The acromion–greater tuberosity impingement index: A new radiographic measurement and its association with rotator cuff pathology

Abstract

Purpose: Several radiographic parameters describe humeral head coverage by the acromion. We describe a new radiographic measurement, the acromion–greater tuberosity impingement index (ATI), and its ability to predict rotator cuff pathology. Methods: The ATI was measured with magnetic resonance imaging (MRI) and X-ray analysis in 83 patients with rotator cuff pathology and 76 patients with acute rotator cuff tears. The lateral acromial angle (LAA), acromion type, the acromion index (AI) and the critical shoulder angle (CSA) were measured to assess their correlations with the ATI. Receiver operating characteristic (ROC) curves were used to predict degenerative rotator cuff pathology. The change in the ATI after acromion surgery was evaluated in both groups. Results: According to the ROC curves, the ATI is a good predictor of degenerative rotator cuff pathology on both X-ray (cut-off, 0.865) and MRI (cut-off, 0.965). Patients with degenerative rotator cuff pathology had a significantly higher average ATI compared to the trauma group ( p = 0.001 for X-ray and MRI). The degenerative group had a significantly lower LAA ( p = 0.001) and a higher ratio of type III acromion ( p = 0.035) than the trauma group. The ATI on X-ray was negatively related to the LAA and positively related to the AI, the CSA and acromion type (each p < 0.05). The ATI on MRI was negatively related to the LAA and positively related to the AI and acromion type (each p <0.05). More patients in the degenerative group than the trauma group needed acromioplasty or acromion decompression ( p < 0.05). The ATI on MRI was significantly lower after acromion surgery compared to before surgery in both groups ( p < 0.05). Conclusion: The ATI is a good predictor of degenerative supraspinatus tendon tears or subacromial impingement syndrome. The ATI on MRI is more accurate and can precisely guide acromion surgery.