Shoulder Anterior Impingement Syndrome (SAIS), first described by Neer in 1972, is caused when the supraspinatus tendon becomes painfully entrapped between the acromion and the greater tuberosity of the humerus during elevation and/or internal rotation of the arm.
Repetitive impingement is thought to precipitate a cascade of shoulder dysfunction including supraspinatus tendon disruption, subacromial bursitis, biceps tendonitis, degeneration of associated joints and eventually, rotator cuff rupture. Neer suggested that 95% of chronic rotator cuff tears are due to impingement.
What Causes Shoulder Impingement Syndrome?
SAIS results from repetitive injury and its development is partially related to the available subacromial space. Conditions that diminish the subacromial space, including acromioclavicular degeneration, osteophytes or a thickened coracoacromial ligament, can predispose patients to “outlet impingement” SAIS.
Perhaps the greatest threat to subacromial space comes from having misshapen acromion. Approximately 20% of the population has a “Flat” (type I) acromion, 55% has a “Curved” (type II) and 25% has a “Beaked” (type III) acromion. Type III is more common in males and is present in 75% of patients with a rotator cuff tear. Neer and others purport that the pathoanatomical changes to the acromion may be the result of longstanding impingement rather than its precursor. “Upper crossed syndrome” and scapular dyskinesis are significant predisposing factors for SAIS.
What does the rotator cuff do?
In addition to its primary function of generating torque, the rotator cuff is a dynamic stabilizer of the glenohumeral joint and works to depress the humeral head during arm elevation. This stabilizing force from the rotator cuff offsets the humeral elevation that would otherwise result from unopposed deltoid contraction during arm elevation. “Non-outlet impingement” SAIS results from loss of normal humeral head depression as a result of rotator cuff muscle weakness or denervation.
Rotator cuff lesions progress in a self-perpetuating cycle of dysfunction. Repetitive insults damage the tendon and lead to tendon degeneration. This weakens the tendon and diminishes its ability to oppose superior shearing force produced by the deltoid during arm abduction. The tendon becomes impinged, producing further insult. As tendon fibers fail, the enduring fibers remain under tension, thereby increasing the load and the likelihood of failure.
How Common Is SAIS?
SAIS is the most common disorder of the shoulder and accounts for 44-65% of all shoulder complaints seen by physicians. Rotator cuff problems are common in younger and middle-aged populations. Those who perform repetitive overhead activity are at greater risk for SAIS. This includes athletes who participate in swimming, baseball, volleyball, weightlifting, and tennis as well as professions like carpenters, electricians, painters, and wallpaper hangers.
The Three Stages of SAIS Degeneration
SAIS is a continuum of degeneration that Neer categorized into three stages.
Stage 1 is common in younger patients and is characterized by acute but reversible pain, swelling, and hemorrhage.
Stage 2 typically affects patients between the ages of 25-40 who have suffered from SAIS for months or years and is characterized by tendonitis and permanent fibrosis of the supraspinatus tendon, biceps tendon and subacromial bursa which may require surgical intervention.
Stage 3 is the culmination of a prolonged irritation that has caused significant tendon degeneration and fibrosis for many years. It typically affects patients over the age of 40 or 50 and is characterized by irreversible mechanical disruption of the rotator cuff tendon. Stage 3 often includes osseous degenerative changes including cystic changes to the greater tuberosity and A/C degenerative changes, i.e. acromial sclerosis and osteophytes. Biceps tendon degeneration and/or rupture is common in stage 3. Acromioplasty and rotator cuff repair are frequently required for the management of stage 3 SAIS.
What are the symptoms of SAIS?
The onset of SAIS is often related to a period of overuse. Initially, symptoms may be limited to a sharp pain during overhead activity or while reaching behind the back to fasten a bra or close a zipper. As the condition progresses, the patient may develop a constant ache that is present at rest.
Nighttime pain is common, often disrupting sleep. Sleeping on the affected side may exacerbate pain. The discomfort is often located over the anterior shoulder and lateral deltoid areas.
The clinical presentation may include decreased active and passive ROM in forward flexion, abduction or internal rotation. The patient often demonstrates a positive “painful arc” between 60-120 degrees of abduction. Forced passive horizontal adduction may provoke pain. Resisted external rotation with the arm at the side or at 90 degrees of elevation (Horn Blowers/ Patte test) is generally painful. Internal rotation resisted strength test (IRRST), may demonstrate a weakness of internal rotation while the shoulder is abducted. Loss of strength from pain inhibition is common. Palpation reveals tenderness over the greater tuberosity and supraspinatus insertion as well as the anterior edge of the acromion.
Will I need an x-ray?
No definitive criteria exist for the imaging of SAIS. In general, shoulder radiographs are appropriate in cases of trauma, severe pain, prolonged pain or the inability to abduct > 90 degrees. Radiographic imaging of the shoulder in cases of suspected SAIS should include A/P, internal rotation, and axillary (lateral) views. An “outlet view” (standard “Y” view with 5-10 degree caudad tilt) is most useful to demonstrate acromial morphology and osteophytes in the supraspinatus space. Ultrasound can identify tendon disruptions but MRI is the imaging of choice for shoulder pathology and is useful to differentiate between findings consistent with SAIS vs. rotator cuff tear. An MRI arthrogram enhances clinical accuracy in detecting tendon tears or labral injury.
How is SAIS treated?
The management of shoulder problems poses a challenge for clinicians. Studies report long-term unfavorable outcomes in 40-50% of primary care patients. Successful management of SAIS should initially focus on restoring range of motion while avoiding aggravating movements i.e. elevation and internal rotation. Patients should avoid overhead presses, lateral raises, and push-ups. Selective rest may be necessary for some patients. Ultrasound, anti-inflammatory modalities, and ice may be useful in the earliest stages. However, most passive therapy modalities provide little benefit for chronic SAIS patients. Low-level laser therapy may be useful.
In-office management should include manual therapy and exercise. Soft tissue manipulation or myofascial release should address associated hypertonic muscles with specific emphasis on the pec, biceps, subscapularis, infraspinatus, teres minor and levator. IASTM may be performed prudently over the supraspinatus tendon and associated adhesions. Shoulder mobilization has been shown to decrease pain and improve range of motion in SAIS patients. Manual manipulation is needed to address restrictions in the cervical, upper thoracic and shoulder areas. There is evidence to suggest that cervical thoracic and thoracic spine manipulation may help decrease shoulder pain while improving mobility and function.
Elastic Therapeutic Tape, applied across the supraspinatus, deltoid and teres minor, may promote scapular movement and strength with faster recovery times and lower disability. Thoracic spine manipulation has been shown to significantly decrease pain and disability for SAIS patients.
Stretching should address tightness in the posterior capsule and internal rotators with specific emphasis on the: pec, biceps, subscapularis, infraspinatus, teres minor, levator and across body stretch. Strengthening may begin incrementally as the patient’s pain-free range of motion allows. Strengthening should begin with isometric exercises and progress as tolerated. Eccentric strengthening of the rotator cuff combined with eccentric/concentric exercises for the scapular stabilizers may produce improved outcomes when compared to less specific programs. The ultimate goal of stability training is to restore normal posture and arthrokinematics. Specific strengthening should include: scapular retractions, shoulder flexion, isolated supraspinatus, horizontal abduction, extension, external rotation and reverse shrugs. Home-based exercises are effective tools for managing SAIS.
When can I get back to normal?
Return to play should begin gradually and release to full activity is appropriate when ROM is full and pain-free and strength testing reveals no significant weakness as compared to normal. Recalcitrant cases may require steroid injections or surgical consult, however, conservative options should be exhausted first. High-quality research investigations “ suggest that a graduated and well-constructed exercise approach confers at least equivalent benefit as that derived from surgery for; subacromial pain (impingement) syndrome, rotator cuff tendinopathy, partial thickness rotator cuff (RC) tears, and atraumatic full-thickness rotator cuff tears.”