Sacrum and coccyx
Learning objectives
After completing this study unit you will be able to:
- Identify the sacrum and the coccyx within the vertebral column.
- List the bony landmarks of each of these bones.
- Name the joints to which the sacrum and the coccyx contribute and the ligaments associated with them.
Watch video
The sacrum and the coccyx are bony structures located at the caudal end of the vertebral column.
The sacrum is a triangular bone comprising five fused sacral vertebrae, S1-S5. It articulates with the iliac components of the hip bones via the sacroiliac joint, therefore contributing to the pelvic girdle and playing an important role in stabilization of the pelvis. Superiorly, it articulates with the inferiormost lumbar vertebra (L5) to form the lumbosacral joint. Inferiorly, it articulates with the coccyx to form the sacrococcygeal joint.
The coccyx is the most inferior part of the spine and consists of three to five fused rudimentary coccygeal vertebrae.
The following video will help you understand the anatomy and bony features of the sacrum and the coccyx and give you an overview of the ligaments associated with these bones.
Take a quiz
Solidify your knowledge by taking the following quiz.
To push yourself further, try our fully customizable quiz on all elements of the spine:
Browse atlas
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Explore each of the structures you learned about today in the gallery below.
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/os-sacrum/KLeBTcqvcRdvvUfhcUjw5g_Sacrum_01.png "Sacrum (Os sacrum); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/sacrum/QzoxgUSkUUuxW8caARviA_Sacrum_02.png "Sacrum (Os sacrum); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/basis-ossi-sacri/LdZiAj7xSlMqDvDKomfw_Basis_ossis_sacri_01.png "Base of sacrum (Basis ossis sacri); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/promontorium/TjPFk33IDaJuHD1Jp3GGQ_B6xYHJAXap_Promontorium_1.png "Promontory of sacrum (Promontorium sacri); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/ala-ossis-sacralis/Wr5vPJeHpaVVyhsV2FQhhw_6nF2tGs1oC_Ala_ossis_sacralis_1.png "Ala of sacrum (Ala ossis sacri); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/crista-sacralis-mediana/LBtr5b5nWZYH9L6FgFEOKA_tPVYXszAzS_Crista_sacralis_mediana_1.png "Median sacral crest (Crista sacralis mediana); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/intermediate-sacral-crest/Q7gcpyedIZ1zN5ql0a78EQ_Intermediate_sacral_crest.png "Intermediate sacral crest (Crista sacralis medialis); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/lateral-sacral-crest-1/VLOTsAlzaxb0usCcAlOQ_262Lateral_sacral_crest.png "Lateral sacral crest (Crista sacralis lateralis); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/foramina-sacralia/m30u5hIZf6nU3xwAiqIFAg_sp8zyp33Bp_Foramina_sacralia_1.png "Anterior sacral foramina (Foramina sacralia anteriora); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/foramenina-sacralia-posteriora/c6rrwZQsBo0MyII1rChFg_9hyGgQK9fqV8lUJdW7WAHg_MRQdH29FNG_Foramina_sacralia_2.png "Posterior sacral foramina (Foramina sacralia posteriora); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/sacral-nerves-s1-s5/H1fCsmpyl7KRyl7My1uig_Nn._sacrales_S1-S5_02.png "Spinal nerves S1-S5 (Nervi spinales S1-S5); Image: Rebecca Betts"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/lateral-sacral-artery-3/xXUtuiJL6cw382QJCEUCtg_11lateral_sacral_artery.png "Lateral sacral artery (Arteria sacralis lateralis); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/apex-ossis-sacri/HRbr0CYKRA2NbUaEWRJA_8xWu5tJyvJ_Apex_ossis_sacri_1.png "Apex of sacrum (Apex ossis sacri); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/sacral-cornu/KXno81IF4nwlhTd4Za8XA_Sacral_cornu_magnified.png "Sacral cornu (Cornu sacrale); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/sacral-hiatus/rwLprKObN1vg9LcGaIUDow_281Sacral_hiatus_magnified.png "Sacral hiatus (Hiatus sacralis); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/os-coccygis/srFtxeuJ25p08BhHQ4Wqig_VAw7HEGCRp_Os_coccygis_1.png "Coccyx (Os coccygis); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/coccyx-bone-6/BPLtlTtUMFBU1OnCLu36w_Coccyx_bone.png "Coccyx (Os coccygis); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/coccygeal-cornu-1/TtQNXsKDQ8hjWYQlp27oQ_Coccygeal_cornu_magnified.png "Coccygeal cornu (Cornu coccygeum); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/articulatio-sacrococcygea/1E1DgP4u43h2KjS8Dxh2ZQ_NdvS6Jfqq9_Articulatio_sacrococcygea_1.png "Sacrococcygeal joint (Articulatio sacrococcygea); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/sacrococcygeal-symphysis-1/kGJZAv5Z681V9Gpxkc82MA_290Sacrococcygeal_symphysis_magnified.png "Sacrococcygeal joint (Articulatio sacrococcygea); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/sacrococcygeal-symphysis/W1wGjDSPOCTptguLFsXePA_zL7PXs88wf_Articulatio_sacrococcygea_2.png "Sacrococcygeal joint (Articulatio sacrococcygea); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/articulatio-lumbosacralis/ummw4HITShvTVfFk7SVOQ_Ha27BJar5p_Articulatio_lumbosacralis_1.png "Lumbosacral joint (Articulatio lumbosacralis); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/superior-articular-process-of-sacrum-1/jJGKYsa2684TJFZzeFGrw_Superior_articular_process_of_sacrum.png "Superior articular process of sacrum (Processus articularis superior sacri); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/sacroiliac-joint-5/NooZFjiGvnuc8fRH4Asg_Sacroiliac_joint_magnified.png "Sacroiliac joint (Articulatio sacroiliaca); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/ligamentum-sacrospinale/BgcCg11t9NZxwdjXs3ZblQ_ESybQsth4B_Ligamentum_sacrospinale_1.png "Sacrospinous ligament (Ligamentum sacrospinale); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/ligamentum-sacrotuberale/5HY8XE1htHRIgWnHYgXDA_NuXmqNAKBw_Ligamentum_sacrotuberale_1.png "Sacrotuberous ligament (Ligamentum sacrotuberale); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/anterior-sacroiliac-ligament/GxiyG7AzXz8OaNqGEJg67w_Anterior_sacroiliac_ligament.png "Anterior sacroiliac ligament (Ligamentum sacroiliacum anterius); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/posterior-sacroiliac-ligament/PNnSxfm88UWaS8qPeRL3g_Posterior_sacroiliac_ligaments.png "Posterior sacroiliac ligament (Ligamentum sacroiliacum posterius); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/interosseous-sacroiliac-ligament/ubcTDGfcAarRJhyRw5M2dQ_Interosseous_sacroiliac_ligament.png "Interosseous sacroiliac ligament (Ligamentum sacroiliacum interosseum); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/anterior-sacrococcygeal-ligament/68sjsWUA2MZauF32tdHYA_Anterior_scarococygeal_ligament.png "Anterior sacrococcygeal ligament (Ligamentum sacrococcygeum anterius); Image: Paul Kim"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/lateral-sacrococcygeal-ligament/vdV3Aspkep9Oks7OMT4g_Lateral_sacrococcygeal_ligament.png "Lateral sacrococcygeal ligament (Ligamentum sacrococcygeum laterale); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/superficial-posterior-sacrococcygeal-ligament/91VCOOeqlwV6zUe9d5yMvQ_Superficial_posterior_sacrococcygeal_ligament.png "Superficial posterior sacrococcygeal ligament (Ligamentum sacrococcygeum posterius superficiale); Image: Liene Znotina"){kind=logo}
:watermark(/images/watermark_only.png,0,0,0):watermark(/images/logo_url.png,-10,-10,0):format(jpeg)/images/anatomy_term/anterior-longitudinal-ligament-4/gIpjcmBEZuRREoo1hevqQ_Anterior_longitudinal_ligament.png "Anterior longitudinal ligament (Ligamentum longitudinale anterius); Image: Liene Znotina"){kind=logo}
Summary
| Structure | Five fused sacral vertebrae (S1-S5) |
| Parts |
Dorsal surface: median crest, intermediate crests, lateral crests, four pairs of posterior sacral foramina, sacral horns Pelvic surface: Transverse ridges, sacral promontory, four pairs of anterior sacral foramina Lateral (auricular) surface: Articulates with ilium Base: Articulates with L5 Apex: Articulates with coccyx |
| Structure | 3-5 fused coccygeal vertebrae |
| Parts | Apex, base, coccygeal horns |
| Joints |
Lumbosacral joint (symphysis): Anterior intervertebral joint Zygapophyseal joints Sacroiliac joint: Synovial articulation between auricular surface of sacrum and auricular surface of ilium Syndesmosis between sacral tuberosity and iliac tuberosity Sacrococcygeal joint: Apex of sacrum and base of coccyx via intervertebral disc Sacrococcygeal zygapophyseal joint Intercoccygeal joints: Cartilaginous or ossified joints between adjacent coccygeal vertebrae |
| Ligaments |
Lumbosacral symphysis: Iliolumbar ligaments Lumbosacral ligaments Sacroiliac joints: Anterior sacroiliac ligament Interosseous sacroiliac ligament Posterior sacroiliac ligament Sacrococcygeal joints: Superficial posterior sacrococcygeal ligament Deep posterior sacrococcygeal ligament Anterior sacrococcygeal ligament Lateral sacrococcygeal ligament Sacrotuberous ligament Sacrospinous ligament Intercoccygeal joints: Supraspinous ligament (sacral part) Anterior longitudinal ligament (sacral part) Anterior sacrococcygeal ligament Lateral sacrococcygeal ligament |
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