A Novel Acromion Radiological Classification and Its Clinical Application Study: Comparing Rockwood Tilt View with Arthroscopic Findings in 101 Shoulders

Background: It is estimated that more than 25% of general population more than 60 years old experience rotator cuff tear, acromial impingement syndrome is one of the most common causes. Morphology of acromion is an important extrinsic factor in the development of rotator cuff tear. The traditional classification of the acromion by Bigliani et al. based on supraspinatus outlet view has been widely used, but due to the high requirements for patients to obtain true supraspinatus outlet view and the poor inter-observer reliability, it brings lots of limitations to the clinical use of this classification. In our clinical work, we have noticed that the formation of acromial anterolateral spur on Rockwood tilt view has some relationship to a rotator cuff tear. Objectives: To develop a new classification of acromion based on the subacromial impingement theory and the Rockwood tilt view. And explore the application value of the new classification in the diagnosis and treatment of rotator cuff tear. Methods: From January 2017 to December 2017, 101 cases of shoulder arthroscopic surgeries for impingement syndrome or rotator cuff tear were retrospectively analyzed. We developed a new classification of the acromion based on the Rockwood tilt view as type I flat acromion, type II bump acromion and type III impingement acromion. The status of the supraspinatus tendon was also recorded as no tear, partial-thickness tear, and full-thickness tear. We tested the inter-observer and intra-observer reliability of the new classification system (Kappa value) and analyzed the correlation between the acromion morphology and the rupture of the supraspinatus tendon. Results: In all 101 cases, the most common type was the impingement acromion with 46 patients (45.5%), followed by bump acromion in 37 patients (36.6%), and the flat acromion in 18 patients (17.8%). The inter-observer reliability of the new classification system was significantly better than that of the traditional classification (0.826 vs. 0.281). The incidence of supraspinatus tendon tear in the patients with impingement acromion was significantly higher than that of the other two types of acromion (chi(2) = 50.316, P < 0.05). Conclusion: The Rockwood tilt view can well demonstrate the exact architecture of the anterolateral acromion spur. The new classification based on Rockwood tilt view has high reliability and good reproducibility. The type III impingement acromion correlates highly with the supraspinatus tendon tear.