Interspinalis Thoracis

musculus interspinalis thoracis

The interspinalis thoracis muscles are small, paired muscle slips connecting adjacent thoracic spinous processes. They are poorly developed in the thoracic spine compared to the cervical and lumbar regions, often being absent at mid-thoracic levels where the spinous processes are steeply angled and overlap. Their role is primarily proprioceptive.

Nerve: Posterior rami of thoracic spinal nerves Blood Supply: Posterior intercostal arteries Region: Chest

Anatomical Data

Origin, Insertion & Supply

Origin	Superior surface of thoracic spinous processes T2-T12
Insertion	Inferior surface of the spinous process immediately above (T1-T11)
Nerve Supply	Posterior rami of thoracic spinal nerves
Blood Supply	Posterior intercostal arteries

Biomechanics

Function & Actions

Actions	Minor assistance to thoracic extension; Proprioceptive sensing of thoracic intersegmental position

Clinical Relevance

Clinical Notes

The interspinalis thoracis muscles are inconsistently present and rarely considered in isolation clinically. Their disruption during thoracic surgery affects the midline tension band. Thoracic interspinous bursitis and interspinalis pain contribute to the midline thoracic pain syndromes seen in osteoporotic compression fractures. Ankylosing spondylitis calcifies these muscles alongside the interspinous ligaments.

Palpation

Not palpable as discrete muscles. Midline thoracic tenderness between spinous processes may indicate interspinalis involvement.

Pathology

Common Injuries & Conditions

Thoracic Interspinous Pain

Midline thoracic pain from interspinalis and adjacent interspinous ligament irritation in thoracic kyphosis and osteoporotic compression fractures, managed with extension exercises and spinal support.