Wikipedia

Coccyx

This article is about the tailbone in apes and analogous structures. For animals with tails, seeCaudal vertebrae.For the moth genus, seeCydia (genus).
"Coccyges" redirects here. For the clade of birds, seeCuculiformesandParrot.

Thecoccyx(pl.:coccygesorcoccyxes), commonly referred to as thetailbone,is the final segment of thevertebral columnin allapes,[1]and analogous structures in certain other mammals such ashorses.In taillessprimates(e.g.humansand othergreat apes) sinceNacholapithecus(aMiocenehominoid),[2][3]the coccyx is the remnant of avestigial tail.In animals with bony tails, it is known astailheadordock,inbird anatomyastailfan.It comprises three to five separate or fused coccygeal vertebrae below thesacrum,attached to the sacrum by afibrocartilaginousjoint,thesacrococcygeal symphysis,which permits limited movement between the sacrum and the coccyx.

Coccyx
The coccyx
The coccyx is the final bone in thevertebral columnthat surrounds thespinal cord.
Details
Pronunciation/ˈkɒksɪks/KOK-siks
Identifiers
Latinos coccygis
MeSHD003050
TA98A02.2.06.001
TA21092
FMA20229
Anatomical terms of bone

Structure

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A coccyx with four vertebrae below the sacrum

The coccyx is formed of three, four or five rudimentaryvertebrae.It articulates superiorly with thesacrum.In each of the first three segments may be traced a rudimentary body andarticularandtransverse processes;the last piece (sometimes the third) is a mere nodule of bone. The transverse processes are most prominent and noticeable on the first coccygeal segment. All the segments lackpedicles,laminaeandspinous processes.The first segment is the largest; it resembles the lowestsacral vertebra,and often exists as a separate piece; the remaining ones diminish in sizerostrally.

Most anatomy books incorrectly state that the coccyx is normally fused in adults. It has been shown that the coccyx may, in some people, consist of up to five separate bony segments, the most common configuration being two or three segments.[4]

Surfaces

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Theanteriorsurface is slightly concave and marked with three transverse grooves which indicate the junctions of the different segments. It gives attachment to theanterior sacrococcygeal ligamentand thelevatores aniand supports part of therectum.Theposteriorsurface is convex, marked by transverse grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles – the undevelopedarticular processesof the coccygeal vertebrae. Of these, the superior pair are the largest, and are called thecoccygeal cornuathey projectcaudally,and articulate with the cornua of the sacrum, and on either side complete theforamenfor the transmission of theposterior divisionof thefifth sacral nerve.

Borders

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The lateral borders are thin and exhibit a series of small bony protrusions, which represent the transverse processes of the coccygeal vertebrae. Of these, the first is the largest; it is flattened anteriorly, and often extends to join the lower part of the thin lateral edge of the sacrum, thus completing the foramen for the transmission of theanterior divisionof the fifth sacral nerve; the others diminish in size from caudally, and are often lacking. The borders of the coccyx are narrow, and give attachment on either side to thesacrotuberousandsacrospinous ligaments,to thecoccygeusandlevator aniin front of the ligaments, and to thegluteus maximusbehind them.

Apex

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The apex is rounded, and has attached to it the tendon of theexternal anal sphincter;it may be divided in two.

Coccygeal fossa

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Thecoccygeal fossais a shallow depression on the posterior surface between thesacrumand theperineum,located in theintergluteal cleftthat runs from just below the sacrum to theperineum.[clarification needed][5]It is not consistently present in all humans. The coccygeal fossa marks the deepest part of thepelvic floor,next to the coccyx. Thelevator anihas itsoriginhere.[6]

Extensor coccygis

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Theextensor coccygisis a slendermuscle fascicle,which is not always present. It extends over the caudal portion of the posterior surface of thesacrumand coccyx. It arises by tendinous fibers from the last segment of the sacrum, or first piece of the coccyx, and passes downward to be inserted into the lower part of the coccyx. It is an evolutionary relic of the extensor muscle of the caudal vertebrae of other animals, enabling limited coccygeal motion.

Sacrococcygeal and intercoccygeal joints

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The joints are variable and may be: (1)synovial joints;(2) thin discs offibrocartilage;(3) intermediate between these two; (4) ossified.[7][8]

Attachments

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The anterior side of the coccyx has attachments to thelevator ani muscle,coccygeus,iliococcygeus,andpubococcygeus,anococcygeal raphe.Attached to the posterior side is thegluteus maximus,which extends thethighat the hip joint.[9]Theligamentsattached to the coccyx include theanteriorandposterior sacrococcygeal ligamentswhich are the continuations of theanteriorandposterior longitudinal ligamentsthat extend along the entire spine.[9]Thelateral sacrococcygeal ligamentscomplete theforaminafor thelast sacral nerve.[10]Some fibers of thesacrospinousandsacrotuberous ligaments(arising from thespine of the ischiumand theischial tuberosityrespectively) also attach to the coccyx.[9]An extension of thepia mater,thefilum terminale,extends from the apex of theconus,and inserts on the coccyx.

Function

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The coccyx is not entirely useless in humans,[11]because it has attachments to various muscles, tendons and ligaments. However, these muscles, tendons and ligaments are also attached at many other points, to stronger structures than the coccyx. It is doubtful that the coccyx attachments are important to the well-being of humans, given the large number ofcoccygectomyprocedures performed annually to treatcoccydynia.Reviews of studies covering more than 700 coccygectomies found the operation was successful in relieving pain in 84% of cases.[12][13]12% of the time, the only major complication faced was infection due to the proximity to the anus. One notablecomplicationof coccygectomy is an increased risk ofperineal hernia.

Clinical significance

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Injuring the coccyx can give rise to a painful condition calledcoccydyniaand one or more of the bones or the connections thereof may be broken,fractured tailbone.[14][15]A number oftumorsare known to involve the coccyx; of these, the most common issacrococcygeal teratoma.Both coccydynia and coccygeal tumors may require surgical removal of the coccyx (coccygectomy). One very rare complication of coccygectomy is a type ofperineal herniaknown as a coccygeal hernia.[16]

Etymology

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The termcoccyxis derived from theancient Greekwordκόκκυξ[17][18]kokkyx"cuckoo";[19]the latter is attested in the writings of the GreekphysicianHerophilusto denote the end of the vertebral column.[20]This Greek name for thecuckoowas applied as the last three or four bones of the coccyx resemble the beak of this bird,[17][20][21][22]when viewed from the side.[9][23]

This established etymological explanation can also be found in the writings of the 16th century anatomistAndreas Vesaliuswho wrote:os cuculi, a similitudine rostri cuculi avis[20](the cuckoo bone shows a likeness to the beak of the cuckoo bird). Vesalius used the Latin expressionos cuculi,withos,bone[24]andcuculus,the Latin name for the cuckoo.[24]The 16th/17th century French anatomistJean Riolan the Youngergives a rather hilarious etymological explanation, as he writes:quia crepitus, qui per sedimentum exeunt, ad is os allisi, cuculi vocis similitudinem effingunt[20](because the sound of the farts that leave the anus and dash against this bone, shows a likeness to the call of the cuckoo). Riolan's explanation is not considered credible.[20][21]

Besidesos cuculi,os caudae,[20][25]withcaudae,of the tail[24]is attested. This Latin expression might be the source of the English,French language,GermanandDutchtermstailbone,l'os de la queue,[25]Schwanzbein[21][25]andstaartbeen.[26]In the current official anatomic Latin nomenclature,Terminologia Anatomica,[27]coccyxandos coccygisis used.

Additional images

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See also

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This article usesanatomical terminology.

References

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  1. ^Weisberger, Mindy (March 23, 2024)."Why don't humans have tails? Scientists find answers in an unlikely place".CNN.Archivedfrom the original on March 24, 2024.RetrievedMarch 24,2024.
  2. ^Nakatsukasa 2004,Acquisition of bipedalism(SeeFig. 5entitledFirst coccygeal/caudal vertebra in short-tailed or tailless primates..)
  3. ^Note: Nacholapithecus and Nakaliphitecus nakayamai are two different species of Miocene hominoids (specimens from Nakali and Nachola respectively). See for example "Comparisons with Other Hominoids" in (Kunimatsu, Nakatsukasaet al.Dec 2007)
  4. ^Tetiker H, Koşar MI, Çullu N, Canbek U, Otağ I, Taştemur Y (2017)."MRI-based detailed evaluation of the anatomy of the human coccyx among Turkish adults".Niger J Clin Pract.20(2): 136–142.doi:10.4103/1119-3077.198313.PMID28091426.{{cite journal}}:CS1 maint: multiple names: authors list (link)
  5. ^Cosmo, L (2017)."Filling the Gap: on the New Micro-toponomic Phenomena and Partial Topologies".Health Research.1(1): 39–49.doi:10.31058/j.hr.2017.11004.
  6. ^Lierse, Werner (2012-12-06).Applied anatomy of the pelvis.Springer. p. 40.ISBN978-3-642-71368-2.
  7. ^Maigne JY; Molinie V; Fautrel B (1992). "Anatomie des disques coccygiens".Revue de Médecine Orthopedique.28:34–35.
  8. ^Saluja PG (1988)."The incidence of ossification of the sacrococcygeal joint".Journal of Anatomy.156:11–15.PMC1261909.PMID3138225.
  9. ^abcdFoye, Patrick M; Buttaci, Charles J (June 3, 2008)."Coccyx Pain".eMedicine.
  10. ^Morris, Craig E. (2005).Low Back Syndromes: Integrated Clinical Management.McGraw-Hill. p. 59.ISBN978-0-07-137472-9.
  11. ^Saladin, Kenneth S. (2003).Anatomy & Physiology: The Unity of Form and Function(3rd ed.). McGraw-Hill. p. 268.
  12. ^Coccygektomi kan være en behandlingsmulighed ved kronisk coccygodyni (Coccygectomy may be a treatment option for chronic coccydynia) Ugeskr Læger 2011 Feb 14; 173(7): 495-500. In Danish. Aarby, Nanett Skjellerup (1), Trollegaard, Anton Mitchell (2) and Hellberg, Steen (2)https://www.coccyx.org/medabs/aarby.htm
  13. ^Heum Dai Kwon et al., Coccygodynia and Coccygectomy.Korean Journal of Spine,9, 4 (2012), 326-333.
  14. ^Maigne, J-Y; Doursounian, L; Chatellier, G (2000)."Causes and Mechanisms of Common Coccydynia. Spine".Spine.25(23). coccyx.org: 3072–3079.doi:10.1097/00007632-200012010-00015.PMID11145819.S2CID25790826.
  15. ^Foye P, Buttaci C, Stitik T, Yonclas P (2006)."Successful injection for coccyx pain".Am J Phys Med Rehabil.85(9): 783–784.doi:10.1097/01.phm.0000233174.86070.63.PMID16924191.
  16. ^Miranda EP, Anderson AL, Dosanjh AS, Lee CK (September 2007). "Successful management of recurrent coccygeal hernia with the de-epithelialised rectus abdominis musculocutaneous flap".J Plast Reconstr Aesthet Surg.62(1): 98–101.doi:10.1016/j.bjps.2007.08.002.PMID17889632.
  17. ^abKlein, E. (1971).A comprehensive etymological dictionary of the English language. Dealing with the origin of words and their sense development thus illustration the history of civilization and culture.Amsterdam: Elsevier Science B.V.
  18. ^Harper, Douglas."coccyx".Online Etymology Dictionary.
  19. ^κόκκυξ.Liddell, Henry George;Scott, Robert;A Greek–English Lexiconat thePerseus Project.
  20. ^abcdefHyrtl, J. (1880).Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart.Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.
  21. ^abcKraus, L.A. (1844).Kritisch-etymologisches medicinisches Lexikon(Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.
  22. ^Panourias, I.G.; Stranjalis, G.; Stavrinou, L.C.; Sakas, D.E. (2011). "The Hellenic and Hippocratic origins of the spinal terminology".Journal of the History of the Neurosciences.20(3): 177–187.doi:10.1080/0964704X.2010.510180.PMID21736439.S2CID22256856.
  23. ^Sugar, Oscar (February 1995). "Historical Perspective Coccyx: The Bone Named for a Bird".Spine.20(3): 379–383.doi:10.1097/00007632-199502000-00024.ISSN0362-2436.PMID7732478.
  24. ^abcos,cuculus,cauda.Charlton T. Lewis and Charles Short.A Latin DictionaryonPerseus Project.
  25. ^abcSchreger, C.H.Th.(1805).Synonymia anatomica. Synonymik der anatomischen Nomenclatur.Fürth: im Bureau für Literatur.
  26. ^Everdingen, J.J.E. van, Eerenbeemt, A.M.M. van den (2012).Pinkhof Geneeskundig woordenboek(12de druk). Houten: Bohn Stafleu Van Loghum.
  27. ^Federative Committee on Anatomical Terminology (FCAT) (1998).Terminologia Anatomica.Stuttgart: Thieme

Further reading

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