Sternalis muscle explained

Sternalis
Latin:musculus sternalis
Origin:Manubrium of sternum or clavicle
Insertion:Xiphoid process, pectoral fascia, lower ribs, costal cartilages or rectus sheath

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.

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. 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 a slightly higher incidence in females.[1] The prevalence ranges from 0.5% to 23.5%, depending on the subpopulation[8] ⁠it has been proposed that the possible reason for the sizable range could be the fact of the existence of small, ill-defined, or tendinous fibres which may or may not be accepted as being asternalis muscle.[9]

Variations

A 2014 study classified the sternalis into three types depending on morphology.

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%.

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.

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]

References

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

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