[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Spine](https://durgical.com/en/anatomy/region/spine/) › Iliolumbar ligament [Joints and ligaments](https://durgical.com/en/anatomy/system/joints-and-ligaments/) · [Spine](https://durgical.com/en/anatomy/region/spine/) # Iliolumbar ligament The iliolumbar ligament is a strong band from L5 to the back of the iliac crest; it ties the lowest vertebra to the pelvis. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=spine&select=iliolumbar_lig&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A strong band from the transverse process of L5 (sometimes L4) to the back of the iliac crest. ## What it does Ties the lowest lumbar vertebra to the pelvis, stopping L5 from slipping forward or bending too far sideways. ## Key points - The strongest link from L5 to the [pelvis](https://durgical.com/en/anatomy/region/pelvis/); an L5 transverse process fracture can be a sign of an unstable pelvic ring injury - By holding L5 firmly, it helps explain why the L4–L5 level is more mobile and more often slips or degenerates than L5–S1 - On MRI it is a landmark for identifying L5, though not a perfect one, especially with transitional vertebrae ## Key facts **Attaches** Tip of L5 transverse process (± L4) to posterior inner lip of iliac crest; lower band (lumbosacral ligament) to sacral ala **Function** Anchors L5 to the pelvis; resists forward slip, rotation and side bending of L5 on S1 **Tight in** Lateral flexion to the opposite side; flexion ## Relations **Above** [Quadratus lumborum](https://durgical.com/en/anatomy/quadratus-lumborum-muscle/), which arises partly from it and from the iliac crest **In front** [Psoas major](https://durgical.com/en/anatomy/psoas-major/), with the [iliolumbar vessels](https://durgical.com/en/anatomy/iliolumbar-artery/) running nearby toward the iliac fossa **Behind** Erector spinae and [multifidus](https://durgical.com/en/anatomy/multifidus-muscles/) **Below** Its lower band, the [lumbosacral ligament](https://durgical.com/en/anatomy/lumbosacral-ligament/), and the anterior sacroiliac ligament, with which it blends ## How to find it Not palpable; its iliac end lies deep at the back of the iliac crest, just in front of the [sacroiliac joint](https://durgical.com/en/anatomy/sacroiliac-joint/). In dissection it is found by following the L5 transverse process outward: psoas major lies in front of it, quadratus lumborum above and the deep back muscles behind. ## On imaging Coronal and axial MRI show it as a dark band from the L5 transverse process to the iliac crest. CT of the pelvis shows L5 transverse process avulsions in pelvic trauma. ## Common problems - Strain can cause low back pain on one side, near the top of the pelvis. ## How it is diagnosed Exam (tenderness and pain with side bending); imaging mainly rules out other causes. ## Treatment - Physical therapy and pain medicine; sometimes an injection. ## Clinical notes - In vertical shear pelvic fractures it can pull off the tip of the L5 transverse process - Iliolumbar syndrome: localised pain at the back of the iliac crest attributed to this ligament; the diagnosis is clinical and debated - A thinner, weaker iliolumbar ligament has been reported with lumbosacral transitional vertebrae, changing how load passes to the level above ## Development In children it is largely muscle, part of quadratus lumborum, and becomes ligament by adulthood. ## Related conditions - [Sacroiliac joint pain](https://durgical.com/en/conditions/sacroiliac-joint-pain/) ## Test yourself Think of the answer, then tap the question to see it. ## Where does the iliolumbar ligament attach? From the tip of the L5 transverse process (sometimes L4) to the posterior inner lip of the iliac crest; its lower band (lumbosacral ligament) reaches the sacral ala. ## What does the iliolumbar ligament do? Anchors L5 to the pelvis, resisting forward slip, rotation and side bending of L5 on S1. ## In pelvic trauma, what can a fracture of the L5 transverse process signal? An unstable pelvic ring injury, such as a vertical shear fracture, where the iliolumbar ligament pulls off the tip of the process. ## How does the iliolumbar ligament help explain why L4–L5 degenerates and slips more than L5–S1? It holds L5 firmly to the pelvis, so the L4–L5 level above is more mobile. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/iliolumbar-ligament/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** ligamentum iliolumbale TA2 1853 **Official Spanish (DeCS)** Ligamento iliolumbar **English (TA2)** Iliolumbar ligament ## Related - [Lumbosacral ligament](https://durgical.com/en/anatomy/lumbosacral-ligament/) - [Iliolumbar vessels](https://durgical.com/en/anatomy/iliolumbar-artery/) - [L5 vertebra](https://durgical.com/en/anatomy/lumbar-vertebra-spine-and-pelvis-l5/) - [Hip bone](https://durgical.com/en/anatomy/hip-bone/) - [L4 vertebra](https://durgical.com/en/anatomy/lumbar-vertebra-spine-and-pelvis-l4/) Sources: Terminologia Anatomica (TA2); [Anatomy, Back, Lumbar Spine](https://www.ncbi.nlm.nih.gov/books/NBK557616/); Anatomy of the Human Body (20th ed.): Articulation of the Vertebral Column with the Pelvis (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain. ## **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/iliolumbar-ligament/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/iliolumbar-ligament/