Development of the Vertebral Column Flashcards
What do the curves of the spine act like to confer?
Act like springs to confer:
- Flexibility
- Resilience
Describe the primary curvatures of the spine
Concave anteriorly:
- Thoracic
- Sacral/Coccygeal
When do the primary curvatures develop and how are they maintained?
Established in fetal development
Maintained through vertebral shape
Describe the secondary curvatures of the spine?
Convex anteriorly:
- Cervical
- Lumb
When do the secondary curvatures develop and how are they maintained?
Develop during infancy:
- Cervical at 2-3 months when child holds up head
- Lumbar at 6-8 months when child sits unaided
Both result in IV disc becoming thicker anteriorly, due to loading, changing the curvature
What does IV disc degeneration result in?
Spine returning to an overall primary curvature (kyphosis)
In what physiological state is lordosis often seen? Why?
Pregnancy:
- Forward pelvic tilt
- Bulk of mass over pelvis
- More efficient walking gait
What is scoliosis?
Lateral deviation >10 degrees
Often accompanied by a rotational defect
How can scoliosis arise?
Congenital
Idiopathic
Secondary to a primary neuromuscular condtion
What is the adult vertebral body derived from?
Juvenile centrum
PLUS
Small portion of neural arch:
- Boutons of the pedicles
Where does ossification of the centra initiate?
Dorsal to notochord
What type of ossification is that of the centra?
True endochondral
Describe the ossification process of the centra?
Mesenchymal template Tissue is hyaline cartilage first: - Chondrification - An avascular model Cartilage starts to ossify Bone forms on surface Core of cartilage starts to die: - Usually receives nutrients from surface via diffusion - Sends angiogenic signals - Blood vessels to core form - Vessels bring osteogenic cells
What factor does the notochord contain? What does this do?
Angiogenic inhibiting factor:
- Delays vascular penetration so bone does not invade it initially
What does the release of the factor from the notochord cause?
Axial avascular area around notochord
Results in ring-shaped area of ossification
Where does ossification of the neural arches commence?
Inner surface of each hemi-arch
What is the method of ossification of the neural arches?
Intramembranous following by endochondral
Where does the first ossification centre for the neural arches appear and when?
Lower cervical and upper thoracic regions
2nd foetal month
What initiates neural arch ossification in the cervical/thoracic region?
Gasp reflex = Muscle contraction
Once the first ossification centre for the neural arches appears, where does it spread?
Cranially and caudally
Where and when does a second group of ossification centres appear for the neural arches?
Lower thoracic and upper lumbar regions
3rd fetal month
What initiates neural arch ossification in the thoracic/lumbar region?
Lower limb movement = Muscle contraction
Once the second ossification centre for the neural arches appears, where does it spread?
Cranially and caudally
What part of the neural arches fuses first?
Fusion starts posteriorly at spinous processes
When does neural arch fusion commence?
During the 1st year
In what region does neural arch fusion begin and what direction(s) does it spread?
Lower thoracic and upper lumbar regions
Spreads cranially and caudally
By what ages have the neural arches in each region fused?
Lower cervical arches = Year 2
Very upper cervical arches = Year 3
Lowest lumbar arches = Year 5 (end of)
What is the implication of neural arches not fusing until a few years into life?
If a child is <6 years old, expect some degree of arch non-fusion on imaging
What is the fusion at the posterior aspect of the neural arches?
A synchondrosis:
- Primary cartilaginous
- Hyaline cartilage so it ossifies
At what part of the vertebra does neurocentral fusion occur?
Ventral to pedicles at neurocentral junction
At what ages does neurocentral fusion occur?
2-5 years
Regarding neurocentral fusion, what parts of the developing vertebrae involved articulate with the costal processes
Only the boutons of the pedicles
NOT the centrum
Until what age is evidence of the neurocentral junction maintained?
Evidence maintained throughout life
Where does neurocentral fusion occur first, second and third and at what ages?
First = (Lower) lumbar at 2-4 years Second = Cervical at 3-4 years Third = (Lower) thoracic at 4-5 years
What are the ossification centres for the atlas? When do they appear?
Three primary centres:
- One for each lateral mass posterior to articular pillar which appear in 7th foetal week
- Anterior arch centre appears in 1st or 2nd year
How can the anterior arch of atlas ossification centre appear?
Single nodule OR
Paired nodules OR
Multifocal nodules OR
How can the anterior arch ossify if its ossification centre does not appear?
Ossification bars can extend from lateral masses
How does C1 appear at birth?
Two bony masses:
- Large concave articular facets on upper surface
- Smaller facets on lower surface
How does the morphology of the atlas change?
Unchanged throughout 1st year
Increases in size
When does the posterior arch of the atlas fuse?
Years 4-5 (synchondrosis)
What happens if the posterior arch of the atlas does not fuse? How does this make the arch appear?
Spina bifida atlantis:
- Ends of each neural arch appears pointed instead of flat (flat = unfused but will fuse)
What is the incidence of failure of posterior arch of atlas fusion?
1%
What are the anterior neurocentral junctions of the atlas between?
Each lateral arch and the anterior arch (x2)
When do the anterior neurocentral junctions of the atlas fuse?
5-6 years
Where does the fusion line of the anterior neurocentral junctions of the atlas lie and what is its clinical implication?
Union line passes across anterior portions of superior articular facet
Can be a fracture point
Endochondral growth occurs at all junctions of the atlas prior to fusion. What does this cause?
Integrated expansion of vertebral canal as 3 units grwo away from one another
When does the atlas reach adult size?
Age 4-6 years
What does the adult size of the atlas act as?
Early limit to vertebral canal size:
- Indicates precocious CNS maturation
What are the primary ossification centres of the axis?
Five primary centres:
- One for each half of neural arch
- One for true centrum
- One for each half of body of dens
When do the ossification centres for the neural arches of C2 appear?
7-8 foetal weeks
When does the true centrum ossification centre for C2 appear?
4-5 foetal months
When do the odontoid centreas appear?
4-6 foetal months
When do the two halves of the dens fuse?
Intradental synchondrosis formed by birth
How does the dens appear at birth?
Forked:
- Due to intradental sulcus
When does the posterior synchondrosis (between neural arches) of C2 fuse?
3-4 years
When does the dens fuse laterally to the neural arches? What is this joint called?
3-4 years
Dentoneural synchondrosis
Where does the fusion line between the dens and the neural arches lie?
Passes across superior articular facet:
- Medial 1/3 of facet is formed by dens
- Lateral 2/3 of facet is formed by neural arch
What part of C2 forms the inferior articular facet?
Neural arch
What does fusion of C2 halt?
Increase in dimensions of vertebral canal
When is fusion of the foramen transversarium complete?
3-5 years
When do the dentocentral and paired neurocentral junctions fuse?
4-6 years
When do lines of fusion within C2 disappear?
9-10 years
What line of fusion may remain in C2? Clinical implication?
Small horizontal crevice in region of posterior dentocentral junction:
- Fracture weakness
When does the ossiculum terminale appear?
~2 years
What is the ossiculum terminale?
A small ossific nodule
Where does the ossiculum terminale appear?
In cartilage plug that fills apical cleft of dens
When does the ossiculum terminale fuse with the dens?
~12 years
What are the secondary ossification centres of C2?
Five secondary centres:
- Two ‘flake-like’ epiphyses for transverse processes
- Two ‘plate-like’ epiphyses for bifid spinous process
- Inferior annular ring (C2 has no superior oe due to os terminale)
Sometimes considered to be 6 secondary centres if os terminale considered epiphyseal
What does a small tongue of bone progressing up posterior surface of dens fill?
Interdental groove
What are the typical cervical vertebrae primary ossification centres and when do they appear?
3 primary centres:
- Centrum = 3-4 foetal months
- Two neural arches = 2-3 foetal months
When do the cervical laminae unite posteriorly?
In 2nd year
When is cervical neurocentral fusion complete?
3-4 years
What structures form following neurocentral fusion of the cervical vertebrae?
Synovial uncovertebral joints of Luschka
When is a typical cervical vertebra fully fused?
~4 years
What are the 6 secondary ossification centres of typical cervical vertebrae?
2x transverse processes
2x spinous processes
1x superior annular ring
1x inferior annular ring
When do the secondary ossification centres appear in the typical cervical vertebrae?
Beginning of puberty
When do the secondary ossification centres of cervical vertebrae begin and finish fusing?
Begin at end of puberty (18+ years)
Complete by 24 years
When do all 3 ossification centres in the thoracic and lumbar vertebrae appear?
By end of 3rd foetal month
Identifiable by 4th foetal month
What are the 5 secondary ossification centres of both thoracic and lumbar vertebrae?
Annular rings: - 1x Superior - 1x Inferior 1x Spinous process 2x Transverse processes
What are the 6th and 7th secondary ossification centres of thoracic vertebrae?
A costal articular surface on each transverse process
What are the 6th and 7th secondary ossification centres of lumbar vertebrae?
Mamillary processes:
- Part of superior articular surface
How many primary ossification centres does the sacrum have?
21
What is each sacral vertebra represented by in regards to primary ossification centres?
3 typical primary ossification centres:
- 1x centrum
- 2x neural arches
What additional primary ossification centres do S1-S3 (sometimes S4) have? What do these form?
Paired lateral elements:
- Form ventral aspect of alae
- Site of SIJ
What sacral primary ossification centres appear in the 3rd foetal month?
S1 and S2 centra
What sacral primary ossification centres appear in the 4th foetal month?
S3 and S4 centra
S1-S3 neural arches
What sacral primary ossification centres appear in the 5th foetal month?
S5 centrum
S4-S5 neural arches
What sacral primary ossification centres appear in the 6th-8th foetal months?
S1-S3 paired costal elements
When do the neural arches fuse to the lateral elements in the sacrum?
2-5 years
When does each united neural arch-lateral element component fuse to the centrum in the sacrum?
2-6 years
By what age have all primary centres (except one) fused within the sacrum? What is the exception?
6 years
Except posteriorly at spinous process:
- Fuses between 7-15 years
When do the sacral vertebrae fuse to form the fused sacrum? What is the pattern of this fusion
Puberty:
- Lateral elements commence fusion
- Fusion is caudocranially directed
How many constant secondary ossification centres are there in the sacrum?
14:
- 10x annular rings
- 2x auricular epiphyses
- 2x lateral margin epiphyses
Where are the variable small secondary ossification centres in the sacrum?
Flake-like epiphyses:
- Spinous processes
- Median sacral crest
- Lateral sacral crest
- Between sacral vertebrae
What age is a skeleton if there are still spaces between sacral vertebral bodies?
<20 years
What age is a skeleton if there is still a space between S1-S2 vertebral bodies?
<27 years
When is there complete union of the sacrum?
25+ years
When do the several ossific nodules for the SIJ appear?
15-16 years
When do the ossific nodules of the SIJ fuse?
18 years
What epiphyses of the sacrum follow the same pattern as the SIJ secondary ossification nodules?
Lateral margin epiphyses
When does the SIJ form and by what action?
2nd fetal month
Cavitating
When is the SIJ joint complete?
7th fetal month
What is the shape of the SIJ at birth?
Straight
Parallel to vertebral column:
- Reflects quadripedal form
What do mechanical forces due to growth and bipedalism cause the SIJ to do?
Curve caudodorsally:
How does the surface area of the SIJ change with milestones?
Increases
How do we know that the SIJ is non-weight bearing?
No dense lines in trabeculae to indicate stress
How do we know there is no sexual dimorphism of the SIJ?
It is not smaller in females:
- Weight bearing joints often smaller in females
Which coccygeal element may appear from multiple primary centres instead of a single centre as they usually do?
Co1
When does the Co1 primary ossification centre appear?
Late foetal period to early life
When does the Co2 primary ossification centre appear?
3-6 years
When does the Co3 primary ossification centre appear?
10 years
When does the Co4 primary ossification centre appear?
Puberty
When is the coccyx fully recognisable?
By puberty
