Anatomy of the spine
Of course, I am not a doctor and therefore there is absolutely no claim for completeness and accuracy.
Gray’s Anatomy 39e
The human spine
32 – 34 bony elements
24 articulating vertebrae and 9 fused vertebrae in the sacrum and the coccyx
Seperated by intervetebral discs
Cervical spine: 7 vertebrae (vertebrae cervicalis) C1-C7.
Thoracic spine: 12 vertebrae (vertebrae thoracicae) T1-T12.
Lumbar spine: 5 vertebrae (vertebrae lumbales) L1-L5.
Sacral spine (Os sacrum): 5 fused vertebrae (vertebrae sacrales) S1-S5.
Coccygeal spine (Os coccygis): 3-5 fused vertebrae Co1-Co5 (tailbone).
A single vertebra consits of:
– Base: Corpora vertebralis.
– Connected through disci intervertebralis.
– Vertebrae of the cervical, thoracic and lumbar spine are moveable → real vertebrae.
– Vertebrae of the sacral and coccygeal spine are fused to the age of 20 → wrong vertebrae.
Function of the spine:
– Support function.
– Protects the spinal cord (medulla spinalis) through the spinal canal (vertebral canal).
– Absorption of shocks form pulses of weight force by intervertebral discs, ligaments and joints.
– Comprehensive mobility due to joint and muscle system.
– Secondary task: red bone marrow → blood cell generation.
Morphology of vertebrae
A vertebra consisist of
the vertebral body (corpus vertebrae)
– A short cylindrical shaped structure.
– The surfaces of adjacent vertebrae (facies intervertebralis superior and inferior) are each provided with a hyaline cartilage connected to the intervertebral disc and two ligaments (anterior and posterior longitudinal ligament) -> support function.
– The vertebral arch (arcus vertebrae) emerges from the corpus.
the arcus vertebra
– Is a arcuate portion on the back (dorsal) side of the vertebra.
– In the middle of it the spinous process is located (processus spinosus).
Here is the beginning of ligaments (ligament supraspinale and interspinale), fascia, and part of the back muscles.
You can easily feel the processus spinosus as an elevation on the back.
– Build the spinal canal → contains the spinal cord.
– Carries the four articular processes.
They allow the spine to move (two to the top, and two to the bottom of the vertebra).
They form as bony protrusions (processes) with cartilage covered articular surfaces the real joints between the vertebrae (the intervertebral joints) → they build a functional unit with the intervertebral discs and the ligaments;
– And the two transverse processes
Approach of ligaments (lig. intertransversaria), fascia and muscles.
At the thoracic vertebrae, the transverse processes also form an articulated connection to the ribs.
Transverse process channel (canal transversarius):
C1-6 has a hole where the vertebral artery, the attendant vein and the sympathetic nerve arise.
– Two adjacent vertebra form a hole where the spinal nerves exit.
– The lig. flava are located between the vertebral arches and define the intervertebral foramen to the middle and the back.
All vertebrae together build the intervertebrate channel (spinal channel, canlis vertebralis)
– The spinal canal (spinal canal, vertebral canal) is the protective channel within the spine (vertebral columna) in which the spinal cord (medulla spinalis) together with its meninges (meningeal encephali) and the cerebrospinal fluid (CSF) are embedded.
– Leads from the occipital foramen (foramen (occipital) magnum) of the occipital bone through the cervical, thoracic and lumbar spine to the sacrum.
– Ventral the spinal canal is limited through the vertebral bodies (corpora vertebrae) and the intervertebral discs,
– and dorsal through the vertebral arches (arcus vertebrae).
– The segmental spinal nerves (nervi spinalis, pl. nervus spinalis) leave the spine through the intervertebral holes (Foramina intervertebralia).
– Structures in the spinal channel:
Spinal cord (medulla spinalis):
Spanned by meninges (meninges encephali).
Meninges medullae spinales:
On the outside a hard layer: Dura mater spinalis.
On the inside the two soft layers: Arachnoidea mater and pia mater.
Epidural space (cavum epidurale):
Also called peridural space.
Is located between dura mater and the connective tissue covered spinal canal.
Filled with connective tissue and fat.
Includes the plexus venosus vertebralis internus.
Here are the nerve roots for the outgoing dorsal spinal cord nerves and the spinal ganglion →
injection of a local anesthetic to switch off these nerve roots (epidural).
The corresponding veins form a dense network (plexus) of vessels on the front of the spinal cord; the plexus vertebralis internus ventralis.
Together with the epidural fat tissue the venous plexus builds a padding for the spinal cord.
Subdural space (cavum subdurale):
Between dura mater and arachnoid mater.
Filled with loose connective tissue.
Because of the vascularity of the dura mater and arachnoidea it can come to tearing of the blood vessels and leakage of blood to the subdural space.
Subarachnoidal space (cavum subarachnoidale):
The arachnoidea together with the pia mater closes the subarachnoid space.
Cerebrospinal fluid circulates here.
Also called outer CSF (cerebral spinal fluid) space.
Places where the subarachnoid space is very wide are called cerebellomedullary cistern.
(The cisterna magna and the cisterna basalis).
The ligaments in the spinal channel:
Lig. longitudinale posterior (at the front of the channel).
Lig. flavum (between the arcus vertebrae of adjacent vertebrae).
The vertebrae are connected through disci intervertebralis (exception: atlas and axis, sacrum and coccyx).
– Disc-shaped structures which connect the vertebrae.
– Symphythical (cartilaginous) bone connections.
– A total of 23 intervertebral discs.
– No discs between the occiput and atlas, and between atlas and axis and also not between sacral and coccygeal spine.
– Consists of an outer fibrous ring (anulus fibrosus) and a centrally located nucleus (nucleus polposus).
An outer zone: tensile connective tissue sheath of collagen fibers.
An inner zone: at the transition the tight connective tissue of the outer zone passes over in cartilage tissue (without a sharp contour) →
unsharp transition towards the nucleus.
Nutrition of the intervertebral disc via influx and efllux of extracellular fluid from the fiber ring.
The biggest part of the intervertebral disc is avascular.
The nucleus polposus
Cell poor tissue.
Consists of glycosaminoglycans → high water binding capacity → high water content.
Because of the swelling pressure the fiber ring is under tension.
If the core emerges it is called a herniated disc.
Function of the intervertebral discs
Absorption of axial impact and allows uniform pressure distribution through weight and momentum forces.
Limiting the range of movement.
The nucleus pulposus moves always to the opposite side when moving ventral, dorsal or lateral.
In addition the accretion of the fiber ring with the edge strips (epiphyses) and with the ligaments (anterior and posterior longitudinal ligament) it protects against horizontal (translational) wrong movements of the vertebral bodies (corpora vertebrae) against each other.
A further limitation of the movement takes place in the rotation around the longitudinal axis.
A spondylolisthesis (a displacement of the vertebrae relative to one another) is prevented by fixing the intervertebral discs on the vertebral body (corpus vertebrae).
– 7 cervical bones (but 8 cervical nerves).
– Bones are small and delicate.
– They have a short spinous processus (except C2 and C7), often bifurcated (C7 is not bifurcated and longer).
– C1 (atlas) and C2 (axis) are special and allow the neck and head to move.
– C1 misses a corpus and the processus spinosus; C2 has the dens axis.
– There is no intervertebral disc between C1 and C2; the first disc is between C2 and 3.
– Ventral konvex (lordosis).
– Ventral → Corpus vertebrae.
– Dorsal → Arcus vertebrae.
– Lig. nuchae, deep extensors (semispinalis, thoracis and cervicis, multfidus, spinales and interspinales) → all attached to the spinous processus.
– Scalenus anterior, longus captis and longus colli are attached to the fourth to sixth anterior tubercles.
– Splenius, longissimus and iliocostalis cervicis, levator scapulae and scalenus posterior and medius → posterior tubercles.
– Bodies are small, and broader from side to side than from front to back.
– The anterior and posterior surfaces are flattened and of equal depth.
– The vertebral foramen is large and of triangular form.
– The processus is short and bifid (because of that, certain superficial muscles attach to the nuchal ligament).
– The articular facets are flat and of an oval form.
– The transverse processes are each pierced by the foramen transversarium, which in the upper six vertebrae, gives passage to the vertebral artery and vein, as well as a plexus of sympathetic nerves.
– The cervical spinal nerves emerge from above the cervical vertebrae.
C7 (Vertebra prominens)
– Long and prominent spinous processus.
Atlas and Axis
– First cervical vertebra.
– Carries the entire load of the head.
– Allows anteflexion and retroflexion.
– Forms with the axis the atlantodental joint.
– Has largely lost his body (forms a ring) and has no spinous process.
– On the dorsal side of the ring runs the spinal cord which is coming from the brain.
It has on both sides outgrowth, called massa lateralis atlantis.
Between the front arch of the atlas (Arcus atlantis anterior) and the posterior vertebral arch (Arcus atlantis posterior).
Continues sideways as the transverse processes.
Carries a joint extension on the top and the bottom (processus articular superior and inferior).
The articular surfaces of the two upper articular processes (Processus articular superior) build together with the articular surface of the two condyles of the occiput of the skull the atlanto occipital joint.
The articular surfaces of the lower two articular processes (Processus articular inferior) build together with the articular surfaces of the upper articular processes of the axis the lateral atlantoaxial joint.
On the cranial surface near the massa lateralis the vertebral arterie furrows (Sulcus arteria vertebralis) are running.
– A front arch (Arcus anterior atlantis).
On the inside the fovea dentis is located.
And ventral, outside, on the front arch lies the tuberculum anterius atlantis.
– A posteror arch of the atlas (Arcus posterior atlantis).
Towards the back (dorsal) a rudiment of the spinous process.
– The transverse processes contain the usual transverse processes foramina through which the vertebral artery passes.
Lig. atlantis transversum
– Short, very strong ligament in the bone ring of the atlas.
– Runs concave to ventral.
– The middle is thicker than the two ends.
– It is at both sides attached to a small tubercle of the medial surfaces of the two atlas arches.
– On height of the dens, it forms a little fiber strand cranial to the occiput and a second one caudal to the dorsal surface of the axis (together with the Lig. atlantis transversum it is called the Lig. cruciatum atlantis.
– Divides the foramen of the atlas into two parts → the front part contains the dens axis, the posterior contains the spinal cord.
Together with the atlas it builds the two lower ocipital joints → allows the rotation of the head.
– Characteristic is the dens axis, which is located right where the body of the atlas is missing.
– The dens has a front and a back articulation surface.
– The upper articular processes are not prominent.
– On the bottom it has the typical articular processes.
– It has a spinous process and the typical transverse processes.
– Between the lower articular surfaces of the atlas and the upper articular surfaces of the axis, also between the anterior articular surface of the dens and the dens pit of the atlas → lower occipital joints (atlantoaxial joints).
– On the down side, towards the 3rd vertebra the axis builds a normal intervertebral joint.
– Branches from the vertebral artery (level of intervertebral foramen for 3rd cervical nerve → form anterior and posterior longitudinal channels) near the base and the apex the branches enter the dens.
The upper cervical joints
You will mainly hear the term:
cranio-cervical instability which means a instability between the cranium (head) and the first vertebra
atlanto-axial instability which means instability between C1 and C2.
paired articulated connections between fossae of the upper articular processes of the atlas and the articular surfaces of the occipital bone.
– Anterior atlantooccipital membrane: connects the foramen magnum to the anterior arch of the atlas.
– Posterior atlantooccipital membrane.
Mainly held by
Paired fibrous joint capsules.
Anterior and posterior atlantooccipital ligament (atlantooccipital membranes).
Ligamentum cruciatum atlantis (ligamentum transversum atlantis + crus superior and inferior), Lig. nuchae.
Posterior neck muscles.
– Pin/pivot joint between the odontoid and the atlas.
– Also held by the transverse ligament of the atlas.
– At the top the axis forms with the atlas the paired atlantoaxial joints.
(3 synovial joints (a pair between the lateral masses and one between dens axis and arch of the atlas).
– Anterior longitudinal ligament
– Transverse atlantal and cruciform ligament
– Membrana tectoria
– Alar ligaments
– Apical ligament of the dens
– Synovial membrane
– Ligaments (transverse atlantal ligament is the strongest)
– Alar ligament
– Fibrous capsules
– Lig. nuchae
– Posterior neck muscles
– Subocipital muscles
Lig. alare (between skull and axis) head rotation & lateral flexion
Lig. cruciatum atlantis
Lig. transversum atlantis
Membrana atlantoocipitalis anterior (extension) and posterior (flexion)
Membrana atlantoaxialis anterior and posterior
Between vertebral bodies:
Lig. longitudinale anterior (extension and reinforces front of anulus fibrosis) and posterior (flexion and reinforces back of anulus fibrosis (from axis to sacrum).
Anterior longitudinal ligament
– Along the anterior surfaces of the vertebral bodies.
– From occipital bone to the anterior tubercle of C1 and the front of the body of C2.
– Continues to the front of the sacrum.
– Strongly adherent to the intervertebral discs.
Posterior longitudinal ligament
– Posterior surfaces of the vertebral bodies in the vertebral canal.
– Between C2 and sacrum.
Between Arcus vertebrae:
Lig. flava (Axis-Sacrum) Flexion
– In the vertebral canal, connects laminae of adjacent vertebrae.
Between transverse processes and spinous processes
Lig. intertransversaria (between transverse processes)
Lig. interspinalia (between spinous processes) / Interspinous Lig.
– Connect adjoining spinal processes.
– Meet the Lig. flava in front.
Lig. supraspinale (between the tips of spinous processes) / Supraspinous Lig.
– Connect the tips of spinous process from C7 to sacrum.
Lig. nuchae (between occiput and Lig. supraspinale) Flexion
– Bilaminar fibraelastic intermuscular septum.
– From occiput to C7.
– Mostly in the absence of bony pathology.
– Transverse ligament is stronger than the dens, so the dens usually fractures before the ligament ruptures.
– Alar ligaments are weaker -> combined head flexion and rotation may rupture both.
– Weakenining of the transverse and adjacent ligaments or of the lateral atlantoaxial joints result in atlantoaxial subluxation.
– Instability after trauma: responsible for atlantoaxial rotational instability.
The 3 column concept of spinal stability
– The anterior column: anterior longitudinal ligament + anterior half of the vertebral body + anterior anulus fibrosus.
– The middle: posterior longitudinal ligament + posterior half of vertebral body + posterior anulus fibrosus (middle is the most important).
– The posterior column: neural arch + facet joints + posterior ligaments.
– The instabilty gets worse the more columns are affected.
Spinal cord injury without radiological abnormality
– Very common in hyperextension injuries.
– Most common: central cord syndrom (hyperextension to an osteoarthritic neck → injury of the grey matter → motor loss in the upper limbs.
– Anterior cord syndrome: flexion compression (damage in the area of supply of the anterior spinal artery) → motor loss more in the lower limbs.
The vertebral arteries
– Arise from the subclavian arteries.
– Enter the spine on the level of C6 and run through the transverse foramina to C1.
– Supply the upper spinal cord, brain stem, cerebellum and parts of the cerebrum with blood.
– If they passed C1 they run across the arch of C1, then the suboccipital triangle and in the end they enter the cranial cavity through the foramen magnum.
– At the level of junction between medulla oblongata and pons they form the basilar artery.
– Near the foramen arise the menigeal branches.
– There are also branches on each cervical level to supply the surrounding muscles.