceps tendon, the bursa, and the coracoacromial ligament.

Any abnormality in the subacromial structures may lead to impingement.

Neer described three stages of subacromial impingement.

Stage-I impingement is characterized by edema and hemorrhage of the subacromial bursa and cuff.

Stage-II impingement represents irreversible changes, such as fibrosis and tendinitis of the rotator cuff, and is typically found in patients who are twenty-five to forty years old.

Stage-III impingement is marked by more chronic changes, such as partial or complete tears of the rotator cuff, and usually is seen in patients who are more than forty years old.

The glenohumeral joint possesses six degrees of freedom, three rotations and three translations.

With active glenohumeral abduction in the scapular plane the humerus concomitantly externally rotates.

External rotation is important for clearance of the greater tuberosity and its associated tissues as it passes under the coracoacromial arch, as well as for relaxation of the capsular ligamentous constraints to allow maximum glenohumeral elevation.

After the initial phase of elevation in abduction, the humeral head remains centered on the glenoid cavity with fluctuations between inferior and superior translations of typically less than 1 mm.

During active glenohumeral flexion, anterior humeral head translation of less than 1 mm occurs over the course of motion.

The height of the subacromial space, from the head of the humerus to the coracoacromial arch, is only 1.0–1.5 cm as seen on radiographs.

Changes of this space occur in subjects with healthy shoulders.

A decrease in the width of the acromio-humeral interval and an increase in the contact between the inferior acromion and underlying subacromial tissues occurs during glenohumeral abduction.

Contact pressure and force in the subacromial space increases during glenohumeral abduction.

Changes in the subacromial space increases in the normal superior and anterior humeral head translation, leading to mechanical compression of the tissues in subacromial space during glenohumeral motion.

The scapula demonstrates a pattern of upward rotation, external rotation, and posterior tilting during glenohumeral elevation.

During glenohumeral elevation the clavicle retracts posteriorly and elevates, putting the scapula in essentially a more superior and posterior position.

Patients with subacromial impingement generally have decreased scapular posterior tilting, decreased upward rotation and increased internal rotation compared to healthy individuals.

There is an encroachment of the subacromial tissues as a result of narrowing of the subacromial space.

Rotator cuff tendinopathy is described as extrinsic, intrinsic or a combination of both.

Intrinsic impingement of partial or full thickness tendon tears occur as a result of the degenerative process that is due to overuse, tension overload, or trauma of the tendons.

Extrinsic impingement, occurs with inflammation and degeneration of the tendon as a result of mechanical compression by structures external to the tendon.

Extrinsic mechanisms of rotator cuff tendinopathy that result in tendon compression include anatomical factors, biomechanical factors, or a combination.

Factors that may narrow the subacromial space and outlet to the rotator cuff tendons include variations in shape and orientation of the acromion, orientation or prominent osseous changes to the inferior aspect of the acromio-clavicular joint or coracoacromial ligament.

A classification system for acromial shape is flat (type I), curved (type II), or hooked (type III).

Another possible cause of encroachment into the subacromial space is thickening of the coracoacromial ligament.

Extrinsic subacromial impingement syndrome is based on narrowing of the subacromial space leading to rotator cuff tendon compression secondary to superior translation of the humeral head or ab2242ant scapular motion that causes the acromion to move inferiorly.

Posterior capsular tightness may cause changes in glenohumeral kinematics leading to subacromial impingement syndrome.

Ab2242ant scapular muscle activity has been identified in patients with subacromial impingement syndrome and been directly linked to abnormal scapular kinematics.

The supraspinatus and other rotator cuff muscles of teres minor, infraspinatus, and subscapularis maintain the congruent contact between the humeral head and the glenoid fossa by producing a compressive force during glenohumeral movements.

Weakness or dysfunctional rotator cuff musculature changes in glenohumeral and scapulothoracic movements.

Rotator cuff weakness can lead to a decrease in the subacromial space during elevation, and thus increased mechanical compression of the subacromial contents.

Pain more typically develops insidiously over a period of weeks to months, but it may be acute following trauma.

Rotator cuff pain is typically localized to the anterolateral acromion and frequently radiates to the lateral mid-humerus.

Rotator cuff pain occurs usually at night, exacerbated by lying on the involved shoulder, or sleeping with the arm overhead.

Rotator cuff pain may be associated with weakness and stiffness.

Shoulder pain is evaluated with X-rays including internal and external rotation anteroposterior, scapular, axillary, and supraspinatus outlet views.

These plain X-rays may show changes of rotator cuff disease, including subacromial osteophytes, subacromial sclerosis, cystic changes of the greater tuberosity, and narrowing of the acromiohumeral distance.

MRI provides detail of sites of subacromial impingement through the supraspinatus outlet.

MRI is performed with the arm adducted.

Treatments are available for impingement syndrome:

physical therapy, shock-wave therapy, medication, and surgery.

Evidence exists that extracorporeal shock-wave therapy is no more effective than placebo, moderate evidence that ultrasound therapy is no more effective than placebo, and limited evidence that laser is no more effective than placebo with regard to functional limitations.

There is limited evidence that exercise is more effective than no intervention.

There is moderate evidence that exercise combined with manual therapy is more effective than exercise alone.

Exercise is more effective than no intervention on functional limitations.

Oral diclofenac is more effective than analgesic injections, both on functional limitations and on ability to work after 1 year.

On the short term,

Arthroscopic acromioplasty is more effective than open acromioplasty in the short term, with regard to functional limitations and return to work.

Moderate evidence exists that on the long term open and arthroscopic acromioplasty are equally effective with regard to functional limitations.

A systematic review by Dorrestijn concluded that there is no evidence from the available randomized controlled trials for differences in outcome in pain and shoulder function between conservatively and surgically treated patients with subacromial impingement syndrome.

Observational studies report better outcomes in operated patients who had not responded to non-operative measures and who had a short symptom duration compared with those who had prolonged symptoms before surgery.

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