V.C - A - Development (2) - Atlas/Axis/Typical/Thoracic/lumbar Vertebra and Sacrum/SI Joint/Coccygeal Ossifciation/Fusion

Question 1

It is generally recognized that C1 ossifies from three primary centres What is the C1 vertbrae also known as? Where are the three ossification centres in the C1 vertebrae?

Answer 1

C1 vertebrae is also known as the atlas 2 ossification centres in the neural arches and one in the anterior arch

Question 2

When do the two ossification centres in the neural arches appear in the atlas? What are they posterior to?

Answer 2

The ossifications centres appear in the 7th week just posterior to the articular pillars (in the cervical vertebra, the articular pillars are formed from the superior and inferior articular processes of the vertebrae)

Question 3

At birth the C1 vertebrae is represented by two bony masses - these are the large articular facets What do the articular facets look like from superior and inferior on C1?

Answer 3

C1 displays larger concave articular facets anteriorly on the upper surface and displays smaller flatter articular facets inferiorly on the lower surface

Question 4

C1 Typically ossifies from three centres. Two in the neural arch and in the anterior arch (bar). The neural arches are the first parts to form. Superiorly there are large articular facets The next part is the anterior bar. When does ossification in the anteriorarch of the atlas commence forming the anterior bar?

Answer 4

Ossification in the anterior arches occurs from year 1 to 2 forming the anterior bar of C1 Image shows - neural arch ossification centres forming at week 7 posterior to articular pillars Anterior ossification centre forming years 1-2 Also shows dates for fusion

Question 5

The anterior arch ossification forming the anterior bar can form in three ways * A single centre * Paired centers * Extensions from lateral masses Describe each?

Answer 5

• Single ossification centre - neurocentral junction on each side of anterior arch
• Paired centres - neurocentral junction on each side of the anterior arch as a well as an anterior synchondrosis
• Extensions from lateral masses - no anterior arch neurocentral jucntion, only an anterior synchrondosis

Question 6

What is the difference between anterior and posterior synchondrosis of the atlas?

Answer 6

Anterior synchrondosis is fusion of the anterior arches Posterior synchrondosis is fusion of the posterior arches Normally the ossification centre at the anterior arch is single anyway and no need for an anterior synchrondosis, inctead just need neurocentral junction fusion

Question 7

Posterior synchondrosis occurs before anterior neurocentral jucntions fuse At what age do both occur?

Answer 7

Posterior arch of atlas ususally uses from 4-5 years Anterior neurocentral junction usually fuses by 5-6 years

Question 8

Where is the fusion line between the anterior arch and the lateral masses?

Answer 8

The fusion line between the anterior arch and the lateral masses passes across the anterior portions of the superior articular facet

Question 9

By 6 years of age you have a fully fused vertebra When is the adult size of the vertebra reached by? What does this suggests about the CNS?

Answer 9

Adult size reached by 4-6yrs – early limitation on size of vertebral canal is a clear indication of the precocious maturation of the CNS As the vertebra is fully fused by 6 years of age, this suggest the CNS will be mature by 6 years of age

Question 10

In some individuals the posterior synchondrosis can remain open, what is this known as? How can you tell the difference between a developing inividuals posterior synchdonris from this condition?

Answer 10

In some individuals the posterior synchondrosis can remain open- this is called congenital abence of the posterior arch of atlas (Type A shown in pic) In a devoping individual the ends of the posterior arches flare out as if trying to meet one another, in this condition they come to a point

Question 11

The atlas ossifies from three primary ossification centres The axis ossifies from five primary ossification centres What are these 5 centres?

Answer 11

One for each half of the neural arch One for the true centrum of the axis One for each half of the body of the dens

Question 12

The three pieces of bone at the front- contribute to the odontoid process (or dens). What is the most anterior small bony process called? It is debated by textbooks whether it contains a primary or secondary ossification centre - it appears at ~2 years

Answer 12

This is the ossiculum terminale

Question 13

The axis ossifies from five primary centres of ossification: One for each half of the neural arch One for the true centrum of the axis One for each half of the body of the dens When do these centres appear?

Answer 13

The centres for each half of neural arches begin first at 7-8 weeks of foetal life The true centrum of the axis commences ossification with a single centre between 4-5 months of intrauterine life The ossifciation for each half of the body of the dens begins around 4-6 months

Question 14

The two halfs of the odontoid process rapidly coalesce so that the intradental synchondrosis has fused by birth The fusing of the two halfs of the dens (at the intradental synchronsis) form a defining dent in the dens. WHat is this known as?

Answer 14

The intradental sulcus

Question 15

When is the posterior synchondrosis between neural arches formed in the atlas? The dens fuses laterally to the neural arches when? What is this called?

Answer 15

Posterior synchondrosis is formed between neural arches at 3-4 years The dens fuses laterally to the neural arches at the dentoneural syncondrosis at 3-4 years also

Question 16

The fusion line at the dentoneural syncondrosis passes obliquely across the superior articular facet. What does this mean for the percentage of contribution to the superior articular facet from the dens and neural arch? What contributes towards the inferior articuar facet?

Answer 16

The medial 1/3rd of the superior articular facet of the facet is formed by the dens and the lateral 2/3rds are formed by the neural arches The inferior articular facet of the atlas forms entirely form the neural arch

Question 17

When is complete fusion of the foramen transversium? (transverse foramen)

Answer 17

Complete fusion is completed by 3-5 years

Question 18

The dentocentral junction and the neurocentral junctions of the atlas fuse around the same time. When is this? At what age will all lines of fusion (ie dentoneural, dentocentral and neurocental junctions) disappear?

Answer 18

Dentocentral junction and neurocentral junction fuse between 4 and 6 years All lines of fusion in the axis will disappear by 9-10 years

Question 19

As said All lines of fusion disappear by 9-10 years Although a Small horizontal crevice may remain in region of posterior dentocentral junction Why is this clinically significant?

Answer 19

This is clinically significant as it is a potential site of fracture weakness

Question 20

What is the small ossific nodule that appears in the apical cleft of the dens around 2 years known as? When does this small nodule fuse with the dens?

Answer 20

This small ossific nodule in the apical cleft of the dens that appears at 2 years is known as the ossiculum temrinale and it fuses with the dens around 12 years of age

Question 21

Just as there are 5 primary ossification centres for the atlas, there are also 5 secondary What are they?

Answer 21

There are two flake like epiphyses for the transverse processes They are two plate-like epiphyses for the bifid spinous process There is a centre for the inferior annular ring

Question 22

Why is it sometimes considered that there are 6 secondary ossification centres? What happens to the interdental sulcus of the dens?

Answer 22

Sometimes if the ossiculum temrminale is considered to be epiphyseal, it is said there are 6 secondary ossifciation centres

A small tongue of bone progresses up the posterior surface of the dens filling in the interdental groove (sulcus)

Question 23

How many annular rings do cervical vertebrae typically have? Why does the axis only have 1?

Answer 23

All typical cervical vertebrae have a superior and an inferior annular ring however the axis only has space for one due to the presence of the odontoid process

Question 24

TYPICAL CERVICAL VERTEBRAE Develop in accordance with the general ossification pattern of any typical vertebra Where would the primary ossifciation centres be if it develops in accordance with general ossifciation of any typical vertebra? When are the primary ossification centres of a typical vertebra recognizable?

Answer 24

Three primary ossifciation centres - 2 in the nerual arches on the inner surface and one in the centrum - just dorsal to the notochord

Question 25

Where do all cervical laminae unite? What is the range for completion of neurocentral fusion in a typical vertebrae? When is neurocentral fusion complete in a typical cervical vertebrae?

Answer 25

All cervical lamina fuse posteriorly within the 2nd year Neurocentral fusion for a typical vertebrae occurs ventral to the pedicles at the neurocentral junction between 2 and 5 years Neurocentral junction fuses between 3-4 years in the cervical segment

Question 26

Typical cervical vertebrae have six secondary ossification centres Where are these?

Answer 26

2x transverse process 2x spinous process 1 superior annular ring 1 inferior annular ring

Question 27

Why does the axis only have an inferior annular ring ossification centre and not a superior?

Answer 27

All typical vertebrae have a superior and inferior annular ring The axis doesnt because the odntoid process takes up this space

Question 28

When do the secondary ossifciation centres off the typical cervical vertebrae appear? When do they begin fusing and when are they fused by?

Answer 28

They appear at the beginning of puberty Begin fusing at 18+ Fused by 24 years

Question 29

Thoracic and lumbar vertebrae primary ossifciation in accordance with the general ossification pattern of vertebra (this was otulined in last set of flashcards remember) Al three primary centres present by end of third intra-uterine month When are the thoracic and lumbar vertbra ossification centres identifiable?

Answer 29

The ossificaiton centres are identifiable by the 4th intra-uterine month

Question 30

What are the thoracic and lumbar secondary ossification centres? Where do secondary ossification centres sometimes exist on the thoracic and lumbar vertebrae?

Answer 30

* Two annular - superior and inferior * Two transverse process - apex of each * One spinous process * Thoracic - sometimes on costal surface * Lumbar - sometimes on mamillary processes Image from radiopedia - Ossification centres of the vertebral column

Question 31

The sacrum ossifciation pattern is very complex How many primary ossification centres are there? Why are there this many?

Answer 31

There are 21 primary ossifciation centres Each sacral vertebra has the typical 3 primary centres - 1 centrum and 2 neural arches As well as S1-3 having a lateral ossification centre on each side 3 typical centres x5 sacra = 15 2 lateral centres x3sacra = 6

Question 32

What are the lateral ossificaiton centres of S1-3 responsible for?

Answer 32

These are responsible for the formation of the sacral ala and sacroiliac joint

Question 33

What direction does sacral ossification pattern occur in? (remember in the other vetebra, it usually has an origin then occurs in a bidirectional progression)

Answer 33

Sacroiliac ossification occurs in a cranial caudal direction starting at S1 and 2

Question 34

Different ossification centres begin from the 3,4,5 and 6-8 IU months What are these?

Answer 34

At * 3 months - S1 & S2 centra * 4 months - S3 and S4 centra, S1-S3 neural arches * 5 months - S5 centra, S4-S5 neural arches * 6-8 months - S1-S3 paired costal elements (the lateral centres) * Birth - All centres represented although may only be small ossific nodule

Question 35

In the sacrum, when does the neural arch fuse with the lateral elements? When does this fused element, fuse with the centrum?

Answer 35

Neural arches fuse wit lateral elements from 2-5 years Fused component fuses with centrum between 2-6 years

Question 36

By 6 years, all primary centres have fused except at posterior spinous process, when does this fuse?

Answer 36

This fuses between 7-15 years

Question 37

The posterior synchondrosis is the last fusion event for the sacrum. The neural arch fuses with the lateral element. These then fuse with the centrum. The final fusion event is the posterior synchondrosis. At this point there is no fusion between adjacent sacral vertebrae When does adjacent sacral vertbra fusion occur?

Answer 37

Adjacent sacral vertebra fusion occurs in teenage years when the lateral elements commence fusion

Question 38

The secondary sacral vertbra ossifciaiton centres are not consistent in number and vary between individuals What are the number of constant centres? there a variable number of small centres ina ddition to this

Answer 38

There are 14 constant in total 10 annular ring centres 2 auricular epiphyses 2 lateral margin epiphyses

Question 39

Sacrum primary ossification begins in a craniocaudal direction At \* 3 months - S1 & S2 centra \* 4 months - S3 and S4 centra, S1-S3 neural arches \* 5 months - S5 centra, S4-S5 neural arches \* 6-8 months - S1-S3 paired costal elements (the lateral centres) What direction does sacral vertebrae fusion occur?

Answer 39

It occurs in a caudo-cranial direction

Question 40

As said it is approx puberty/teenage years when fusion of adjacent vertbra begins \* ~12 years when lateral elements are fusing the annular epiphyses commence fusion in a caudocranial direction There is a general rule for the age of the person if looking for spaces in the sacrum. What is this rule?

Answer 40

If space can be identified between the bodies - person is less than 20 If space can only be identified between S1 and 2 - person is 27 years Complete union not observed until 25 + years

Question 41

When does the sacroiliac joint form and when is it completed?

Answer 41

Sacroiliac joint forms at 2 IU months and is completed by 7 IU months but doesn’t look like the adult one. It is a more vertical structure.

Question 42

At birth, the SI joint is said to be straight and parallel to vertebral column reflecting quadripedal form How does the SI joint grow into the adult morphology?

Answer 42

Mechanical forces associated with growth and bipedalsim cause the SI joint to curve caudodorsally into adult morphology

Question 43

What happens to the surface area of the SI joint with important development milestones being met?

Answer 43

Surface area of joint increases substantially throughout development in line with important developmental milestones

Question 44

There is at least one ossification centre for each coccygeal vertbra When does the ossification centre appear in each? When are the ossifications centres recognisable by?

Answer 44

* Co1 appears between late foetal period and 1st year of life * Co2 - 3-6 years * Co3 - 10 years * Co4 - puberty Ossification centres recognisable by puberty