T1 Vertebra

The T1 vertebra is the first thoracic vertebra of the spine, positioned immediately below the C7 cervical vertebra and above the T2 vertebra. It marks the transition from the cervical to thoracic spine and exhibits features of both regions. T1 plays a key role in supporting the thoracic cage and providing articulation for the first pair of ribs.

Location

T1 is located at the top of the thoracic spine, posterior to the superior thoracic aperture and just inferior to the base of the neck. It articulates superiorly with C7 and inferiorly with T2. Laterally, it supports the first ribs, forming part of the thoracic inlet.

Structural Characteristics

T1 has both cervical and thoracic features, making it a transitional vertebra:

• Vertebral body: Larger and more robust than C7; heart-shaped like other thoracic vertebrae
• Spinous process: Long and nearly horizontal, similar to C7 but thicker
• Transverse processes: Short and thick; each has a costal facet for articulation with the first rib
• Vertebral foramen: Large and triangular (like cervical vertebrae)

Articulations

• Superior: Articulates with the inferior articular facets of C7
• Inferior: Articulates with the superior articular facets of T2
• Rib articulation: Has a full superior costal facet on the body for rib 1 and an inferior demifacet for rib 2
• Transverse costal facet: For articulation with the tubercle of the first rib

Muscle Attachments

• Trapezius: Attaches to the spinous process
• Rhomboid minor: Attaches near the medial border of the scapula, anchored via T1
• Spinalis and semispinalis thoracis: Deep back muscles anchoring to the spinous process

Ligament Attachments

• Anterior and posterior longitudinal ligaments
• Ligamentum flavum (between laminae)
• Interspinous and supraspinous ligaments
• Facet joint capsules

Function

• Supports the thoracic cage via rib 1 articulation
• Allows passage of spinal cord and anchors upper back muscles
• Provides limited rotational and flexion-extension motion
• Acts as a structural junction between the flexible cervical spine and the rigid thoracic spine

Blood Supply

• Arterial: Segmental arteries from the supreme intercostal artery and posterior intercostal arteries
• Venous: Drains via vertebral venous plexuses into the azygos and brachiocephalic veins

Innervation

• Spinal nerves: The T1 spinal nerve exits below the T1 vertebra via the T1–T2 intervertebral foramen
• Brachial plexus: T1 contributes to the lower trunk of the brachial plexus, which innervates the intrinsic hand muscles

Clinical Relevance

• Thoracic outlet syndrome: T1 is anatomically close to the thoracic inlet; abnormalities may compress neurovascular structures
• Fractures: Can occur from axial trauma or hyperflexion injuries; may affect rib articulation and spinal stability
• Nerve root compression: T1 nerve root impingement may cause pain or weakness in the medial forearm and intrinsic hand muscles
• Radiological landmark: T1 is often used as a reference point in spinal imaging and surgery