|Year : 2021 | Volume
| Issue : 2 | Page : 84-88
Osteological study of morphometric analysis of acromion process and its implication in impingement syndrome
Hamzah Muzammil Hafezji
Tutor, Department of Anatomy, Surat Municipal Institute of Medical Education and Research, Surat, Gujarat, India
|Date of Submission||14-Dec-2020|
|Date of Decision||03-Jan-2021|
|Date of Acceptance||16-Jan-2021|
|Date of Web Publication||09-Apr-2021|
Hamzah Muzammil Hafezji
B/302, Silver Palace, Opp. Dairy World, Haripura, Surat - 395 003, Gujarat
Source of Support: None, Conflict of Interest: None
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 Sep 20];10:84-8. Available from: http://www.njca.info/text.asp?2021/10/2/84/313520
| Introduction|| |
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. 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. Significant relation has been demonstrated between acromion morphology, severity of rotator cuff lesion, and range of shoulder movements. 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. Arthroscopic rotator cuff repair combined with acromioplasty is more effective in regaining shoulder mobility and also provides significant relief from pain.
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|| |
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.
- Acromion category as per curvature (lateral view-as per Bigliani et al.): flat (Category I), curved (Category II), and hooked (Category III); [Figure 1]
- Acromion shape (posterior view-as per Sinha et al.): quadrangular, triangular, and tubular [Figure 2].
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.
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.
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].
- 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].
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|| |
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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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|| |
In this study, the shape of the acromion (as per Bigliani et al.) 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.,, 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.,,,,,, Some studies,, 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., Vinay and Sheela, and Balke et al. while lower than findings of Bigliani et al. 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.,, Logically, type-4 acromion should compromise subacromial space, but it has no association with rotator cuff tears so it is not given more importance. Considering the sex-wise distribution of acromion shape, Category III was common in males and Category I in females. Some reported Category I as most common in both males and females.
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. and Mansur et al. found quadrangular as the most common shape in their studies.
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 and South Indian scapulae. It is less than Nepalese scapulae, Chilean scapulae, Turkish scapulae, Greek scapulae, and Egyptian scapulae. The mean acromial breadth was 24.89 mm which is more than that found in North Indian scapulae and Greek scapulae but less than Nepalese scapulae, Chilean scapulae, South Indian scapulae, and Egyptian scapulae.
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., In the present study, the thickness was >8 mm in 12.67%. Rockwood et al., found acromion thickness between 8.2 and 8.8 mm in rotator cuff tear patients. Acromion thickness found by Mohamed and Abo-Sheishan 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 and Saha and Vasudeva. 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.
The acromiocoracoid, acromioglenoid, and coracoglenoid distances will determine subacromial space. Compression of subacromial space increases the risk of impingement syndrome. Acromioglenoid distance (AH) in this study was 30.06 mm, which is comparable to South Indian scapulae. It is less than Nepalese scapulae but more than North Indian scapulae, Chilean scapulae, Greek scapulae, and Egyptian scapulae [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. 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, Nepalese scapulae, Chilean scapulae, Turkish scapulae, Greek scapulae, South Indian scapulae, and Egyptian scapulae. In Turkish scapulae and Greek scapulae, these values were very low [Table 5].
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. found 31.39° acromion slope, while in the German population, it was 21°. 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. found 43.78° mean acromion tilt. The findings of acromion tilt by Balke et al. 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. 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|| |
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.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]