UCLA UCLA Previously Published Works Title Imaging shoulder impingement. Permalink https://escholarship.org/uc/item/0kg9j32r Journal Skeletal radiology, 22(8) ISSN 0364-2348 Authors Gold, RH Seeger, LL Yao, L Publication Date 1993-11-01 DOI 10.1007/bf00197135 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Skeletal Radiol (1993) 22:555-561 Skeletal Radiology Review Imaging shoulder impingement Richard H. Gold, M.D., Leannc L. Seeger, M.D., Lawrence Yao, M.D. Department of Radiological Sciences, UCLA School of Medicine, 10833 Le Conte Avenue, Los Angeles, CA 90024-1721, USA Abstract. Appropriate imaging and clinical examinations more components of the coracoacromial arch superiorly. may lead to early diagnosis and treatment of the shoulder The coracoacromial arch is composed of five basic struc- impingement syndrome, thus preventing progression to a tures: the distal clavicle, acromioclavicular joint, anteri- complete tear of the rotator cuff. In this article, we discuss or third of the acromion, coracoacromial ligament, and the anatomic and pathophysiologic bases of the syn- anterior third of the coracoid process (Fig. 1). Repetitive drome, and the rationale for certain imaging tests to eval- trauma leads to progressive edema and hemorrhage of uate it. Special radiographic projections to show the the rotator cuff and hypertrophy of the synovium and supraspinatus outlet and inferior surface of the anterior subsynovial fat of the subacromial bursa. In a vicious third of the acromion, combined with magnetic reso- cycle, the resultant loss of space predisposes the soft nance images, usually provide the most useful informa- tissues to further injury, with increased pain and disabili- tion regarding the causes of impingement. ty. The SIS most commonly affects young athletes who engage in repetitive overhead throwing, and older indi- Key words" Shoulder impingement syndrome - Painful viduals with degenerative changes of the coracoacromial arc syndrome - Subacromial spur - Acromioclavicular arch. spur - Supraspinatus outlet view - Os acromiale As long ago as 1931, Meyer [20] proposed that attri- tion of the rotator cuff by the undersurface of the acro- mion was the main cause of cuff rupture. Codman [3], in 1934 described a "critical zone" of hypovascularity The shoulder impingement syndrome (SIS) is a common, progressively painful and disabling disorder resulting primarily from compression of the subacromial bursa or supraspinatus tendon between the greater tuberosity of the humerus and the coracoacromial arch. A combi- nation of clinical findings and appropriate imaging eval- uations may lead to an early diagnosis, permitting con- servative, nonsurgical treatment or arthroscopic decom- pression before the disorder progresses to a complete tear of the rotator cuff. Even at a later stage of disability, imaging studies may delineate a specific cause of im- pingement, facilitating surgical intervention for pain re- lief. The SIS, also known as the painful arc syndrome, is characterized by intense pain in the shoulder when the arm is either abducted and externally rotated or ele- ,"'C ~.. x vated forward and internally rotated. The pain is caused by repeated entrapment and compression of the suprasp- inatus tendon between the proximal end of the humerus Fig. 1. Coracoacromial arch as it appears in a supraspinatus outlet inferiorly, particularly its greater tuberosity, and one or view. The arch consists of the distal clavicle, acromioclavicular joint, anterior third of the acromion (A), coracoacromial ligament Correspondence to: Richard H. Gold, M.D. (CL), and anterior third of the coracoid process (C) 1993 International Skeletal Society 556 R.H. Gold et al. : Imaging shoulder impingement in the supraspinatus tendon in the region of its attach- under 25 years of age, and often reversible with conser- ment at the greater tuberosity of the humerus. In 1949, vative treatment; stage II - fibrosis of the subacromial the "supraspinatus syndrome" (the term anteceding bursa and inflammation of the supraspinatus tendon, "SIS") and the effect of acromionectomy upon its clini- typically found in individuals between 25 and 40 years cal course were characterized [1]. Neer [25], in 1972, of age, and treatable with bursectomy or division of recounted his success with anterior acromioplasty in the coracoacromial ligament; and, with further wear, treating the syndrome, which he attributed primarily to stage III - a tear of the rotator cuff or tendon of the abnormalities of the anterior third of the acromion. In- long head of the biceps, and osteophytes and other alter- vestigating dissected scapulae, Neer found that some ations of the anterior acromion and greater tuberosity, specimens contained abnormalities of the acromion, in- typically seen in individuals over 40 years of age, and cluding proliferative spurs along the anterior lip and treatable with anterior acromioplasty combined with re- undersurface of the anterior third. He hypothesized that pair of the rotator cuff. Neer [25] also showed that a the abnormalities were caused by impingement, includ- laterally placed or shallow bicipital groove exposed the ing excessive traction by the coracoacromial ligament tendon of the long head of the biceps to impingement subsequent to its repeated impaction by the humeral by the anterior third of the acromion, resulting in inflam- head. Neer's clinical observations confirmed that the mation or rupture of the intra-articular portion of the critical site for degenerative tendinitis and tendon rup- tendon, and demonstrated that a timely anterior acro- ture was the supraspinatus tendon, extending at times mioplasty may lead to clinical improvement. Should to include the tendons of the infraspinatus and long head conservative treatment fail, current opinion favors su- of the biceps. Neer described an "impingement-injec- bacromial or acromioclavicular therapeutic decompres- tion" clinical test in which the examiner elevates the sion. While the therapeutic approach to impingement humerus of the patient with one hand while preventing lesions has evolved since Neer's earliest work, his con- scapular rotation with the other [26]; pain is produced cept of the progressive nature of impingement continues when the greater tuberosity impinges against the acro- to guide clinical practice. mion. Although this maneuver alone cannot be used Impingement thus results from depression of one or to distinguish SIS from other painful disorders of the more components of the coracoacromial arch or rough- shoulder, a diagnosis of SIS may be made should the ening of its undersurface. Abnormalities of the acromion resultant pain be relieved by injection into the subacro- that may lead to the SIS include an acromion that is mial space of a short-acting anesthetic agent. excessively low-lying in relation to the distal end of the Prior to Neer's investigations, the treatment of SIS clavicle (Fig. 2), an acromion whose anterior third is consisted of complete or lateral acromionectomy, proce- excessively downward-sloping (Fig. 3) [5] or downward dures which not only weakened the deltoid muscle, "hooking" [6, 9], osteophytic spurs along the inferior whose strength is essential when the rotator cuff is defi- surface of the anterior third of the acromion (Fig. 4) cient, but also removed a portion of the acromion that [25], an os acromiale (Fig. 5) [24], and hypertrophic was normal. Neer subsequently stressed the importance changes of the acromioclavicular joint (Fig. 6) [34]. of excising only that part of the acromion that mani- Rarely, a downward sloping coracoid process causes im- fested the spurs and roughened surface upon which the pingement of the subscapularis tendon or indirectly re- supraspinatus tendon was rubbing. He advocated ex- sults in supraspinatus impingement by depressing the cision of no more than the anterior third of the acromion coracoacromial ligament [4, 11]. Another rare cause of along with the attached coracoacromial ligament. If impingement is post-traumatic calcification or ossifica- other sites of pathology were discovered at operation, tion of the coracoacromial ligament (Fig. 7) [23]. such as a hypertrophied acromioclavicular joint, spurs An os acromiale (Fig. 5) results from a failure of fu- of the greater tuberosity, or adhesions involving the long sion of one or more of the three ossification centers head of the biceps, Neer proposed that they also should of the acromion: the metaacromion (the most proximal be removed. Should the supraspinatus tendon become center), the mesoacromion, and the preacromion (the impinged between the greater tuberosity and a degener- most distal center). The most common site of nonunion ated acromioclavicular joint which has undergone osteo- is the junction of the mesoacromion and metaacromion phyte formation and capsular hypertrophy, treatment [24]. Instability may cause repeated trauma to the rota- might combine anterior acromioplasty and partial or tor cuff. The abnormality, bilateral in over 60% of indi- complete excision of the acromioclavicular joint [34]. viduals, is best seen on radiographs in the axillary projec- Rockwood and Lyons [30] have increased their rate of tion, where it may be mistaken for a fracture. favorable operative results by using a modification of In summary, SIS primarily reflects supraspinatus im- the Neer acromioplasty, in which more of the anterior pingement related to abnormalities of the coracoacro- aspect of the acromion is resected than had been