The spinalis is the most medial and smallest column of the erector spinae, connecting spinous processes over short distances. It blends with the semispinalis in the thoracic spine. The spinalis is rarely the primary source of clinical symptoms but contributes to the paraspinal bulk and to the interspinous pressure that increases with extension loading. Its anatomy is relevant in distinguishing the three erector columns on axial MRI.
| Origin | Thoracis: T11-L2 spinous processes. Cervicis: C7 spinous process and ligamentum nuchae. Capitis: often blends with semispinalis capitis |
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| Insertion | Thoracis: T2-T8 spinous processes (most medial erector). Cervicis: C2-C5 spinous processes |
| Nerve Supply | Dorsal rami of spinal nerves |
| Blood Supply | Posterior intercostal arteries |
| Actions | Bilateral: spinal extension (the most medial and smallest erector column); Interconnects adjacent spinous processes for fine extensor control |
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The three erector spinae columns (iliocostalis, longissimus, spinalis) are distinguishable on axial MRI from lateral to medial — the spinalis is the small medial column adjacent to the spinous processes. Fat infiltration of all three columns indicates generalised deconditioning or denervation.
The spinalis is not individually identifiable from surface palpation — it blends with the longissimus in the paraspinal muscle mass adjacent to the spinous processes.
Spinalis and longissimus atrophy from posterior spinal surgery denervation or chronic LBP disuse managed with progressive back extensor rehabilitation.
