Original Article Acta Radiologica 2019, Vol. 60(5) 608–614 ! The Foundation Acta Radiologica The relationship between rotator cuff tear 2018 Article reuse guidelines: and four acromion types: cross-sectional sagepub.com/journals-permissions DOI: 10.1177/0284185118791211 study based on shoulder magnetic journals.sagepub.com/home/acr resonance imaging in 227 patients Jong Moon Kim1,2, Yong Wook Kim1, Hyoung Seop Kim3 , Sang Chul Lee1, Yong Min Chun4, Seung Ho Joo5 and Hyun Sun Lim6 Abstract Background: Rotator cuff tear (RCT) has been believed to be related to specific types of the acromion. However, most of the studies were performed on a small number of patients with surgical findings not considering the severity of RCT. Purpose: To analyze the relationship between age, gender, the side of the shoulder, the acromion type, and the severity of RCT using shoulder magnetic resonance arthrography (MRA). Material and Methods: A total of 277 shoulder MRA findings were analyzed by a radiologist specializing in the musculoskeletal system. The relationship between variables (age, gender, side of the shoulder, and acromion type) and the injury of the supraspinatus (no rupture, partial rupture, full rupture, complete rupture) was confirmed. The partial tear of the supraspinatus tendon was divided into bursal and articular side tear in order to investigate the damage caused by the anatomical difference of the acromion. We also confirmed the differences between single supraspinatus injury and multiple RCTs. Results: The severity of supraspinatus tear and multiple RCTs were statistically significant with the old age and the right side of the shoulder, but not with a specific acromion type. In supraspinatus partial tear, there was no statistical difference between bursal and articular side tears. Conclusion: Our study revealed that the age at which degeneration could occur also was associated with multiple RCTs and is considered to be the most important factor in RCT, not anatomical structures such as acromion type. Keywords Acromion, rotator cuff, supraspinatus, shoulder impingement syndrome Date received: 10 July 2017; accepted: 17 June 2018 1Department and Research Institute of Rehabilitation Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea Introduction 2Department of Rehabilitation Medicine, CHA Bundang Medical Center, CHA University, Seoul, Republic of Korea Rotator cuff tear (RCT) is one of the most common 3Department of Physical Medicine and Rehabilitation, National Health causes of shoulder pain found in the middle-aged popu- Insurance Service Ilsan Hospital, Seoul, Republic of Korea lation (1). However, the etiology and pathogenesis of 4Department of Orthopedic Surgery, Yonsei University College of RCT have not been clearly elucidated and are fre- Medicine, Seoul, Republic of Korea 5Department of Radiology, National Health Insurance Service Ilsan quently debated topics (2). Neer first mentioned the Hospital, Seoul, Republic of Korea term ‘‘shoulder impingement syndrome’’ in 1972, sug- 6Department of Policy Research Affairs, National Health Insurance gesting enthesophytes protruding into the subacromial Service Ilsan Hospital, Seoul, Republic of Korea space is the cause of subacromial impingement and RCT (3). Bigliani et al. classified the shape of the acro- Corresponding author: Hyoung Seop Kim, Department of Physical Medicine and Rehabilitation, mion into three types: type I (flat), type II (curved), and National Health Insurance Ilsan Hospital, 100 Ilsan-roilsan-donggu, type III (hooked). In addition, they popularized the Goyang 10444, Republic of Korea. theory of extrinsic subacromial impingement and Email: [email protected] Kim et al. 609 suggested that type III is relatively rare in asymptom- classified into four types previously described by atic individuals. Lastly, they noted that the occurrence Bigliani and Gagey (4,5). A type I acromion had an of RCT is associated with type III acromion and con- acromial angle of 0–12; a type II, 13–27; a type siderable subsequent studies have confirmed this correl- Ill, > 27; and a type IV, < 0 (Fig. 2) (8,9). The acro- ation (4). Later, Gagey et al. added type IV, a convex mial angle is the sharp bend of acromion where the inferior surface, to the acromial type classification (5). lateral border becomes continuous with the spine of These studies have been the theoretical background for the scapula. acromioplasty. The degree of supraspinatus injury was categorized According to the data of the American Board of into no tear, partial tear, full thickness tear, and com- Orthopedic Surgeons and the ambulatory surgical data- plete rupture (Fig. 3). In T2-weighted (T2W) coronal base of the New York statewide planning and research scan with fat suppression, the radiologist graded cooperative system, acromioplasty has been rapidly normal if there was no abnormality, partial tear if a increasing since the early 2000s (6). high signal line was seen at the articular or bursal However, recently it has been reported that releasing side, full thickness tear if there was a high signal cleft the coracoacromial ligament and removing the suba- through the entire thickness of the tendon with contrast cromial bursa without acromioplasty have shown no media being present in the subacromial bursa and the difference in prognosis with acromioplasty (7). shoulder joint while the continuity of tendon still was Although there have been many studies on the RCTs maintained, and complete rupture if the continuity of according to acromion type, there have been no large- tendon was disrupted. Multiple RCTs were defined as scale studies using magnetic resonance imaging (MRI) subscapularis or infraspinatus tear combined with to confirm the tears. Most studies confirmed only the supraspinatus injury over the partial tear. existence of complete tear using arthroscopy. If the acromion type indeed determines the occur- We aimed to suggest a possible pathophysiology of rence of supraspinatus tendon injury, partial tears RCT by analyzing the relationship of age, gender, the should be dominant on the articular side. To verify side of the shoulder, and the four types of acromion this hypothesis, we subdivided partial tears into the compared with the severity of supraspinatus tear and articular side and bursa side. Articular-sided partial multiple RCTs in MRI findings. tear was defined as a disruption of the smooth under- surface of the tendon, with the accumulation of the Material and Methods contrast medium within a part of the tendon. Bursal sided partial tear was defined as a disruption of the The study was conducted in accordance with the smooth upper surface of the tendon on T2W images Helsinki Declaration and was approved by the institu- obtained at MRA. tional review board (NHIMC 2014-10-008-001). The One-way ANOVA was used to compare age to the Institutional Review Board approved this study severity of supraspinatus tear, bursal/articular partial before its implementation. Between January 2013 and tear, and multiple RCTs. Pearson’s Chi-squared test December 2013, 233 individuals with shoulder pain or a was used to determine the significance between the painful arc which implied shoulder impingement syn- severity of supraspinatus tear and gender, the side of drome underwent a magnetic resonance arthography the shoulder, and acromion type. Ordinal and binary (MRA) scan. All MR images were interpreted by one logistic regression was used to correct confounding fac- resident of radiology and one radiologist who was tors and to compare supraspinatus tear and multiple experienced in musculoskeletal radiology for five RCTs with related factors (age, gender, the side of years and blinded to patients’ clinical information the shoulder, and acromion type). Statistical analyses To verify Neer’s theory that supraspinatus tear occurs were performed with SPSS for Windows (Korean due to repetitive impingement, the inclusion criteria were version 21.0) statistical package (SPSS Inc, Chicago, as follows: (i) clinical diagnosis of impingement syn- IL, USA). drome; and (ii) patients who had undergone MRA. Exclusion criteria included: (i) shoulder pain due to Results trauma; (ii) previous shoulder surgery; (iii) shoulder joint arthritis; (iv) inflammatory arthritis; and (v) con- Variables of the patients, which include age, gender, genital acromion deformity. Two patients with shoulder side of the shoulder, and acromion type in correlation pain due to trauma, one patient with previous surgery, with the severity of supraspinatus tear, are shown in and three patients with rheumatoid arthritis were Table 1. The results demonstrate that severity of excluded and a total of 227 patients were studied (Fig. 1). supraspinatus tears is statistically correlated with The acromial shape was evaluated from the oblique older age and female gender (P < 0.05) but not with sagittal plane lateral to the glenohumeral joint and acromion type. After adjusting for confounding 610 Acta Radiologica 60(5) Fig. 1. Flow chart of the patient selection. Fig. 2. Four types of acromion on MRI findings: (a) type I (flat undersurface) acromion in a 61-year-old man, an acromial angle of 0–12; (b) type II (curved convex inferior surface) acromion in a 44-year-old woman, an acromial angle of 13–27; (c) type III (inferiorly beak or hook) acromion in a 68-year-old woman, an acromial angle > 27; and (d) type IV (upward convexity of the inferior border) acromion in a 46-year-old man, an acromial angle < 0. The acromial angle is the sharp bend of acromion where the