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, 12 (4), e0176193

Relationship Between Acromial Morphological Variation and Subacromial Impingement: A Three-Dimensional Analysis


Relationship Between Acromial Morphological Variation and Subacromial Impingement: A Three-Dimensional Analysis

Xinyu Li et al. PLoS One.


Purpose: To evaluate the association of acromial morphology and subacromial impingement.

Methods: Bilateral shoulder computed tomography was performed in 138 patients who received shoulder arthroscopy. Measured parameters included: acromial tilt (AT), modified acromial tilt (mAT), acromial slope (AS), acromiohumeral interval (AHI), lateral acromial angle (LAA), acromial index (AI), critical shoulder angle (CSA), acromial anterior protrusion (AAP), and acromial inferior protrusion (AIP). Acromial morphological characteristics were compared between groups. Side-to-side differences were assessed between affected and non-affected shoulders. Intra- and inter-observer agreements for each parameter were calculated.

Results: AT (25.90 vs. 29.41°), mAT (18.88 vs. 22.64°), and AHI (5.46 vs. 6.47 mm) were significantly smaller in impinged patients. The impingement group demonstrated significantly larger AI (63.50 vs. 59.84%), CSA (31.78 vs. 28.74°), AAP (7.13 vs. 5.32 mm), and AIP (5.51 vs. 4.04 mm). Regarding side-to-side comparison, the acromial morphology was significantly different between the affected and non-affected shoulders in impinged patients, while the difference was slight and insignificant in control patients. All, except AS and LAA, measured parameters demonstrated good intra- and inter-observer agreements.

Conclusions: Three-dimensional reconstructed CT scan is a reliable method to measure shoulder morphology. The acromial morphological variation is related with sub acromial impingement, however, the causal relationship of them should be further explored.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Fig 1
Fig 1. True anteroposterior view.
The plane of the scapula was derotated so that the anterior and posterior glenoid edges were overlapped.
Fig 2
Fig 2. Standard outlet view.
The view perpendicular to the glenoid plane with overlapped medial and lateral scapular margins.
Fig 3
Fig 3. Superior view.
The viewing angle was downwardly perpendicular to the plane of the acromioclavicular joint.
Fig 4
Fig 4. Humeral head removal.
The humeral head was removed to facilitate measurement.
Fig 5
Fig 5. The measurement of acromial tilt (AT) in standard outlet view.
The postero-inferior edge (point A), antero-inferior edge (point B), and the inferior tip of the coracoid process (point C) were marked. The angle ∠BAC represented the AT angle.
Fig 6
Fig 6. The measurement of modified acromial tilt (mAT) in standard outlet view.
The supraglenoid tubercle was marked as point D, the angle ∠BAD defined mAT.
Fig 7
Fig 7. Acromial slope (AS) measurement in standard outlet view.
Points A, B and the midway point on the inferior aspect of acromion (point E) were marked. The supplementary angle of ∠BEA represented the AS.
Fig 8
Fig 8. Acromiohumeral interval (AHI) measurement in standard outlet view.
The distance between the inferior aspect of the acromion and the most superior point of the humeral head was AHI.
Fig 9
Fig 9. Lateral acromial angle (LAA).
One line was drawn along the superior-most and inferior-most points of the glenoid fossa, another line was drawn parallel to the acromion undersurface. The angle formed by these 2 lines represented the LAA.
Fig 10
Fig 10. Acromion index (AI).
The AI was defined as the ratio of the distance from the glenoid plane to the lateral acromion to the distance from the glenoid plane to the lateral aspect of the humeral greater tubercle.
Fig 11
Fig 11. Critical shoulder angle (CSA).
The superior-most (point F) and inferior-most (point G) points of the glenoid fossa, as well as the most inferolateral point of the acromion (point H) were marked. The angle ∠FGH represented the CSA.
Fig 12
Fig 12. Acromial anterior protrusion (AAP).
AAP was measured on the superior view. A line coincident with the anterior aspect of the distal clavicle was drawn. The distance from the most anterior point of the acromion to this line was the AAP.
Fig 13
Fig 13. Acromial inferior protrusion (AIP).
AIP was measured on the true anteroposterior view. It was defined as the distance from the most inferior point of the anterior acromion to the line which was coincident with the inferior aspect of the distal clavicle.

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    1. Khan Y, Nagy MT, Malal J, Waseem M. The painful shoulder: shoulder impingement syndrome. Open Orthop J. 2013; 7: 347–351. doi: 10.2174/1874325001307010347 - DOI - PMC - PubMed
    1. Neer CS 2nd. Impingement lesion. Clin Orthop Relat Res. 1983; 173: 70–77. - PubMed
    1. Budoff JE, Rodin D, Ochiai D, Nirschl RP. Arthroscopic rotator cuff debridement without decompression for the treatment of tendinosis. Arthroscopy. 2005; 21: 1081–1089. doi: 10.1016/j.arthro.2005.05.019 - DOI - PubMed
    1. Henkus HE, de Witte PB, Nelissen RG, Brand R, van Arkel ER. Bursectomy compared with acromioplasty in the management of subacromial impingement syndrome: a prospective randomised study. J Bone Joint Surg Br. 2009; 91: 504–510. doi: 10.1302/0301-620X.91B4.21442 - DOI - PubMed
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Grant support

The authors received no specific funding for this work.