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Coccyx

What Is It, Function, Injuries, and More

Author:Anna Hernández, MD

Editors:Alyssa Haag,Józia McGowan, DO,Kelsey LaFayette, DNP, ARNP, FNP-C

Illustrator:Jessica Reynolds, MS

Copyeditor:Stacy M. Johnson, LMSW


What is the coccyx?

The coccyx, or tailbone, is a small triangle-shaped bone derived from the fusion of four coccygeal vertebrae at the end of the vertebral column. It represents the embryonic remnant of the caudal eminence, a tail-like structure found in human development between weeks four and eight. 

Posterior view of the bones of the low back with the coccyx labeled.

Where is the coccyx located?

The coccyx is located in the terminal part of the vertebral column, or spinal column, which consists of 33 vertebrae organized into five regions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal. In some individuals, there can be one more or one less coccygeal vertebrae with the resulting coccyx being the fusion of five or three vertebrae, respectively. 

The coccyx consists of a base, apex, anterior surface, posterior surface, and two lateral surfaces. The base is located superiorly and attaches to the apex of the sacrum, forming the sacrococcygeal joint. The apex is a rounded prominence that forms the endpoint of the vertebral column and serves as a site of attachment for muscles and ligaments of the pelvic floor. The anterior surface is smooth and slightly concave, whereas the posterior surface is convex. The coccygeal cornua are two large articular processes that project upwards from the base of the coccyx to articulate with the sacrum. Finally, the lateral surfaces of the coccyx are marked by two small transverse processes similar to those of the rest of the vertebrae. 

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What is the function of the coccyx?

The coccyx serves as an important site of attachment for multiple pelvic floor structures, which includes parts of the gluteus maximus and coccygeus muscles, as well as the anococcygeal ligament, which extends between the coccyx and the anus. In addition to being an attachment site, the coccyx helps support the position of the anus and provides weight-bearing support to a person in a seated position. 

Can you injure your coccyx?

The coccyx can become injured due to several mechanisms. The most common injury is a fall onto the buttocks, which may occur when someone falls backwards or falls from a chair. Direct trauma to the tailbone can result in a bruised, dislocated, or broken coccyx. This condition is often managed conservatively with pain medications and rest while the bone heals. 

Another common condition is pain in the region of the coccyx called coccydynia. The most common cause of coccydynia is trauma to the coccyx, either due to a backwards fall or prolonged sitting on a hard or uncomfortable surface. In addition, the location of the coccyx makes it particularly susceptible to injury during childbirth, especially with prolonged or instrumented vaginal births. Finally, non-traumatic coccydynia can result from a number of causes, including degenerative disc disease; hypermobility or hypomobility of the sacrococcygeal joint; infectious causes (e.g. pilonidal cyst); sacrococcygeal tumors; or psychological disorders, like somatization disorder. 

Individuals with coccydynia typically experience pain over the coccyx, referred to as tailbone pain. The pain generally worsens with prolonged sitting, leaning back while seated, prolonged standing, and when arising from a seated position. Pain may also get worse with sexual intercourse or with defecation. Fortunately, many cases of coccygodynia resolve without any treatment or with simple supportive measures. Common measures include adopting a proper sitting position; using modified wedge-shaped cushions to relieve pressure from the coccyx when sitting; applying hot or cold compresses to the area; and medications, like acetaminophen or NSAIDs, to help relieve the pain. In cases of chronic coccydynia, treatment may include physical therapy; pelvic floor rehabilitation; osteopathic manipulative treatment; and interventional procedures, such as injections of local anesthetic around the coccyx area. If all other treatments fail, coccygectomy, or surgical removal of the coccyx, may be indicated. 

What are the most important facts to know about the coccyx?

The coccyx, or tailbone, is a small triangle-shaped bone derived from the fusion of the four rudimentary coccygeal vertebrae at the bottom of the vertebral column. The coccyx functions as a site of attachment for muscles and ligaments of the pelvic floor, to support the position of the anus, and to provide weight-bearing support to a person in a seated position. Injury or damage to the tailbone area may result in coccydynia. Treatment depends on the underlying cause and may include general supportive measures; pain medications; rehabilitation; and local procedures, like anesthetic injections or surgical removal of the coccyx. 

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Related links

Bones of the vertebral column
Anatomy of the pelvic cavity
Anatomy of the vertebral canal

Resources for research and reference

Drake, R. L., Vogl, A. W., & Mitchell, A. (2019). Gray’s anatomy for students: With student consult online access (4th ed.). Elsevier.

Lirette, L. S., Chaiban, G., Tolba, R., & Eissa, H. (2014). Coccydynia: an overview of the anatomy, etiology, and treatment of coccyx pain. The Ochsner Journal, 14(1): 84–87. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3963058/

Loscalzo, J., Fauci, A. S., Kasper, D. L., Hauser, S., Longo, D., & Jameson, J. L. (2022). Harrison’s principles of internal medicine (21st ed.). McGraw Hilll.

Mostafa E., & Varacallo M. (2022). Anatomy, back, coccygeal vertebrae. In StatPearls. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK549870/