The lumbar interspinous ligaments are the thickest in the spine, resisting the highest flexion loads at L4-L5 and L5-S1. Interspinous spacer devices (Coflex, X-Stop) work by distracting these ligaments in extension to reduce foraminal narrowing in extension-worsened lumbar stenosis. The interspinous space is the target for interlaminar lumbar epidural steroid injections.
| Origin | Inferior border of each lumbar spinous process |
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| Insertion | Superior border of the adjacent lower spinous process — the intraspinous space between L4-L5 and L5-S1 is targeted by Coflex and Superion interspinous process devices |
| Actions | The strongest interspinous segment in the spine — resists lumbar flexion and assists in zygapophyseal joint load sharing |
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Interspinous process devices are indicated for extension-worsened lumbar stenosis (neurogenic claudication) when the patient is not a candidate for formal decompression. Baastrup disease (kissing spines) from interspinous ligament fibrosis produces a midline low back pain reproduced by extension and palpation between the spinous processes.
Interspinous ligament fibrosis from spinous process contact producing midline extension-worsened pain managed with interspinous injection.
