Review Article Subacromial Impingement Syndrome Abstract Alicia K. Harrison, MD Subacromial impingement syndrome (SIS) represents a spectrum Evan L. Flatow, MD of pathology ranging from subacromial bursitis to rotator cuff tendinopathy and full-thickness rotator cuff tears. The relationship between subacromial impingement and rotator cuff disease in the etiology of rotator cuff injury is a matter of debate. Both extrinsic compression and intrinsic degeneration may play a role. Management includes physical therapy, injections, and, for some patients, surgery. There remains a need for high-quality studies of the pathology, etiology, and management of SIS. ubacromial impingement syn- ment requires a thoughtful and Sdrome (SIS) is a common cause of thorough history and physical exam- shoulder pain.1 Possible etiologies of ination as well as appropriate imag- shoulder pain related to SIS include a ing. spectrum ranging from subacromial bursitis and rotator cuff tendinopa- thy to partial- and full-thickness ro- History tator cuff tears. Localizing and ad- From the Department of Much of the early literature is diffi- dressing the etiology of shoulder Orthopaedic Surgery, University of cult to interpret in the context of SIS Minnesota Medical School, dysfunction can be challenging due because glenohumeral conditions, es- Minneapolis, MN (Dr. Harrison), and to the interplay of pathology in SIS. the Department of Orthopaedic pecially arthritis and frozen shoulder, Surgery, Mt. Sinai Medical Center, For example, the etiology of rotator were conflated with rotator cuff and New York, NY (Dr. Flatow). cuff disease has long been debated bursal conditions. Duplay2 was likely Dr. Harrison or an immediate family and the cause is likely multifactorial, focusing on glenohumeral disease member serves as a board member, with contributions from external when he described “périarthrite,” owner, officer, or committee member compression, age-related degenera- of the American College of but he also spoke of the role of bur- Surgeons. Dr. Flatow or an tion, trauma, and vascular compro- sal inflammation under the acro- immediate family member serves as mise. Despite controversy regarding mion. Beginning in 1904, Codman3-15 a board member, owner, officer, or the importance of these factors, most wrote a series of articles that drew committee member of the American Shoulder and Elbow Surgeons and investigators believe that external attention to the bursa and the adja- the Arthroscopy Association of North compression from the anterior acro- cent rotator cuff tendons. In hind- America; has received royalties from mion, coracoacromial ligament sight, Codman’s detailed writings Innomed and Zimmer; is a member (CAL), and acromioclavicular joint of a speakers’ bureau or has made can be interpreted in many ways; paid presentations on behalf of and plays a significant role in rotator cuff however, he generally favored a trau- serves as an unpaid consultant to disease by the time treatment is con- matic explanation for supraspinatus Zimmer; and has received research sidered. Secondary causes of im- tears, whereas Meyer16-22 argued for or institutional support from Wyeth. pingement include tuberosity frac- “use attrition,” in which the rotator J Am Acad Orthop Surg 2011;19: ture nonunion or malunion, a mobile cuff tendon and biceps were “ground 701-708 os acromiale, calcific tendinitis, in- between the acromion and the hu- Copyright 2011 by the American stability, and iatrogenic factors. Ac- meral head.” Codman rejected this Academy of Orthopaedic Surgeons. curate diagnosis and effective treat- theory. In his description of supraspi- November 2011, Vol 19, No 11 701 Subacromial Impingement Syndrome 3 natus tears, Codman noted that of the impingement process. Stage I in- Figure 1 “Dr. Meyer finds similar lesions al- volves acute bursitis with subacromial though he explains them as the result edema and hemorrhage. If extrinsic of attrition,” a mechanism that Cod- compression continues, the bursa no man found “unlikely” except as a longer lubricates the underlying rota- secondary effect. He concluded, tor cuff, leading to tendinopathy of the however, that “one is tempted to rotator cuff tendons, which is classified compromise by saying that many as stage II (Figure 1). In this stage, the causes or combinations of causes anterior fibers of the supraspinatus may produce the same lesion” (ie, may become frayed and may progress rotator cuff tear). to a partial-thickness tear. Stage III is characterized by progression of a partial-thickness tear to a full-thickness Theories tear. Variations in acromial morphology The connection between SIS and ro- were originally described by Bigliani tator cuff disease has been controver- et al31 and classified into three types sial. Some believe that rotator cuff based on acromial shape: type I, flat; disease is due to primary extrinsic type II, curved; and type III, hooked. 23-25 compression; others think that They also noted that a hook-shaped the disease is generally due to intrin- acromion was associated with cuff 26,27 sic tendon degeneration, with degeneration. Since then, others have Coronal T2-weighted magnetic resonance image demonstrating subacromial impingement secondary reported a higher incidence of cuff to cuff weakness and humeral ascent rotator cuff disease and a partial- tears with type III acromial impinge- thickness tear (arrow) in a patient against the overlying structures. ment.32,33 It has been suggested that with subacromial impingement the spurs and excrescences are the re- syndrome. Extrinsic Compression sult of ossification of the CAL inser- The theory of subacromial impinge- tion.30 Chambler et al34 proposed ment has been dominated by debate that this ossification is secondary to anatomic study of CAL morphology regarding the precise location of tensile forces on the ligament and demonstrated that variants with an extrinsic compression source. demonstrated that shoulder abduc- more than one band were associated 37 Watson-Jones28 described impinge- tion places a tensile force on the liga- with rotator cuff degeneration. ment of the lateral acromion on the ment. A recent cadaver study of con- Confusion regarding whether acro- cuff in the midarc of abduction. The tact and forces between the cuff and mial shape is a primary or secondary corrective surgery, lateral or even subacromial arch revealed that sub- factor in cuff disease likely resulted radical (ie, total) acromionectomy, acromial contact and CAL bending from confusing acquired spurs with caused deltoid damage; Neer and occurred in all motions in normal native acromial shape. Nicholson 38 Marberry29 felt that the procedure shoulders.35 The authors suggest that et al helped to reduce this confu- was unnecessary. In his dissection of repetitive contact and bending of the sion in a study of age cohorts of 100 cadaver scapulae, Neer30 identi- CAL may lead to degenerative scapulae from a museum collection. fied spurs and excrescences on the changes, including the proliferative They found that the incidence of undersurface of the anterior acro- acromial spurs. spurs increased with age, whereas mion. He proposed that these Detailed anatomic studies of the overall acromial shape remained un- changes, resulting from impingement CAL have further illustrated aspects changed. of the rotator cuff and humeral head of subacromial space anatomy that against the undersurface of the ante- may play a role in the development Intrinsic Degeneration rior acromion and CAL, were pri- of impingement. In a study of 56 ca- Citing intrinsic characteristics of the marily anterior, not lateral.30 This daver shoulders, Fealy et al36 identi- rotator cuff, some authors assert that finding led Neer to propose the use fied two distinct ligamentous bands: extrinsic compression is not the pri- of anterior acromioplasty to manage an anterolateral and a posteromedial mary cause of rotator cuff disease. this pattern of impingement.24 band. Spurs were commonly found Proposed intrinsic etiologies include Neer30 initially identified three stages in the anterolateral band. Another diminished vascular supply, aging, 702 Journal of the American Academy of Orthopaedic Surgeons Alicia K. Harrison, MD, and Evan L. Flatow, MD and tensile forces leading to rotator acromion. Once this occurs, the phyte formation, acromial entheso- cuff failure. Interestingly, Ogata and changes commonly associated with phytes or sclerosis, and cystic Uhthoff39 found that the incidence SIS are seen: osteophytic spurring of changes of the humeral head are the and severity of cuff tears increased the acromion and tuberosity erosion. more common radiographic findings with age, whereas acromial degener- Supporters of the intrinsic theory related to impingement. However, all ation did not. The authors also iden- cite results in patients with partial- of these findings may be present in tified degenerative changes on the thickness cuff tears treated with asymptomatic subjects, making the acromial undersurface in 31 of 36 débridement without formal acro- relationship of such findings to the (86%) shoulders with articular-sided mioplasty and the frequency of iso- diagnosis of impingement controver- partial cuff tears. They found that lated articular-sided, partial-thick- sial. A recent study found that acro- bursal surface tears were relatively 42 ness tears. Based on results of their miohumeral distance better reflected uncommon, suggesting that cuff ten- study of this management method, the clinical status of patients with