Acromion morphology and morphometry in the light of impingement syndrome and rotator cuff pathology

Mythraeyee Prasad; Sipra Rout; Priyanka Clementina Stephen

doi:10.4103/JASI.JASI_32_19

ORIGINAL ARTICLE

Year : 2019 | Volume : 68 | Issue : 1 | Page : 27-33

Acromion morphology and morphometry in the light of impingement syndrome and rotator cuff pathology

Mythraeyee Prasad, Sipra Rout, Priyanka Clementina Stephen
Department of Anatomy, Christian Medical College, Vellore, Tamil Nadu, India

Date of Web Publication

16-Jul-2019

Correspondence Address:
Dr. Sipra Rout
Department of Anatomy, Christian Medical College, Vellore, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JASI.JASI_32_19

Abstract

Introduction: Acromion process of the scapula and the subacromial space plays an important role in shoulder impingement syndrome and rotator cuff pathology. The aim is to study the morphological and morphometric parameters of the acromion process of human dry scapula in the South Indian population for its relevance in shoulder impingement syndrome and rotator cuff pathology. Material and Methods: Seventy adult unpaired dry scapulae (35 right and 35 left) of unknown age, gender, and without deformity were studied. The various shapes of acromion process were identified. Parameters such as acromioglenoid (AG) distance, coracoglenoid (CG) distance, coracoacromial (CA) distance, and height of the coracoacromial arch (HtCAA) were measured using a digital vernier caliper. The data were statistically analyzed. Results: The three types of acromion process observed were Type I flat in 57.14%, Type II curved in 40%, and Type III hooked in 2.86%. The mean ± standard deviation of AG distance was 24.9 ± 3.7 mm, CG distance was 22.7 ± 4.2 mm, AC distance was 30.9 ± 5.4 mm, and HtCAA was 19.2 ± 2.7 mm. A significant difference was observed with respect to AG (P = 0.04) and CG (P = 0.0007) between both sides of the scapula. Discussion and Conclusion: Knowledge about the common variant and morphometric dimensions of acromion process can aid to better understanding and planning for the treatment of rotator cuff pathology due to impingement syndrome.

Keywords: Acromion morphology, morphometry, rotator cuff pathology, shoulder impingement syndrome

How to cite this article:
Prasad M, Rout S, Stephen PC. Acromion morphology and morphometry in the light of impingement syndrome and rotator cuff pathology. J Anat Soc India 2019;68:27-33

How to cite this URL:
Prasad M, Rout S, Stephen PC. Acromion morphology and morphometry in the light of impingement syndrome and rotator cuff pathology. J Anat Soc India [serial online] 2019 [cited 2023 Mar 24];68:27-33. Available from: https://www.jasi.org.in/text.asp?2019/68/1/27/262717

Introduction

Scapula is a flat, triangular bone lying on the posterolateral aspect of chest wall. The processes of the scapula include the spinous process and its continuation, the acromion, and the coracoid. The tip of the acromion and the lateral border of the coracoid are bridged by the coracoacromial (CA) ligament.

The acromion along with coracoid process and the CA ligament forms the protective CA arch over the shoulder joint. The underneath subacromial space contains the tendons of rotator cuff muscles and biceps brachii. Any factor leading to reduction in the subacromial space can produce shoulder impingement syndrome. Structural abnormalities of the CA arch have been noted to reduce this space.^[1] The morphological variant of acromion process plays a key role in this regard. Accordingly, the acromion process has been classified into three different types based on the degree of concavity of its under surface as Type I flat, Type II curved, and Type III hooked by Bigliani et al. (1986).^[2] This classification system has been considered to be one of the dominant diagnostic tools for shoulder impingement syndrome and rotator cuff pathologies. Farley et al. also described significant clinical correlation of CA arch anatomy in rotator cuff pathologies.^[3] The importance of the subacromial space in impingement syndrome was also shown by Sperner.^[4]

Several authors all over the world studied the morphological variants and morphometric parameters of the acromion in different population.^{[5],[6],[7],[8],[9],[10]} These parameters have shown to alter the anatomy of the CA arch to a variable extent. Hence, a detailed knowledge about the morphology and the morphometry of the acromion is required for the orthopedicians while treating cases of shoulder impingement syndrome and rotator cuff pathology.

Material and Methods

This study was conducted in the Department of Anatomy, Christian Medical College, Vellore, after obtaining ethical clearance and approval from the Institutional Review Board. Seventy unpaired dry adult human scapulae (35 right and 35 left) of unknown age and gender, available in the department were studied. Scapula with deformed acromion process, coracoid process, and supraglenoid tubercle (SGT) due to fracture or bony mass was excluded from the study.

Morphology of acromion process

For the observation of morphology of acromion and morphometric measurements, the position of dry scapula was fixed with the help of bench vises. The various shapes of the acromion were noted by observing the inferior surface of the acromion from the lateral aspect and were classified as three types as Type I (flat), Type II (curved), and Type III (hooked) based on the classification by Bigliani et al. for both sides.^[2] The most common type was identified for each side.

Morphometric parameters of the acromion

For morphometric parameters, the bony landmarks such as the tip of acromion, the tip of coracoid process, and the SGT were identified and marked. All these measurements were done using a Sliding Digital Vernier Caliper (Robust, Germany) with an accuracy of up to 0.01 mm. The following parameters were studied.

Acromioglenoid (AG) distance: Distance between the tip of the acromion and the SGT
Coracoglenoid (CG) distance: Distance between the tip of the coracoid process and the SGT
CA distance: Distance between the tip of coracoid process and the tip of acromion process. The CA ligament was represented using a white thread extending between the coracoid process and acromion
Height of the CA arch (HtCAA): To measure the HtCAA, the midpoint of the CA distance was identified and marked on the white thread. The vertical distance between this point and the SGT was measured. This HtCAA represented the underneath subacromial space.

The data were entered in the Microsoft Excel 2010 sheet and statistically analyzed using Stata Statistical Software: Release 13 (StataCorp., College Station, TX: StataCorp LP, USA). The incidence for the most common type on both sides of the dry scapula was identified. The mean, standard deviation, and range were calculated for each of the above-said morphometric parameters. The comparison between these morphometric measurements was made between the sides of the unpaired specimens using two-sample t- test. P < 0.05 was considered statistically significant.

Results

Shape of the acromion

The most common type of the acromion observed in the current study was Type I or flat [Figure 1] in 57.14% and Type II or curved [Figure 2] in 40% of cases, and the least common was the Type III, i.e., hooked [Figure 3], in 2.85% of cases [Table 1].

Figure 1: Flat acromion process

Click here to view

Figure 2: Curved acromion process

Click here to view

Figure 3: Hooked acromion process

Click here to view

Table 1: Comparison of the shape of the acromion on both right and left scapula

Click here to view

Morphometric parameters of the acromion

The mean distance from acromion to SGT was 24.9 ± 3.7 mm (range 18.07–35.3 mm), coracoid to SGT was 22.7 ± 4.2 mm (range 14.18–34.4 mm), acromion to coracoid process was 30.9 ± 5.4 mm (range 13.32–41.8 mm), and HtCAA was 19.2 ± 2.7 mm (range 13.75–25.3 mm) [Table 2].

Table 2: Morphometric parameters of the acromion

Click here to view

Comparison of the morphometric parameters between both sides of scapula

The mean distance from acromion to SGT was 25.81 ± 3.36 mm on the right side and was 24.01 ± 3.88 mm on the left side. There was a significant difference observed between the AG distance (P = 0.04) of either side.

The mean distance from coracoid process to SGT was 21.06 ± 3.22 mm on the right side and was 24.40 ± 4.5 mm on the left side. There was a significant difference observed between the CG distance of either side (P = 0.0007).

The mean distance from acromion to coracoid process was 29.61 ± 3.88 mm on the right side and was 32.15 ± 6.44 mm on the left side. There was no significant difference observed between the CA distances (P = 0.05) of either side.

The mean distance of the HtCAA was 19.32 ± 2.98 mm on the right side and was 19.09 ± 2.50 mm on the left side. There was no significant difference observed between the HtCAA (P = 0.73) of either side [Table 3].

Table 3: Comparison for the morphometric parameters between right and left scapula

Click here to view

Discussion

The present study was done in dry adult human scapula of unknown age and gender. The morphological variants and the morphometric parameters of the acromion were studied in detail in the present study. Comparison of the present study was done with the similar previous studies done on different populations by various authors and comparison is shown in [Table 4]. There were differences noted between the current and previous studies.

Table 4: Comparison of the shapes of the acromion of human dry scapula of present study with the previous studies

Click here to view

Shapes of the acromion

In the present study, Type I (flat) was the most common, while Type II (curved) was the most common type which has been reported in the previous studies done by Getz et al., Natsis et al., Paraskevas et al., Schetino et al., Naidoo et al., Gosavi et al., El-Din and Ali, Saha et al., Kumar Panigrahi and Mishra, Singroha et al., Vinay and Sivan, and Ravindranath et al.^{[1],[5],[6],[8],[9],[10],[11],[12],[13],[14],[15],[16]} There were differences also reported in the incidence of the type of acromion on both sides. In the present study, Type I was more on the right side with Type II being more prevalent on the left side. The incidence of Type III was found to be equal on both sides. Previous studies have documented the Type III to be more common on the left side in a study done by Singroha et al. in the Indian population ^[16] [Table 4]. This reveals that there exist racial differences and also there are chances for the occurrence of the shoulder impingement syndrome on either right or left depending on the handedness of the individual.

There were gender differences reported in the incidence of the different types of the acromion. Type I was common in females in the present study whereas Type III (hooked) was common in males in the previous studies done by Getz et al. and Paraskevas et al. and Type III was found to be common in females in the study done by Singroha et al.^{[1],[14],[16]} In the present study, gender and age were unknown.

Nicholson et al. showed that these variants in the morphology of the acromion were described to play an important role in the impingement syndrome.^[18] Type III was found to be the most important predisposing factor for impingement syndrome in the study done by Epstein et al.^[19] The incidence of rotator cuff tears was found to be higher in patients with Type II and Type III acromion in the radiological study done by Worland et al., 2003.^[20] The incidence of hooked type was found to be higher in patients with rotator cuff tears in the study done by Balke et al., 2013.^[21]

The morphological parameters of the acromion thus contribute significantly to the anatomy of the CA arch and subacromial space, thus playing an important role in the impingement syndrome and rotator cuff pathology..

Coracoacromial distance

The mean value of the CA distance was similar to the study done by Ravindranath et al.^[9] The mean value of the CA distance on the left side was higher than the right side in the present study, but it was not statistically significant. This was similar to the study done by Mansur et al. in the Nepalese population and Vinay G and Sivan S in the South Indian Population ^[8],[22] [Table 5]. However, in the current study, the mean value of CA distance was found to be significantly lesser than the study done by Kumar Panigrahi and Mishra ^[10] and Sinha et al.^[17] This also shows that there exist racial differences. This lesser CA distance has clinical relevance in shoulder impingement syndrome as it is one of the contributing factors in the formation of the CA arch.

Table 5: Comparison of the morphometric parameters of the acromion process of human dry scapula of the present study with the previous studies

Click here to view

Acromioglenoid distance

The mean value of the AG distance was similar to the study done by Ravindranath et al. and Kumar Panigrahi and Mishra.^[9],[10] The mean value of the AG distance on the right side was higher than the left side (P = 0.04) in the present study. This was similar to studies done by Vinay G and Sivan S, Ravindranath et al., and Kumar Panigrahi and Mishra on the Indian Population.^[8],[9],[10] This statistically significant difference might be due to the higher mobility of the right side in right-handed persons as mentioned by Kumar Panigrahi and Mishra.^[10]

Height of the coracoacromial arch

The mean value of the HtCAA was similar to the study done by Kumar Panigrahi and Mishra.^[10] The mean value of the HtCAA was similar on both sides in the present study, and it was not statistically significant. This was different compared to the study done by Kumar Panigrahi and Mishra where there was a significant difference between the sides and the right side had a higher value than the left side and it was statistically significant (P < 0.004)^[10] [Table 6].

Table 6: Comparison of the height of the coracoacromial arch of the present study with the previous studies

Click here to view

Coracoglenoid distance

The mean value of CG distance was lower than the AG distance in the present study. There was statistically significant difference observed between the right and left sides of the scapula (P = 0.007) in the current study population. There are no previous studies available to compare this value.

Conclusion

In the present study, the Type I (flat) was the most common among the three morphological variants of the acromion process of scapula. The AG and CG distances which contribute to the architecture of the CA arch and the subacromial space were significantly higher on the right side as compared to the left side. The differences between the present study and the other studies in these morphometric parameters show that there are racial and regional variations. This knowledge will be helpful for the orthopedicians in diagnosing and planning treatment procedures for patients with impingement syndrome and rotator cuff pathology.

Limitation

Age and gender of the scapulas were not known. The sample size was less in the present study.

Acknowledgments

We thank the Fluid Research Committee, Christian Medical College, for funding this project. Special thanks to Dr. Angelo Christopher for the valuable suggestions and the statistician Miss. Hepsy Chelliah who helped us with the statistical analysis.

Financial support and sponsorship

We thank the Fluid Research Committee, Christian Medical College, for funding this project.

Conflicts of interest

There are no conflicts of interest.

References

1.	Paraskevas G, Tzaveas A, Papaziogas B, Kitsoulis P, Natsis K, Spanidou S. Morphological parameters of the acromion. Folia Morphol (Warsz) 2008;67:255-60.
2.	Bigliani LU, Morrison DS, April EW. The morphology of the acromion and its relationship to rotator cuff tears. Orthop Trans 1986;10:228.
3.	Farley TE, Neumann CH, Steinbach LS, Petersen SA. The coracoacromial arch: MR evaluation and correlation with rotator cuff pathology. Skeletal Radiol 1994;23:641-5.
4.	Sperner G. Role of the subacromial space on development of the impingement syndrome. I. Unfallchirurg 1995;98:301-8.
5.	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.
6.	El-Din WA, Ali MH. A morphometric study of the patterns and variations of the acromion and glenoid cavity of the scapulae in Egyptian population. J Clin Diagn Res 2015;9:AC08-11.
7.	Saha S, Vasudeva N. Morphometric evaluation of adult acromion process in North Indian population. J Clin Diagn Res 2017;11:AC08-11.
8.	Vinay G, Sivan 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.
9.	Ravindranath Y, Abraham A, Thelekatt DJ, Oomen AT, Johnsia S. Acromion – anatomic study of South Indian dry scapulae. Int J Contemp Med Res 2018;5:11-4.
10.	Kumar Panigrahi T, Mishra D. JCDR morphometric anatomy of acromion tapasa. Int J Anat Radiol Surg 2018;7:29-32.
11.	Saha S, Vasudeva N, Saffar Aneja P, Saxena A. Acromial morphology and subacromial impingement syndrome: A clinico-anatomical study. J Evol Med Dent Sci 2016;5:5645-9.
12.	Naidoo N, Lazarus L, Osman SA, Satyapal KS. Acromial morphology and subacromial architecture in a South African population. Int J Morphol 2015;33:817-25.
13.	Gosavi S, Jadhav S, Garud R. Morphometry of acromion process: A study of Indian scapulae. Int J Pharm Res Health Sci 2015;3:8:31-5.
14.	Getz JD, Recht MP, Piraino DW, Schils JP, Latimer BM, Jellema LM, et al. Acromial morphology: Relation to sex, age, symmetry, and subacromial enthesophytes. Radiology 1996;199:737-42.
15.	Schetino LP, Sousa Junior RR, Amâncio GP, Schetino MA, Almeida-Leite CM, Silva JH. Anatomical variations of acromions in Brazilian adult's scapulas. J Morphol Sci 2013;30:98-102.
16.	Singroha R, Verma U, Malik P, Kanta Rathee S. Morphometric study of acromion process in scapula of North Indian population. Int J Res Med Sci 2017;5:49-65.
17.	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.
18.	Nicholson GP, Goodman DA, Flatow EL, Bigliani LU. The acromion: Morphologic condition and age-related changes. A study of 420 scapulas. J Shoulder Elbow Surg 1996;5:1-11.
19.	Epstein RE, Schweitzer ME, Frieman BG, Fenlin JM Jr., Mitchell DG. Hooked acromion: Prevalence on MR images of painful shoulders. Radiology 1993;187:479-81.
20.	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.
21.	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.
22.	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.