sternalis muscle
{{Short description|Muscle seen in some humans}}
{{Infobox muscle
| Name = Sternalis
| Latin = musculus sternalis
| Image = Grant 1962 27b.png
| Caption = Sternalis muscle, in line with rectus abdominis and sternomastoid, was found in 6% of 535 cadavera (R. N. Barlow)
| Origin = Manubrium of sternum or clavicle
| Insertion = Xiphoid process, pectoral fascia, lower ribs, costal cartilages or rectus sheath
| Blood =
| Nerve =
| Action =
| Antagonist =
}}
The rectus 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.{{Cite journal|title = Sternalis muscle: a new crossed subtype, classification, and surgical applications|journal = Annals of Plastic Surgery|date = 2011-12-01|issn = 1536-3708|pmid = 21407048|pages = 646–648|volume = 67|issue = 6|doi = 10.1097/SAP.0b013e31820d688b|first = Athanasios|last = Raikos|first2 = George K.|last2 = Paraskevas|first3 = Faisal|last3 = Yusuf|first4 = Panagiota|last4 = Kordali|first5 = Orestis|last5 = Ioannidis|first6 = Beate|last6 = Brand-Saberi}}{{Cite journal|title = On the clinical significance of the sternalis muscle|journal = Folia Medica|date = 2009-09-01|issn = 0204-8043|pmid = 19957564|pages = 53–56|volume = 51|issue = 3|first = Georgi P.|last = Georgiev|first2 = Lazar|last2 = Jelev|first3 = Vladimir A.|last3 = Ovtscharoff}}{{Cite web|title = Anatomy 2008; 2: 67-71 [Case Report]|url = http://www.anatomy.org.tr/issue/200801/fulltext/case_13.asp|website = www.anatomy.org.tr|accessdate = 2015-09-05}} It may be present unilaterally or bilaterally.{{cite journal | last=Raikos | first=Athanasios | last2=Paraskevas | first2=George K | last3=Tzika | first3=Maria | last4=Faustmann | first4=Pedro | last5=Triaridis | first5=Stefanos | last6=Kordali | first6=Panagiota | last7=Kitsoulis | first7=Panagiotis | last8=Brand-Saberi | first8=Beate | title=Sternalis muscle: an underestimated anterior chest wall anatomical variant | journal=Journal of Cardiothoracic Surgery | volume=6 | issue=1 | date=2011 | issn=1749-8090 | pmid=21575244 | pmc=3117696 | doi=10.1186/1749-8090-6-73 | doi-access=free | page=}} There is still a great deal of disagreement about its innervation and its embryonic origin.
In a review,{{Cite journal|title = Case report: bilateral sternalis muscles with a bilateral pectoralis major anomaly|journal = Journal of Anatomy|date = 1998-08-01|issn = 0021-8782|pmc = 1467849|pmid = 9827645|pages = 289–292|volume = 193|issue = Pt 2|doi = 10.1046/j.1469-7580.1998.19320289.x|first = M. N.|last = O'NEILL|first2 = J.|last2 = FOLAN-CURRAN}} 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.{{Cite journal|title = Sternalis muscle: topic for debate|journal = Clinical Anatomy|date = 2000-01-01|issn = 0897-3806|pmid = 10679858|pages = 138–140|volume = 13|issue = 2|doi = 10.1002/(SICI)1098-2353(2000)13:2<138::AID-CA8>3.0.CO;2-4|first = M. Y.|last = Kida|first2 = A.|last2 = Izumi|first3 = S.|last3 = Tanaka}} This appears to indicate that the sternalis is not always derived from the same embryonic origin.Harper WF. The sternalis muscle in the anencephalous foetus. Anat Notes 1936;317-20.
= Prevalence =
Cadaveric studies have shown that the sternalis muscle has a mean prevalence of around 7.8% in the population,{{Cite journal|title = Sternalis muscle, what every anatomist and clinician should know|journal = Clinical Anatomy|date = 2014-09-01|issn = 1098-2353|pages = 866–884|volume = 27|issue = 6|doi = 10.1002/ca.22361|pmid = 24431029|first = Michael|last = Snosek|first2 = R. Shane|last2 = Tubbs|first3 = Marios|last3 = Loukas}} with a significantly higher incidence of unilateral rather than bilateral presentation and a slightly higher incidence in females. The prevalence among subpopulations ranges from 0.5% to 23.5%{{Cite journal|title = Prevalence and variance of the sternalis muscle: a study in the Chinese population using multi-detector CT|journal = Surgical and Radiologic Anatomy|date = 2014-04-01|issn = 1279-8517|pmid = 23912561|pages = 219–224|volume = 36|issue = 3|doi = 10.1007/s00276-013-1175-4|first = Zufeng|last = Ge|first2 = Yunlong|last2 = Tong|first3 = Shiqiang|last3 = Zhu|first4 = Xiong|last4 = Fang|first5 = Lang|last5 = Zhuo|first6 = Xiangyang|last6 = Gong}}{{mdash}}a possible reason for this sizable range could be that small, ill-defined, or tendinous fibers may or may not be accepted as constituting a
= Variations =
A 2014 study 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%.
In addition to the above classification, triple-bellied/double-headed sternalis has also been reported.{{Cite journal|last=Dudgeon|first=Sarah N.|last2=Marcotte|first2=Kayla M.|last3=Fox|first3=Glenn M.|last4=Alsup|first4=B. Kathleen|date=2017-12-01|title=A previously unclassified variant of sternalis muscle|journal=Surgical and Radiologic Anatomy|language=en|volume=39|issue=12|pages=1417–1419|doi=10.1007/s00276-017-1883-2|pmid=28593340|issn=0930-1038}}
Function
There is no apparent physiological function of the sternalis muscle.{{cite journal |last1=Snosek |first1=M |last2=Tubbs |first2=RS |last3=Loukas |first3=M |title=Sternalis muscle, what every anatomist and clinician should know. |journal=Clinical Anatomy |date=September 2014 |volume=27 |issue=6 |pages=866–84 |doi=10.1002/ca.22361 |pmid=24431029}} However, there are many theories for a function. It may function as a proprioceptive sensor for thoracic wall movements.{{Cite journal|title = A rare accessory muscle of the anterior thoracic wall|journal = Clinical Anatomy|date = 2007-11-01|issn = 0897-3806|pmid = 17948292|pages = 980–981|volume = 20|issue = 8|doi = 10.1002/ca.20534|first = Konstantinos|last = Natsis|first2 = Trifon|last2 = Totlis}} It may also take part in the movement of the shoulder joint or have an additional role in elevation of the chest wall.{{Cite journal|title = The sternalis muscles: incidence and imaging findings on MDCT|journal = Journal of Thoracic Imaging|date = 2006-08-01|issn = 0883-5993|pmid = 16915061|pages = 179–183|volume = 21|issue = 3|doi = 10.1097/01.rti.0000208287.04490.db|first = Bae|last = Young Lee|first2 = Jae|last2 = Young Byun|first3 = Hak|last3 = Hee Kim|first4 = Hyun|last4 = Sook Kim|first5 = Song|last5 = Mee Cho|first6 = Kang|last6 = Hoon Lee|first7 = Kyung|last7 = Sup Song|first8 = Bum|last8 = Soo Kim|first9 = Jae|last9 = Mun Lee}}
Clinical significance
File:Musculus sternalis rechts - CT sagittal und Volume rendering - 001.jpg
The presence of the sternalis is asymptomatic but aesthetic complaints have been reported as it was reported to cause chest asymmetry or deviation of the nipple-areola complex.{{Cite journal|title = The sternalis muscle: a normal finding encountered during breast surgery|journal = Plastic and Reconstructive Surgery|date = 1999-04-01|issn = 0032-1052|pmid = 10088505|pages = 1189–1190|volume = 103|issue = 4|first = P. M.|last = Bailey|first2 = C. D.|last2 = Tzarnas|doi=10.1097/00006534-199904040-00013}} The presence of the sternalis may cause alterations in the electrocardiogram{{Cite journal|title = Left musculus sternalis|journal = Clinical Anatomy|date = 2003-07-01|issn = 0897-3806|pmid = 12794922|pages = 350–354|volume = 16|issue = 4|doi = 10.1002/ca.10120|first = L. A.|last = Arráez-Aybar|first2 = J.|last2 = Sobrado-Perez|first3 = J. R.|last3 = Merida-Velasco}} or confusion in mammography.{{Cite journal|title = The sternalis muscle: an unusual normal finding seen on mammography|journal = AJR. American Journal of Roentgenology|date = 1996-01-01|issn = 0361-803X|pmid = 8571900|pages = 33–36|volume = 166|issue = 1|doi = 10.2214/ajr.166.1.8571900|first = F. M.|last = Bradley|first2 = H. C.|last2 = Hoover|first3 = C. A.|last3 = Hulka|first4 = G. J.|last4 = Whitman|first5 = K. A.|last5 = McCarthy|first6 = D. A.|last6 = Hall|first7 = R.|last7 = Moore|first8 = D. B.|last8 = Kopans}} 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.Turner W (1867) On the musculus sternalis. J Anat Physiol 1(2):246–378 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.
Additional images
Image:PSM_V25_D748_Rectus_sternalis_and_the_great_pectoral_chest_muscle.jpg|The sternalis muscle as it lies on top the pectoralis major.
Image:Braus 1921 137.png|Sternalis muscle visible in an individual who also has an accessory abdominal pectoralis major, and an axillary arch of the latissimus dorsi.
Image:Musculus sternalis rechts - CT axial und Volume rendering - 001.jpg|Musculus sternalis seen at axial CT and volume rendering.