Vertebral column

Ultrasound

Soft tissue not bone.

As you progress caudally along the thoracic region, the dorsal spinous processes become progressively shorter in length until one is reached that has very short, vertical dorsal spinous processes. What is this called and where is it located?

Anticlinal vertebra, T11 in the dog and T16 in the horse

In the horse, the longest dorsal spinous process is around T6 - withers. Anticlinal vertebra in the horse is T16. Transverse processes of lumbar vertebrae are very large and abdominal wall muscles attach here and they have a huge weight of abdominal contents to support

Cow has fewer ribs than horse

What do the intervertebral foraminae allow the spinal nerves to do?

Leave the vertebral canal to supply the peripheral regions of the body.

What does the combination of the atlanto-occipital and atlanto axial joint form?

Occipito-atlanto-axial complex Allows full range of movement without damage to the spinal cord.

What are the 5 diagnostic imaging modalities available?

Radiography, CT, MRI, nuclear scintigraphy, ultrasound

How does each vertebra articulate with the ones cranial to and caudal to it?

Formation of a synovial joint between the articular facets. The orientation of the articular facets of each vertebra relative to their neighbours varies along the length of the vertebral column depending on how much movement between each vertebra is permitted in each region but there are exceptions (atlanto-occipital joint where atlas articulates with occopital condyles of the skull rather than with an adjacent vertebra, sacrum where bones arefused into a single boney unit, caudal/coccygeal region where the vertebra have reverted to a more basic form) Fluid is present between the articular surfaces (produced by synovial membrane and contained within the joint capsule. Stabilised by ligaments and movement across the joints are produced by action of the relevant musculature.

What are the components of the nuchal ligament in the horse?

Funicular part - same as fibroelastic band of tissue present in the dog and represents a continuation of the supraspinous ligament but it runs all the way to the nuchal crest of the skull Laminar part - fenestrated sheets of fibrous tissue that run from the funicular part of the nuchal ligament to the dorsal spinous processes of the cervical vertebrate. Series of fluid filled bursae associated with it located between it and the adjacent boney features. Atlantal bursa - located between nuchal ligament and atlas and the supraspinous bursa is located dosal to the dorsal spinous processes of the first few thoracic vertebrae.

What does the radiate ligament hold in place?

Head of the rib and supports the joint capsule and merges with fibres of the annulus fibrosus of the intervertebral disc space

What is CT good/bad for?

(boney window setting) Good for visualising the boney components of the vertebral column (appear white) but because the CT images each represent an individual thin slice through the animal, not all of the anatomical features of each vertebrae can be seen on each image so a series of images have to be examined to visualise all of the regions of the vertebra - but this means that there is no superimposition of the structures on top of each other Features that are clearly visible include the dorsal spinous process, the transverse process, the vertebral body. Features like the intervertebral foramen and the articular facets will only be visible if the particular slice happens to cut through them (brain/soft tissue windows) can be used to assess the brain and spinal cord.

What is the vertebral arch composed of?

A right and left vertical wall known as pedicles. A right and left lamina that come together to form the roof. Pedicle + lamina = vertebral arch.

Where does the dorsal longitudinal ligament run?

Along the dorsal aspect of the vertebral bodies, so on the ventral floor of the vertebral canal. It is present along the entire length of the vertebral column from the level of C2 to the sacrum.

What is the vertebral arch?

An arch of bone that is located dorsal to the vertebral body.

What are vertebrae made of?

An outer layer of compact bone (solid white line in CT image) A cancellous centre that is less compact and spongier that appears greyer and less uniform than the compact bone

The intervertebral disk is made up of what 2 parts?

Annulus fibrosis - series of concentric rings of fibrous tissue arranged a bit like the rings of the onion. The fibres run between the endplates of the adjacent vertebral bodies, physically holding them together and providing stability by resisting stretching of the intervertebral disc space Nucleus pulposus - remnant of the notochord that is involved with the embryological development of the vertebral column. It takes the form of a jelly filled cushion that is embedded within the annulus fibrosis and surrounded by it - provides shock absorption by resisting compression of the intervertebral disc space

What are the two ways that degeneration of a disc can occur?

As an age related change or spontaneously in some predisposed breeds. The nucleus pulposus becomes dehydrated and this reduction in fluid content means that it is no longer bright white on MR and the disc loses some of its compliance. Associated with areas where most movement is possible - cervical and lumbar regions.The thoracolumbar junction represents the transition between an area of low motion to high motion so it is prone to problems Not in areas of low motion - intercapital ligament helps to stabilise the disk

Where does the interspinous ligament run?

Between adjacent dorsal spinous processes

Where does the intercapital ligament run?

Between the heads of each pair of corresponding right and left ribs. It runs over the dorsal surface of the intervertebral disc space and merges with the fibres of the dorsal longitudinal ligament and the annulus fibrosis of the intervertebral disc so it stabilises ribs and intervertebral disk - so reduces the risk of the intervertebral disc space moving dorsally into the vertebral canal. It is only present in association with ribs 1-10.

In the dog, C6 has prominent ventral projections on its transverse processes that are visible radiographically.

Cat bones are more slender than dogs so appear longer and finer on radiographs

What are the 5 regions of the vertebral column?

Cervical Thoracic (dorsal boundary thoracic cavity) Lumbar (dorsal boundary abdominal cavity) Sacral (dorsal boundary pelvic cavity) Caudal/coccygeal (tail)

Where should contrast medium be injected into the subarachnoid space to create a myelogram?

Cervical region - access can be gained via the cisterna magna and is located by flexing the neck and placing a finger on the occipital crest of the skill and palpating the dorsal spinous process of the axis and the transverse processes/wings of the atlas are palpated Lumbar region - palpate dorsal spinous process of L6 and introducee the needle immediately cranial to it in the midline. The needle will pass through the interspinous ligament and into the vertebral canal.

What happens beyond the anticlinal vertebra?

Dorsal spinous processes become angled in a cranial direction - this remains the case through the lumbar region. Marks the point of transition in the vertebral column from a region of low mobility in the thoracic region to one of relatively high mobility in the lumbar region

Where are the expaxial muscles located?

Dorsal to the transverse processes. These are a series of muscles arranged into 3 systems that run along the length of the vertebral column. They function to extend the vertebral column and create lateral movement.

Nuclear scintigraphy

Images are obtained by injected the animals with a bone seeking agent that has been tagged with radioisotope marker and after a specific period of time the animal is placed in front of a gamma camera that detects where the marker has become located. The marker accumulates preferentially in bone that is active (equine)

What is the function of the dorsal spinous process?

Increase surface area of the vertebra to provide sites for muscle and ligament attachment. Length and inclination therefore vary along the length of the vertebral column depending on the forces that it is subjected to.

When the individual vertebrae line up to form the vertebral column, there is a space that results between the adjacent vertebral endplates. What is it called? What is it occupied by in life?

Intervertebral disk space. Intervertebral disk

What kind of bones are vertebrae classified as?

Irregular bones

How does C1 differ from typical vertebra?

It does not have a vertebral body because during the embryological development the cranial section of the sclerotome responsible for the production of the vertebral body remains associated with its corresponding caudal section. This means that C1 develops from only the caudal section of the sclerotome - it has a vertebral arch and foramen. No dorsal spinous process but 2 very well developed transverse processes that are called the wings of the atlas

Describe the atlanto-axial joint

Joint formed between C1 and C2. The dens of C2 sits on the ventral floor of the vertebral foramen of C1 and is held in place by a transverse ligament. The large dorsal spinous process of C2 limits the atlanto-axial joint to lateral rotation - sideways shaking motion

Describe the atlanto-occipital joint

Joint formed between the atlas and the occipital epicondyles of the skull. The large transverse processes of C1 limits movement at this joint to flexion and extension (restricts movement to up and down)

What are the most common views taken of the vertebral column in radiography?

Lateral (lateral recumbency) Ventrodorsal (dorsal recumbency)

How do transitional vertebra occur?

Located at the boundary between different regions of the vertebral column, and get confused as to which region they belong to.

What are the characteristics of the lumbar vertebrae?

Long vertebral bodies Long transverse processes that provide the origin for the abdominal wall muscles and support the weight of the abdominal contents. Dorsal spinous processes are short and uniform in length with a slight cranial orientation

In the embryo, how many somites does the paraxial mesoderm form and how many parts do they split into? Dsecribe embryological development

More than 40 pairs of somites. These each split into 3 parts Dermatome -> skin Myotome -> musculature Sclerotome -> axial skeleton All of the sclerotomes develop a diffuse cranial section and a dense caudal section. The dense caudal section of the sclerotomes on the LHS of the neural tube combine with the diffuse cranial section of the adjacent sclerotome to form the left half of the same vertebra. The same process occurs on the RHS of the neural tube. This means that there are contributions from 2 adjacent sclerotomes in each hemi or half vertebra and contributions from 4 sclerotomes in each entire vertebra. The dense caudal sections will ultimately develop into the neural arch and the intervertebral disc while the diffuse cranial part will form the vertebral body of the vertebra. The left and right hemivertebra then fuse to form a single unit. As this happens, the neural arch, which is formed from the caudal sections of the sclerotome encloses the neural tube and fuses dorsally, in this way forming the vertebral foramen and canal. The vertebral body arises from the cranial section of the sclerotome and when it fuses it obliterates the notochord, but the notochord does still remain in the spaces between adjacent vertebral bodies. This space is occupied by the intervertebral k and these remnants of the notochord are incorporated into the intervertebral disk as the nucleus pulposus which has an important role to play in cushioning and shock absorption between adjacent vertebra.

What does the nucleus pulposus/annulus fibrosis look like on MR images?

Nucleus pulposus - appears very white on T2 weight MRI images and can be easily distinguished from the black region representing the annulus fibrosis

Where is the dorsal spinous process located?

On the dorsal aspect of the vertebral arch where the laminae meet in midline.

Where are the transverse processes located and what is their function?

On the lateral aspect of the vertebra arising where the pedicle meets the vertebral body. They function to increase the SA of the vertebra for muscle attachment so their length varies along the length of the vertebral column

What is the function of the anticlinal vertebra?

Prevent overcrowding of the dorsal spinous processes when the vertebral column is hyperextended. This is most relevant in species which have mobile vertebral columns like the carnivore.

What is unique about C2?

Produces a boney projection at the cranial aspect of the bone called the dens. During embyological development in the uterus, the cranial section of the sclerotome responsible for the production of the vertebral body of C1 remains associated with its corresponding caudal section rather than separating as it should, so C2 develops from 2 cranial sections and 1 caudal section - the dens therefore represents the vertebral body of C1 that is associated with C2 instead C2 has only very small transverse processes but has a very prominent dorsal spinous process that is palpable in the live animal/visible in radiographs

What are the functions of the lumbar vertebrae?

Protection to the contents of the abdominal cavity Provide points of attachment for the various muscles associated with the vertebral column Provides origin for many abdominal wall muscles

What are the main functions of the vertebral column?

Provide internal support for the body and protection from the spinal cord. Provide a large surface area for muscle attachment including the extrinsic muscles of the fore and hindlimb In locomotion for the transfer of propulsive forces generated by the hindlimb across the trunk

The vertebral column in the dog forms part of the axial skeleton that runs along the axis of the animal and includes the skull. What does the appendicular skeleton do?

Provides support within the limbs

The thoracic vertebrae articulate with the ribs ro form the body ribcage that encases and protects the thoracic cavity. The presence of the ribs does what?

Restricts movement between adjacent vertebrae in this region and therefore there is little lateral movement possible. What little movement that is possible is limited to flexion and extension

What is the function of thoracic vertebrae?

Support and protection for vital interthoracic structures such as the heart and lungs.

What are the other functions of the thoracic region?

Surface area for attachment of various muscles associated with the vertebral column and body wall and points of origin for some of the extrinsic muscles of the forelimb.

MRI

T2 weighted images - cerebrospinal fluid that surrounds the spinal cord appears white/hyperintense - outlines the margins of the spinal cord in a similar way to a myelogram Intervertebral disc space is easy to identify between adjacent vertebral bodies. Nucleus pulposus is relatively fluid filled and so appears white or hyperintense while the annulus fibrosis appears dark or hypointense Boney features - appear dark so not well visualised.

What is C1 also called?

The atlas

What is the caudal surface of the vertebral body known as and what shape is it?

The caudal endplate and it is slightly concave

What does the head of each rib articulate with?

The cranial costal fovea of the thoracic vertebrae of the same number and the caudal costal fovea of the thoracic vertebra immediately cranial to it. It bridges the intervertebral disk space (rstricting movement) and the tuberculum of the rib articulates with the very small transverse process of the thoracic vertebra of the same number. This is the case for ribs 1-10 in the dog so... Head of the first rib articulates with T1 and C7 and C7 has a pair of caudal costal fovea to accommodates this In ribs 11-13, the head articulates only with the thoracic vertebra of the same number and no longer bridges the intervertebral disc space, so more movement is possible between adjacent vertebra towards the caudal part of the thoracic region and the thoracolumbar junction.

What is the cranial surface of the vertebral known as and what shape is it?

The cranial endplate. It is slightly convex

What happens to the cranial and caudal notches when the vertebrae align to form the vertebral column?

The notches line up with each other to form a series of gaps or spaces between each adjacent vertebrae. Each space is called the intervertebral foramen.

What are the cranial and caudal notches?

The notches present at the cranial and caudal aspect of each pedicle. The vertebrae are the same on both the left and right sides which means that there are a total of 4 notches per vertebra.

What does the number of vertebrae present in the thoracic region correspond with?

The number of pairs of ribs present in that species

Where do the interarcuate ligaments fill?

The space between the cranial and caudal notches of adjacent vertebral arches and therefore also covers the intervertebral foramen

The combination of the vertebral arch dorsally and the vertebral body ventrally forms a hole through the vertebra. What is this called and what does it do?

The vertebral foramen provides a route for the spinal cord to run through the bone. When the vertebrae align, the foraminae also align to form a hollow channel running the length of the vertebral column - vertebral canal and in life contains the spinal cord.

What does the cranial portion of the sacrum articulate with?

The wing of the ilium to form the sacro-iliac join. Propulsive forces are transferred to the trunk during locomotion which is aided by the rigidy of the sacrum Provides points of origin for some of the extrinsic muscles of the hindlimb as well as protection for the contents of the pelvic cavity, of which it forms the roof.

The sacral region develop in the foetus as separate structure but fuse before birth to form a single bone called the sacrum therefore...

There are no intervertebcral disc spaces present in this region and no movement possible between the components of the sacrum - functions as a single unit.

Why is there a hole present at the back of the transverse process of the cervical vertebrae?

This is the transverse foramen and it provides protection for the vertebral artery and vein which run through it.

Why do cervical vertebrae generally have short dorsal spinous and transverse processes and flat articular facets?

To allow a large range of movement

Why do the transverse processes of the cervical vertebrae have an extra ventral projection?

To increase the surface area for the attachments of the hypaxial muscles

What are the functions of the cervical region?

To support and move the head, protection for the important structures running along the ventral aspect of the neck like the trachea, oesophagus and major blood vessels Provides attachment points for various muscles associated with the vertebral column and ventral neck region.

The absence of ribs in this regions means that it is more flexible than the thoracic region. However, the presence of what still restricts lateral movement?

Transverse processes Also orientation of articular facets limit movement Amount of flexion and extension possible is greater than the thorax so does contribute to movement of the trunk.

What does the costo-transverse ligament hold in place?

Tuberculum of each rib articulates with the short transverse process of the corresponding vertebra

Where are the hypaxial muscles located?

Ventral to the transverse processes of the vertebral column. The muscles that are involved with movement of the vertebral column are abdominal wall muscles and ventral neck muscles. These produce flexion and lateral movement of the vertebral column. Diagram 44

What happens when hemivertebrae occur?

Vertebral body fails to form properly. Vertebral body is triangular instead of cylindrical - butterfly/wedge vertebrae. Can cause deviation of vertebral column.

What are the typical features of the thoracic region?

Very short bodies and very long dorsal spinous processes that are angled in a caudal direction (provide a large surface area for the epaxial muscles to attach to that cause extension of the vertebral column) Short transverse processes to accommodate the presence of the rubs Costal fovea - flattened areas located on each side of the vertebral body at the cranial and caudal notches and provide a smooth surface area that articulates with the head of the corresponding ribs. 4 present on each vertebrae.

What is radiography good/bad for?

Visualising the boney components of the vertebral column Superimposition - not all features are visible in all views: Dorsal spinous processes are vicible in lateral view but transverse processes are visible in the ventrodorsal view but vertebral bodyc an be seen in both and the intervertebral foraminae Not good for soft tissue structures Radiographs on ppt

How do block vertebra occur?

When the cranial and caudal parts of the sclerotome fair to separate properly - these are basically 2 adjacent vertebrae which are fused together without an intervertebral disk space or articulations.

When does intervertebral disc protrusion occur?

When the disc material bulges dorsally from the disc space, pushing the dorsal longitudinal ligament into the vertebral canal. Since the annulus fibrosis is thinner dorsally than ventrally, the nucleus pulposus always moves in a dorsal direction. This can happen due to trauma but dogs with degenerative discs may be predisposed to this as the nucleus pulposus is more rigid and less flexible than normal.

When does intervertebral disc extrusion occur?

When the disc ruptures through the dorsal longitudinal ligament and disc material becomes located within the vertebral canal itself. This is obvious a very serious condition as there is not much space in the vertebral canal an therefore a very real risk that this material will cause compression of the spinal cord itself. May be due to trauma but the presence of degenerative changes may predispose to it

Where in the vertebral column is the highest risk of damage?

Where a transition is made from an area of low motion to an area of high motion (cervicothoracic/thoracolumbar junctions)

How is MRI performed?

With animal in sternal or dorsal recumbency

How many centres of ossification does the vertebral body form from?

3 - one for the body and one for each of the endplate. The growth plates between these centres of ossification are visible on radiographs of young animals

What is the vertebral body?

A large region of bone that is roughly cylindrical in shape.

Diagram 43 - Articular facets. What do they allow the vertebra to do and where are they located?

Allow it to articulate with the vertebrae cranial and caudal to it to form synovial joint. They are located at the junction between the pedicle and lamina at the cranial and caudal aspects of the vertebra and are present on the L/R sides of the vertebra so there are a total of 4per vertebra. The orientation of the facets relative to each other varies along the length of the vertebral column depending on how much movement is permitted.

Where does the supraspinous ligament run?

Along the dorsal aspect of the dorsal spinous processes and is present from the level of T1 to CC3. In the dog, it continues in a cranial direction to the caudal aspect of C2 as a cord of fibroelastic material called the nuchal ligament. It functions to provide passive support for the weight of the head.

Where does the ventral longitudinal ligament run?

Along the ventral aspect of the vertebral body and is present from the level of C2 to the sacrum

How can you visualise the spinal cord on a radiograph?

Myelography - inject an iodine based radiographic contrast medium into the vertebral canal and subarachnoid space.

What is the vertebral column composed of?

Series of individual bones called vertebrae that are held together by a series of soft tissue structurse so they act together to form a single function unit.

How is CT performed?

With animal in either sternal or dorsal recumbency