Anatomy of the Spine

The vertebral column
The vertebral column, also known as the backbone or technically called columna vertebralis, consists of 32 vertebrae , which are separated from one another by fibrous cartilage discs .

It is divided into five sections: cervical spine, thoracic spine, lumbar spine, sacrum and coccyx.

The cervical vertebrae are made up of small vertebrae, the vertebral bodies of the lumbar and sacral vertebrae are much larger because the body weight puts a greater strain on the lower vertebrae.
Viewed from the side (sagittal plane), the spine has 4 curvatures: 2 kyphoses and 2 lordoses .

The lordosis is in the neck and loin area, where the spine curves forward.
The lordosis of the cervical spine is less pronounced than that in the lumbar region.
In the case of kyphoses in the thoracic and sacral section, which also includes the coccyx, the curve is backwards, with the latter being more pronounced than that of the thoracic spine.
The spine has a double S shape:

If the curvature is pronounced in the frontal plane, there is scoliosis , ie a permanent lateral deviation of the spine from the longitudinal axis with rotation (twisting).
Scoliosis can affect any part of the spine: cervical, thoracic, lumbar and cause back and neck pain .

g causes increased pressure on the area to which the spine inclines, causing greater wear and tear on articular cartilage, typical of osteoarthritis .
The width of the vertebral bodies increases from top to bottom as the spine progresses, because most of the weight has to be carried in the lower area; there is no weight on the coccyx and therefore the coccyx are small.
The vertebrae are formed in front by the vertebral body and in the back by the vertebral arch.
There are seven processes that arise from the vertebral arch:

  • two articular processes directed upwards and two downwards, forming the articulation between the vertebrae.
  • two transverse processes and a spinous process, which represent the origin or insertion of the back muscles.

Numerous muscles and ligaments hold the spine firmly together.

The vertebral bodies are held together by the anterior and posterior longitudinal ligaments, while the vertebral arch and posterior processes are stabilized by yellow ligament, interspinous process ligament, supraspinous process ligament, intertransverse process ligament, and the interprocess ligaments.


Biomechanics of the spine

The spine has three main functions.
The first task is to protect the spinal cord, which lies in the spinal canal and is surrounded by strong ligaments.
Second, it carries most of the body weight and keeps the head upright.
The third function is to absorb internal and external trauma and micro-trauma and transmit it to the sacroiliac joint (sacroiliac joint) or distribute it to the upper limbs, head and trunk. In this way, the internal organs are protected.
The spine shows 4 curves in side view:

  • Forward bending of the cervical and lumbar spine (lordosis).
  • Backward bending of the thoracic spine and sacrum/coccyx (kyphosis).

A curved spine can withstand greater pressure than a straight one; more specifically, the weight that a straight spine can support can be multiplied by the number of curves squared plus one.
The following calculation results for the spine: 3*3+1=10; the human spine can therefore withstand a weight ten times greater than a straight spine.
Bone is composed partly of a stable substance in the cortical area (compact) and partly of bony trabeculae found particularly in bones such as the calcaneus and vertebrae, which consist of vertical and horizontal lamellae. Depending on the orientation of this skeleton, some directions will be more resistant than others, depending on the direction of the lines of force; for example, the vertically arranged bony trabeculae carry the body weight in an upright position.
In the case of the vertebrae, this alignment means less strength in the front part, with a significantly greater risk of fracture than in other areas.
From a functional point of view, the spine can be viewed as a tripod: the front bearing surface is formed by the vertebral body, the two rear bearing surfaces by the lower processes.
The vertebral body, located at the front of the spine, bears almost the entire weight of the body, while the posterior processes regulate movement.

mobility of the joints

The vertebral joints can be divided into two categories:

  • Between the vertebral bodies are symphysis, the mobility of which is restricted in all directions.
  • Between the vertebral bodies are symphysis, the mobility of which is restricted in all directions.

Possible movements are bending-extending (flexion-extension), sideways bending (lateral flexion) and twisting movement (rotation).
The maximum range of motion of the trunk is:

  • Diffraction up to 75/ 80°
  • Elongation up to 25/30°
  • lateral inclination up to 30/35°
  • Rotation up to 40/45°

In the area of ​​the cervical spine, the mobility is greater than in the other sections, the values ​​​​are around:

  • Diffraction up to 50°
  • Elongation up to 45°
  • lateral inclination up to 45°
  • Rotation up to 65°

Flexion -extension is a movement performed on the sagittal plane and transverse axis. When stretching, the opening of the intervertebral foramen is reduced, vice versa when bending.
This movement is performed almost exclusively by the cervical and lumbar spine, while it is impossible for the thoracic spine; This is mainly because of the rib joints and – to a lesser extent – because the intervertebral discs are much thinner compared to the vertebral bodies.
In the lumbar region, the range of motion is 60° in flexion and 45° in extension.
lateral tilt.
The movement occurs on the frontal plane and on the sagittal axis of the body; in the case of scoliosis, it is limited.
The rotation occurs on the transverse plane and on the longitudinal axis.

Anatomy of the cervical vertebrae

The vertebrae of the cervical, thoracic and lumbar spine consist of a vertebral body and 7 processes .
In each of these sections of the spine, the bones are different in shape and size.
A typical cervical vertebra is small and has a very wide central hole. The transverse processes
located laterally contain a round opening, the transversarium foramen , through which the vertebral artery and vein run. The   7th cervical vertebra, the prominent , has no hole for the jugular artery and a very long spinous process; it is not split and protrudes far outwards.

There are some peculiarities among the cervical vertebrae, the first two vertebrae have proper names, the first is called Atlas , the second Axis (or Epistropheus).
The atlas has no vertebral body, instead two vertebral arches; one normal and one in place of the vertebral body; they are called the anterior and posterior vertebral arches.
This vertebra lacks the spinous process.
The atlas has a large vertebral foramen , most of which is occupied by the joint formed with the second vertebra. The second cervical vertebra is called the axis or epistropheus and has a bony process above the vertebral body called
the thorn or tooth of the axis (dens axis).
It has a short, forked spinous process.
The dental process of the axis is very long, towering over the atlas and reaching the level of the large occipital foramen; in severe whiplash, if fractured, it can hit the spinal cord and cause death.

In the case of death by hanging, the cause of death is fracture of the axis tooth.
In fractures of the cervical spine, the neck must not be moved because the dens axis projects into the large occipital foramen and can compress the brainstem and medulla, which contain the respiratory centers.
Destruction of this part of the brain leads to death because vital functions are concentrated here.

The vertebral column is connected to the base of the skull by the atlas in accordance with the articular surfaces on the sides of the greater occipital foramen.
This joint is the upper head joint and is called the atlanto-occipital joint ; it only allows flexion and extension, ie nodding movements.
The rotational movement of the head occurs through the joint between the atlas and axis (lower head joint, atlantoaxial joint).

Thoracic vertebrae

The thoracic vertebrae have a larger vertebral body than the cervical vertebrae, but the latter have a larger transverse diameter.
The spinous process becomes more oblique towards the lumbar vertebrae and is not forked.
The transverse processes have an articulating surface.
The first thoracic vertebra has only one costal articular surface (Facies costalis), the second to tenth thoracic vertebrae have two semi-articular surfaces, because the ribs articulate with the corresponding and the previous vertebra.
The vertebral hole is smaller than in the cervical vertebrae and has the shape of a pentagon.
The transverse processes of the thoracic vertebrae allow the ribs to rise when the intercostal muscles contract.
The head of the rib articulates with two vertebrae, except for the 1st, 11th and 12th ribs. The other vertebrae articulate with the numerically matched rib.

lumbar vertebrae

There are five lumbar vertebrae, they have a large vertebral body and a very small vertebral foramen in relation to it; the spinous process is large and square.
The vertebral foramen is wider than that of the thoracic vertebrae but smaller than that of the cervical vertebrae and has a triangular shape.
The upper articular surfaces are concave, the lower convex.
The upper articular processes point forward, the lower ones backward; the opposite is true for the thoracic vertebrae.
The fifth lumbar vertebra has some differences from the other four: in the sagittal plane it has the shape of a right-angled trapezium, the short side of which lies near the spinous process; in addition, the transverse processes and lower articular surfaces are more lateral than in the other vertebrae.


The sacrum is located between the lumbar spine and the coccyx and resembles an inverted pyramid in shape. It consists of 5 united vertebral bodies without intervertebral discs.
Laterally, the transverse processes are fused together, forming protrusions called wings. The intervertebral foramina, foramina sacralia , are arranged as four paired openings in front and behind on each side, where the spinal nerves exit.
The sacrum has an articular surface on both sides, facies auricularis, the shape of which is reminiscent of an ear.
It articulates with a relatively narrow joint surface in the hip bone and forms the sacroiliac joint (sacroiliac joint).
In the lower part, the sacrum articulates with the coccyx.

intervertebral disc

The intervertebral disc is a fibrocartilaginous cushion that lies between two vertebral bodies.
It is present between the vertebrae of the cervical, thoracic, and lumbar spines, but not in the sacrum and coccyx.
Their shape roughly corresponds to that of the vertebral bodies; it adapts well to their contour.
The vertebrae are about the same height in front and behind, except for the thoracic vertebrae, which are higher at the back.
The intervertebral discs are higher in the lumbar and cervical region in front and in the thoracic region at the back; This results in the characteristic shape of the spine with the three natural curves.
The intervertebral discs increase in thickness from the cervical spine towards the lumbar spine.
The proportional relationship between disc height and vertebral body height is maximum in the cervical vertebrae and minimum in the thoracic vertebrae. In the sections where the disc is thicker than the vertebral body, the range of motion of the spine is greater.
The intervertebral disc consists of collagen, cartilage and connective tissue fibers and  does not contain blood vessels or nerve endings .
It has a shock-absorbing function to reduce and absorb the pressure exerted on the spine from above and below throughout the day.
It is formed by two concentric structures:

  • The inner gelatinous core (nucleus pulposus) has a gel-like substance and consists mainly of hydrophilic glycosaminoglycans and water.

The pressure of the intervertebral disc is largely discharged onto the gelatinous core.
During the day, when standing or sitting, the weight of the upper body lies on the vertebrae, but also on the intervertebral discs; the water contained in the gelatinous core is shifted to the vertebral body. The body size is therefore about 1-1.5 cm smaller in the evening than in the morning.
The gelatinous nucleus is not exactly in the middle of the fibrocartilage ring, but is shifted slightly backwards towards the vertebral arch.
When the spine bends and stretches or bends sideways, the intervertebral disc is compressed in the direction of movement of the back . Degenerate
with agethe intervertebral disc, the gelatinous core dehydrates, which means that the fibrous cartilage ring is exposed to greater stress and can tear.

This means less elasticity and a reduced size.
A sedentary lifestyle, obesity and poor posture all contribute to disc dehydration.
Under these circumstances, an abrupt movement of the back can be enough to cause the gelatinous core to come out of the fibrous ring, i.e. a herniated disc.

Protrusion or bulging of the nucleus, thus compressing the spinal cord or spinal nerve roots, is thought to be the cause of back pain , although the majority of people with proven herniated discs do not have back pain or lumbar sciatica .

Spinal cord

The spinal cord is a bundle of nerves that, together with the brain, make up the central nervous system .
It originates from the brain, more precisely from the lower brainstem and ends in the so-called conus medullaris at the level of the lumbar vertebra L2.

The spinal cord has a cone-shaped appearance and runs in the protective spinal canal, which is formed from the vertebral foramen (foramen vertebrale) between the vertebral body and the vertebral arch.
The spinal cord is protected primarily by the liquor cerebrospinalis and the spinal cord skin (meninx spinalis) , a triple membrane layer: the dura mater (outside), arachnoid (spider tissue skin) and the pia mater (inside).

The neurons are the functional unit of the nervous system and make up the gray matter of the spinal cord, which has an “H”-like shape in the transverse plane.
Outside the gray matter is the white matter, made up of ascending and descending nerve bundles; the first carry sensitive information, the second motor commands to the muscles.
The posterior roots are sensitive, the anterior roots are motor.
On the side of the spine, between the pedicles of two adjacent vertebrae, are the intervertebral or intervertebral foramina, through which the spinal nerves run.

The anterior and posterior spinal nerve roots emerge from the spinal cord. Once they have left the intervertebral foramen, they unite to form a single spinal nerve, which innervates the internal organs and the musculoskeletal system.

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