Acromion
Acromion | |
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Details | |
Identifiers | |
Latin | acromion |
MeSH | D000174 |
TA98 | A02.4.01.009 |
TA2 | 1152 |
FMA | 23260 |
Anatomical terms of bone |
In human anatomy, the acromion (from Greek: akros, "highest", ōmos, "shoulder", pl.: acromia) is a bony
Structure
The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid fossa.[1] It starts from the base of acromion which marks its projecting point emerging from the spine of scapula.[2]
Surfaces
Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and concave.[1]
Borders
Its lateral border is thick and irregular, and presents three or four
Variation
There are three morphologically distinct types of acromia and a correlation between these morphologies and rotator cuff tear:
Type | Appearance | Prevalence[3] | Angle of anterior slope[3] |
Rotator cuff tear[3] |
---|---|---|---|---|
Flat | 17.1% | 13.18 | 3.0% | |
Curved | 42.9% | 29.98 | 24.2% | |
Hooked | 39.3% | 26.98 | 69.8% |
Os acromiale
The acromion has four ossification centers called (from tip to base) pre-acromion, meso-acromion, meta-acromion, and basi-acromion. In most cases, the first three fuse at 15–18 years, whereas the base part fuses to the scapular spine at 12 years. However, in between 1% and 15% of cases, this osseous union fails and the acromion remains separate as an accessory bone. This condition is referred to as os acromiale, but rarely causes pain. Earlier estimates of its prevalence were as low as 1.4%, and this higher estimate was made by Sammarco in the year 2000, based on radiographic and anatomical studies.[4][5]
Four types of os acromiale can be distinguished:[6]
- A non-union between the meso- and meta-acromia, the most common or typical os acromiale
- A non-union between the pre- and meso-acromia
- A non-union between the pre- and meso-acromia; and between the meso- and meta-acromia, atypical
- A non-union between the pre- and meso-acromia; between the pre- and meso-acromia; and between the meta- and basi-acromia
This feature was common in skeletons recovered from the
Although historically regarded as an incidental finding, the os acromiale may occasionally produce symptoms from subacromial impingement or instability at the site of non-union.[7] In people with symptoms of os acromiale, dynamic ultrasound sometimes shows hypermobility in the area during shoulder movement, or graded compression with the probe[clarify].[8]
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Plan of ossification of the scapula. Posterior side. Acromion visible at upper left, in blue.
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Radiograph of the shoulder showing an os acromiale
In other animals
The acromion process of
In modern
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The shoulder girdle of asnapping turtle. (1) Acromion, (2) scapula, and (3) coracoid
Additional images
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Left scapula. Acromion shown in red.
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Animation. Acromion shown in red.
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Acromial angle shown in red.
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Left scapula. Posterior view. Acromion labeled at top left.
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Left scapula.Lateral view.
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Left scapula. Posterior view. Acromion is "10"
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Left scapula. Anterior view. Acromion labeled at top right.
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Left scapula. Anterior view. Acromion is "2"
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Left scapula. Lateral view. Acromion is "4"
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The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. Anterior view.
Notes
This article incorporates text in the public domain from page 203 of the 20th edition of Gray's Anatomy (1918)
- ^ a b c Gray's Anatomy 1918, see infobox
- S2CID 237348158.
- ^ a b c Habermeyer, Magosch & Lichtenberg 2006, pp. 1–3
- ^ Warner, Beim & Higgins 1998, Introduction
- S2CID 25541990. Archived from the originalon 2013-04-15. Retrieved March 2, 2013.
- ^ Habermeyer, Magosch & Lichtenberg 2006, p. 4
- ^ Kurtz CA, Humble BJ, Rodosky MW, Sekiya JK. Symptomatic os acromiale. J Am Acad Orthop Surg 2006; 14:12-9.
- ^ Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Chapter on os acromiale available at ShoulderUS.com
- ^ Rieppel & Reisz 1999
- S2CID 7836810.
- ^ Lee 1996, Abstract
- Habermeyer, Peter; Magosch, Petra; Lichtenberg, Sven (2006). Classifications and Scores of the Shoulder. Heidelberg: Springer. ISBN 978-3-540-24350-2.
- Lee, Michael S. Y. (January 22, 1996). "The Homologies and Early Evolution of the Shoulder Girdle in Turtles". Proc. R. Soc. Lond. B. 263 (1366): 111–117. S2CID 84529868.
- Rieppel, Olivier; Reisz, Robert R. (1999). "The Origin and Early Evolution of Turtles". Annual Review of Ecology and Systematics. 30: 1–22. doi:10.1146/annurev.ecolsys.30.1.1. Archived from the original(PDF) on 2018-12-26. Retrieved 2020-06-08.
- Warner, Jon J.P.; Beim, Gloria M.; Higgins, Laurence (September 1998). "The Treatment of Symptomatic Os Acromiale". The Journal of Bone and Joint Surgery. 80 (9): 1320–6. PMID 9759817.