Spine

Thoracic Spine Anatomy

Thoracic spine is also called dorsal spine and is constituted by next 12 vertebrae after cervical spine.

If you palpate back of neck from above downwards in mid line, you would come across a sudden projection or bump in the lower part of neck. This projection is 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 first vertebra in lumbar spine. Between these two are ten other thoracic vertebra connected to each other.

Following features are unique to thoracic spine when compared to cervical spine

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 first, eleventh, and twelfth pair of ribs articulate with their named vertebra only.

The second through tenth ribs articulate both with their named vertebral body and with the intervertebral disk and the vertebra above.

Each pair of ribs also articulates with the anterior surface of the transverse process of its named vertebrae.

Thoracic spine and rib cage provide both stability and a protect vital organs in 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 at the cervical or lower spine.

Narrower Canal

Spinal canal is narrowest canal in the thoracic spine.

Identification of Thoracic Vertebra

The thoracic vertebrae are identified by the presence of costal facets on the sides of the vertebral bodies. Costal facets of each vertebra articulate with corresponding rib. The costal facets may be 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 and the remaining 5 i.e.1st, 9th, 10th, 11th and 12th are atypical.

Typical Thoracic Vertebra

The body is heart shaped with roughly the same measurements from side to side and anteroposteiroly. 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 vertebral foramen is comparatively small and circular.

The vertebral Arch

The pedicles are directed straight backwards. The superior vertebral notch is shallow, while the inferior vertebral notch is deep and conspicuous.
The laminae overlap each other from above.
The superior articular processes project upwards from the junction of the pedicles and laminae. The articular facets are flat and are directed backwards and a little 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 forwards and slightly downwards and medially.
The transverse processes are large, and are directed laterally and backwards from the junction of the pedicles and laminae. The anterior surface of each process bears a facet near its tip, for articulation with the tubercile of the corresponding rib. In the upper 6 vertebrae the costal facets on the transverse processes are concave, and face forwards and laterally. In others the facets are flat and face upwards, laterally and slightly forwards.
The spine is long, and is directed downwards and backwards. The 5th to 9th spines are the longest, more vertical and overlap each other. The upper and lower spines are less oblique in direction.

Attachments on a Typical Thoracic Spine Vertebra

The upper and lower borders of the body give attachment, in front and behind respectively, to the anterior and posterior longitudinal ligaments.
The upper borders and lower parts of the anterior surfaces of the laminae provide attachment to the ligamenta flava.
The transverse process gives attachment to (i) the lateral costotransverse ligament (at the tip); (ii) the superior costotransverse ligament (lower border); the inferior costotransverse ligament (anterior surface); (iv) the intertransverse muscles (to upper and lower borders); (v) the levator costae (posterior surface).
The spines gives attachment to the supraspinous and interspinous ligaments. They also give attachment to several muscles including the trapezius, the rhomboids, the latissimus dorsi, the serrate posterior superior and inferior, and many deep muscles of the back.

Atypical Thoracic Vertebrae

First Thoracic Vertebra

The body 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 spine is thick, long and nearly horizontal.
The superior vertebral notches are well marked, as in cervical vertebrae.

Ninth Thoracic Vertebra

It resembles a typical thoracic vertebra except that the body has only the superior costal facets (demifacets). The inferior costal facets are absent.

Tenth Thoracic Vertebra

It resembles a typical thoracic vertebra except that the body has a single complete superior costal facet on each side, extending on to the root of the pedicle.

Eleventh Thoracic Vertebrae

The body has a single large costal facet on each side, extending on to the upper part of the pedicle.
The transverse process is small, and has no articular facet. Sometimes it is difficult to differentiate between vertebrae T10 and T11.

Twelfth Thoracic Vertebra

The shape of the body, pedicles, transverse processes and spine are similar to those of a lumbar vertebra. However the body bears a single costal facet on each side, which lies more on the lower part of the pedicle than on the body.
The transverse process is small and has no facet, but has superior, inferior and lateral tubercles.
The inferior articular facets are lumbar in type, and are directed laterally (everted), but the superior articular facets are thoracic in type.

Joints of Thoracic Spine

Present throughout Vertebral Column

These joints are present in other regions of spine as well.

There are two types of joints present throughout the vertebral column

Symphyses

Adjacent vertebral bodies are joined by intervertebral discs, made of fibrocartilage.

Facet Joints

These are synovial joints formed by the articulation of superior and inferior articular processes from adjacent vertebrae.

Following joints are unique to thoracic spine.

Costovertebral Joint

Each costovertebral joint consists of the head of the rib articulating with:

Superior costal facet of the corresponding vertebra
Inferior costal facet of the superior vertebra
Intervertebral disc separating the two vertebrae

The joint is stabilized by the intra-articular ligament of head of rib which attaches the rib head to the intervertebral disc. Only slight gliding movements can occur at these joints.

Costotransverse Joint

The costotransverse joints are formed by the articulation of transverse processes of a thoracic vertebra and the tubercle of the adjacent rib. They are present in all vertebrae except T11 and T12.

Ligaments of Thoracic Spine

The thoracic spine is strengthened by the presence of numerous ligaments.

Ligaments Present in Other Parts of Spine Also

Anterior Longitudinal Ligament

The anterior longitudinal ligament runs down the anterior surface of the vertebral bodies from the occiput to the sacrum. The anterior longitudinal ligament is thicker and narrower in the thoracic region. The ligament firmly attaches to the edges of the vertebral bodies.

This is thick and slightly more narrow over the vertebral bodies and thinner but slightly wider over the intervertebral discs. It also loosely attaches to annulus of disc.

It is a three layered ligment – superficial, intermediate and deep.

Posterior Longitudinal Ligament

The posterior longitudinal ligament arises from the posterior aspect of the basiocciput, is continuous with the membrana tectoria, and runs over the posterior surfaces of the bodies of the vertebrae, down to the coccyx. It is within the vertebral canal.

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

The capsular ligaments are attached to the articular margins of the articular processes. The fibers are oriented perpendicular to the facet joint and are stronger in the thoracic and lumbar region than in the cervical region.

Ligamentum Flavum

Also called Yellow Ligament, the ligamentum flavum connects the anteroinferior edge of the lamina to the posterosuperior edge of the lamina below. The ligamentum flavum is thicker in the thoracic region. This ligament is composed mainly of elastic fibers, and that elasticity serves to preserve the upright posture, and to assist the vertebral column to resume after flexion.

Interspinous Ligaments

The interspinous ligaments connect 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

This strong ligament is a strong fibrous cord, which connects together 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

Ligaments Unique to 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 ligament

This connects the neck of the rib and the transverse process.

Lateral costotransverse ligament

It extends from the transverse process to the tubercle of the rib.

Superior costotransverse ligament

It passes from 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 types of muscles in the back

Extrinsic which are responsible for limb and respiratory movements
Intrinsic which maintain posture and carry out spinal movements.

Extrinsic Back Muscles

The extrinsic back muscles include superficial and intermediate muscles.

The superficial extrinsic back muscles

Trapezius, latissimus dorsi, levator scapulae, and rhomboids.

The function of this muscle group is to connect the upper limbs to the trunk and produce and control limb movements.

The intermediate extrinsic back muscles include serratus posterior superior and inferior. Those are thin, superficial respiratory muscles.

Intrinsic Back Muscles

The intrinsic or deep back muscles maintain posture and control movements of the vertebral column.

The deep back muscles can be grouped into superficial, intermediate, and deep layers

Superficial layer

Splenius capitis
Splenius cervicis muscles.

Intermediate layer [Erector spinae muscles]

Iliocostalis
Longissimus
spinalis muscles.

This group is the chief extensor of the vertebral column.

Deep Layer [Transversospinal muscle]

Semispinalis
Multifidus
Rotators

Apart from these, following muscles are present.

Interspinals which connect spinous processes
Intertransverse which connects transverse processes

Anterior spinal muscles

The anterior musculature is found in the cervical and lumbar regions, not in the thoracic region.

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Anatomy of Cervical Spine

By Arun Pal Singh

The portion of the spine encompassing neck region forms the cervical spine. The cervical spine is formed by the first seven vertebrae which are named as C1 to C7.

Anatomically, cervical spine starts where the top vertebra (C1) connects to the bottom of the skull.

Normal cervical spine has a lordosis. That means it is curved with convexity on the anterior aspect. It ends when C7 joins with the first thoracic vertebra.

Understanding the anatomy of cervical spine is vital to understand the various problems and abnormalities of the neck. Anatomy of cervical spine is easier to understand by dividing it in upper and lower cervical regions

Anatomy of Upper Cervical Spine

The bones of the upper cervical spine include

The base of skull surrounding the foramen magnum
Pair of occipital condyles
Atlas vertebra (C1)
Axis vertebra (C2)

Occipital Condyles

The occipital condyles are under-surface facets of the occipital bone which articulates with the superior facets of the atlas vertebra.

The condyles are oval in shape, and their anterior extremities and they are directed forward and medialward.

The articular surfaces of the condyles are convex from before backward and from side to side and look downward and lateralward.

Occipital condyles are covered by hyaline cartilage.

Atlas Vertebra

Atlas (C1) is the first cervical vertebra of the spine.

It is named for the Atlas of mythology because it supports the globe of the head.

The atlas along with the Axis (C2)– forms the joint connecting the skull and spine and are specialized to allow a greater range of motion.

Together they are responsible for the nodding and rotation movements of the head.

Atlas has no body and consists of an anterior and a posterior arch and two lateral masses. It appears like a ring.

Two lateral masses on either lateral side provide the bulk of the atlas bone mass. The transverse foramina are located to the lateral aspect of the lateral masses

Axis Vetebra

The axis is the second vertebra and has a unique shape. It consists of a large bony protuberance and a pars articularis separating the superior from inferior articular processes.

The odontoid process or dens is a 2 to 3 cm long corticocancellous structure with narrowed waist and thickened cortical tip emanating in a rostral (towards the head) direction from the vertebral body.

The odontoid rests in a recess behind the anterior arch of the atlas and the medial walls of the two lateral masses.

The superior articular surface of the axis is the cranial (towards the head) surface of the vertebral body of the axis and lies separated by a narrow osseous recess lateral to the odontoid.

The two inferior articular processes of the axis are located on the inferolateral corner of the neural arch. The transverse foramen of the axis is located in the lateral aspect of the vertebral bodies on either side.

Ligaments of Upper Cervical Spine

The joint surfaces of these three bony components of the upper cervical spine have little or no inherent stability. Thus the stability of this region is mainly determined almost entirely by ligamentous structures

The alar ligaments connect the medial surface of the occipital condyles to the lateral tip of the odontoid. A small portion also attaches obliquely along the medial upper wall of the atlas.

The apical ligament connects between a bony protuberance of the basion (The mid-point on the anterior margin of the foramen magnum on the occipital bone) to the superior tip of the odontoid.

The transverse atlantal ligament connects the medial wall of the anterior third of either lateral mass of the atlas with one another.

Tectorial membrane is the rostral continuation of the posterior longitudinal ligament and is composed of a deep and a superficial layer.

Between the apical ligament and the deep layer of the tectorial membrane is the cruciate ligament bridging the basion and the axis body and a narrow transverse ligament, which extends between the upper ends of the lateral masses of the atlas.

Posteriorly, the upper cervical spine does not have well-developed ligamentous support structures.

The atlantoaxial and atlanto-occipital membranes, respectively form a thin protective barrier rather than an effective restraint mechanism.

Accessory atlantoaxial ligaments and the atlanto-occipital and atlantoaxial joint capsules are additional well-defined ligamentous support structures

Neurovascular Structures

The spinal cord at the craniocervical junction is located between the posterior halves of the lateral masses of the atlas and the pars interarticularis of the axis. It fills about 50% of the neural canal in the upper cervical spine.

C-1 roots emerge from the spinal cord at a right angle and are located posterior to the occipital condyles superior to the lamina of the atlas.
C-2 roots are larger than the C-1 roots and are located posterior and slightly caudal (towards foot) to the atlantoaxial joints.
The vertebral arteries emerge from the transverse foramina of the vertebral body of the axis in a cranial direction lateral to the pars interarticularis and the atlantoaxial joints.

At the level of the atlas the vertebral arteries will enter the transverse foramen, course medially in a shallow bony groove located on the superior surface of the lateral third of the atlas lamina, and then head into the cerebellar fossa.

Anatomy of Lower Cervical Spine or Subaxial Spine

The lower cervical spine or subaxial [below axis vertebra] cervical spine, includes the C3 to C7 vertebral segments. Lower cervical vertebrae have a relatively uniform anatomic configuration as compared to the anatomy of upper cervical spine.

Anterior Elements

The vertebral body is larger in coronal (left to right) than its sagittal diameter (anterior to posterior). Bilateral prominences called uncinate processes are present along the lateral aspects of the superior endplates. The uncinate processes articulate with rounded inferolateral borders of the superior vertebral body and the articulation is called an uncovertebral joint.

This joint marks the lateral extent of the vertebral body.

C3-C6 vertebrae have a typical anatomical structure –

Small body, and broader from side to side than from front to back.
Flattened anterior and posterior surfaces
The upper surface
- Concave transversely
- Presents a projecting lip on either side.
The lower surface
- Concave from front to back
- Convex from side to side
- On either side laterally they have shallow concavities
- Concavities receive uncinate processes to form uncovertebral joints
The vertebral foramen is large and of a triangular form.
The transverse processes are each pierced by the foramen transversarium

Transverse foramina are present consistently in upper six vertebrae but variable in C7. Even when it is present, it is small.

The transverse foramen is formed by the fusion of the anterior and posterior part of the transverse process and part of the pedicle.

Transverse foramina give passage to the vertebral artery and vein in upper six cervical vertebrae. In C7 it contains only vein as well as a plexus of sympathetic nerves.

C7 has enlarged spinous process called vertebra prominence. It is the most prominent structure that can be palpated when we pass our finger downwards from the skull.

Neural foramina of cervical spine allow exit of cervical spinal nerves which are eight in number and are named as C1 to C8.

Between two adjacent vertebrae is interposed intervertebral disc.

The longus colli muscles lie directly over and insert onto the anterolateral aspects of each cervical vertebra.

The sympathetic plexus lies on top of the lateral muscle belly and may be injured aggressive dissection or retraction which can lead to Horner’s syndrome.

The prevertebral (deep) and alar (superficial) fascial layers separate the spine from the overlying esophagus.

Posterior Elements

Pedicles in lower cervical vertebrae project in a posterolateral to anteromedial orientation.

Articular facets are flat

Superior articular facets face backward, upward, and slightly medially
The Inferior facets are forward, downward, and slightly laterally.

The facet joints are formed by the interaction of superior and inferior articular processes. They are also known as the zygapophyseal articulations. The articular surfaces are angled approximately 45 degrees in relation to the transverse axis.

The pillar of bone between the superior and inferior articular processes is commonly referred to as the lateral mass and is It is a useful site for posterior screw or wire stabilization.

The laminae are narrow, and thinner above than below.

The laminae arise from the posteromedial border of the lateral masses project posterior and toward the midline to form bifid spinous processes.

The spinous process is short and bifid.

Ligamentum flavum or yellow ligament is present between space between two laminae.

Ligaments like interspinous and supraspinous ligaments or ligamentum nuchae form a posterior ligamentous complex and its disruption may lead to mechanical instability.

Cervical Nerves

The cervical nerves control many bodily functions and sensory activities.

C1: Head and neck

C2: Head and neck

C3: Diaphragm

C4: Upper body (e.g. Deltoids, Biceps)

C5: Wrist extensors

C6: Wrist extensors

C7: Triceps

C8: Hands

Injury to cervical spine or involvement of spinal nerves affects the area they supply.

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Spine Anatomy Overview

By Arun Pal Singh

Human spine or vertebral column is a structure made of multiple small units called vertebra and extends from just below the base of the skull to a point just below the beginning of gluteal cleft. You can palpate the lower part by following the spine till its lower end.

A vertebra is the smallest unit of the vertebral column. Plural term is vertebrae. Vertebrae have been modified according to the function they are expected to serve in different parts of the spine.

To a naked and unaccustomed eye, the spine appears as a straight column. But that is not the case. It appears straight in anteroposterior view (That means looking from front or back) but in lateral view or looking from a side, we can see multiple curves in different regions.

These curves are called kyphotic if they are concave in anterior(front) and convex on posterior (back) and lordotic if they are convex in anterior and concave on posterior.

Regions of Spine

It is divided into five regions

Cervical

This part is present in the neck and consists of first seven vertebrae. Each vertebra is known by C followed by

the number of the vertebra. Thus the first vertebra is called C1 and the last vertebra is called C7. It has a normal lordotic curve.

Thoracic

This is also called the dorsal spine. It is below cervical and spans upper trunk or thorax or area corresponding to the chest. It contains a total of 12 vertebrae designated as T1 to T12 in a fashion similar to we discussed for cervical vertebrae. It has a normal kyphotic curve.

Lumbar

It follows Thoracic and consists of 5 vertebrae, L1 to L5. Some of the people might have anatomical variations in which 4 or 6 vertebrae might be present in Lumbar spine. In both cases, the extra vertebra is added to or taken from Sacral spine. Accordingly,if there are 4 lumbar vertebrae, it is called sacralization of lumbar vertebra and if there are 6 lumbar vertebrae, it is called lumbarization of sacral vertebra.

Sacral

It is composed of five sacral vertebrae S1 to S5. In contrast to other parts we just discussed, vertebrae in the sacral spine are fused to each other. This part of spine follows lumbar spine and is present in the pelvic area.

Coccyx or Coccygeal

This is also known as the tailbone. It is the final segment of the human vertebral column, of four fused vertebrae (the coccygeal vertebrae) below the sacrum.

The function of the spine is to support and transmit weight of trunk to lower limbs, to aid in the motion of the trunk and to support and protect spinal cord & other vital organs. Spinal Cord is the structure that transmits neural fibers. These fibers further supply the organs in form of nerves.

Structural Arrangement

Vertebrae are the structural units of the spine. They are stacked together to form the entire vertebral column. Between each vertebra, are cushion-like structures called intervertebral discs which act as shock absorbers and also permit some movement between the vertebral bodies. Various ligaments stabilize the spine and also allow movements.

Movements of the spine occur at special joints called facet joints that are formed between two adjacent vertebrae. Various muscles carry out the movements of the spine. These muscles are important for maintaining posture and transmission of loads created during normal activities, work, and play. The strength of these muscles is important and lack of strength would lead to various backache problems.

Vertebrae are shaped in such a way that the spinal cord is protected from damage by the bones of the entire spinal column.

Vertebrae

The vertebrae are responsible for transmission of the weight. Each vertebra consists of an anterior body which is attached to a posterior ring called posterior neural arch. Two struts of bones called pedicles arise from the body and join two converging struts called laminae. Pedicles, laminae and posterior surface of body forms boundaries of spinal canal. This spinal canal is the space where the spinal cord passes. There is a transverse process on either side of the arch which serves as an attachment to various muscles and ligaments. Dead posteriorly is the posterior spinous process that can be felt on our back as bumps. Posterior spinous processes also serve as an attachment to ligaments and muscles of the spine.

Adjacent to the base of transverse processes are bony projections that go superior and inferior. These are called superior and inferior articular facets and take part in the formation of facet joints. There are two facet joints between each between each pair of vertebrae one on each side. They are primarily designed to allow the vertebral bodies to rotate with respect to each other.

Intervertebral Disc

The discs are designed to absorb the stresses carried by the vertebral column while allowing the vertebral bodies to move with respect to each other. They made up of a strong outer ring of fibers called the annulus fibrosus that contains nucleus pulposus.

Neural Foramen

The neural foramen is the opening where the nerve roots exit the spine and travel to the rest of the body. There are two neural foramina located between each pair of vertebrae, one on each side.

Muscles and Ligaments

Various muscles and ligaments attach to the spine. They help the spine to stabilize and allow it to carry various movements.