Subacromial (SA) impingement is defined as the mechanical compression of subacromial structures between the coraco-acromial arch and the humerus during active elevation of the arm above shoulder height.
There are two types of subacromial impingement:
• Structural impingement: Impingement is a reduction of the subacromial area, the structural impingement can be caused by bone growth, inflammation, osteofytes, calcifications, … 
• Functional impingement: can be caused by glenohumeral instability and muscle imbalance. The functional impingement is a secondary consequence.[33,11]
Clinically Relevant Anatomy
The girdle of the shoulder consists out of three bones:
The joints in the girdle of the shoulder are:
• the sternoclavicular joint
• the acromioclavicular joint
• the glenohumeral joint
• the scapulathoracal plane
• the cervicothoracic transition
The first three joints are synovial joints.  The glenohumeral is the most mobile joint. It has static stabilizers and dynamic stabilizers (muscles around the shoulder).
Static stabilisers: Dynamic stabilisers:
- Intracapsular pressure - Bony geometry - Proprioception
- Suction effect - Glenoid labrum - Muscles: rotator cuff and scapular muscles
- Adhesion cohesion - Capsule
Structures involved in subacromial impingement:
• the coracoacromial arch composed of the acromion, processus coracoideus and ligamentum coracoacromiale
• the humerus
• the tendons of the Rotator Cuff: supraspinatus, infraspinatus, teres minor
• the long head of the m. biceps brachii
• the subacromial bursa
• shoulder capsule
• deltoid muscle
• muscle imbalance of the lower and middle trapezius, serratus anterior, infraspinatus and deltoid, coupled with tightness of the upper trapezius, pectorals and levator scapula (= upper crossed syndrome). The tightness of the muscles creates a deltoid shear (crossing of rotator cuff under AC joint), leading to shoulder impingement, tendonitis and bursitis syndromes.
Looking at possible causes of subacromial impingement, it is important to understand that there are 3 types of acromial shape can be distinguished:
Type I acromion: flat shape
Type II acromion: curved shape
Type III acromion: hooked shape (most likely to contribute to impingement and irritation)
Usually, it is the tendon of the supraspinatus muscle that gets stuck between the subacromial space. The origin of the supraspinatus muscle is on the fossa and fascia supraspinata, the insertion is on the tuberculum majus humeri.
Impingement syndrome occurs in one out of three persons and 20% of all people will experience symptoms of subacromial impingement.
It occurs when the subacromial space is narrowed and the soft tissues gets compressed in the subacromial space. Several causes for subacromial impingment have been detected.
occur secondary to an acute (trauma) or chronical process.
• Anatomical variations such as narrow SA space, type II or III acromion (see above)
Osteofytes beneath the acromioclavicular joint: secondary to osteoarthritis
• Subacromial bursitis
• Rotator cuff weakness: causing the humeral head to drift more superior
• Chronic rotator cuff irritation due to overuse
• Posterior glenohumeral capsule tightness
• Poor posture: forward shoulder posture can cause functional narrowing of the subacromial space
• Abnormal muscle activation
• Impaired scapulohumeral rhythm
• Scapular instability
Mentioned biomedical aspects but also psychological factors as kinesiophobia or catastrophizing can have negative influence and thus cause chronic pain and disability.
Subacromial impingement characteristics[3,26]:
- age 40 – 60
- pain during elevation is located anterior and lateral to the
- painful arc: 90-120 degrees with anteflexion or abduction
- pain gets worse with overhead activities[3,26]
- no pain radiating below the elbow
- positive impingement tests: Hawkins, Kennedy and empty can
- rolling on the shoulder during the night is painful (bad sleeping)
Symptoms include altered normal range of motion and loss of pain free function of the affected upper extremity.
The symptoms can be acute or chronic. Most of the time it is a gradual, degenerative condition that causes impingement, rather than due to a strong external force. Therefore, patients often have difficulties with determining the exact time of the complaints.
Neer divided impingement syndrome into three stages:
• First stage:
Moderate pain during exercise, no loss of strength and no limitation in movement.
Stage I also involves edema and/or hemorrhage. This stage generally occurs in patients less than 25 years of age and is frequently associated with an overuse injury. At this stage the syndrome is most of the time still reversible.[13,29]
• Second stage:
Pain during ADL-activities and especially during the night loss of mobility.
Stage II is more advanced and tends to occur in patients 25 to 40 years of age. The pathologic changes show fibrosis as well as irreversible tendon changes.[13,29]
• Third stage:
Strong restriction in movement due to calcifications and loss of muscle strength.
Stage III generally occurs in patients over 50 years of age and frequently involves a tendon rupture or tear. Stage III is largely a process of attrition and the culmination of fibrosis and tendinosis that have been present for many years.[13,29]
There are a variety of shoulder conditions that can initially be confused with subacromial impingement, although a thorough examination is usually sufficient for identifying this condition. [3,24,25,13]
• Rotator cuff tears (partial/full)
• Thoracic outlet syndrome
• Cervical spondylosis
• Rotator cuff tendinitis
• Subluxating shoulder
• Acromioclavicular joint arthritis
• Adhesive capsulitis (“frozen shoulder”)
• Glenohumeral arthritis
• Paralysis of the Trapezius
• Calcific tendinitis
• Acute/chronic inflammation of the bursa subacromialis
• Cuff tear arthropathy
• Glenohumeral instability
• Nerve palsy
Diagnosis should be based on:
→ Clinical examination
History and clinical examination are necessary. Radiographs may be used to detect anatomical variants, calcific deposits or acromioclavicular joint arthritis. The three recommended views are:
- The antero-posterior view with the arm at 30 degrees external rotation. The anteroposterior view is useful for assessing the glenohumeral joint, subacromial osteophytes and sclerosis of the greater tuberosity. 10
- The outlet Y view is useful because it shows the subacromial space and can differentiate the acromial processes.
- The axillary view is helpful in visualizing the acromion and the processus coracoideus, as well as coracoacromial ligament calcifications.
The size of the subacromial space can also be measured. MRI can show full or partial tears in the tendons of the rotator cuff, cracks in the capsule and inflammation to weak structures.
Ultrasonography and arthrography are being used when rotator cuff tears are suspected or in doubtful (complex) cases. However, arthrography is invasive and expensive, it is the best diagnostic modality. Magnetic resonance imaging is also expensive but it provides the best imaging mode for rotator cuff pathology.
Also see Impingement Cluster page
Following tests help to confirm or rule out subacromial impingement:
→ Neer impingement test (useful screening test to rule out SAI)
→ Painful Arc (between 60° and 120°) (useful screening and helpful confirming test to rule out SAI)
→ Empty can (Jobe): integrity Supraspinatus (helpful test to confirm SAI)
→ External rotation resistance tests (useful screening and helpful confriming test to rule out SAI)
→ Drop arm sign: to test the integrity of the Infraspinatus.
Patient elevates the arm and returns slowly. The test is positive when the patient has suddenly severe pain or the arm drops all of the suddenly.
→ Lift-off test (or gerber lift test): Integrity Subscapulary muscle. Patient performs an internal rotation by putting his hand on the ipsilateral buttock. Next the patient needs to lift the hand from the buttock against resistance.
→ The horizontal adduction test: arm is in adduction directed to the other shoulder and the elbow is flexed. If pain occurs, then the test is positive.
→ Yergason test: the elbow is flexed at 90 degrees and the forearm pronated. The patient brings actively the forearm in supination against resistance. If there is pain in the bicipital groove area, then there is a disorder of the biceps tendon.
→ Speed test: the elbow is extended and the forearm is supinates. The patient brings his arm in a forward elevation of the humerus ( 60degrees is resisted). When there is pain in the bicipital groove area, then is the test positive.
The most sensitive diagnostic test : Hawkins test, Neer test, horizontal adduction test.
The most specificity test: drop arm test, Yergason test and the speed test.
The combination of the Hawkins-Kennedy test (testing the pain-ful arc) and the infraspinatus muscle test have a considerably higher predictive value (the higher the value, the better):
- 3 tests are positive: the probability that the patient has an impingement is 10,56
- 2 tests are positive: the probability that the patient has an impingement is 5,03
- 1 test is positive: the probability that the patient has an impingement is 0,90
- 0 tests are positive: the probability that the patient has an impingement is 0,17
add links to outcome measures here (see Outcome Measures Database)
Medical Management (current best evidence)
Surgical intervention is needed when the subacromial impingement lasts 3-6 months without significant improvement, dispite of an appropriate conservative treatment.
Especially when the passive range of motion of the patient is restricted surgery has it benefits. Surgery is also beneficial with a type III acromion in combination with large spurs, a positive response to a lidocaine subacromial injection or changes in the tendon of the rotator cuff (for example inflammation).[14,25]
Several surgical techniques are available, depending on the character and severity of the injury:
Surgical repair of torn tissues, mostly of supraspinatus muscle, long head of biceps tendon or joint capsule. Note: a rotator cuff tear is not an indication for surgery. 
Bursectomy or removal of the subacromial bursa.
Subacromial decompression to increase the subacromial space by removing bony spurs or prominences on the underside of the os acromiale or the coracoacromial ligament
Acromioplasty to increase the subacromial space by removing a part of the acromion. Arthroscopic acromioplasty is less invasive and requires lesser rehabilitation than the open (Neer) acromioplasty.
Physical Therapy Management (current best evidence)
There is strong evidence that non-operative rehabilitation - when supervised - both decreases pain in the shoulder and increases function. Non-operative treatment should therefore be attempted first, assuming there is no tear that requires surgery. There is no evidence to suggest that treatment is more effective than conservative treatment.
Several conservative treatments are available:
• RICE therapy in the acute phase to reduce pain and swelling
• NSAIDS or nonsteroidal anti-inflammatory drugs
• Corticosteroid injections
• Physical therapy
• Stability and postural correction exercises
• Stretching exercises
• Manual therapy techniques of the shoulder
• Electrical stimulation
• Ultrasound and musculoskeletal ultrasound
• Low-level laser therapy has positive effects on all symptoms except on muscle strength
• Advice and exercise leaflet
Although exercise therapy alone has proved efficient, the addition of manual therapy insures further increase in muscle strength. Exercise therapy is a vital part of treatment for subacromial impingement but results showed no significant difference between home-based exercises and clinical exercise.
Therapeutic exercises should include:
→ Rotator cuff strengthening: External rotation with thera-tubing - Horizontal abduction
→ Lower and middle trapezius strengthening: Eated press up - Unilateral scapular rotation- Bilateral shoulder external rotation - Unilateral shoulder depression
Strengthening of the lower part of the trapezius muscle is an important part of exercise therapy. Individuals with impingement syndrome show greater ratios of upper and lower trapezius activity than asymptomatic individuals. Soft tissue mobilization to normalize muscle spasm and other soft tissue dysfunction has been shown to be effective alongside joint mobilizations to restore motion in treatment of SAI. 
→ Anterior and posterior shoulder stretching: Anterior shoulder stretch - Posterior shoulder stretch
Patients with stage 1 impingement often improve with conservative treatment. Conservative training consists of resting and stopping activities. NSAIDS and ice can relieve the pain.
When the acute pain is relieved, a specific strengthening program for the rotator cuff is recommended for prevention of future injuries. The motions of the rotator cuff that are emphasized for strengthening are internal rotation, external rotation and abduction. It is important to remember that the function of the rotator cuff, in addition to generating torque, is to stabilize the glenohumeral joint. Thus, stronger rotator cuff muscles result in better glenohumeral joint stabilization and less impingement. A typical initial exercise program involves the use of 4 to 8 weights, with 10 to 40 repetitions performed three to five times a week.
Patients with stage II impingement may require a formal physical therapy program. Isometric stretches are useful in restoring range of motion. Isotonic (fixed-weight) exercises are preferable to variable weight exercises. Thus, the shoulder exercises should be done with a fixed weight rather than a variable weight such as a rubber band. Repetitions are emphasized, and a relatively light weight is used. Sometimes, sports-specific techniques are useful, particularly for strengthening the throwing motion, the serving motion or swimming motions. In addition, physical therapy modalities such as electrogalvanic stimulation, ultrasound treatment and transverse friction massages can be helpful.
The treatment depends on age, activity level and general health of the patient. The goal is to reduce pain and regain function.Conservative treatment[22,23,26]
Is used at the beginning, for several weeks to months until improvement and return tot function are noticed.
Rest: or avoiding overhead activities
NSAID’s to reduce pain and swelling
Physical therapy (see above)
Steroid injection: when the resources above don’t help relieving pain. Often cortisone because of its anti-inflammatory and pain reducing effect.[26,27]
Is recommended when the conservative treatments don’t reduce the pain.
Sugery is performed and followed by physical therapy.
Neer defined three stages of impingement (see above). Regarding those three stages, the treatment is different.
• Stage I: Often is conservative treatment sufficient. This involves resting and not doing the provocative activity. Pain can be relieved by applying ice (20 minutes, 3 times/day) and using NSAID’s (nonsteroidal anti-inflammatory drugs).
Physical therapy is also part of the treatment.
• Stage II: Physical therapy
Recent Related Research (from Pubmed)
1. KATCHINGWE AF, PHILLIPS B, SLETTEN E, PLUNKETT SW., Comparison of Manual Therapy Techniques with Therapeutic Exercise in the Treatment of Shoulder Impingement: A Randomized Controlled Pilot Clinical Trial. The Journal of Manual fckLRManipulative Therapy 2008;16(4): p238-¬‐247
Level of evidence: 2A
2. TATE A.R., MCCLURE P.W., YOUNG I.A., SALVATOR R., MICHENER L.A., Comprehensive impairment-based exercise and manual therapy intervention for patients with subacromial impingement syndrome: a case series. The Journal of orthopaedic and sports physical therapy 2010; 40(8): p474-93
Level of evidence: 4
3. BIRRER R.B., O’CONNOR F.G., Sports medicine for the primary care physician. 3rd edition, Boca Raton: RCR PRESS, 2004: p507- 10
4. DE BIE R.A., BASTIANENEN C.H.G. Effectiveness of individualized physiotherapy on pain and functioning compared to a standard exercise protocol in patients presenting with clinical signs of subacromial impingement syndrome. A randomized controlled trial. BMC Musculoskeletal Disorders. 2010 Jun 9; 11:114
Level of evicence: 1B
5. MICHENER L.A., WALSWORTH M.K., DOUKAS W.C., MURPHY K.P. Reliability and Diagnostic Accuracy of 5 Physical Examination Tests and Combination of Tests for Subacromial Impingement. Archives of Physical Medicine and Rehabilitation. 2009 Nov; 90(11): 1898-903
Level of evicence: 1C
6. DORRESTIJN O., STEVENS M., WINTERS J.C., VAN DER MEER C.,DIERCKS R.l. Conservative or surgical treatment for subacromial impingement syndrome? A systematic review.Journal of shoulder and elbow surgery board of trustees.2009 Jul-Aug;18(4):652-60
Level of evidence: 1A
7. YELDAN I., CETIN E., OZDINCLER A.R. The effectiveness of low-level laser therapy on shoulder function in subacromial impingement syndrome. Disability and rehabilitation. 2009; 31(11): 935–940
Level of evidence: 1C
8. Bang MD, Deyle GD. Comparison of Supervised Exercise With and Without Manual Physical Therapy for Patients with Shoulder Impingement Syndrome. Journal of Orthopaedic and Sports Physical Therapy. 2000;30(3):126-137
Level of evidence: 1B
9. Kuhn JE. Exercise in the treatment of rotator cuff impingement: A systematic review and synthesized evidence-based rehabilitation protocol. Journal fo Shoulder and Elbow Surgery. 2009;18:138-160
Level of evidence: 1A
10. Smith M, Sparkes V, Busse M, Enright S. Upper and Lower trapezius muscle activity in subjects with subacromial impingement symptoms: Is there imbalance and can taping change it? Physical Therapy in Sport. 2009:10, 45-50
Level of evidence 3A
16. KILCOYNE R.F., REDDY P.K., LYONS F., ROCKWOOD C.A. Jr, Optimal Plain film Imaging of the Shoulder Impgingement Syndrome, American Journal of Roentgenology 1989. 13(4): 795
Level of evidence 2C
18. READ J.W., PERKO M., Ultrasound diagnosis of subacromial impingement for lesions of the rotator cuff, AJUM 2010. 13(2): 11-15
Level of evidence 5
20. MORRISON D.S., FROGAMENI AD, WOODWORTH P., Non-operative treatment of subacromial impingement syndrome?, J Bone Joint Surg Am 1997. 79(5): 732
Level of evidence 3
21. ESCAMILLA R.F., HOOKS T.R., WILK K.E., Optimal management of shoulder impingement syndrome, open acces journal of sports medicine 2014. 2014(5):13-24
Level of evidence 1A
22. Rhon DI, Boyles RE, Cleland JA, Brown DL, A manual physical therapy approach versus subacromial corticosteroid injection for treatment of shoulder impingement syndrome: a protocol for a randomized clinical trial, BMJ Open 2011
Level of evidence 1A
25. Differential Diagnosis between common shoulder conditions, Leeds Community Healthcare, NHS Trust: www.leedscommunityhealthcare.nhs.uk/msk
27. AKGUN K, BIRTANE M., AKARIMAK U., Is local subacromial corticosteroïd injection beneficial in subacromial impingement syndrome?, Clin Rheumatol 2004, 23(6): 496-500
Level of evidence 2
28. ALGUNAEE M, GALVIN R, FAHEY T, Diagnostic accuracy of clinical tests for subacromial impingement syndrome: a systematic review and meta-analysis. Ach Phys Med Rehabil 2012, 93(2): 229-36
Level of evidence 1A
29. KHAN Y, NAGY MT, MALAL J, WASEEM M, The painful shoulder: shoulder impingement syndrome. Open Orthop J Sept 2013, 6(7): 347-51
Level of evidence 5
31. Mustafe çalis, Kenen Akgun, murat Birtane, Ilhan Karacan,Havva çalis,Fikret Tüzün, diagnostic values of clinical diagnostic tests in subacromial impingement syndrome, Ann Rheum Dis 1999
Level of evidence 1A
32. Phil Page, PhD, PT, ATC, LAT, CSCS, FACSM, SHOULDER MUSCLE IMBALANCE AND SUBACROMIAL IMPINGEMENT SYNDROME IN OVERHEAD ATHLETES, int J sport phys. Ther., 2011
Level of evidence 3
33. Michael S. Thurner, PT, DPT, CSCS,1 Robert A. Donatelli, PhD, PT,1 and Randa Bascharon, DO, ATC2, SUBSCAPULARIS SYNDROME: A CASE REPORT, Int J Sports Phys Ther. Dec 2013
level of evidence 5
34. Robert A. McCabe, MS, PT, OCS,a Karl F. Orishimo, MS,a Malachy P. McHugh, PhD,a and Stephen J. Nicholas, MDa N Am J Sports Phys Ther. Feb 2007; Surface Electromygraphic Analysis of the Lower Trapezius Muscle During Exercises Performed Below Ninety Degrees of Shoulder Elevation in Healthy Subjects
Level of evidence 3
40. Diagnostic accuracy of clinical tests for the different degrees of subacromial impingement syndrome by Hyung Bin Park, MD, Atsushj Yokoia, MD, PHD, Harpkeet S. Gill, MD, George El Rassi, MD, and Edward G. Mcfarland, MD.
Level of evidence 1
42. COOLS A, Kinesitherapeutisch Onderzoek: Bovenste Lidmaat, UGent 2010-2011
44. Lockhart RD. Movements of the Normal Shoulder Joint and of a case with Trapezius Paralysis studied by Radiogram and Experiment in the Living. J Anat 1930; 64: 288-302
Level of evicence 3a