## Why "Massive rotator cuff tear with acromiohumeral distance narrowing" is right The acromiohumeral distance (AHD) is measured on AP shoulder X-ray as the gap between the humeral head and the acromion (structure **C**). Normal AHD ranges from 7–14 mm. A measurement of 4 mm indicates significant narrowing, which is a classic radiographic sign of massive rotator cuff tear. The loss of rotator cuff (SITS muscles) support allows superior migration of the humeral head toward the acromion. This finding, combined with the clinical presentation of progressive shoulder pain and loss of abduction (supraspinatus function), is pathognomonic for massive cuff pathology. (Maheshwari 10e; Harrison 21e) ## Why each distractor is wrong - **Anterior shoulder dislocation with Hill-Sachs lesion**: Anterior dislocation presents acutely with severe pain, loss of deltoid contour, and arm held abducted and externally rotated. The humeral head is displaced anteriorly and inferiorly on X-ray. The AHD would be normal or widened, not narrowed. Hill-Sachs is a posterolateral humeral head impaction seen on axillary view, not AHD narrowing. - **Acromioclavicular joint separation (Rockwood Grade III)**: AC separation disrupts the alignment of the clavicle and acromion (structure **C**), but the question explicitly states normal alignment of these structures. AC separation does not cause AHD narrowing; it is a ligamentous injury graded by displacement severity, not by humeral head position. - **Adhesive capsulitis with preserved joint space**: Frozen shoulder presents with pain and stiffness but preserves the glenohumeral joint space and normal AHD on X-ray. There is no superior migration of the humeral head. MRI may show capsular thickening, but plain X-ray findings are typically normal. **High-Yield:** AHD <7 mm on AP shoulder X-ray = massive rotator cuff tear until proven otherwise; normal is 7–14 mm. [cite: Maheshwari 10e; Harrison 21e]
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