The interspinales lumborum are the smallest and most medial of the deep back muscles, consisting of paired muscle slips connecting adjacent lumbar spinous processes. There are four pairs in the lumbar spine (L1-L2 through L4-L5), with none between L5 and S1 where the interspinous space is occupied by the interspinous ligament. Their primary functional role is proprioceptive rather than force-generating.
| Origin | Superior surface of each lumbar spinous process (L2-L5) |
|---|---|
| Insertion | Inferior surface of the spinous process immediately above (L1-L4) |
| Nerve Supply | Posterior rami of lumbar spinal nerves (medial branches) |
| Blood Supply | Lumbar segmental arteries (dorsal branches) |
| Actions | Assist lumbar extension at individual motion segments; Provide proprioceptive feedback for intersegmental position sense |
|---|
The interspinales lumborum are routinely divided during posterior lumbar surgery when the spinous processes are separated or removed. Their loss contributes to the altered intersegmental proprioception seen in post-operative lumbar instability. Interspinales trigger points are identified during deep paraspinal dry needling at the spinous process level. Ossification of the interspinales (along with the supraspinous and interspinous ligaments) produces the bamboo-spine appearance of ankylosing spondylitis.
Not directly palpable as distinct muscles. Deep midline pressure between adjacent lumbar spinous processes may elicit tenderness in interspinales pathology.
Tearing of the interspinales lumborum during hyperflexion injury or surgical approach, contributing to reduced intersegmental proprioceptive feedback and altered spinal loading patterns post-operatively.
