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Disease/ Disorder


Impingement syndrome of the shoulder or shoulder impingement syndrome (SIS) is technically a clinical sign, not a diagnosis.

SIS occurs when the myotendinous junction of the rotator cuff tendons, most often the supraspinatus tendon comes into contact with either the undersurface of the acromion, a subacromial spur, or an enlarged acromioclavicular (AC) joint.

SIS is divided into two categories:1

  1. External impingement (Primary and Secondary)
  2. Internal impingement


Causes of primary external impingement include subacromial bone spurs, type 2 or 3 acromion,2 or an os acromiale, which may contribute due to increased motion of the acromion.3

Causes of secondary external impingement include improper rotator cuff outlet size due to inadequate muscular stabilization of the scapula.4

Internal impingement is caused by compression of the posterior rotator cuff between the glenoid and humeral head.5

Epidemiology including risk factors and primary prevention

Primary external impingement is the most common cause of shoulder pain and accounts for 40% of shoulder disorders.

It primarily affects persons forty years or older but can present in younger patients.

Secondary external impingement affects younger throwing athletes, less than thirty-five years old and is fairly uncommon compared to primary impingement.


The superior border of the subacromial outlet consists of the coracoacromial arch, which is made of the coracoacromial ligament, the coracoid process, and the acromion. The supraspinatus tendon and the subacromial bursa pass through this outlet.

Pathologic changes in primary external impingement include subacromial bone spurs, bursal hypertrophy, AC joint arthrosis and/or osteophytes, or abnormally shaped acromion. While these entities are noted with true impingement, it is not clear if it is a progressive disorder in which each of these factors is truly an etiologic agent.

Impingement in both primary and secondary external impingement may lead to tendinopathy or tearing of the rotator cuff.

Overhead athletes develop adaptive changes in their shoulder that allow them to have a change in the arc of rotation, specifically greater glenohumeral (GH) external rotation with reduced glenohumeral (GH) internal rotation, increased humeral head and glenoid retroversion and anterior capsular laxity.7 Clinically this is commonly referred to as GIRD (Glenohumeral Internal Rotation Deficit). This adaptive physiology may become pathologic, causing injury to the rotator cuff or labrum.

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

New onset/acute: The initial insult in SIS may only result in mechanical irritation of the rotator cuff tendons.

Subacute: Repeated exposure from external impingement may lead to subacromial bursitis or bursal side tearing.

Chronic: Chronic cases may lead to larger tears, including full-thickness tears of the rotator cuff as well as labral injuries.

Specific secondary or associated conditions and complications

Associated conditions include glenohumeral internal rotation deficit (GIRD), instability, labral tears, biceps tendinopathy, and scapular dyskinesia.

Essentials of Assessment


The hallmark symptom for external impingement is anterolateral shoulder pain with overhead activities and abduction. Patients may also describe a painful arc of motion or pain with lying on their side.

For internal impingement, the athlete typically reports posterior shoulder pain, particularly in the late cocking phase of throwing.

Physical Examination

Inspection is often normal for primary external impingement, but may demonstrate evidence of lateralization of the scapula, flattening of the anterior deltoid, and scapular winging in cases of secondary external impingement.

Overhead athletes with internal impingement may demonstrate muscular asymmetry.

Palpation may demonstrate tenderness in the region of the rotator cuff tendons. Patients with internal impingement may demonstrate tenderness in the posterior-superior GH joint.

In early stages of SIS external impingement, typically active ROM in arcs of flexion and abduction is affected in greater proportion than passive ROM and may elicit a painful arc of motion. This is in contrast to disorders such as adhesive capsulitis, which results in multi-axial loss of motion with both active and passive ROM testing. Athletes with internal impingement will demonstrate increased external rotation and decreased internal rotation with end range pain.

Other findings may include weakness of the cuff musculature, early fatigue, and micro instability.

  • Special tests that can reproduce pain include the Neer impingement sign, Empty/Full Can test, and Yocum’s test, and the Kennedy/Hawkins sign. Patients with associated scapular dyskinesis may have improvement with a painful arc with scapular positioning tests such as Scapular Assist. Patients with associated biceps tendinopathy may exhibit positive findings on tests stressing the long head of the biceps, such as with Speed’s and Yergason’s tests.

Other special tests may help assess for significant rotator cuff tendon tears. These include the Internal Lag test for subscapularis tears, the External Lag test for infraspinatus tears, and the Drop-Arm test for supraspinatus tears. However, it should be noted that while these tests have fair levels of specificity, they are significantly limited in their sensitivity.

Evaluate the cervical spine and elbow as needed. Pain and pathology at adjacent sites may cause the patient to use altered shoulder mechanics and contribute to impingement.

Clinical Functional assessment

Activities of daily living (ADL) may be limited, particularly in the elderly; these may include self-care activities above shoulder level and behind the back. Consider biomechanical evaluation of athletes and workers to improve form during loading activities. Sites remote to the shoulder may need to be addressed to help limit the amount of stress placed at the shoulder. This is based on the principle of the closed kinetic chain. Force is generated in the lower limb and transferred through a stable trunk distally into the arm.5 For example, hip range of motion and strength may be deficient in baseball pitchers who are experiencing upper extremity pain.6

Laboratory studies

Radiographs and imaging as below:


Radiography may help evaluate the morphology of the acromion, the presence of AC joint arthrosis os acromiale, or calcific tendinopathy, and rule out lesions of the humeral head or subluxation.

Musculoskeletal (MSK) ultrasound is an excellent tool to obtain dynamic real-time anatomic information about the severity and etiology of shoulder pathology.

Magnetic resonance imaging (MRI) can pinpoint partial and full-thickness rotation cuff tendon injuries with high sensitivity. Magnetic resonance arthrogram (MRA) can be used to evaluate damage to the labrum or to assess capsular laxity and should be considered in cases when the patient had prior surgery.

Magnetic resonance imaging should be considered in patients who have not adequately progressed with conservative measures and who may qualify for surgical intervention to assess the degree of any rotator cuff lesion and concomitant muscle fatty infiltrate that may be present.27 Further discussion of rotator cuff lesions can be found here.

Early predictions of outcomes

If the patient fails conservative measures, surgical treatment including subacromial decompression, distal clavicle resection, rotator cuff repair and labral injury repair may be considered. Recent studies have questioned the effectiveness of these procedures for shoulder impingement. Although the success rate for surgery has been reported to be as high as 80%-90%8, surgery has not consistently been shown to provide superior outcomes to conservative options.9

Although many recreational athletes do return to a good level of sport, elite athletes have less success overall. For example, it is widely accepted that the success rate for pitchers returning from rotator cuff surgery is lower than the return rate for Tommy John surgery. One recent study reported that a concomitant rotator cuff tear diminished the outcome of pitchers who had labral surgery.10


Consider an ergonomic evaluation of the workspace. Poor positioning of computer equipment and other items in the workspace may result in postural and overuse factors which contribute to impingement.11

Social role and social support system

Concern is increasing over the rising incidence of shoulder injuries in the pediatric population due to the increase in year-round sports. Sports participants with significant overhead demands such as baseball should have a minimum of two to three months away from overhead sports during the year.12

Injury prevention must focus on targeting proper throwing mechanics, monitoring the amount of training, and the number of throws. Consider the use of pitch counts in youth baseball players by age group.

Professional Issues


Rehabilitation Management and Treatments

Available or current treatment guidelines

Current treatment guidelines require initial course of conservative treatments, followed by surgical referral for recalcitrant cases.13

Initial treatment involves activity modification, physical therapy and analgesic medications. The rehabilitation program should include allowing the injured tissue to heal, minimizing the effects of immobility from pain, focus on shoulder ROM, scapular stabilization followed by a gradual increase of strength of the rotator cuff. Therapy that included eccentric exercises for the rotator cuff and scapula stabilizers with a progression in load have been shown to reduce the need for surgery.14

If the patient fails to make progress due to pain limiting participation in therapy, a subacromial corticosteroid injection may provide significant pain control and allow progression in physical therapy. Ultrasound-guided injections have shown improved short-term outcomes compared to landmark-guided techniques.15 Nonsteroidal anti-inflammatory medications, cold modalities, low level laser therapy, extracorporeal shockwave therapy, taping, and suprascapular nerve blocks15 may also be used to help treat the pain and inflammation. Therapeutic ultrasound does not appear to provide significant benefits.16

Surgery should be considered only after a 3- to 6-month period of targeted rehabilitation. If the patient has not improved and the diagnosis is in question, a more extensive work-up such as using advanced imaging should be considered prior to surgical referral.

At different disease stages

Treatment depends on the accuracy of determining the anatomic and biomechanical deficits.

Symptom relief is approached through avoiding provocative activities, relative rest, modalities, medications, or injections, as necessary.

Rehabilitation strategies include correction of kinetic chain deficits and re-establishing normal shoulder ROM, muscle recruitment patterns and scapulohumeral rhythm. This is followed by proprioceptive and neuromuscular training, then integrating the entire kinetic chain into occupational and sport-specific training.

Coordination of care

Most patients with SIS can be successfully treated within 3 months when placed in a well-structured rehabilitation program.17 The physiatrist must coordinate the care of multiple providers who can function as a team to help the patient with symptoms. Members of the team include physical therapists, trainers, for sports injuries, coaches and trainers and for injured workers sometimes case managers need to be part of the team – that of course, includes the patient.

Patient & family education

Patients need to be educated on SIS as an entity and the various treatment options available, specifically the critical role of the home exercise program in the overall management plan. Patient expectations also must be assessed so that the patient is aware that recovery can be slow.

Emerging/unique Interventions

The most common shoulder outcome form used for clinical and research purposes is the Disabilities of the Arm, Shoulder and Hand (DASH) Outcome Questionnaire. Multiple other shoulder-base scales exist, including the Constant Score, UCLA Shoulder Score, Western Ontario Rotator Cuff Index (WORC), Rotator Cuff Quality of Life Questionnaire (RC-QOL), and Shoulder Pain and Disability Index (SPADI).

The Penn Shoulder Score is a 100-point shoulder-specific self-report questionnaire consisting of 3 subscales of pain, satisfaction, and function. This scale is typically utilized by surgeons to assess postoperative functional gains.

Translation into practice

Strive to make sure that the athlete is fully pain free with normal ROM and strength prior to letting him or her return to full play. Consider the strength and rehabilitative needs of the entire kinetic chain.

Rehabilitation starts first with reversing typical kyphosis by retracting the scapula, opening up the thoracic outlet and reducing impingement.

Rehabilitation then consists of strengthening the scapula stabilizers and upper trunk core muscles; only after this step is accomplished does one begin looking at strengthening the rotator cuff muscles, after tendon pain has resolved.

Sport specific or work specific exercises must be included at the end of the rehabilitation to complete the treatment and prevent future injury.

Cutting Edge/ Emerging and Unique Concepts and Practice

MSK ultrasound is fast becoming a popular imaging modality for direct visualization of the rotator cuff. Ultrasound has the advantage of being a quick and dynamic technique and allows for image-guided injections. Ultrasound guided injections have greater accuracy, clinical efficacy, and cost-effectiveness compared to landmark-guided injections.18 However, the technique is heavily dependent on operator experience.

Emerging/unique interventions

Several new interventions for SIS are emerging, such as regenerative therapies (eg, mesenchymal stem cells, platelet-enriched plasma [PRP], autologous blood), prolotherapy, acupuncture and botulinum toxin, but strong evidence to support them is thus far lacking.20,21 Prolotherapy and PRP have shown improvement for rotator cuff disease in a small number of studies.22,23 In cases of shoulder impingement related to calcific tendonitis, ultrasound-guided barbotage and extracorporeal shockwave therapy have shown benefit.24

Gaps in the Evidence- Based Knowledge

Additional epidemiologic information would be beneficial, including the prevalence by acromial type and the association of this condition with medical and social (e.g. smoking) factors.

Rehabilitation techniques and modalities should continue to be studied, such as any marginal benefits of using isotonic and isokinetic exercises.19 Few studies have shown support for scapular-focused exercise therapy, mobilization, and taping. More high-powered studies will be needed to determine the true effect.25

There are limited studies on the use of PRP, prolotherapy, and mesenchymal stem cells. More information is needed to determine their role in this condition. No standard technique has been established for these therapies, making them more difficult to study.

Conservative interventions and modalities such as hyaluronate, long-duration ultrasound, pulsed electromagnetic field, transcutaneous electrical nerve stimulation, myofascial trigger point therapy, acupuncture, diacutaneous fibrolysis, microwave and interferential light therapy should continue to be studied.

There is some controversy on the role of oral medicines, particularly NSAIDs, in conditions with tendinopathic components, as NSAIDs may impair the recovery of the tendon quality of the rotator cuff and/or increase the risk for injury. There is recent controversy on the true efficacy of surgical interventions, and in what patients subacromial decompression work best. Studies have suggested that surgical intervention has little, if any, benefit in comparison to conservative measures such as physical therapy in the middle-aged adult population.26


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Original Version of the Topic

Kevin Pak, MD. Impingement Syndromes of the Shoulder. 11/10/2011.

Previous Revision(s) of the Topic

Daniel C. Herman, MD and Jason L. Zaremski, MD. Impingement Syndromes of the Shoulder. 4/5/2017.

Author Disclosure

Glenn H. Sapp, MD
Nothing to Disclose

Daniel C. Herman, MD, PhD, FACSM, FAAPMR, CAQSM
Nothing to Disclose

Jason L. Zaremski, MD, CAQSM, FACSM, FAAPMR
Nothing to Disclose