Original Articles
Shape of the acromion: Congenital or acquired—A macroscopic, radiographic, and microscopic study of acromion*

https://doi.org/10.1067/mse.2001.114681Get rights and content

Abstract

Debate continues as to whether the differing shapes of the acromion are congenital or acquired. This has been investigated by neonatal cadaver study, adult cadaver study, radiographic study, magnetic resonance imaging study, or various other means. No one, to our knowledge, has investigated this by histologic study. A macroscopic and histologic study of 22 cadaveric shoulder joints was carried out to establish what, if any, developmental changes occur in the differing patterns of acromion. The cadaveric shoulders were dissected and examined macroscopically. All of the acromion processes were transected and photographed, and the histology of the anterior and inferior surfaces was studied. In all of the curved and hooked types of acromion, a common pattern of degeneration of collagen, fibrocartilage, and bone was observed, consistent with a traction phenomenon. None of the flat acromions exhibited these changes. Extensive histologic changes were noted on the anterior surface of acromion as compared to the inferior surface in curved or hooked acromion. We conclude that the different shapes of acromion are, therefore, acquired as a response to traction forces applied via the coracoacromial ligament and are not congenital in origin. (J Shoulder Elbow Surg 2001;10:309-16.)

Introduction

Irregularity in the shape of coracoid and acromion was first reported by Goldwaite in 1909.1 In 1987 Morrison and Bigliani2 described 3 different types of acromion process (flat, curved, and hooked). They also correlated the rotator cuff tear with the shape of the acromion. Although the data from that study indicate a strong association between cuff tear and hooked acromion, it cannot be determined whether different shapes of acromion process occur as a result of the rotator cuff dysfunctions or rotator cuff tears occur as a result of the curved or hooked shape of the acromion process. So, is the hooking of the acromion a cause of impingement, a result of the impingement, or both? Are the different shapes of the acromion process congenital or acquired?

To determine the answers to these questions, we carried out a cadaveric study of the shoulder joint. Our aim was to investigate the morphology and developmental changes of the acromion by macroscopic, radiographic, and microscopic examination of the acromion process.

Section snippets

Materials and methods

The study included 22 randomly selected cadaveric shoulder joints. Twelve specimens were paired from 6 cadavers, and 10 were unpaired. All of the cadavers were preserved in a standard embalming fluid (a mixture of formalin, phenol, glycerine, spirit, and water). All had died of medical problems such as pulmonary or cardiac conditions. None had upper limb deformity. Their age at death ranged from 69 to 93 years (mean, 81.5 years). There were 8 specimens from female cadavers and 14 from male

Results

Twenty-two cadaveric shoulder joints were studied, but failure in processing left 18 for the final analysis.

Discussion

Our histologic findings have demonstrated that the flat acromions—despite the advanced age of the specimens—show no change in collagen, fibrocartilage, or bone of the anterior and inferior surfaces. However, curved acromions all exhibit marked degenerative changes in the collagen of the coracoacromial ligament and the inferior periosteum. They also showed characteristic hypertrophy in Sharpey's fibers and secondary changes in the underlying bone. In all of these specimens, collagen,

Acknowledgements

We thank Mr J. Stothard (MSc Course Director, University of Teesside), Mr S. C. Deshmukh (Consultant Orthopaedic Surgeon), Carol Cresswell (Histopathology Department, RVI), Dr A. Coulthard (Consultant Radiologist, RVI, Newcastle upon Tyne), Mrs C. E. Harkness, and Dr D. Shanahan (Anatomy Department, University of Newcastle upon Tyne), and Dr G. Weston for their help in this project.

References (7)

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Reprint requests: Nirav N. Shah, MBBS, MS(Orth), MSc(Orth), 42, Sandhurst Rd, Tunbridge Wells, Kent, TN2 3JT, United Kingdom.

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