[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/) › Sacroiliac ligaments [Joints and ligaments](https://durgical.com/en/anatomy/system/joints-and-ligaments/) · [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) # Sacroiliac ligaments The sacroiliac ligaments are very strong bands joining the [sacrum](https://durgical.com/en/anatomy/sacrum/) to the hip bones; they allow only tiny movements. Official name: Anterior, interosseous and posterior sacroiliac ligaments [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=lower_limb&select=sacroiliac_ligs&side=r) Opens in the Durgical app, no sign-up needed. ## What it is Very strong ligaments in front of, behind and between the sacrum and the hip bones, holding the sacroiliac (SI) joints together. ## What it does Lock the [pelvis](https://durgical.com/en/anatomy/region/pelvis/) into a strong ring that passes the body's weight from the spine to the legs. They allow only a few degrees of movement. ## Key points - The thin anterior ligament fails first: in an open-book (anteroposterior compression) pelvic injury it tears while the posterior ligaments may hold - The long posterior sacroiliac ligament can be felt just below the posterior superior iliac [spine](https://durgical.com/en/anatomy/region/spine/) and is often tender in pregnancy-related pelvic girdle pain - Pain provocation tests are interpreted as a cluster: several positive tests make the joint a likelier pain source than any single test - The [sacroiliac joint](https://durgical.com/en/anatomy/sacroiliac-joint/) is synovial in front, between the ear-shaped auricular surfaces, and fibrous behind, where the interosseous ligament fills the gap; it moves only a few degrees (nutation), a little more in pregnancy ## Key facts **Attaches** Anterior, interosseous and posterior sacroiliac ligaments: sacrum to ilium; interosseous between the tuberosities **Function** Bind sacrum to ilia; interosseous is strongest; transfer trunk weight to pelvis with tiny movement **Tight in** Sacral nutation; long posterior sacroiliac ligament in counternutation ## Relations **In front** [Iliacus](https://durgical.com/en/anatomy/iliacus-muscle/) and psoas; the lumbosacral trunk and the [L5 nerve root](https://durgical.com/en/anatomy/l5/) cross in front of the joint, beside the internal iliac vessels **Behind** [Multifidus](https://durgical.com/en/anatomy/multifidus-muscles/) and erector spinae, the [thoracolumbar fascia](https://durgical.com/en/anatomy/thoracolumbar-fascia/) and the origin of [gluteus maximus](https://durgical.com/en/anatomy/gluteus-maximus-muscle/) **Below** Sacrotuberous and sacrospinous ligaments, which continue the support below ## How to find it The posterior superior iliac spine, under the [skin](https://durgical.com/en/anatomy/skin/) dimple level with the second sacral spine, sits over the middle of the joint, and the posterior ligaments lie deep to it. The long posterior ligament can be pressed as a firm cord just below the spine; the interosseous and anterior ligaments are out of reach. ## Examination - FABER (Patrick) test: pain in the back of the pelvis points to the sacroiliac joint; pain in the groin points to the hip - Gaenslen test: one hip held flexed while the other leg hangs into extension off the table; pain at the sacroiliac joint is positive - Distraction and compression tests: pressure apart on both ASIS (supine) or down on the iliac crest (side-lying) reproducing sacroiliac pain - Thigh thrust: hip flexed to 90° and pushed back along the [femur](https://durgical.com/en/anatomy/femur/); buttock pain on that side is positive ## On imaging AP pelvis X-ray shows widening in pelvic ring injuries and erosions, sclerosis or fusion in sacroiliitis. CT is best for fractures and joint widening. MRI (fat-suppressed sequences) shows the bone-marrow oedema of active sacroiliitis. ## Common problems - SI joint pain: low back and buttock pain, sometimes into the thigh, from strain, a fall, uneven leg loading or arthritis. - Loosening during pregnancy, from hormones that relax the ligaments. - Inflammation of the joint (sacroiliitis), for example in some types of arthritis. - Tears with pelvic fractures from high-energy injuries. ## How it is diagnosed Physical exam with pain provocation tests; X-rays, CT or MRI; a numbing injection into the joint can confirm the source of pain. ## Treatment - Physical therapy, a pelvic belt and anti-inflammatory medicine. - Injections into the joint, or treatment of the small nerves that carry pain from it. - SI joint fusion surgery for selected long-lasting cases; surgical fixation for unstable fractures. ## Clinical notes - Pelvic ring injuries are graded by which sacroiliac ligaments are torn: anterior only (APC II) or anterior and posterior (APC III, unstable) - Iliosacral screws are placed close to the L5 root and the lumbosacral trunk in front of the joint - Sacroiliitis is an early sign of axial spondyloarthritis ## Anatomical variants - Accessory sacroiliac joints between the ilium and the sacrum, behind the main joint; reported frequency varies widely, and they are more common in older people ## Related conditions - [Sacroiliac joint pain](https://durgical.com/en/conditions/sacroiliac-joint-pain/) - [Psoriatic arthritis](https://durgical.com/en/conditions/psoriatic-arthritis/) ## Test yourself Think of the answer, then tap the question to see it. ## In an open-book pelvic injury, which sacroiliac ligament fails first? The thin anterior sacroiliac ligament; the posterior ligaments may hold (APC II), and if they also tear the injury is unstable (APC III). ## Which is the strongest of the sacroiliac ligaments? The interosseous sacroiliac ligament, between the tuberosities of the sacrum and ilium. ## Which sacroiliac ligament is felt just below the posterior superior iliac spine and is often tender in pregnancy? The long posterior sacroiliac ligament, often tender in pregnancy-related pelvic girdle pain. ## How should sacroiliac pain provocation tests be interpreted? As a cluster: several positive tests (such as FABER, Gaenslen, distraction, compression, thigh thrust) make the joint a likelier source than any single test. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/sacroiliac-ligaments/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** ligamentum sacroiliacum anterius; ligamentum sacroiliacum interosseum; ligamentum sacroiliacum posterius TA2 1862 **Official Spanish (DeCS)** Ligamentos sacroilíacos DeCS D012446 **English (TA2)** Anterior, interosseous and posterior sacroiliac ligaments **Also called** ligamenta sacroiliaca anteriora · ligamenta sacroilica ventralia ## Related - [Hip bone](https://durgical.com/en/anatomy/hip-bone/) - [Sacrum](https://durgical.com/en/anatomy/sacrum/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=12822&filter=ths_termall&q=Articulaci%C3%B3n%20Sacroiliaca); [Anatomy, Abdomen and Pelvis, Sacroiliac Joint](https://www.ncbi.nlm.nih.gov/books/NBK507801/); Anatomy of the Human Body (20th ed.): Surface Markings of the Lower Extremity (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain; Anatomía humana (4.ª ed.), tomo 1, cap. 64: Cintura pelviana. ## **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/sacroiliac-ligaments/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/sacroiliac-ligaments/