The semispinalis thoracis spans five or more vertebral levels from the mid-thoracic transverse processes to the lower cervical and upper thoracic spinous processes, providing extension and contralateral rotation to the thoracic spine. It is the most medial of the transversospinalis group in the thorax and forms the deepest layer of the posterior thoracic musculature beneath the longissimus and iliocostalis.
| Origin | Transverse processes of T6 through T10 |
|---|---|
| Insertion | Spinous processes of C6 through T4 |
| Nerve Supply | Posterior rami of thoracic spinal nerves |
| Blood Supply | Posterior intercostal arteries |
| Actions | Extension of the thoracic spine; Contralateral rotation of the thoracic spine |
|---|
By connecting mid-thoracic transverse processes to upper thoracic and lower cervical spinous processes, it acts as a long-lever contralateral rotator that is important for thoracic rotation during trunk twisting activities.
Semispinalis thoracis tightness contributes to thoracic hypomobility in rotation, which is a significant biomechanical factor in shoulder impingement (limited thoracic rotation compensated by excessive glenohumeral and scapulothoracic motion) and in low back pain (thoracic rotation restriction compensated at the lumbar spine). Thoracic spine manipulation specifically targets the rotational restriction of this muscle and the facet joints.
Palpable deep to the erector spinae in the thoracic region by sustained pressure with the thumbs adjacent to the spinous processes during the application of a thoracic extension mobilisation technique.
Semispinalis and deep thoracic muscle tightness limiting thoracic rotation, contributing to shoulder and lumbar pathology managed with thoracic mobilisation and rotation exercises.
