[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) › Coccyx [Skeletal system](https://durgical.com/en/anatomy/system/skeletal-system/) · [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) # Coccyx The coccyx, or tailbone, is the small bone at the very bottom of the [spine](https://durgical.com/en/anatomy/region/spine/), just below the sacrum. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=lower_limb&select=coccyx&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The tailbone: three to five small fused bones at the very bottom of the spine. ## What it does Anchors ligaments and pelvic floor muscles, and takes some weight when you lean back while sitting. ## Key points - The ganglion impar, where the two sympathetic trunks end, lies in front of the sacrococcygeal junction: target of a block for coccygeal and perineal pain - Sacrococcygeal teratoma, from remnants of the primitive streak, is the commonest tumour in newborns - A pilonidal sinus forms in the skin of the natal cleft over the sacrococcygeal region, not in the bone ## Key facts **Joints with** Sacrum (sacrococcygeal joint) **Landmarks** 3–5 fused rudimentary vertebrae (usually 4); coccygeal cornua; attachment of [gluteus maximus](https://durgical.com/en/anatomy/gluteus-maximus-muscle/), coccygeus, levator ani and anococcygeal ligament ## Relations **In front** Ganglion impar; the [rectum](https://durgical.com/en/anatomy/rectum/) and anococcygeal body below and in front **Behind** [Skin](https://durgical.com/en/anatomy/skin/) and fat of the natal cleft; dorsal sacrococcygeal ligaments **Lateral** [Coccygeus](https://durgical.com/en/anatomy/coccygeus-muscle/) and the [iliococcygeus](https://durgical.com/en/anatomy/iliococcygeus-muscle/) part of [levator ani](https://durgical.com/en/anatomy/levator-ani/); edge of the sacrotuberous and sacrospinous ligaments **Above** [Sacrum](https://durgical.com/en/anatomy/sacrum/) at the [sacrococcygeal joint](https://durgical.com/en/anatomy/sacrococcygeal-joint/), a symphysis that may fuse with age **Below** Tip with the anococcygeal ligament running to the [external anal sphincter](https://durgical.com/en/anatomy/external-anal-sphincter/) ## How to find it Felt in the natal cleft a few centimetres behind the anus as the lower continuation of the sacrum. On rectal examination it can be held between a finger inside and the thumb outside to judge its tenderness and mobility. ## Examination - Rectal manipulation: moving the coccyx between a gloved finger in the rectum and the thumb outside reproduces the usual pain in coccydynia and shows whether the bone is too mobile or fixed ## On imaging A lateral view shows its angle; lateral views taken standing and sitting can show abnormal mobility (hypermobility or subluxation) in coccydynia. Normal angulation and segmentation vary a lot and are easily mistaken for fractures. ## Common problems - Coccydynia: tailbone pain, often after a fall or childbirth. ## Clinical notes - A fall onto the buttocks can fracture or dislocate the sacrococcygeal joint, sometimes with the coccyx displaced forward on rectal examination - Coccydynia is more common in women; childbirth and rapid weight loss are recognised triggers ## Anatomical variants - Its shape ranges from a gentle forward curve to a sharp forward angle or a backward tilt; some shapes are linked to coccydynia ## Development The remnant of the embryonic tail, which regresses by about the eighth week of development. ## Related conditions - [Pilonidal disease](https://durgical.com/en/conditions/pilonidal-disease/) - [Anorectal abscess and fistula](https://durgical.com/en/conditions/anorectal-abscess-and-fistula/) ## Test yourself Think of the answer, then tap the question to see it. ## Which sympathetic structure lies in front of the sacrococcygeal junction and is blocked for coccygeal and perineal pain? The ganglion impar, where the two sympathetic trunks end. ## What is the commonest tumour in newborns related to the coccyx, and where does it come from? Sacrococcygeal teratoma, from remnants of the primitive streak. ## What are recognised triggers of coccydynia? A fall onto the buttocks, childbirth and rapid weight loss; it is more common in women. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/anatomy/coccyx/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** os coccygis TA2 1092 **Official Spanish (DeCS)** Cóccix DeCS D003050 **English (TA2)** Coccyx **Also called** coccygeal bone · vertebrae coccygeae · vertebrae coccygeae I-IV · vertebrae Co1-Co4 · vertebrae coccygicae · vertebrae caudales ## Related - [Sacrum](https://durgical.com/en/anatomy/sacrum/) - [Gluteus maximus](https://durgical.com/en/anatomy/gluteus-maximus-muscle/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=3079); [Anatomy, Back, Coccygeal Vertebrae](https://www.ncbi.nlm.nih.gov/books/NBK549870/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/coccyx/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/coccyx/