Sternalis muscle

The sternalis muscle is an anatomical variation that lies in front of the sternal end of the pectoralis major parallel to the margin of the sternum. The sternalis muscle may be a variation of the pectoralis major or of the rectus abdominis.

Sternalis
Sternalis muscle, in line with Rectus Abdominis and Sternomastoid, was found in 6% of 535 cadavera (R. N. Barlow)
Details
Originmanubrium of sternum or clavicle
Insertionxiphoid process, pectoral fascia, lower ribs, costal cartilages or rectus sheath
Identifiers
LatinMusculus sternalis
TAA04.4.01.001
FMA9717
Anatomical terms of muscle

Structure

The sternalis is a muscle that runs along the anterior aspect of the body of the sternum. It lies superficially and parallel to the sternum. Its origin and insertion are variable. The sternalis muscle often originates from the upper part of the sternum and can display varying insertions such as the pectoral fascia, lower ribs, costal cartilages, rectus sheath, aponeurosis of the abdominal external oblique muscle.[1][2][3] There is still a great deal of disagreement about its innervation and its embryonic origin.[1]

In a review,[4] it was reported that the muscle was innervated by the external or internal thoracic nerves in 55% of the cases, by the intercostal nerves in 43% of the cases, while the remaining cases were supplied by both nerves.[4] However, innervation by the pectoral nerves has also been reported.[5] This appears to indicate that the sternalis is not always derived from the same embryonic origin.[6]

Prevalence

Cadaveric studies showed that the sternalis muscle has a mean prevalence of around 7.8% in the population[7] with the range from 0.5% to 23.5%.[8] It has a slightly higher incidence in females.[1] Though, It was proposed that a possible reason for the high prevalence may result from the existence of small, ill-defined or tendinous fibres, which could be misidentified for a sternalis muscle.[9]

Variations

A recent study[8] classified the sternalis into three types depending on morphology.

  • Type I (single head and single belly)
  • Type II (double-headed/multi-headed)
  • Type III (double-bellied/multi-bellied)

Type I, the single head and single belly was seen in the majority of reported cases (58.5%), type II in 18.1%, and type III in 23.4%.[8]

In addition to the above classification, triple-bellied/double-headed sternalis has also been reported.[10]

Function

There is no apparent physiological function of the sternalis muscle.[11] However, there are many theories for a function. It may function as a proprioceptive sensor for thoracic wall movements.[12] It may also take part in the movement of the shoulder joint or have an additional role in elevation of the chest wall.[13]

Clinical significance

The presence of the sternalis is asymptomatic[1] but aesthetic complaints have been reported as it was reported to cause chest asymmetry or deviation of the nipple-areola complex.[1][14] The presence of the sternalis may cause alterations in the electrocardiogram[15] or confusion in mammography.[16] However, there is a potential benefit of the muscle as it can be used as a flap in a reconstructive surgery of the head and neck and the anterior chest wall.[14]

History

The sternalis was first reported by Carbolius in 1604 and the name was first given by Turner in 1867.[17] Different terminologies have been given to the sternalis due to its highly varied morphology and the disagreement on its embryonic origin. The sternalis was referred to as the rectus sternalis, sternalis brutorum, musculus sternalis, episternalis, parasternalis, presternalis, rectus sterni, rectus thoracis, rectus thoracicus superficialis, superficial rectus abdominis, japonicas, and thoracicus depending on studies.[7][17]

Additional images

References

  1. Raikos, Athanasios; Paraskevas, George K.; Yusuf, Faisal; Kordali, Panagiota; Ioannidis, Orestis; Brand-Saberi, Beate (2011-12-01). "Sternalis muscle: a new crossed subtype, classification, and surgical applications". Annals of Plastic Surgery. 67 (6): 646–648. doi:10.1097/SAP.0b013e31820d688b. ISSN 1536-3708. PMID 21407048.
  2. Georgiev, Georgi P.; Jelev, Lazar; Ovtscharoff, Vladimir A. (2009-09-01). "On the clinical significance of the sternalis muscle". Folia Medica. 51 (3): 53–56. ISSN 0204-8043. PMID 19957564.
  3. "Anatomy 2008; 2: 67-71 [Case Report]". www.anatomy.org.tr. Retrieved 2015-09-05.
  4. O'NEILL, M. N.; FOLAN-CURRAN, J. (1998-08-01). "Case report: bilateral sternalis muscles with a bilateral pectoralis major anomaly". Journal of Anatomy. 193 (Pt 2): 289–292. doi:10.1046/j.1469-7580.1998.19320289.x. ISSN 0021-8782. PMC 1467849. PMID 9827645.
  5. Kida, M. Y.; Izumi, A.; Tanaka, S. (2000-01-01). "Sternalis muscle: topic for debate". Clinical Anatomy. 13 (2): 138–140. doi:10.1002/(SICI)1098-2353(2000)13:2<138::AID-CA8>3.0.CO;2-4. ISSN 0897-3806. PMID 10679858.
  6. Harper WF. The sternalis muscle in the anencephalous foetus. Anat Notes 1936;317-20.
  7. Snosek, Michael; Tubbs, R. Shane; Loukas, Marios (2014-09-01). "Sternalis muscle, what every anatomist and clinician should know". Clinical Anatomy. 27 (6): 866–884. doi:10.1002/ca.22361. ISSN 1098-2353. PMID 24431029.
  8. Ge, Zufeng; Tong, Yunlong; Zhu, Shiqiang; Fang, Xiong; Zhuo, Lang; Gong, Xiangyang (2014-04-01). "Prevalence and variance of the sternalis muscle: a study in the Chinese population using multi-detector CT". Surgical and Radiologic Anatomy. 36 (3): 219–224. doi:10.1007/s00276-013-1175-4. ISSN 1279-8517. PMID 23912561.
  9. JELEV, L.; GEORGIEV, G.; SURCHEV, L. (2001-09-01). "The sternalis muscle in the Bulgarian population: classification of sternales". Journal of Anatomy. 199 (Pt 3): 359–363. doi:10.1046/j.1469-7580.2001.19930359.x. ISSN 0021-8782. PMC 1468341. PMID 11554516.
  10. Dudgeon, Sarah N.; Marcotte, Kayla M.; Fox, Glenn M.; Alsup, B. Kathleen (2017-12-01). "A previously unclassified variant of sternalis muscle". Surgical and Radiologic Anatomy. 39 (12): 1417–1419. doi:10.1007/s00276-017-1883-2. ISSN 0930-1038. PMID 28593340.
  11. Snosek, M; Tubbs, RS; Loukas, M (September 2014). "Sternalis muscle, what every anatomist and clinician should know". Clinical Anatomy (New York, N.Y.). 27 (6): 866–84. doi:10.1002/ca.22361. PMID 24431029.
  12. Natsis, Konstantinos; Totlis, Trifon (2007-11-01). "A rare accessory muscle of the anterior thoracic wall". Clinical Anatomy. 20 (8): 980–981. doi:10.1002/ca.20534. ISSN 0897-3806. PMID 17948292.
  13. Young Lee, Bae; Young Byun, Jae; Hee Kim, Hak; Sook Kim, Hyun; Mee Cho, Song; Hoon Lee, Kang; Sup Song, Kyung; Soo Kim, Bum; Mun Lee, Jae (2006-08-01). "The sternalis muscles: incidence and imaging findings on MDCT". Journal of Thoracic Imaging. 21 (3): 179–183. doi:10.1097/01.rti.0000208287.04490.db. ISSN 0883-5993. PMID 16915061.
  14. Bailey, P. M.; Tzarnas, C. D. (1999-04-01). "The sternalis muscle: a normal finding encountered during breast surgery". Plastic and Reconstructive Surgery. 103 (4): 1189–1190. doi:10.1097/00006534-199904040-00013. ISSN 0032-1052. PMID 10088505.
  15. Arráez-Aybar, L. A.; Sobrado-Perez, J.; Merida-Velasco, J. R. (2003-07-01). "Left musculus sternalis". Clinical Anatomy. 16 (4): 350–354. doi:10.1002/ca.10120. ISSN 0897-3806. PMID 12794922.
  16. Bradley, F. M.; Hoover, H. C.; Hulka, C. A.; Whitman, G. J.; McCarthy, K. A.; Hall, D. A.; Moore, R.; Kopans, D. B. (1996-01-01). "The sternalis muscle: an unusual normal finding seen on mammography". AJR. American Journal of Roentgenology. 166 (1): 33–36. doi:10.2214/ajr.166.1.8571900. ISSN 0361-803X. PMID 8571900.
  17. Turner W (1867) On the musculus sternalis. J Anat Physiol 1(2):246–378
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