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| ORIGINAL ARTICLE |
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| Year : 2021 | Volume
: 70
| Issue : 2 | Page : 97-100 |
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A cadaveric study on subclavius posticus muscle
BS Bhavya, Maheshwari Myageri, M Smitha, Rajeshwari C Eligar
Department of Anatomy, Karnataka Institute of Medical Sciences, Hubballi, Karnataka, India
| Date of Submission | 02-Mar-2020 |
| Date of Acceptance | 26-Apr-2021 |
| Date of Web Publication | 30-Jun-2021 |
Correspondence Address:
Dr. Maheshwari Myageri
Department of Anatomy, Karnataka Institute of Medical Sciences, Hubballi, Karnataka
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/JASI.JASI_45_20
Introduction: Subclavius posticus muscle (SPM) is a rare anomalous muscle that traverses from costal cartilage of first rib posterolaterally to superior border of scapula. The aim of the study was to study the prevalence of SPM in adult cadavers. Material and Methods: Fifty upper limbs from embalmed cadavers allotted for routine dissection practical for first MBBS students were used for the study. There were twenty male and five female cadavers, with ages ranging from 60 to 80 years, specimens of both sides were used. Results: The SPM was found in seven cases out of fifty cases, two on left, and five on the right side of pectoral region. Discussion and Conclusion: The presence of variant SPM could be a predisposing causative factor of thoracic outlet syndrome.
Keywords: Coracoid process of scapula, subsclavius posticus muscle, thoracic outlet syndrome
How to cite this article:
Bhavya B S, Myageri M, Smitha M, Eligar RC. A cadaveric study on subclavius posticus muscle. J Anat Soc India 2021;70:97-100 |
| Introduction | |  |
The anatomical variations in the anterior thoracic region has been well documented in literature but paid scant attention to a small muscle subclavius posticus which is a predisposing factor for thoracic outlet syndrome. The present study was aimed to scrutinize this muscle particularly its attachments.
Subclavius posticus originates from first costal cartilage, gets inserted into upper margin of coracoid process of scapula, and is innervated by nerve to subclavius or suprascapular nerve or phrenic nerve.[1]
It is speculated that the muscle might develop from an analage of the hypobranchial musculature near and/or in the junctional region between the hypobranchial and the pectoral regions of the body trunk. The region might phylogenetically and ontogenetically, concomitantly with the development of the heart and lungs, undergo remarkable changes, to which variations of this muscle, and its innervation could be attributed.[2]
| Material and Methods | | |
Inclusion criteria
All the cadavers available during the study period were included in the study.
Exclusion criteria
Deformed axillae were excluded from the study.
Fifty upper limbs from embalmed cadavers allotted for dissection over a period of 3 years (2017–2019) were used for the study. Twenty male and five female cadavers were studied with ages ranging from 60 to 80 year. Specimens of both sides were used.
The axillary region was dissected and exposed according to the methods described in Cunningham's Manual of Practical Anatomy.[3] Detailed dissection of subclavius posticus muscle (SPM) was done. Pattern of muscular attachments, innervations were examined, recorded, and photographed. Total length of the muscle and maximum width were measured.
| Results | | |
The overall incidence was 14%. The SPM was found in seven cases out of fifty cases, two on left and five on right.
In all the cases, SPM took origin from superior surface of first costal cartilage. The insertion and nerve supply in our study is depicted in the tabular format [Table 1]. The muscle coursed dorsolaterally beneath the clavicle crossing the axillosubclavian vessels and cords of brachial plexus. Photographs of dissected SPM have been included in [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]. | Figure 1: Left infraclavicular region (subclavius posticus muscle 1) before removal of clavicle
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 | Figure 2: Superior view (subclavius posticus muscle 1). After removal of clavicle
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 | Figure 4: Left subclavius posticus muscle, inserted into coracoid process and transverse scapular ligament (subclavius posticus muscle 7)
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 | Figure 6: Left subclavius posticus muscle, inserted into coracoid process (subclavius posticus muscle 4)
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Among seven specimens one received innervation from a direct branch from brachial plexus, in which all three cords were united, four from suprascapular nerve, and two from nerve to subclavius.
The length of subclavius posticus ranged from 12.5 cm to 15.5 cm and breadth of the muscle ranged between 0.8 cm and 1.3 cm. The maximum width of muscle was found to cross the neurovascular bundle. A comparison of the measurements have been given in [Table 2]. | Table 2: Comparison of measurements of subclavius posticus muscle observed by various authors
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All the muscular components in axillary and scapular regions were normal.
| Discussion | | |
Eisler reported a muscle in 1912, termed by Rosenmuller as SPM, which arose from first costal cartilage and inserted into the coracoid process or upper margin of the scapula.[4]
The incidence of SPM in Japanese was 8.9% and 36% in Thais, as compared to 14% in our study, all the studies were done on cadavers.[5]
Piyawinijwong and Sirisathira describe the classification of subclavius muscle according to its insertion, in which muscles in Type II–IV corresponds to SPM [Table 3]. Prevalence of SPM Type II in a study conducted in Thais was 17.97%, but in our study, it is 12%, SPM Type III in Thais was 15.62%, and in our study, it is 2%.[5] | Table 3: Classification of subclavius muscle according to its insertion[5]
Click here to view |
Relationship to structures at the root of neck stated by previous authors as well as in our study was superficial to subclavian vessels and brachial plexus. The comparison of attachments and nerve supply as observed by various authors are depicted in [Table 3].[2],[5],[6],[7],[8]
Akita et al. described SPM as an aberrant muscle between inferior belly of omohyoid and subclavius muscle. They reported a common matrix for these muscles. Accordingly, the matrix is divided into three parts and middle part becomes the aberrant muscle.[9] [Table 4] gives a summary of results of SPM of present study in relation to results of various other studies.
Cogar et al. presented a case of an athlete with suprascapular nerve compression associated with subclavius posticus diagnosed by magnetic resonance imaging (MRI). Symptoms were relieved and function was restored by decompression of the nerve and excision of the anomalous muscle.[7]
| Conclusion | | |
The presence of SPM could be a predisposing causative factor of thoracic outlet syndrome, suprascapular nerve compression. Radiologists and surgeons should be aware of this muscle. High-resolution MRI examination is recommended in such suspected cases. A band of nonenhancing tissue stretching from the first costal cartilage to the superior angle of scapula, isointense to the adjacent muscles in the presence of a normal subclavius muscle are the classical MRI features of SPM.[10]
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
| 1. | Kutoglu T, Ulucam E, Gurbuz H. A case of the subclavius muscle. Trakia J Sci 2005;3:77-8.  |
| 2. | Shetty P, Pai MM, Prabhu LV, Vadgaonkar R, Nayak SR, Shivanandam R. The subclavius posticus muscle: Its phylogenetic retention and clinical relevance. Int J Morphol 2006;24:599-600. |
| 3. | Romanes GJ. Cunningham's Manual of Practical Anatomy. 15 th ed., Vol. 1. Oxford: ELBS; 1992. p. 29-31. |
| 4. | Sarikcioglu L, Sindel M. A case with subclavius posticus muscle. Folia Morphol (Warsz) 2001;60:229-31. |
| 5. | Piyawinijwong S, Sirisathira N. Supernumerary subclavius muscle in Thais: Predisposing cause of thoracic outlet syndrome. J Med Assoc Thai 2010;93:1065-9. |
| 6. | Muellner J, Kaelin-Lang A, Pfeiffer O, El-Koussy MM. Neurogenic thoracic outlet syndrome due to subclavius posticus muscle with dynamic brachial plexus compression: A case report. BMC Res Notes 2015;8:351-3. |
| 7. | Cogar AC, Johnsen PH, Potter HG, Wolfe SW. Subclavius posticus: An anomalous muscle in association with suprascapular nerve compression in an athlete. Hand (N Y) 2015;10:76-9. |
| 8. | Singhal S, Rao VV, Manjunath KY. Subclavius posticus muscle – A case report. Int J Morphol 2008;26:813-5. |
| 9. | Akita K, Ibukuro K, Yamaguchi K, Heima S, Sato T. The subclavius posticus muscle: A factor in arterial, venous or brachial plexus compression? Surg Radiol Anat 2000;22:111-5. |
| 10. | Gupta G, Prakash S, Ojha P. A case report of bilateral subclavius posticus muscle. J Evol Med Dent Sci 2013;2:761-4. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4]
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