Classifications in Brief: Bigliani Classification of Acromial Morphology.

The diagnostic spectrum from rotator cuff tendinopathy through cuff tear arthropathy causes pain and disability that can result in surgical intervention [15]. In 1931, Codman and Akerman [5] proposed that degenerative changes of the tendons initiate rotator cuff tears. Subsequently, in 1949, Armstrong [1] proposed that mechanical impingement of the rotator cuff tendons under the acromion causes supraspinatus syndrome. Neer [21] also postulated that mechanical impingement was responsible for up to 95% of rotator cuff tears and reported successful treatment with anterior acromioplasty [20]. Regardless of the etiology, acromioplasty is commonly used as a surgical adjunct for the treatment of rotator cuff tendinopathy and tears. In 1986, Bigliani and colleagues [3] were the first to classify acromial morphology and correlate it with rotator cuff tears. They described three types of acromion: Type I (flat), Type II (curved), and Type III (hooked) (Fig. 1). A Type IV acromion was later described as a convex acromion [28]. Bigliani et al. [3] and other authors [2, 6–8, 10, 13] have reported that Type III acromia have been associated with rotator cuff tears. Conversely, other authors have found no such correlation [23, 24]. Since Bigliani et al.’s [3] original description, there have been other attempts to quantify acromial morphology. Bigliani et al. [3] and Kitay [12] described the acromial slope, a measure of anterior acromial slope and the relationship between increased acromial slope and rotator cuff tears. In the same paper, Kitay [12] also described acromial tilt, the angle between a line drawn connecting the most posterior point of the inferior acromion to the most anterior point of the inferior acromion and a line drawn connecting the same most posterior point of the inferior acromion to the inferior tip of the coracoid process. Decreased acromial tilt was associated with rotator cuff tears [12]. Nyffeler et al. [22] described the acromial index, a ratio of the distance from the glenoid plane to the acromion divided by the distance from the glenoid plane to the lateral aspect of the humeral head. The authors observed that the acromion of patients with a rotator cuff tear appeared to have a more lateral extension, thus a greater acromial index, than that of patients with an intact cuff [22]. Most recently, the critical shoulder angle (CSA) was described, which not only includes acromial morphology but also considers glenoid morphology [16]. The authors observed patients with rotator cuff tears were more likely to have a CSA > 35° than a control group of patients without rotator cuff tears. Although there have been numerous attempts to find an association between rotator cuff tears and scapular morphology [2, 3, 12, 17, 18], there is no consensus as to the role of scapular morphology in the etiology of rotator cuff tears. Each author certifies that neither he, nor any member of his immediate family, have funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his institution waived approval of the reporting of this investigation and that all investigations were conducted in conformity with ethical principles of research. This work was performed at Gold Coast University Hospital, Gold Coast, Australia.