The spinalis is the most medial column of the erector spinae, running from spinous process to spinous process and providing a direct posterior tension band for spinal extension. Its spinous process-to-spinous process attachment gives it the shortest lever arm of the three erector spinae muscles but makes it the most efficient at controlling intersegmental extension. The thoracic portion is most consistently present; the cervicis is variable and often blends with the semispinalis.
| Origin | Spinous processes of T10 through L3; Spinous processes of C5 through T2; Usually described as inseparable from the semispinalis capitis |
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| Insertion | Spinous processes of T2 through T8; Spinous processes of C2 through C4 |
| Nerve Supply | Posterior rami of spinal nerves at each level |
| Blood Supply | Posterior intercostal and lumbar arteries |
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Its spinous process attachments allow it to exert direct extension force between individual vertebral levels, making it important for controlled intersegmental extension in activities requiring precise spinal positioning.
The spinalis is rarely assessed or treated on its own, as it cannot be reliably separated from longissimus by palpation, and it is included in erector spinae assessment and extension endurance training. In posterior spinal surgery it is the first muscle stripped from the sides of the spinous processes; extensive stripping, denervation and prolonged retraction of the spinalis and multifidus during multilevel laminectomy contribute to postoperative weakness of the extensor tension band and, especially in the neck, to post-laminectomy kyphosis. Muscle-sparing approaches and limited retraction reduce this risk.
The spinalis is palpable as the medial column of the erector spinae mass immediately adjacent to the spinous processes, though reliable separation from the longissimus requires imaging rather than clinical palpation.
Acute injury to the erector spinae including the spinalis from sudden loading or sustained postural overload, producing posterior spinal pain with extension restriction managed with active mobilisation and progressive loading.
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