Lumbosacral ligament !
The lumbosacral ligament is a band from L5 down to the wing of the sacrum that helps hold L5 to the sacrum; the L5 nerve runs just under it.
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What it is
A band from the L5 transverse process down to the wing of the sacrum, under the iliolumbar ligament.
What it does
Helps hold L5 to the sacrum. The L5 nerve passes just under it.
Key facts
- Attaches
- Lower edge of L5 transverse process to the sacral ala; lower band of the iliolumbar ligament; also called sacrovertebral ligament (Bichat)
- Function
- Helps hold L5 on the sacrum; L5 ventral ramus passes just beneath it
- Tight in
- Lateral flexion to the opposite side
Relations
- Above
- Main band of the iliolumbar ligament and the L5 transverse process
- Below
- Sacral ala, with the L5 ventral ramus passing underneath
- In front
- Psoas major; medially, the L5–S1 disc and the sacral promontory
- Behind
- Multifidus and erector spinae over the sacrum; the L5 dorsal ramus runs in the groove between the ala and the S1 superior articular process
How to find it
Not palpable. In dissection from the front, lift the psoas and follow the L5 ventral ramus down onto the sacral ala: the band runs from the lower edge of the L5 transverse process to the ala, with the nerve passing beneath it.
On imaging
Hard to see on routine MRI. Coronal and oblique axial MRI or CT of the lumbosacral junction show the space between the L5 transverse process and the ala, where the L5 nerve may be pinched.
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
- Far-out compression is more likely with a degenerative or isthmic slip, scoliosis, or a large L5 transverse process in a lumbosacral transitional vertebra
- The L5 nerve lies on the sacral ala: a structure at risk with iliosacral screws and anterior approaches to the lumbosacral junction
- Bertolotti syndrome: in a transitional vertebra an enlarged L5 transverse process forms a joint or fusion with the sacral ala or ilium, in the corner this ligament crosses, and is a proposed source of low back pain in young adults
Test yourself
Think of the answer, then tap the question to see it.
What are the attachments of the lumbosacral ligament?
From the lower edge of the L5 transverse process to the sacral ala; many texts describe it as the lower band of the iliolumbar ligament.
Which nerve passes just beneath the lumbosacral ligament?
The L5 ventral ramus, running between the ligament and the sacral ala on its way to join L4 as the lumbosacral trunk.
What is far-out syndrome?
Compression of the L5 nerve outside the foramen, between the L5 transverse process and the sacral ala, where the lumbosacral ligament adds to the squeeze.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Spanish (DeCS)
- Ligamento lumbosacro
- English (TA2)
- Lumbosacral ligament
Related
Sources: Anatomy, Back, Lumbar Spine.
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Representative model, for educational purposes only.
