Coccyx

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Coccyx
Coccyx - anterior view02.png
The coccyx
Illu vertebral column.svg
The coccyx is the final bone in the vertebral column that surrounds the spinal cord.
Details
Pronunciation /ˈkɒksɪks/ KOK-siks
Identifiers
Latin os coccygis
MeSH D003050
TA98 A02.2.06.001
TA2 1092
FMA 20229
Anatomical terms of bone

The coccyx (pl.: coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, [1] and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and other great apes) since Nacholapithecus (a Miocene hominoid), [2] [3] the coccyx is the remnant of a vestigial tail. In animals with bony tails, it is known as tailhead or dock, in bird anatomy as tailfan. It comprises three to five separate or fused coccygeal vertebrae below the sacrum, attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.

Contents

Structure

A coccyx with four vertebrae below the sacrum Gray100.png
A coccyx with four vertebrae below the sacrum

The coccyx is formed of three, four or five rudimentary vertebrae. It articulates superiorly with the sacrum. In each of the first three segments may be traced a rudimentary body and articular and transverse 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 lack pedicles, laminae and spinous processes. The first segment is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the remaining ones diminish in size rostrally.

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] [5]

Surfaces

The anterior surface is slightly concave and marked with three transverse grooves which indicate the junctions of the different segments. It gives attachment to the anterior sacrococcygeal ligament and the levatores ani and supports part of the rectum. The posterior surface is convex, marked by transverse grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles – the undeveloped articular processes of the coccygeal vertebrae. Of these, the superior pair are the largest, and are called the coccygeal cornua they project caudally, and articulate with the cornua of the sacrum, and on either side complete the foramen for the transmission of the posterior division of the fifth sacral nerve.

Borders

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 the anterior division of 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 the sacrotuberous and sacrospinous ligaments, to the coccygeus and levator ani in front of the ligaments, and to the gluteus maximus behind them.

Apex

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

Coccygeal fossa

The coccygeal fossa is a shallow depression on the posterior surface between the sacrum and the perineum, located in the intergluteal cleft that runs from just below the sacrum to the perineum.[ clarification needed ] [6] It is not consistently present in all humans. The coccygeal fossa marks the deepest part of the pelvic floor, next to the coccyx. The levator ani has its origin here. [7]

Extensor coccygis

The extensor coccygis is a slender muscle fascicle, which is not always present. It extends over the caudal portion of the posterior surface of the sacrum and 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

The joints are variable and may be: (1) synovial joints; (2) thin discs of fibrocartilage; (3) intermediate between these two; (4) ossified. [8] [9]

Attachments

The anterior side of the coccyx has attachments to the levator ani muscle, coccygeus, iliococcygeus, and pubococcygeus, anococcygeal raphe. Attached to the posterior side is the gluteus maximus, which extends the thigh at the hip joint. [10] The ligaments attached to the coccyx include the anterior and posterior sacrococcygeal ligaments which are the continuations of the anterior and posterior longitudinal ligaments that extend along the entire spine. [10] The lateral sacrococcygeal ligaments complete the foramina for the last sacral nerve. [11] Some fibers of the sacrospinous and sacrotuberous ligaments (arising from the spine of the ischium and the ischial tuberosity respectively) also attach to the coccyx. [10] An extension of the pia mater, the filum terminale, extends from the apex of the conus, and inserts on the coccyx.

Function

The coccyx is not entirely useless in humans, [12] 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 of coccygectomy procedures performed annually to treat coccydynia. Reviews of studies covering more than 700 coccygectomies found the operation was successful in relieving pain in 84% of cases. [13] [14] 12% of the time, the only major complication faced was infection due to the proximity to the anus. One notable complication of coccygectomy is an increased risk of perineal hernia.

Clinical significance

Injuring the coccyx can give rise to a painful condition called coccydynia and one or more of the bones or the connections thereof may be broken, fractured tailbone. [15] [16] A number of tumors are known to involve the coccyx; of these, the most common is sacrococcygeal teratoma. Both coccydynia and coccygeal tumors may require surgical removal of the coccyx (coccygectomy). One very rare complication of coccygectomy is a type of perineal hernia known as a coccygeal hernia. [17]

Etymology

The term coccyx is derived from the ancient Greek word κόκκυξ [18] [19] kokkyx "cuckoo"; [20] the latter is attested in the writings of the Greek physician Herophilus to denote the end of the vertebral column. [21] This Greek name for the cuckoo was applied as the last three or four bones of the coccyx resemble the beak of this bird, [18] [21] [22] [23] when viewed from the side. [10] [24]

This established etymological explanation can also be found in the writings of the 16th century anatomist Andreas Vesalius who wrote: os cuculi, a similitudine rostri cuculi avis [21] (the cuckoo bone shows a likeness to the beak of the cuckoo bird). Vesalius used the Latin expression os cuculi, with os, bone [25] and cuculus, the Latin name for the cuckoo. [25] The 16th/17th century French anatomist Jean Riolan the Younger gives a rather hilarious etymological explanation, as he writes: quia crepitus, qui per sedimentum exeunt, ad is os allisi, cuculi vocis similitudinem effingunt [21] (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. [21] [22]

Besides os cuculi, os caudae, [21] [26] with caudae, of the tail [25] is attested. This Latin expression might be the source of the English, French language, German and Dutch terms tailbone, l'os de la queue, [26] Schwanzbein [22] [26] and staartbeen. [27] In the current official anatomic Latin nomenclature, Terminologia Anatomica , [28] coccyx and os coccygis is used.

Additional images

See also

Related Research Articles

<span class="mw-page-title-main">Levator ani</span> Broad, thin muscle group, situated on either side of the pelvis

The levator ani is a broad, thin muscle group, situated on either side of the pelvis. It is formed from three muscle components: the pubococcygeus, the iliococcygeus, and the puborectalis.

<span class="mw-page-title-main">Sacrum</span> Triangular-shaped bone at the bottom of the spine

The sacrum, in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1–S5) between ages 18 and 30.

<span class="mw-page-title-main">Spinal nerve</span> Nerve that carries signals between the spinal cord and the body

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.

Coccydynia is a medical term meaning pain in the coccyx or tailbone area, often brought on by a fall onto the coccyx or by persistent irritation usually from sitting.

<span class="mw-page-title-main">Anterior longitudinal ligament</span> Ligament running down the front of the vertebral column

The anterior longitudinal ligament is a ligament that extends across the anterior/ventral aspect of the vertebral bodies and intervertebral discs the spine.

<span class="mw-page-title-main">Anococcygeal nerve</span> Nerve in the pelvis

The anococcygeal nerve is a sensory nerve of the pelvis that arises from the coccygeal plexus. It pierces the coccygeus muscle and the sacrotuberous ligament to supply a small area of skin between the coccyx and anus, as well as the sacrococcygeal joint. The number of anococcygeal nerves varies between one and three.

<span class="mw-page-title-main">Sacrotuberous ligament</span>

The sacrotuberous ligament is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends.

The pelvic portion of each sympathetic trunk is situated in front of the sacrum, medial to the anterior sacral foramina. It consists of four or five small sacral ganglia, connected together by interganglionic cords, and continuous above with the abdominal portion. Below, the two pelvic sympathetic trunks converge, and end on the front of the coccyx in a small ganglion, the ganglion impar, also known as azygos or ganglion of Walther.

<span class="mw-page-title-main">Sacrococcygeal symphysis</span> Joint in the pelvis

The sacrococcygeal symphysis is an amphiarthrodial joint, formed between the oval surface at the apex of the sacrum, and the base of the coccyx.

<span class="mw-page-title-main">Anterior sacrococcygeal ligament</span>

The anterior sacrococcygeal ligament or ventral sacrococcygeal ligament consists of a few irregular fibers, which descend from the anterior surface of the sacrum to the front of the coccyx, blending with the periosteum.

<span class="mw-page-title-main">Posterior longitudinal ligament</span> Ligament connecting vertebral bodies of all of the vertebrae

The posterior longitudinal ligament is a ligament connecting the posterior surfaces of the vertebral bodies of all of the vertebrae of humans. It weakly prevents hyperflexion of the vertebral column. It also prevents posterior spinal disc herniation, although problems with the ligament can cause it.

<span class="mw-page-title-main">Posterior sacrococcygeal ligament</span>

The posterior sacrococcygeal ligament or dorsal sacrococcygeal ligament is a ligament which stretches from the sacrum to the coccyx and thus dorsally across the sacrococcygeal symphysis shared by these two bones.

<span class="mw-page-title-main">Coccygeal plexus</span> Nerve plexus near the coccyx bone

The coccygeal plexus is a small nervous plexus upon the pelvic (anterior) surface of the coccygeus muscle.

Coccygectomy is a surgical procedure in which the coccyx or tailbone is removed. It is considered a required treatment for sacrococcygeal teratoma and other germ cell tumors arising from the coccyx. Coccygectomy is the treatment of last resort for coccydynia which has failed to respond to nonsurgical treatment. Non surgical treatments include use of seat cushions, external or internal manipulation and massage of the coccyx and the attached muscles, medications given by local injections under fluoroscopic guidance, and medications by mouth.

<span class="mw-page-title-main">Rump (animal)</span> Part of an animal that is behind the loins and below the tail

The rump or croup, in the external morphology of an animal, is the portion of the posterior dorsum – that is, posterior to the loins and anterior to the tail. Anatomically, the rump corresponds to the sacrum.

In the human body, the lateral sacrococcygeal ligament is bilaterally paired ligament extending between the transverse process coccyx, and the inferolateral angle of the sacrum. The ligament forms a foramen for an anterior ramus of the fifth sacral nerve (S5). The ligament may become ossified. There may be up to three lateral sacrococcygeal ligaments on either side of the sacral hiatus.

<span class="mw-page-title-main">Coccyx fracture</span> Medical condition

A coccyx fracture is a fracture of the coccyx, commonly called a broken tailbone or ‘puzzle fracture.’

<span class="mw-page-title-main">Pelvis</span> Lower torso of the human body

The pelvis is the lower part of the trunk, between the abdomen and the thighs, together with its embedded skeleton.

<span class="mw-page-title-main">Vertebral column</span> Bony structure found in vertebrates

The vertebral column, also known as the backbone, spine, or spinal column, is the core part of the axial skeleton in vertebrate animals. The vertebral column is the defining characteristic of vertebrate endoskeleton in which the notochord found in all chordates has been replaced by a segmented series of mineralized irregular bones called vertebrae, separated by fibrocartilaginous intervertebral discs. The dorsal portion of the vertebral column houses the spinal canal, a cavity formed by alignment of the neural arches that encloses and protects the spinal cord.

<span class="mw-page-title-main">Vertebra</span> Bone in the vertebral column

Each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal segment and the particular species.

References

  1. ↑ Weisberger, Mindy (March 23, 2024). "Why don't humans have tails? Scientists find answers in an unlikely place". CNN . Archived from the original on March 24, 2024. Retrieved March 24, 2024.
  2. ↑ Nakatsukasa 2004, Acquisition of bipedalism (See Fig. 5 entitled First 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, Nakatsukasa et al. Dec 2007)
  4. ↑ Postacchini F; Massobrio M] (October 1983). "Idiopathic coccygodynia. Analysis of 51 operative cases and a radiographic study of the normal coccyx". The Journal of Bone and Joint Surgery. American Volume. 65 (8): 1116–1124. doi:10.2106/00004623-198365080-00011.
  5. ↑ Kim NH, Suk KS (June 1999). "Clinical and radiological differences between traumatic and idiopathic coccygodynia". Yonsei Medical Journal . 40 (3): 215–220. doi: 10.3349/ymj.1999.40.3.215 . PMID   10412331.
  6. ↑ 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 .
  7. ↑ Lierse, Werner (2012-12-06). Applied anatomy of the pelvis. Springer. p. 40. ISBN   978-3-642-71368-2.
  8. ↑ Maigne JY; Molinie V; Fautrel B (1992). "Anatomie des disques coccygiens". Revue de Médecine Orthopedique. 28: 34–35.
  9. ↑ Saluja PG (1988). "The incidence of ossification of the sacrococcygeal joint". Journal of Anatomy. 156: 11–15. PMC   1261909 . PMID   3138225.
  10. 1 2 3 4 Foye, Patrick M; Buttaci, Charles J (June 3, 2008). "Coccyx Pain". eMedicine.
  11. ↑ Morris, Craig E. (2005). Low Back Syndromes: Integrated Clinical Management. McGraw-Hill. p. 59. ISBN   978-0-07-137472-9.
  12. ↑ Saladin, Kenneth S. (2003). Anatomy & Physiology: The Unity of Form and Function (3rd ed.). McGraw-Hill. p. 268.
  13. ↑ 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
  14. ↑ Heum Dai Kwon et al., Coccygodynia and Coccygectomy. Korean Journal of Spine, 9, 4 (2012), 326-333.
  15. ↑ 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. PMID   11145819. S2CID   25790826.
  16. ↑ 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 . PMID   16924191.
  17. ↑ 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. PMID   17889632.
  18. 1 2 Klein, 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.
  19. ↑ Harper, Douglas. "coccyx". Online Etymology Dictionary .
  20. ↑ κόκκυξ . Liddell, Henry George ; Scott, Robert ; A Greek–English Lexicon at the Perseus Project.
  21. 1 2 3 4 5 6 Hyrtl, J. (1880). Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart. Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.
  22. 1 2 3 Kraus, L.A. (1844). Kritisch-etymologisches medicinisches Lexikon (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.
  23. ↑ 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. PMID   21736439. S2CID   22256856.
  24. ↑ Sugar, Oscar (February 1995). "Historical Perspective Coccyx: The Bone Named for a Bird". Spine. 20 (3): 379–383. doi:10.1097/00007632-199502000-00024. ISSN   0362-2436. PMID   7732478.
  25. 1 2 3 os, cuculus, cauda . Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project .
  26. 1 2 3 Schreger, C.H.Th.(1805). Synonymia anatomica. Synonymik der anatomischen Nomenclatur. Fürth: im Bureau für Literatur.
  27. ↑ Everdingen, J.J.E. van, Eerenbeemt, A.M.M. van den (2012). Pinkhof Geneeskundig woordenboek (12de druk). Houten: Bohn Stafleu Van Loghum.
  28. ↑ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme

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