Last Updated on March 15, 2025
The thoracic spine also called the dorsal spine, is constituted by the next 12 vertebrae after the cervical spine. From above downwards, these vertebrae are named T1 to T12 (or D1 to D12).
If you palpate back of the neck from above downwards in the midline, you would come across a sudden projection or bump in the lower part of the neck. This projection is the posterior spinous process of C7 vertebra and projects out due to its large size. C7 connects on top of T1.
Similarly, the lowest vertebra of the thoracic spine, T12, connects with L1, or the first vertebra in the lumbar spine. Between these two are ten other thoracic vertebrae stacked over one another.
The thoracic spine has more number of vertebrae than other regions of the spine. It is thus the longest part of the spine. The thoracic spine runs from the base of the neck down to the abdomen and is the only spinal region to be attached to the rib cage.
Thus, in addition to protection of the spinal cord and regional mobility, the thoracic spine also anchors the rib cage by providing attachments for the ribs.
The thoracic spine forms a natural kyphotic curve.
Structure of Spine
The spine extends from the skull to the coccyx and is composed of stacked vertebrae along with intervertebral discs between them. The sacrum and coccyx contain fused vertebrae and hence do not contain discs. The spine is divided into the following regions
- Cervical- contains the first 7 vertebrae placed under the skull. Vertebrae are named C1 to C7.
- Thoracic- It contains 12 vertebrae named T1-T12. The T1 is below C7 and T12 is above L1
- Lumbar- From L1-L5. L5 articulates with lower S1 vertebrae.
- Sacral and Coccygeal regions – The sacral region has 5 vertebrae, of which the lower 4 are fused. The coccyx is the lowermost region and is composed of 4 fused vertebrae
The spine has many functions like transferring the weight of the skull and trunk to lower limbs, protection of the spinal cord, and branching spinal nerves. It supports the thorax and abdomen. It also provides flexibility and mobility of the body by providing a multijointed lever that can move in various planes.
The thoracic spine is unique from other regions in the following ways –
- Rib Cage: Each thoracic segment is accompanied by a pair of ribs. The ribs articulate with the spinal column posteriorly, and the sternum anteriorly. The thoracic spine and rib cage provide both stability and protect vital organs in the thorax.
- Thinner Discs: Discs are cushions in between two vertebrae that act as shock absorbers. In the thoracic spine, the intervertebral discs are thinner than cervical or lumbar spine.
- Narrower Canal: The spinal canal is the narrowest in the thoracic spine. It is one of the reasons that thoracic injuries cause more spinal cord injuries as compared to lumbar where the canal is wider.
Bony Structure of Thoracic Spine
The thoracic vertebrae are identified by the presence of costal facets on the sides of the vertebral bodies. The costal facets of each vertebra articulate with the corresponding rib. The coastal facets maybe two or only one on each side.
There are twelve thoracic vertebrae [both typical and atypical thoracic vertebrae], out of which the 2nd to 8th are typical or have a similar structure and the remaining 5 i.e. 1st, 9th, 10th, 11th, and 12th are atypical or differ in structure from typical vertebrae.
Generally, the thoracic vertebrae are larger than the cervical but smaller than the lumbar and there is an increase in size as they approach lumbar region. Each thoracic vertebra has a corresponding pair of ribs attached to it, on on either side. This is unique of thoracic vertebrae. This is unique since no other vertebrae have ribs attached to them. Therefore, thoracic vertebra has the following parts
- Body
- Spinous process
- Transverse process
- Superior and inferior articular facets
- Lamina
- Intervertebral foramen
- Vertebral foramen
- Costal facets: superior costal facet, inferior costal facet and transverse costal facet,
Features of a Typical Thoracic Vertebra
- Body: The body of the typical thoracic vertebra is heart-shaped with roughly the same measurements from side to side and anteroposteriorly. On each side, it bears 2 costal facets (demifacets). The superior costal facets are larger and placed on the upper border of the body near the pedicle. They articulate with the head of the numerically corresponding rib. The inferior costal facets are smaller and placed on the lower border in front of the inferior vertebral notch. They articulate with the next lower rib.
The two facets together form the complete articular surface for the head of the rib. Thus, the rib articulates with the superior articular facet of the corresponding vertebra and the inferior costal facet of the upper vertebrae. For example, 3rd rib will articulate with the superior costal surface of the T3 vertebra and the inferior costal facet of the T2. - Articular Processes: The superior articular processes are thin plates that project upwards from the junction of the pedicles and laminae. The articular facets are flat and directed backward, laterally, and upwards. This direction permits rotatory movements of the spine. The inferior articular processes are fused to the laminae. Their articular facets are directed forward and slightly downwards and medially.
- Transverse processes: These are directed laterally and backward from the junction of the pedicles and laminae. The anterior surface of each process bears a facet near its tip, for articulation with the tubercle of the corresponding rib.
- Spinous Process: The spinous process is long, and is directed downwards and backwards. The 5th to 9th spinous processes are the longest, more vertical, and overlap.
- Pedicles and Laminae: The pedicles are directed straight backward. The superior vertebral notch is shallow, while the inferior vertebral notch is deep and conspicuous. The laminae overlap each other from above.
Atypical Thoracic Vertebrae
These are the vertebrae that differ in structure from the typical thoracic vertebrae. These are T1, T9, T10, T11 and T12.
- 1st Thoracic Vertebraor T1: The body of the T1 vertebra resembles that of a cervical vertebra. It is broad and not heart-shaped. Its upper surface is lipped laterally and beveled anteriorly. The superior costal facet on the body is complete. It articulates with the head of the first rib. The inferior costal facet is a “demifacet” for the second rib. The superior vertebral notches are well marked, as in cervical vertebrae.
- 9th Thoracic Vertebra or T9: The body has only the superior costal facets (demifacets). The inferior costal facets are absent.
- 10th Thoracic Vertebra or T10: The body has a single complete superior costal facet on each side, extending onto the root of the pedicle.
- 11th Thoracic Vertebra or T11: The body has a single large costal facet on each side, extending onto the upper part of the pedicle. The transverse process is small and has no articular facet.
- 12th Thoracic Vertebra or T12: The features are similar to that of a lumbar vertebra. However, the body bears a single costal facet on each side and the transverse process is small and without facets. The inferior articular facets are directed laterally like lumbar vertebrae.
Joints of Thoracic Spine
Symphyses and facet joints are present in other regions of the spine as well. Costovertebral joints are unique to thoracic spine.
- Symphyses: Symphsis refers to the joint between two vertebral bodies with an intervening disc.
- Facet Joints: These joints are formed between superior and inferior articular processes of vertebrae. Each vertebra articulates via its superior facets with inferior facets of the upper vertebra and superior facets of the lower vertebra via its inferior facets. The facet joints are synovial joints.
The following joints are unique to the thoracic spine because they involve articulation with the rib.
- Costovertebral Joint: This is formed between the head of the rib articulating with:
- Superior costal facet of the corresponding vertebra
- Inferior costal facet of the superior vertebra
- The intervertebral disc separating the two vertebrae
The joint is stabilized by the intra-articular ligament of the head of the rib which attaches the rib head to the intervertebral disc. Very little movement is present in this joint.
- Costotransverse Joint: The joint between the transverse processes of a thoracic vertebra and the tubercle of the rib. They are present in all vertebrae except T11 and T12.
Ligaments of Thoracic Spine
Many ligaments strengthen the thoracic spine. Some ligaments attaching to ribs are unique to the thoracic spine while others are also present in the rest of the spine.
- Anterior Longitudinal Ligament or ALL: The anterior longitudinal ligament runs down the anterior surface of the vertebral bodies from the occiput to the sacrum. ALL is thicker and narrower in the thoracic region. The ligament firmly attaches to the edges of the vertebral bodies. The ligament is thicker and narrower over the vertebral bodies and thinner but slightly wider over the intervertebral discs. It also loosely attaches to the annulus of the disc.
- Posterior Longitudinal Ligament or PLL: The posterior longitudinal ligament arises from the posterior aspect of the basiocciput, is continuous with the tectorial membrane in the upper cervical spine, and runs over the posterior surfaces of the bodies of the vertebrae, down to the coccyx. It lies within the vertebral canal.
- Ligamentum Flavum: It is also called the Yellow ligament. It connects the anteroinferior edge of the upper lamina to the posterosuperior edge of the lamina below. It is thicker in the thoracic region. Its elastic fibers help to preserve the upright posture and assist the vertebral extension after the flexion.
- Interspinous Ligaments: It connects adjacent spinous processes, and runs obliquely from the anterior inferior aspect of the spinous process above to the posterior superior aspect of the spinous process
- Supraspinous Ligament: it is like a fibrous cord that connects the tips of the spinous processes from the C7 to the sacrum. In the cervical spine, the interspinous and supraspinous ligaments thicken and combine to form the nuchal ligament
- Intertransverse Ligaments: These ligaments are situated between the transverse processes. In the thoracic region, they are closely connected with the deep muscles of the back.
- Capsular Ligaments: These form the capsules of facet joints. These are stronger in the thoracic and lumbar regions than cervical region.
The following ligaments are unique to the thoracic Spine
- Radiate ligament of head of rib: This ligament fans outwards from the head of the rib to the bodies of the two vertebrae and intervertebral disc.
- Costotransverse ligaments: Three ligaments reinforce the costotransverse joint between the tubercle of the rib and the transverse process
- Costotransverse ligament- connects the neck of the rib and the transverse process.
- Lateral costotransverse ligament: Connects the transverse process to the tubercle of the rib.
- Superior costotransverse ligament: Connects the upper border of the neck of the rib to the transverse process of the vertebra superior to it.
Muscles of Thoracic Spine
There are two groups of muscles in the back – extrinsic and intrinsic.
- Extrinsic back muscles: These are superficial muscles that are responsible for limb and respiratory movements. Also called immigrant muscles, these represent muscles of the upper limb that migrate to the back during fetal development. These muscles are divided into superficial and intermediate.
- Superficial- Associated with limb movements- trapezius, latissimus dorsi, levator scapulae, and rhomboids
- Intermediate- Superficial respiratory muscles- serratus posterior superior and inferior
- Intrinsic back muscles: These are true back muscles. They are located deep in the extrinsic muscles and separated from them by the thoracolumbar fascia. They are associated with movements of the vertebral column. The muscles of the thoracic area lie deep in the thoracolumbar fascia, while the muscles of the lumbar area lie between the superficial and middle layers of the fascia. Almost all of them receive their nerve supply from the posterior (dorsal) rami of spinal nerves and are called the intrinsic group because they act specifically on the vertebral column These muscles are divided into superficial, intermediate, and deep layers.
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- Superficial layer-splenius capitis, splenius cervicis muscles.
- Intermediate layer [Erector spinae muscles]- spinalis, longissimus, iliocostalis
- Deep Layer [Transversospinal muscles]- semispinalis, multifidus, Rotatores
- The deepest layer- interspinales (connects spinous process) and intertransversarri (which connects transverse processes).
The muscles of the thoracic region are deep to the thoracolumbar fascia as compared to those in the lumbar region which lie between the superficial and middle layers of the fascia
In this article, we will only discuss the intrinsic muscles of the back as those are mainly concerned with spinal movements.
Superficial Layer of Intrinsic Back Muscles
The splenius capitis arises from the spinous processes of vertebrae C7-T3 and the nuchal ligament. it inserts just below the lateral superior nuchal line of the occipital bone, and the mastoid process of temporal bone.
The splenius cervicis arises from the spinous processes of vertebrae T3-T6 and inserts onto the transverse processes of vertebrae C1-C3.
Posterior rami of the middle and lower cervical spinal nerves supply these muscles.
Splenius muscles extend the head on bilateral contraction. Unilateral contraction produces lateral flexion and rotation of the head to the same side.
Intermediate Layer of Intrinsic Back Muscle (Erector Spinae Muscle)
The erector spinae muscle is a large extensor of the spine that consists of three columns of muscle and extends from the cervical to the lumbar region. These muscles are located on either side of the spine. The muscles of the erector spinae group are
- Spinalis muscle: regionwise it is divided into spinalis capitis, spinalis cervicis or colli, and spinalis thoracis (dorsi). They attach between the spinous processes of the vertebrae of their corresponding regions. The Spinalis thoracic muscle extends from the spinous process of T11-L2 until the spinous process of T2-T8.
- Longissimus muscle: It also has three parts capitis, cervicis (colli), and thoracis. They attach between the transverse processes of the vertebrae of their corresponding regions. The Longissimus thoracis muscle further consists of thoracic and lumbar parts. The thoracic part extends from the L1-L5 vertebrae, sacrum, and posterior iliac crest until the thoracic vertebrae and lower 6 ribs. The lumbar part is between the anteromedial ilium and L1-L5 vertebrae.
- Iliocostalis muscle: is divided into iliocostalis cervicis (colli), iliocostalis thoracis and iliocostalis lumborum. Iliocostalis thoracic arises from the angles of ribs 7-12 and attaches to the angles of ribs 1-6 and the transverse process of vertebra C7.
The iliocostalis lumborum muscle originates from the lateral crest of the sacrum, the medial end of the iliac crest, and the thoracolumbar fascia. It attaches to the angle of ribs 5-12, transverse processes of vertebrae L1-L4 and adjacent thoracolumbar fascia.
All the muscles are supplied by the posterior rami of the respective region.
The erector spinae muscle is an extensor of the spine and on bilateral contraction it causes extension of the spine. On unilateral contraction (one sided contraction) it fexes the spine laterally.
Deep Layer of Intrinsic Back Muscle (Transversospinales)
These are also called transversospinal muscles. There are three transversospinal muscles
- Semispinalis muscle: It is further divided into the semispinalis capitis, semispinalis cervicis, and semispinalis thoracis. They originate from transverse processes of the lower vertebrae and are inserted into the spinous process of higher vertebrae of the region.
Bilateral contraction of semispinalis causes extension of head, cervical and thoracic spine. Unilateral contraction leads to lateral flexion of these regions on the same side and rotation to opposite side. - Multifidus muscle: Consists of the multifidus cervicis, multifidus thoracic, and multifidus lumborum. Their origin is from the articular, transverse, and mammillary processes of the regional vertebra and is inserted into the spinous processes of the vertebrae 2-5 levels above. Bilateral multifidus muscles cause extension of the spine. The unilateral contraction causes lateral flexion of the spine on the same side and rotation of the spine on the opposite side.
- Rotatores muscles: These are divided into rotatores breves and rotatores long. They both take origin from the transverse processes of the thoracic vertebrae. The breves insert into the processes of the vertebra one level above, while the rotatores longi span two levels above.
Bilateral contraction of rotatores causes extension of the thoracic spine. Unilateral contraction causes rotation of the thoracic spine to the opposite side.
Deepest Layer
- Interspinales: The interspinales are the short muscles that span the adjacent spinous processes of the vertebrae. The thoracic part is often not well developed when compared to the cervical and lumbar parts are well developed. Interspinales muscles contribute to the extension of the cervical and lumbar spine.
- Intertransversarii: These span the adjacent transverse processes of vertebrae and are often absent in the thoracic region. They are best formed in the cervical and lumbar spine and often rudimentary in the thoracic area. These help in the stabilization of the spine and assist in lateral flexion of the spine.
Blood Supply of Thoracic Spine
Branches of the posterior intercostal arteries are the main blood supply to thoracic vertebrae. The first two posterior intercostal arteries branch off the subclavian artery, while the remaining are branches of the thoracic aorta.
These arteries branch into the periosteal and equatorial arteries. These further branch into anterior and posterior canal branches. Nutrient arteries are branches of the anterior canal branches.
The blood is drained by spinal veins. These form venous plexuses inside and outside the vertebral canal. The blood drains into the segmental veins of the trunk.
Thoracic Spinal Nerves
The thoracic spine has 12 nerve roots (T1 to T12) branching out from the spinal cord on each side. These nerves serve motor and sensory signals to the upper back, chest, and abdomen.
At each level, the thoracic spinal nerve after originating from the spinal cord comes out through the intervertebral foramen. Then it divides into two different nerve bundles ventral ramus and dorsal ramus. At the T1 through T11 levels, the ventral ramus eventually becomes an intercostal nerve that travels along the ribs. At T12, the ventral ramus becomes subcostal nerve that travels beneath the twelfth rib. The dorsal ramus supplies the back skin and muscles.
Generally speaking, the different levels of nerve root function as follows-
- T1 and T2– top of the chest as well as limb muscles and sensations.
- T3- T8- mainly chest wall and aid in breathing. The last few roots may supply the abdomen
- T9- T12– abdomen and/or lower in the back
Clinical Significance
Thoracic spine motion
The motion of the spine is determined by the orientation of the facet joints at that level. Therefore, different thoracic vertebral levels would have different range of motion. Thoracic spine has limited anteroposterior and lateral motion, for more rotation but towards the end the motion starts having more lumbar character i.e. increased forward/backward movements, increased lateral bending but a reduced ability for axial rotation.
Back pain
Upper back pain is a common complaint and could typically be due to one of the following:
- Muscular problems- poor posture, myofascial pain, muscle strain or spasm
- Joint pathologies- Facet joint degeneration, costovertebral joint degeneration
- Vertebral body – post-injury deformities, kyphosis, scoliosis, osteoporotic fractures, infections
Spinal deformities
Throacic spine has a natural kyphotic curve with around 35 degrees of angle. But people can have excessive kyphosis that can either be postural or due to some disease. Scheurmann’s kyphosis is a common cause of kyphosis in children. Scoliosis is abnormal side-to-side spinal curvature and is another possible cause of pain.
Disc herniations
Intervertebral discs act as shock absorbers. A disc may herniate (nucleus pulposus moves posteriorly through a tear in the annulus fibrosus), when the spine is loaded like lifting a heavy object, coughing sneezing, etc. The dis may impinge on the nerve leading to back pain with and without radicular limb pain. With age, the disc degenerates and one can have back pain du to degenerative disc disease.
Spinal injuries
Thracolumbar spine accounts for the majority of spinal injuries. About half of these injuries are associated with neurologic deficits. As the thoracic spine has a relatively narrow vertebral canal, it has a higher risk of cord damage. which predisposes it to spinal cord damage and neurological deficit.
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