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Morphometry of the Acromion Process in Dry Human Scapulae and its Clinical Implications: A Cross-sectional Study |
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Muralidhar Reddy Sangam, Gangavarapu Sreedevi, Namburu Bhanu Sudha Parimala 1. Additional Professor, Department of Anatomy, All India Institute of Medical Sciences, Guwahati, Assam, India. 2. Associate Professor, Department of Anatomy, NRI Medical College and General Hospital, Guntur, Andhra Pradesh, India. 3. Professor, Department of Anatomy, NRI Medical College and General Hospital, Guntur, Andhra Pradesh, India. |
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Correspondence Address : Dr. Muralidhar Reddy Sangam, Additional Professor, Department of Anatomy, AIIMS, Changsari, Guwahati-781101, Assam, India. E-mail: murali_sangam@yahoo.co.in |
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ABSTRACT | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
: The coracoacromial arch, which extends laterally over the shoulder joint, is formed by the acromion process, coracoid process, and coracoacromial ligament. The acromion process plays an important role in shoulder joint formation. Morphological variations of the acromion process play a key role in determining the subacromial space. Acromioplasty is an important step in rotator cuff repair. Aim: To investigate the morphometry of the acromion process in dry human scapulae and determine the various types of acromion processes. Materials and Methods: An observational cross-sectional study was conducted in the Department of Anatomy at NRI Medical College and General Hospital, Chinakakani, Guntur, Andhra Pradesh, India. The study duration was one year and four months, from November 2020 to March 2022. A total of 100 dry human scapulae (50 right and 50 left) of unknown age and gender were included. Various types of acromion processes were identified. Measurements were taken using a digital vernier caliper (accurate to 0.01 mm) and protractor to measure parameters such as length, breadth, and thickness of the acromion process, acromiocoracoid distance, acromioglenoid distance, height of the coracoacromial arch, acromial slope, and acromial tilt. The data were analysed using Statistical Package for Social Sciences (SPSS) version 24.0. Mean, Standard Deviation (SD), and range were calculated for each morphometric parameter. Results: Three types of acromion processes were observed: type I (31%), type II (48%), and type III (21%). The mean length, breadth, and thickness of the acromion process were 43.21±2.82 mm, 25.48±2.56 mm, and 6.84±1.24 mm, respectively. The mean acromiocoracoid distance, acromioglenoid distance, and height of the coracoacromial arch were 39.87±7.63 mm, 27.34±3.58 mm, and 21.52±1.98 mm, respectively. The mean acromial slope and acromial tilt observed were 32.34±4.62° and 37.46±6.37°, respectively. Conclusion: The present study provides data on the shape, dimensions, slope, tilt, and various distances of the acromion process in dry human scapulae. The majority of the scapulae on both sides exhibited type II acromion process. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Keywords : Acromioplasty, Coracoid process, Impingement syndrome | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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INTRODUCTION | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The scapula is a flat irregular bone located on the posterolateral aspect of the thoracic cage. It has three processes: the spine, acromion, and coracoid. The acromion (Greek: akros=highest; omos=shoulder) is a bony process of the scapula that is continuous with the spinous process. The acromion is formed from various ossification centres-preacromion, mesoacromion, and meta-acromion. These merge to form a triangular epiphyseal bone and finally fuse with the basiacromion. The basiacromion fuses with the scapular spine at 12 years, and all four centres fuse by 15 to 18 years (1). In 1% to 15% of cases, this osseous union fails, and the acromion remains separate as an accessory bone called os acromiale (2). The coracoacromial arch is formed by the acromion process and the coracoid process, bridged by the coracoacromial ligament. The arch extends laterally over the shoulder joint and articulates with the clavicle to form the acromioclavicular joint. The subacromial space lies between the humeral head inferiorly, the anterior third of the acromion, coracoacromial ligament, and the acromioclavicular joint superiorly. On radiographs, the height of the space between the acromion and humeral head ranges from 1.0 to 1.5 cm (3). This space contains the rotator cuff tendons, the tendon of the long head of the biceps brachii, and a bursa. Reduction in the subacromial space can lead to shoulder impingement syndrome. Various structural abnormalities of the coracoacromial arch may cause a reduction in the subacromial space (4),(5). Morphological variations of the acromion process play a key role in determining the subacromial space. Bigliani LU et al., classified the acromion process into type I (flat), type II (curved), and type III (hooked), based on its concavity (6). The initial thickness of the acromion process helps orthopaedic surgeons decide how much bone needs to be removed and how much can be saved to maintain rotator cuff dynamics post-surgery (7). Variation in the morphology of the acromion process is one of the aetiological factors for impingement syndrome or rotator cuff injuries (8),(9). As acromioplasty is still the standard operative treatment for shoulder impingement (10), a comprehensive understanding of the morphology and morphometry of the acromion process may play an important role in the treatment of shoulder impingement syndrome. Additionally, the dimensions and shape of bones vary within and between populations. The morphology and morphometry of the acromion process have been described by various authors in different populations (11),(12),(13),(14),(15),(16). Considering the variability and clinical relevance, the present study aimed to document the morphometry of the acromion process in the South Indian population. The secondary objectives of the study were to determine the various types of acromion processes following the classification of Bigliani LU et al., (6). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MATERIAL AND METHODS | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
An observational cross-sectional study was conducted in the Department of Anatomy at NRI Medical College and General Hospital, Chinakakani, Guntur, Andhra Pradesh, India. The study duration was one year and four months, from November 2020 to March 2022. Ethical clearance was exempted by the Institutional Ethics Committee (IEC) with reference number IEC/NRIMC&GH/245/2020. NRIMC and GH, as the study involved the use of dry bones obtained from cadavers. Inclusion criteria: A total of 100 dry human scapulae (50 right and 50 left) of unknown age and gender were included in the study. Exclusion criteria: Scapulae with damaged or fractured acromion or any pathological changes in the acromion were excluded from the study. Study Procedure A digital vernier caliper, accurate to 0.01 mm, of Yuzuki make, and a stainless-steel digital protractor of Mitutoyo make were used to measure various morphometric parameters (17). Each measurement was taken twice by the same observer, and the mean of the two values was taken as the final value to minimise error. The following data were evaluated: • Type of the acromion process: The acromion process was classified into type I (flat), type II (curved), and type III (hooked) by observing its concavity (Table/Fig 1)a-c (6). • Length of acromion process (AB): The distance between the superiormost point (A) and the inferiormost point (B) on the acromion (Table/Fig 2)a. • Breadth of acromion process (CD): The distance between the outermost point (C) and the innermost point (D) on the acromion (Table/Fig 2)a. • Thickness of acromion: The thickness was measured at the point X (1 cm posterior to the anterior border and 1 cm medial to the lateral border) (Table/Fig 2)a. • Acromiocoracoid distance (ACD): The distance measured from the tip of the coracoid process (E) to the tip of the acromion process (F) (Table/Fig 2)b. • Acromioglenoid distance (AGD): The distance measured from the supraglenoid tubercle (G) to the tip of the acromion process (F) (Table/Fig 2)b. • Height of coracoacromial arch (HG): The distance between the midpoint of a line joining the tips of the coracoid and acromion processes (H) and the supraglenoid tubercle (G) (Table/Fig 2)b. • Acromion slope: The angle between two lines marked on the undersurface of the acromion on a lateral photograph-one line from the anteriormost point to the midpoint and another line from the midpoint to the posteriormost point (Table/Fig 3)a (17). • Acromion tilt: The angle between two lines marked on a lateral photograph-one line drawn from the anteriormost point to the posteriormost point on the undersurface of the acromion, and another line from the coracoid tip to the posteriormost point on the undersurface of the acromion (Table/Fig 3)b (17). Statistical Analysis The data were analysed using SPSS version 24.0. The mean, standard deviation, and range were calculated for each of the morphometric parameters. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
RESULTS | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The most common type of acromion process observed in the present study was type II (curved) in 48% (Table/Fig 1)a, followed by type I (flat) in 31% [Table/Fig-1b], and type III (hooked) in 21% of the scapulae (Table/Fig 1)c. The morphology of the acromion process on the right and left sides was studied in the present study and found that the majority on both sides (left and right) had type II acromion process, followed by type I and type III (Table/Fig 4). The mean length, mean breadth, and mean thickness of the acromion process in the present study were 43.21±2.82 mm, 25.48±2.56 mm, and 6.84±1.24 mm, respectively. The mean acromiocoracoid distance, mean acromioglenoid distance, and mean height of the coracoacromial arch in the present study were 39.87±7.63 mm, 27.34±3.58 mm, and 21.52±1.98 mm, respectively (Table/Fig 5). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DISCUSSION | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The most common type of acromion process in the present study was type II curved (48%). This was followed by type I flat (31%) and type III hooked (21%). The morphology of the acromion process reported by various authors was compared in [Table/ Fig-6] (4),(7),(8),(9),(11),(12),(13),(14),(15),(16),(17),(18),(19),(20),(21),(22). Type II was reported as the most common type of acromion process in most of the previous studies (4),(7),(8),(9),(11),(12),(13),(14),(15),(16), while a few studies described type I as the most common (21),(23). The variations in the morphology of the acromion play an important role in shoulder impingement syndrome (24). Epstein RE et al., described that type III is the most important factor causing impingement syndrome (25). Worland RL et al., observed a high incidence of rotator cuff tears in patients with type II and type III acromion (26). Balke M et al., described that the incidence of type III acromion was higher in patients with rotator cuff tears (27). The mean length, mean breadth, and mean thickness of the acromion process in the present study were 43.21±2.82 mm, 25.48±2.56 mm, and 6.84±1.24 mm, respectively. These values are consistent with other studies done in the Indian population (8),(17),(20). A comparative description of morphometric parameters reported by various authors is given in (Table/Fig 7) (4),(7),(8),(14),(17),(20),(28),(29),(30). There is a higher chance of impingement when the thickness of the acromion is more than 8 mm (31). In the present study, no scapulae were found with a thickness of the acromion process greater than 8 mm. The mean acromiocoracoid distance, acromioglenoid distance, and height of the coracoacromial arch (mm) in the present study were 39.87±7.63 mm, 27.34±3.58 mm, and 21.52±1.98 mm, respectively. These parameters were compared with previous studies (Table/Fig 8) (4),(7),(8),(14),(17),(19),(20),(22),(28),(29),(30). The acromiocoracoid distance signifies the length of the coracoacromial ligament. A lesser acromiocoracoid distance may be associated with shoulder impingement syndrome (21). The acromiocoracoid distance, acromioglenoid distance, and the height of the coracoacromial arch determine the subacromial space. A decrease in the subacromial space increases the risk of impingement syndrome (4). The acromial slope and acromial tilt in the present study were 32.34±4.62 mm and 37.46±6.37 mm, respectively. The acromial slope observed in the present study was higher, and the tilt was lower compared to the findings of Hafezji HM and Sinha MB et al., (Table/Fig 9) (17),(20). Acromial slope denotes the relation of the anterior segment of the acromion with its posterior segment, while acromial tilt denotes the relation of the acromion process with the coracoid process. Acromial tilt and slope also determine the subacromial space. If the angles are smaller, the risk of impingement will be greater (17). In the present study, acromial slope and tilt were higher, as reported by previous authors in India, suggesting a lesser predisposition to shoulder impingement. The differences in the type and morphometric parameters of the acromion process of the scapula in various studies can be attributed to differences in the methodology of the study, as well as ethnic and racial differences. Limitation(s) The scapulae used in the present study were of unknown age and gender. As the scapulae were obtained from different cadavers, the parameters of the right and left side cannot be compared. Hence, variations in the morphology and morphometry of the acromion process in relation to age, gender, and side were not studied. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CONCLUSION | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
In the present study, type II (curved) acromion was found to be the most common morphological variant. Various morphometric parameters of the acromion process observed in the present study are consistent with other studies conducted in the Indian population. The higher acromial slope and tilt in the present study suggest a lesser predisposition to shoulder impingement among the Indian population. This information may be useful to radiologists and orthopaedic surgeons in planning the treatment and surgical repair of shoulder impingement. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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