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.

A high acromion-greater tuberosity impingement index increases the risk of retear after arthroscopic rotator cuff repair

“…In a previous study, we demonstrated that the ATI is a good predictor of degenerative supraspinatus tendon tears and subacromial impingement syndrome. 12 The preoperative ATI may be used to plan and implement the range of acromioplasty required to reduce the incidence of postoperative subacromial impingement. Additionally, we speculated that a reduced ATI could lower the risk of retear after ARCR.…”

“…The ATI was calculated using the following equation: ATI = CT/CA, where CT is the distance from the centre of rotation of the humeral head to the humeral greater tuberosity, and CA is the distance from the centre of rotation of the humeral head to the undersurface of the acromion. 12 The AI was calculated using the following equation: AI = AG/HG, where AG is the distance from the acromion to the glenoid, and HG is the distance from the lateral part of the humeral greater tuberosity and the glenoid. 16 The LAA was defined as the angle between a line drawn parallel to the lateral glenoid surface and a line along the undersurface of the acromion.…”

“…10,11 Because these indicators do not provide information about the greater tuberosity of the humerus, they do not reflect the kinematics of the glenohumeral joint or the distance from the lateral aspect of the acromion to the humeral head. 12 The acromion-greater tuberosity impingement index (ATI) has recently gained interest as an important risk factor for RCT. 12 The ATI is calculated by measuring the distance from the centre of rotation of the humeral head to the humeral greater tuberosity and dividing it by the distance from the centre of rotation of the humeral head to the undersurface of the acromion.…”

“…12 The acromion-greater tuberosity impingement index (ATI) has recently gained interest as an important risk factor for RCT. 12 The ATI is calculated by measuring the distance from the centre of rotation of the humeral head to the humeral greater tuberosity and dividing it by the distance from the centre of rotation of the humeral head to the undersurface of the acromion. This index combines the subacromial space width and acromion type into a single quantifiable parameter.…”

“…Studies have reported that the ATI is strongly related to degenerative supraspinatus tendon tears and subacromial impingement syndrome. 12 However, to date, no study has evaluated the relationship between the ATI and retear after ARCR.…”