The iliolumbar ligament is the primary restraint at the lumbosacral junction, connecting the L5 transverse process to the iliac crest. It limits lateral flexion, rotation, and anterior translation at L5-S1 — the most mobile and loaded lumbosacral segment. Iliolumbar ligament strain produces low back pain at the iliac crest level radiating to the groin (referred pain pattern from L5). Weakening from degeneration contributes to L5-S1 spondylolisthesis.
| Origin | L5 transverse process (and occasionally L4) |
|---|---|
| Insertion | Anterior iliac crest and superior iliac fossa — two main bands: anterior (to the iliac crest) and posterior (to the iliac fossa) |
| Actions | Limits L5-S1 motion; resists lateral flexion and rotation at the lumbosacral junction; the primary restraint against L5 forward translation on S1 |
|---|
Iliolumbar ligament pain is reproduced by ipsilateral lateral trunk flexion loading the contralateral ligament. Prolotherapy or corticosteroid injection at the posterior iliac crest targets the iliolumbar ligament insertion. In high-grade L5-S1 spondylolisthesis, the stretched iliolumbar ligament contributes to the lumbosacral instability requiring surgical fusion.
Ligament strain producing low back and groin pain from repeated lateral flexion loading managed with targeted injection and stabilisation exercises.
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