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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 10  |  Issue : 2  |  Page : 84-88

Osteological study of morphometric analysis of acromion process and its implication in impingement syndrome


Tutor, Department of Anatomy, Surat Municipal Institute of Medical Education and Research, Surat, Gujarat, India

Date of Submission14-Dec-2020
Date of Decision03-Jan-2021
Date of Acceptance16-Jan-2021
Date of Web Publication09-Apr-2021

Correspondence Address:
Hamzah Muzammil Hafezji
B/302, Silver Palace, Opp. Dairy World, Haripura, Surat - 395 003, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/NJCA.NJCA_86_20

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  Abstract 


Background: Acromial morphology along with its position (slope/tilt) has a role in shoulder impingement. Acromioplasty is an important step in rotator cuff repair. Thus, knowledge of morphometric variations of the acromion is necessary. The aim of the study was to determine acromion morphometry and to correlate the morphometry of acromion with the dimensions of the scapula. Methodology: The study was performed on 150 dried adult human scapulae, for which age and sex were not known. The shape of the acromion was observed from posterior and lateral view and different dimensions were measured. Results: The acromial curvature (as per Bigliani classification) was found to be flat (Category I) in 23.33%, curved (Category II) in 49.33%, and hooked (Category III) in 27.34% of scapulae. The acromial shape (from posterior view) was found to be quadrangular in 22%, triangular in 31.33%, and tubular in 46.67% of scapulae. The mean values of length, breadth, and thickness of acromion were 41.14 mm, 24.89 mm, and 6.95 mm, respectively. The acromion thickness was <8 mm in 87.33% and >8 mm in 12.67%. The mean of acromion slope and tilt were 28.23° and 42.47°, respectively. Conclusions: From the study, it may be concluded that a small proportion of the population (12.67%) may be prone to develop impingement due to more acromial thickness (>8 mm). The acromion slope and tilt are larger in our population which suggests lesser predisposition to impingement syndrome.

Keywords: Acromion process, acromioplasty, arthroscopy, impingement syndrome, subacromial space


How to cite this article:
Hafezji HM. Osteological study of morphometric analysis of acromion process and its implication in impingement syndrome. Natl J Clin Anat 2021;10:84-8

How to cite this URL:
Hafezji HM. Osteological study of morphometric analysis of acromion process and its implication in impingement syndrome. Natl J Clin Anat [serial online] 2021 [cited 2021 Jun 18];10:84-8. Available from: http://www.njca.info/text.asp?2021/10/2/84/313520




  Introduction Top


Impingement of the shoulder is distinguished by shoulder pain during the overhead elevation of the arm and weakness of rotator cuff muscles. These muscles connect the proximal humerus and scapula through the subacromial space, a narrow space between the coracoacromial arch above and the proximal humerus below. This space contains rotator cuff tendons, tendons of the long head of biceps brachii, subacromial bursa, and coracoacromial ligament.[1] Impingement syndrome may be due to intrinsic factors (degenerative tendinopathy) or extrinsic factors or both. Anatomical extrinsic factors which cause excessive narrowing of subacromial space include morphometric variations of the acromion, variations in acromion position (slope/tilt), bony spur on the under surface of the acromion, or ossification of coracoacromion ligament.[2] Significant relation has been demonstrated between acromion morphology, severity of rotator cuff lesion, and range of shoulder movements.[3] Acromioplasty is an important step in rotator cuff repair in order to reduce its compression, to enhance surgical visualization as well as to enable free mobilization of underneath structures.[4] Arthroscopic rotator cuff repair combined with acromioplasty is more effective in regaining shoulder mobility and also provides significant relief from pain.[5]

A study related to acromion morphometry has not been conducted in Gujarat so far. In the present study, different dimensions of the acromion, both linear and angular, were measured and correlated with scapular dimensions and also compared with other ethnic population.


  Materials and Methods Top


The present study was performed on 150 dried adult human scapulae collected from the department, for which age and sex were not known. As cadaveric scapulae were used, ethical clearance was not required for the study. Each bone was examined for nonparametric data. Fixed points were marked on each bone to measure different dimensions. A digital Vernier caliper (accurate to 0.01 mm) was used to measure various parameters. To minimize error, each measurement was done twice, and the mean of the two values was taken as the final value. The following data were evaluated.

Nonparametric data

  1. Acromion category as per curvature (lateral view-as per Bigliani et al.[1]): flat (Category I), curved (Category II), and hooked (Category III); [Figure 1]
  2. Acromion shape (posterior view-as per Sinha et al.[6]): quadrangular, triangular, and tubular [Figure 2].
Figure 1: Acromion categories as per curvature (lateral view)

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{Figure 2s}

Parametric data

Linear parameters

The points marked on each scapula are mentioned below and shown in [Figure 3]. A: Superior most point on acromion; B: Inferior most point on acromion; C: Outermost point on acromion; D: Innermost point on acromion; E: A point 1 cm inside to point C and 1 cm below point A on acromion; F: Point on the coracoid tip; G: Posterior most point on the horizontal part of coracoid; H: Point on the top of superior glenoid tubercle; P: Superior most point on the superior angle; Q: Inferior most point on the inferior angle; R: Point on inferior glenoid tubercle and S: Point on the apex of the spine of the scapula.
Figure 3: Points to measure linear dimensions

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The following dimensions were defined and measured.

AB: Acromion length; CD: Acromion breadth; E: At point E, acromion thickness; AF: Distance between acromion tip and coracoid tip; AG: Distance between acromion tip and dorsum of coracoid; AH: Distance between acromion tip and superior glenoid tubercle; PQ: Length of scapula and RS: Width of the scapula. Considering acromion thickness, scapulae are divided into two groups; those with less than 8 mm thickness and those with more than 8 mm thickness because the population with acromion thickness more than 8 mm is prone to develop impingement.[4]

Angular parameters

Angles of acromion slope (X°) and acromion tilt (Y°) were measured between various marked points using angle measuring software (Corel Draw X3 version 13) after taking a photograph of each scapula [Figure 4].
Figure 4: Angular parameters of the acromion

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  • Acromion slope (X°): It is the angle measured between two lines marked on the under surface of acromion; one line from the anterior most point to the middle point and another line from the middle point to the posterior most point [Figure 4]
  • Acromion tilt (Y°): It is the angle measured between two lines; one line is drawn from the anterior most point to the posterior most point on the under surface of the acromion and another line from the coracoid tip to the posterior most point on the under surface of acromion [Figure 4].


Statistical analysis

The mean, standard deviation, and range of each parameter were obtained using SPSS software, version 26, IBM Corporation (SPSS Inc., USA). Correlations between different parameters were obtained using Pearson's Index. To find the difference of mean between different categories, ANOVA test was applied (OpenEpi software).


  Results Top


The nonparametric data obtained from the study are mentioned in [Table 1] and [Table 2], while parametric data in [Table 3]. In this study, the acromion thickness was less than 8 mm in 87.33% and more than 8 mm in 12.67%. On applying Pearson's correlation, it was found that acromial length has moderate correlation with the length of the scapula, while the poor correlation with the width of the scapula. Acromial breadth has fair correlation with the length of the scapula and excellent correlation with the width of the scapula.
Table 1: Distribution of acromion process based on its curvature (lateral view)

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Table 2: Distribution of acromion process based on its shape (posterior view)

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Table 3: Dimensions of acromion process and scapula

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In this study, the mean of acromion slope (X°) and acromion tilt (Y°) was 28.23° and 42.47°, respectively. For acromion slope (X°), the mean value was higher for Category I, followed by Category III and Category II, respectively. The difference of mean is statistically not significant (P = 0.63) [Table 4]. For acromion tilt (Y°), the mean value was higher for Category I, followed by Category II and Category III, respectively. The difference of mean is statistically not significant (P = 0.24) [Table 4].
Table 4: Acromion angles in different categories of the acromion process.

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  Discussion Top


Nonparametric data

In this study, the shape of the acromion (as per Bigliani et al.[1]) was found to be flat (Category I) in 23.33%; curved (Category II) in 49.33%, and hooked (Category III) in 27.34% scapulae. Other studies also found Category II as the most prevalent category.[1],[6],[7] In the present study, the prevalence was Category II, followed by Category III followed by Category I. A similar prevalence was also found in other studies.[1],[6],[8],[9],[10],[11],[12] Some studies[13],[14],[15] reported Category II as the most prevalent, followed by Category I and Category III, respectively. Category III which is prone to develop impingement was found in 27.34%. This is higher than the findings of Mansur et al.,[7] Vinay and Sheela,[13] and Balke et al.[16] while lower than findings of Bigliani et al.[1] Some studies classified acromion into four types as flat, curved, hooked, and fourth additional type of acromion having a convex undersurface in its anterior one third.[17],[18],[19] Logically, type-4 acromion should compromise subacromial space, but it has no association with rotator cuff tears so it is not given more importance.[19] Considering the sex-wise distribution of acromion shape, Category III was common in males and Category I in females.[10] Some reported Category I as most common in both males and females.[17]

In this study, on the basis of the acromion shape from the posterior view, the tubular category was most common (46.67%), followed by triangular (31.33%) and quadrangular (22%). Sinha et al.[6] and Mansur et al.[7] found quadrangular as the most common shape in their studies.

Linear dimensions

Comparison of different linear dimensions in different regional and international population is presented in [Table 5].
Table 5: Comparison of linear acromial dimensions in national and international population

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In this study, the mean acromion length was 41.14 mm, which is comparable to North Indian[6] and South Indian[13] scapulae. It is less than Nepalese scapulae,[7] Chilean scapulae,[8] Turkish scapulae,[9] Greek scapulae,[11] and Egyptian scapulae.[14] The mean acromial breadth was 24.89 mm which is more than that found in North Indian scapulae[6] and Greek scapulae[11] but less than Nepalese scapulae,[7] Chilean scapulae,[8] South Indian scapulae,[13] and Egyptian scapulae.[14]

In this study, the acromion thickness was between 4.12 and 9.15 mm (mean 6.95 mm). People with acromion thickness more than 8 mm are at risk of impingement.[4],[20] In the present study, the thickness was >8 mm in 12.67%. Rockwood et al.[4],[20] found acromion thickness between 8.2 and 8.8 mm in rotator cuff tear patients. Acromion thickness found by Mohamed and Abo-Sheishan[21] using magnetic resonance imaging was 7.5 mm in control and 8.6 mm in rotator cuff tear patients. Among Indian studies, the findings of this study are similar to the findings of Vinay and Sheela[13] and Saha and Vasudeva.[22] In acromioplasty, at first, the projecting part of the acromion (beyond the clavicle) is removed, and then, its undersurface is made smooth so as to render thickness <8 mm.[20]

The acromiocoracoid, acromioglenoid, and coracoglenoid distances will determine subacromial space. Compression of subacromial space increases the risk of impingement syndrome.[11] Acromioglenoid distance (AH) in this study was 30.06 mm, which is comparable to South Indian scapulae.[13] It is less than Nepalese scapulae[7] but more than North Indian scapulae,[6] Chilean scapulae,[8] Greek scapulae,[11] and Egyptian scapulae[14] [Table 5]. Acromiocoracoid distance depends on the length of the acromiocoracoid ligament and resecting this ligament without acromioplasty results in significant relief in pain in impingement patients. However, it results in the instability of the humerus.[23] In this study, the mean value of the distance of the acromion tip from the coracoid tip (AF) was 41.77 mm and from the posterior point of the coracoid (AG) was 41.85 mm. These values were greater than North Indian scapulae,[6] Nepalese scapulae,[7] Chilean scapulae,[8] Turkish scapulae,[9] Greek scapulae,[11] South Indian scapulae,[13] and Egyptian scapulae.[14] In Turkish scapulae[9] and Greek scapulae,[11] these values were very low [Table 5].

Acromion angles

Acromion slope denotes the relation of the anterior segment of the acromion to its posterior segment. In this study, its mean value was 28.23° with a range of 15°–44° [Table 3]. Sinha et al.[6] found 31.39° acromion slope, while in the German population, it was 21°.[15] Acromion tilt denotes the relation of the acromion with the coracoid. It is the predictor of subacromial space compression. A lesser angle increases the risk of impingement. In this study, the mean acromion tilt was 42.47° with a range of 24°–60° [Table 3]. Sinha et al.[6] found 43.78° mean acromion tilt. The findings of acromion tilt by Balke et al.[16] were 29° in control, 33° in impingement, and 34° in rotator cuff tear patients. In a cadaveric study, acromion tilt of 33.5° was found by Zukerman et al.[24] The larger acromion slope and tilt in my study may be due to different regional groups and also due to study performed on the naked bone.


  Conclusions Top


The present study provides morphometric data of the acromion process. From the study, it is evident that the acromion parameters differ considerably in different races. As per the present study, around 12.67% of our population may develop impingement syndrome because of acromion thickness more than 8 mm. The larger values of acromion slope and acromion tilt suggest lesser predisposition to shoulder impingement in our population. This information will be of great help to radiologists and orthopedic surgeons who need to know acromion morphometry before rotator cuff repair and related surgeries.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Bigliani LU, Ticker JB, Flatow EL, Soslowsky LJ, Mow VC. The relationship of acromial architecture to rotator cuff disease. Clin Sports Med 1991;10:823-38.  Back to cited text no. 1
    
2.
Seitz AL, McClure PW, Finucane S, Boardman ND 3rd, Michener LA. Mechanisms of rotator cuff tendinopathy: Intrinsic, extrinsic, or both? Clin Biomech (Bristol, Avon) 2011;26:1-2.  Back to cited text no. 2
    
3.
Michener LA, McClure PW, Karduna AR. Anatomical and biomechanical mechanisms of subacromial impingement syndrome. Clin Biomech (Bristol, Avon) 2003;18:369-79.  Back to cited text no. 3
    
4.
Rockwood CA Jr. The management of patients with massive rotator cuff defects by acromioplasty and rotator cuff debridement. Orthop Trans 1986;10:622.  Back to cited text no. 4
    
5.
Faber E, Kuiper JI, Burdorf A, Miedema HS, Verhaar JA. Treatment of impingement syndrome: A systematic review of the effects on functional limitations and return to work. J Occup Rehabil 2006;16:7-25.  Back to cited text no. 5
    
6.
Sinha MB, Sinha HP, Joy P. The acromial morphology and its implication in impingement syndrome: An anatomical study. J Anat Soc India 2018;67:30-4.  Back to cited text no. 6
    
7.
Mansur DI, Khanal K, Haque MK, Sharma K. Morphometry of acromion process of human scapulae and its clinical importance amongst Nepalese population. Kathmandu Univ Med J (KUMJ) 2012;10:33-6.  Back to cited text no. 7
    
8.
Collipal E, Silva H, Ortegal L, Espinoza E, Martinez C. The acromion and its different forms. Inter J Morphol 2010;28:1189-92.  Back to cited text no. 8
    
9.
Coskun N, Karaali K, Cevikol C, Demirel BM, Sindel M. Anatomical basics and variations of the scapula in Turkish adults. Saudi Med J 2006;27:1320-5.  Back to cited text no. 9
    
10.
Natsis K, Tsikaras P, Totlis T, Gigis I, Skandalakis P, Appell HJ, et al. Correlation between the four types of acromion and the existence of enthesophytes: A study on 423 dried scapulas and review of the literature. Clin Anat 2007;20:267-72.  Back to cited text no. 10
    
11.
Paraskevas G, Tzaveas A, Papaziogas B, Kitsoulis P, Natsis K, Spanidou S. Morphological parameters of the acromion. Folia Morphol (Warsz) 2008;67:255-60.  Back to cited text no. 11
    
12.
Toivonen DA, Tuite MJ, Orwin JF. Acromial structure and tears of the rotator cuff. J Shoulder Elbow Surg 1995;4:376-83.  Back to cited text no. 12
    
13.
Vinay G, Sheela S. Morphometric study of the acromion process of scapula and its clinical importance in South Indian population. Int J Anat Res 2017;5:4361-4.  Back to cited text no. 13
    
14.
El-Din WA, Ali MH. A morphometric study of the patterns and variation of the acromion and glenoid cavity of the scapulae in Egyptian population. J Clin Diagn Res 2015;9:8-11.  Back to cited text no. 14
    
15.
Worland RL, Lee D, Orozco CG, SozaRex F, Keenan J. Correlation of age, acromial morphology, and rotator cuff tear pathology diagnosed by ultrasound in asymptomatic patients. J South Orthop Assoc 2003;12:23-6.  Back to cited text no. 15
    
16.
Balke M, Schmidt C, Dedy N, Banerjee M, Bouillon B, Liem D. Correlation of acromial morphology with impingement syndrome and rotator cuff tears. Acta Orthop 2013;84:178-83.  Back to cited text no. 16
    
17.
Basvanna PN, Bajpe R. Study of acromial shapes in relation to gender. Natl J Clin Anat 2019;8:87-90.  Back to cited text no. 17
    
18.
Vanarthos WJ, Monu JU. Type 4 acromion: A new classification. Contemp Orthop 1995;30:227-9.  Back to cited text no. 18
    
19.
Chang EY, Moses DA, Babb JS, Schweitzer ME. Shoulder impingement: Objective 3D shape analysis of acromial morphologic features. Radiology 2006;239:497-505.  Back to cited text no. 19
    
20.
Rockwood CA Jr., Burkhead WZ. Management of patients with massive rotator cuff defects by acromioplasty and rotator cuff debridement. Orthop Trans 1988;12:190-1.  Back to cited text no. 20
    
21.
Mohamed RE, Abo-Sheishan DM. Assessment of acromial morphology in association with rotator cuff tears using magnetic resonance imaging. Egypt J Radio Nucl Med 2014;45:169-80.  Back to cited text no. 21
    
22.
Saha S, Vasudeva N. Morphometric evaluation of adult acromion process in north Indian population. J Clin Diagn Res 2017;11:AC08-11.  Back to cited text no. 22
    
23.
Su WR, Budoff JE, Luo ZP. The effect of coracoacromial ligament excision and acromioplasty on superior and anterosuperior glenohumeral stability. Arthroscopy 2009;25:13-8.  Back to cited text no. 23
    
24.
Zuckerman JD, Kummer FJ, Cuomo F, Simon J, Rosenblum S, Katz N. The influence of coracoacromial arch anatomy on rotator cuff tears. J Shoulder Elbow Surg 1992;1:4-14.  Back to cited text no. 24
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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