Author(s): Jared Stowers, MD, Glenn Sapp, MD, Jason L. Zaremski, MD, FAAPMR, Daniel Herman, MD, PhD
Originally published: November 10, 2011 Last updated: May 8, 2024
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Disease/Disorder

Definition

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

  • External impingement (Primary and Secondary)
  • Internal impingement

Etiology

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

Causes of secondary external impingement include improper rotator cuff outlet size due to inadequate muscular stabilization of the scapula1 and weakness of the trapezius and serratus anterior muscles resulting in restricted external rotation and scapular rise with upper extremity abduction.2

Internal impingement is caused by compression of the articular surface of the rotator cuff between the glenoid and humeral head.3

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 predominantly affects athletes who participate in overhead sports including baseball, softball, volleyball, tennis, and swimming. These athletes are younger, typically less than 35 years old at the development of symptoms. Secondary external impingement is less common than primary external impingement.4

Patho-anatomy/physiology

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.5 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

History

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 and cannot be used as sole diagnostic tools when evaluating for full thickness rotator cuff tears.6

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. For example, hip range of motion and strength may be deficient in baseball pitchers who are experiencing upper extremity pain.

Laboratory studies

Radiographs and imaging as below:

Imaging

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 (US) is an excellent tool for obtaining dynamic real-time anatomic information about the severity and etiology of shoulder pathology. Dynamic testing can include passive range of motion such as shoulder abduction to assess supraspinatus tendon movement and bursal pooling at the lateral aspect of the acromion, and internal and external rotation to assess subscapularis tendon movement and fluid pooling lateral to the coracoid process, related to subacromial and subcoracoid bursitis respectively.7

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. Further discussion of rotator cuff lesions can be found on the PM&R KnowledgeNOW topic Rotator Cuff Shoulder Tendon and Muscle Injuries.

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. However, the effectiveness of these interventional procedures for shoulder impingement is controversial in the literature. A recent randomized controlled trial showed that arthroscopic subacromial decompression had no clinically relevant improvement after 5-years compared to diagnostic arthroscopy or exercise therapy.8 Although the success rate for surgery has been reported to be as high as 80%-90%, surgery has not consistently been shown to provide superior outcomes to conservative options.9

Although many recreational athletes ultimately return to a good level of sport, elite athletes have less success overall. One study analyzed return to play rates of competitive and non-competitive athletes and found that recreational sports participants had a higher rate of return to pre-injury level of play compared to competitive athletes and those who play overhead sports after arthroscopic rotator cuff repair.10 It is widely accepted that the success rate for pitchers returning from rotator cuff surgery is lower than the return rate for UCL reconstruction, also known as Tommy John surgery. One recent study reported that a concomitant rotator cuff tear diminished the outcome of pitchers who had labral surgery.11

Environmental

It is critical to 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.12 One observational study determined that older age and low educational attainment were socioeconomic variables associated with a higher risk of developing non-traumatic shoulder pain in the workplace. However, informative policies detailing workplace risks and an occupational emphasis on posture, ergonomics and safety prove to be protective against the development of shoulder pain.13  

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.

The prevalence of youth participation in year-round sports has been implicated in the increasing incidence of shoulder injuries in the pediatric population. The American Academy of Pediatrics recommends that young athletes reduce the risk of development of overuse injuries and overtraining by encouraging maintenance of 1-2 days per week absent from competition and sport specific training to promote physical and psychological recovery.14 While single sport specialization is typically discouraged for young athletes, the AAP recommends that pediatric athletes take at least 2-3 months away from any specific sport throughout the year, broken into 1 month intervals if necessary.14

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.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

N/A

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.

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.15

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.16 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. Compared to traditional exercise based rehabilitation, therapeutic ultrasound does not appear to provide significant benefits.17

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.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 are promoted to have greater accuracy, clinical efficacy, and cost-effectiveness compared to landmark-guided injections,18 though some recent studies have argued that there is little difference in the efficacy of ultrasound-guided subacromial corticosteroid injections compared to landmark-guided injections.19 However, the technique is heavily dependent on operator experience.

Emerging/unique interventions

Several new interventions for SIS are emerging, such as regenerative therapies and orthobiologics including mesenchymal stem cells, platelet-enriched plasma [PRP], autologous blood) and prolotherapy. Studies have shown that orthobiologics are safe alternatives to more invasive therapies, but there is a lack of evidence that supports their efficacy as a treatment modality for rotator cuff pathologies. Additional non-surgical modalities such as acupuncture and botulinum toxin injections have mixed evidence for treating intraarticular and rotator cuff pathologies,20 though small case series have shown similar short term efficacy between Botox and corticosteroid injection when treating chronic shoulder pain.21 A recent double blind randomized controlled trial found that for patients with rotator cuff tendinopathy or partial thickness rotator cuff tears, PRP is superior to corticosteroid injections in short term pain relief and functional improvement though there is no clinically significant difference between modalities after 1 year.22  Other small studies have shown Prolotherapy and PRP to provide some improvement for rotator cuff disease.23  In cases of shoulder impingement related to calcific tendonitis, ultrasound-guided barbotage and extracorporeal shockwave therapy have shown benefit.One case series demonstrated the safety and efficacy of ultrasonic tenotomy and debridement as an alternative treatment to  in patients with calcific tendinopathy involving the supraspinatus in patients who have failed conservative management.24 

Gaps in the Evidence-Based Knowledge

Additional epidemiologic information would be beneficial, including contributing social factors to the development of shoulder impingement such as the effect of tobacco use and alcohol consumption. While a few cases suggest that down-sloped Type II and hooked Type III acromion may have higher incidence than expected in younger patients, including asymptomatic cases in overhead athletes, more studies are necessary to understand the correlation between anatomical variations and the development of shoulder impingement syndrome.25

Rehabilitation techniques and modalities should continue to be studied, such as any marginal benefits of using isotonic and isokinetic exercises.26  Multiple studies have shown that exercise based therapy has the strongest evidence in treatment of shoulder impingement syndrome. Although scapular dyskinesis has been implicated in shoulder impingement syndrome, a recent randomized controlled trial failed to show an increased benefit of the addition of scapular mobilization in the treatment of shoulder impingement syndrome. Ultimately, 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.27

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 patient population subacromial decompression works 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.28

References

  1. Deutsch A, Altchek D, Schwartz E, Otis JC, Warren RF. Radiologic measurement of superior displacement of the humeral head in impingement syndrome. J Shoulder Elbow Surg. 1996;5(3):186e93.
  2. Consigliere P, Haddo O, Levy O, Sforza G. Subacromial impingement syndrome: management challenges. Orthop Res Rev. 2018 Oct 23;10:83-91. doi: 10.2147/ORR.S157864. PMID: 30774463; PMCID: PMC6376459.
  3. Ioanna K Bolia, Kevin Collon, Jacob Bogdanov, Rae Lan & Frank A Petrigliano (2021) Management Options for Shoulder Impingement Syndrome in Athletes: Insights and Future Directions, Open Access Journal of Sports Medicine, 12:, 43-53, DOI: 10.2147/OAJSM.S281100
  4. Tucker WS, Armstrong CW, Gribble PA, Timmons MK, Yeasting RA. Scapular muscle activity in overhead athletes with symptoms of secondary shoulder impingement during closed chain exercises. Arch Phys Med Rehabil. 2010 Apr;91(4):550-6. doi: 10.1016/j.apmr.2009.12.021. PMID: 20382286.
  5. Drakos MC, Rudzki JR, Allen AA, Potter HG, Altchek DW. Internal impingement of the shoulder in the overhead athlete. J Bone Joint Surg. 2009; 91(11):2719-2728.
  6. Miller CA, Forrester GA, Lewis JS. The validity of the lag signs in diagnosing full-thickness tears of the rotator cuff: a preliminary investigation. Arch Phys Med Rehabil. 2008 Jun;89(6):1162-8. doi: 10.1016/j.apmr.2007.10.046. PMID: 18503815.
  7. Park J, Chai JW, Kim DH, Cha SW. Dynamic ultrasonography of the shoulder. Ultrasonography. 2018 Jul;37(3):190-199. doi: 10.14366/usg.17055. Epub 2017 Aug 26. PMID: 29103250; PMCID: PMC6044221.
  8. Paavola M, Kanto K, Ranstam J For the Finnish Shoulder Impingement Arthroscopy Controlled Trial (FIMPACT) Investigators, et alSubacromial decompression versus diagnostic arthroscopy for shoulder impingement: a 5-year follow-up of a randomised, placebo surgery controlled clinical trialBritish Journal of Sports Medicine 2021;55:99-107.
  9. Verhagen AP, et.al. Ergonomic and physiotherapeutic interventions for treating work-related complaints of the arm, neck or shoulder in adults. Eura Medicophys 2007;43:391-405
  10. Altintas B, Anderson N, Dornan GJ, Boykin RE, Logan C, Millett PJ. Return to Sport After Arthroscopic Rotator Cuff Repair: Is There a Difference Between the Recreational and the Competitive Athlete? The American Journal of Sports Medicine. 2020;48(1):252-261. doi:10.1177/0363546519825624
  11. Neri BR, El Attrache NS, Owsley KC, Mohr K, Yocum LA. Outcome of type II superior labral anterior posterior repairs in elite overhead athletes: effect of concomitant partial-thickness rotator cuff tears. Am J Sports Med. 2011;39(1):114-120.
  12. Jevne J. The sexy scalpel: unnecessary shoulder surgery on the rise. Br J Sports Med. 2015;49:1031-1032
  13. Rodríguez-Blanes G M, Lobato-Cañón J R, Sánchez-Payá J, Ausó-Pérez J R, Cardona-Llorens A F J. The influence of information on the prevention of occupational risks and ergonomic requirements in the development of non-traumatic osteomuscular diseases of the shoulder – a pilot study. Int J Occup Med Environ Health. 2019;32(6):825-839. doi:10.13075/ijomeh.1896.01429.
  14. Joel S. Brenner, Andrew Watson, COUNCIL ON SPORTS MEDICINE AND FITNESS; Overuse Injuries, Overtraining, and Burnout in Young Athletes. Pediatrics February 2024; 153 (2): e2023065129. 10.1542/peds.2023-065129
  15. Hallgren HCB, Holmgren T, Öberg B, et al.  A specific exercise strategy reduced the need for surgery in subacromial pain patients.  British Journal of Sports Medicine 2014;48:1431-1436
  16. Steuri R, Sattelmayer M, Elsig S, et al.  Effectiveness of conservative interventions including exercise, manual therapy and medical management in adults with shoulder impingement: a systematic review and meta-analysis of RCTs.  British Journal of Sports Medicine 2017;51:1340-1347
  17. Shanker, Bhargava & Reddy, D. & Balaji, N.S.S.N.. (2021). Comparison of exercise therapy and ultrasonic therapy in the treatment of shoulder impingement syndrome. International Journal of Physiotherapy and Research. 9. 3825-3833. 10.16965/ijpr.2021.121.
  18. Finnoff JT, et.al. American Medical Society for Sports Medicine (AMSSM) position statement: interventional musculoskeletal ultrasound in sports medicine. PMR. 2015 Feb;7(2):151-68
  19. Roddy E, Ogollah RO, Oppong R, Zwierska I, Datta P, Hall A, Hay E, Jackson S, Jowett S, Lewis M, Shufflebotham J, Stevenson K, van der Windt DA, Young J, Foster NE. Optimising outcomes of exercise and corticosteroid injection in patients with subacromial pain (impingement) syndrome: a factorial randomised trial. Br J Sports Med. 2021 Mar;55(5):262-271. doi: 10.1136/bjsports-2019-101268. Epub 2020 Aug 19. PMID: 32816787; PMCID: PMC7907566.
  20. Hermans J, et.al. Does This PatientWith Shoulder Pain Have Rotator Cuff Disease? The Rational Clinical Examination Systematic Review. JAMA. 2013;310(8):837-847.
  21. Hsu PC, Wu WT, Han DS, Chang KV. Comparative Effectiveness of Botulinum Toxin Injection for Chronic Shoulder Pain: A Meta-Analysis of Randomized Controlled Trials. Toxins (Basel). 2020 Apr 12;12(4):251. doi: 10.3390/toxins12040251. PMID: 32290577; PMCID: PMC7232231
  22. Kwong CA, Woodmass JM, Gusnowski EM, Bois AJ, Leblanc J, More KD, Lo IKY. Platelet-Rich Plasma in Patients With Partial-Thickness Rotator Cuff Tears or Tendinopathy Leads to Significantly Improved Short-Term Pain Relief and Function Compared With Corticosteroid Injection: A Double-Blind Randomized Controlled Trial. Arthroscopy. 2021 Feb;37(2):510-517. doi: 10.1016/j.arthro.2020.10.037. Epub 2020 Oct 28. PMID: 33127554.
  23. Lee DH, Kwack KS, Rah UW, Yoon SH. Prolotherapy for Refractory Rotator Cuff Disease: Retrospective Case-Control Study of 1-Year Follow-Up. Arch Phys Med Rehabil. 2015 Nov;96(11):2027-32. doi: 10.1016/j.apmr.2015.07.011. Epub 2015 Aug 5. PMID: 26254952
  24. Erickson JL, Jagim AR. Ultrasonic Tenotomy and Debridement for Calcific Tendinopathy of the Shoulder: A Pilot Case Series. Journal of Primary Care & Community Health. 2020;11. doi:10.1177/2150132720964665
  25. Inklebarger J, Gyer G, Parkunan A, Galanis N, Michael J. Rotator cuff impingement associated with Type III acromial morphology in a young athlete-a case for early imaging. J Surg Case Rep. 2017 Jan 16;2017(1):rjw234. doi: 10.1093/jscr/rjw234. PMID: 28096319; PMCID: PMC5241717.
  26. Ortega-Castillo M, Medina-Porqueres I. Effectiveness of the eccentric exercise therapy in physically active adults with symptomatic shoulder impingement or lateral epicondylar tendinopathy: A systematic review. J Sci Med Sport. 2016 Jun;19(6):438-53
  27. Reijneveld EA, Noten S, Michener LA, Cools A, Struyf F. Clinical outcomes of a scapular-focused treatment in patients with subacromial pain syndrome: a systematic review. Br J Sports Med. 2017 Mar;51(5):436-441. doi: 10.1136/bjsports-2015-095460. Epub 2016 Jun 1. PMID: 27251897.
  28. Khan M, Alolabi B, Horner N, Bedi A, Ayeni OR, Bhandari M. Surgery for shoulder impingement: a systematic review and meta-analysis of controlled clinical trials. CMAJ Open. 2019 Mar 7;7(1):E149-E158. doi: 10.9778/cmajo.20180179. PMID: 30846616; PMCID: PMC6411477   

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.

Glenn H. Sapp, MD, Daniel C. Herman, MD Jason L. Zaremski, MD. Impingement Syndromes of the Shoulder. 5/7/2021

Author Disclosure

Jared Stowers, MD
Nothing to Disclose

Glenn Sapp, MD
Nothing to Disclose

Jason L. Zaremski, MD, FAAPMR
Nothing to Disclose

Daniel Herman, MD, PhD
Nothing to Disclose