This study measured how consistently four experienced reviewers applied the Bigliani flat/curved/hooked acromial classification. Each read 26 sagittal oblique MR studies and 26 matched Y-view or supraspinatus outlet radiographs of the same shoulders. The question: does MR, a tomographic technique, produce more reproducible shape grading than plain film?
The Bigliani acromial classification anchors the anatomic side of the impingement story: hooked (type III) acromions carry the highest rate of full-thickness cuff tears (70%) versus 3% for flat. This paper is the critical-appraisal counterweight. Assigning a shape reliably is hard, with kappa only 0.23 on MR and 0.43 on radiographs.
The practical lesson: do not treat a single reader's "type III" as a fixed fact, because a second experienced reader will often disagree, especially on MR. When you do need to profile the acromion on plain film, order the supraspinatus outlet view, not the plain Y view, because the Y view was nondiagnostic 41% of the time versus 3% for the outlet view.
Also know the pitfall the authors flag: a coracoacromial ligament enthesophyte or AC joint osteophyte is a spur, not a true hook, which bends the whole acromion down. Mislabeling one as the other inflates your type III reads.
This study measured how consistently four experienced reviewers applied the Bigliani flat/curved/hooked acromial classification. Each read 26 sagittal oblique MR studies and 26 matched Y-view or supraspinatus outlet radiographs of the same shoulders. The question: does MR, a tomographic technique, produce more reproducible shape grading than plain film?
The Bigliani acromial classification anchors the anatomic side of the impingement story: hooked (type III) acromions carry the highest rate of full-thickness cuff tears (70%) versus 3% for flat. This paper is the critical-appraisal counterweight. Assigning a shape reliably is hard, with kappa only 0.23 on MR and 0.43 on radiographs.
The practical lesson: do not treat a single reader's "type III" as a fixed fact, because a second experienced reader will often disagree, especially on MR. When you do need to profile the acromion on plain film, order the supraspinatus outlet view, not the plain Y view, because the Y view was nondiagnostic 41% of the time versus 3% for the outlet view.
Also know the pitfall the authors flag: a coracoacromial ligament enthesophyte or AC joint osteophyte is a spur, not a true hook, which bends the whole acromion down. Mislabeling one as the other inflates your type III reads.