Development of the Vertebral Column Flashcards
1
Q
What do the curves of the spine act like to confer?
A
Act like springs to confer:
- Flexibility
- Resilience
2
Q
Describe the primary curvatures of the spine
A
Concave anteriorly:
- Thoracic
- Sacral/Coccygeal
3
Q
When do the primary curvatures develop and how are they maintained?
A
Established in fetal development
Maintained through vertebral shape
4
Q
Describe the secondary curvatures of the spine?
A
Convex anteriorly:
- Cervical
- Lumb
5
Q
When do the secondary curvatures develop and how are they maintained?
A
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
6
Q
What does IV disc degeneration result in?
A
Spine returning to an overall primary curvature (kyphosis)
7
Q
In what physiological state is lordosis often seen? Why?
A
Pregnancy:
- Forward pelvic tilt
- Bulk of mass over pelvis
- More efficient walking gait
8
Q
What is scoliosis?
A
Lateral deviation >10 degrees
Often accompanied by a rotational defect
9
Q
How can scoliosis arise?
A
Congenital
Idiopathic
Secondary to a primary neuromuscular condtion
10
Q
What is the adult vertebral body derived from?
A
Juvenile centrum
PLUS
Small portion of neural arch:
- Boutons of the pedicles
11
Q
Where does ossification of the centra initiate?
A
Dorsal to notochord
12
Q
What type of ossification is that of the centra?
A
True endochondral
13
Q
Describe the ossification process of the centra?
A
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
14
Q
What factor does the notochord contain? What does this do?
A
Angiogenic inhibiting factor:
- Delays vascular penetration so bone does not invade it initially
15
Q
What does the release of the factor from the notochord cause?
A
Axial avascular area around notochord
Results in ring-shaped area of ossification
16
Q
Where does ossification of the neural arches commence?
A
Inner surface of each hemi-arch
17
Q
What is the method of ossification of the neural arches?
A
Intramembranous following by endochondral
18
Q
Where does the first ossification centre for the neural arches appear and when?
A
Lower cervical and upper thoracic regions
2nd foetal month
19
Q
What initiates neural arch ossification in the cervical/thoracic region?
A
Gasp reflex = Muscle contraction
20
Q
Once the first ossification centre for the neural arches appears, where does it spread?
A
Cranially and caudally
21
Q
Where and when does a second group of ossification centres appear for the neural arches?
A
Lower thoracic and upper lumbar regions
3rd fetal month
22
Q
What initiates neural arch ossification in the thoracic/lumbar region?
A
Lower limb movement = Muscle contraction
23
Q
Once the second ossification centre for the neural arches appears, where does it spread?
A
Cranially and caudally
24
Q
What part of the neural arches fuses first?
A
Fusion starts posteriorly at spinous processes
25
When does neural arch fusion commence?
During the 1st year
26
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
27
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)
28
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
29
What is the fusion at the posterior aspect of the neural arches?
A synchondrosis:
- Primary cartilaginous
- Hyaline cartilage so it ossifies
30
At what part of the vertebra does neurocentral fusion occur?
Ventral to pedicles at neurocentral junction
31
At what ages does neurocentral fusion occur?
2-5 years
32
Regarding neurocentral fusion, what parts of the developing vertebrae involved articulate with the costal processes
Only the boutons of the pedicles
| NOT the centrum
33
Until what age is evidence of the neurocentral junction maintained?
Evidence maintained throughout life
34
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
```
35
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
36
How can the anterior arch of atlas ossification centre appear?
Single nodule OR
Paired nodules OR
Multifocal nodules OR
37
How can the anterior arch ossify if its ossification centre does not appear?
Ossification bars can extend from lateral masses
38
How does C1 appear at birth?
Two bony masses:
- Large concave articular facets on upper surface
- Smaller facets on lower surface
39
How does the morphology of the atlas change?
Unchanged throughout 1st year
| Increases in size
40
When does the posterior arch of the atlas fuse?
Years 4-5 (synchondrosis)
41
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)
42
What is the incidence of failure of posterior arch of atlas fusion?
1%
43
What are the anterior neurocentral junctions of the atlas between?
Each lateral arch and the anterior arch (x2)
44
When do the anterior neurocentral junctions of the atlas fuse?
5-6 years
45
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
46
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
47
When does the atlas reach adult size?
Age 4-6 years
48
What does the adult size of the atlas act as?
Early limit to vertebral canal size:
| - Indicates precocious CNS maturation
49
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
50
When do the ossification centres for the neural arches of C2 appear?
7-8 foetal weeks
51
When does the true centrum ossification centre for C2 appear?
4-5 foetal months
52
When do the odontoid centreas appear?
4-6 foetal months
53
When do the two halves of the dens fuse?
Intradental synchondrosis formed by birth
54
How does the dens appear at birth?
Forked:
| - Due to intradental sulcus
55
When does the posterior synchondrosis (between neural arches) of C2 fuse?
3-4 years
56
When does the dens fuse laterally to the neural arches? What is this joint called?
3-4 years
| Dentoneural synchondrosis
57
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
58
What part of C2 forms the inferior articular facet?
Neural arch
59
What does fusion of C2 halt?
Increase in dimensions of vertebral canal
60
When is fusion of the foramen transversarium complete?
3-5 years
61
When do the dentocentral and paired neurocentral junctions fuse?
4-6 years
62
When do lines of fusion within C2 disappear?
9-10 years
63
What line of fusion may remain in C2? Clinical implication?
Small horizontal crevice in region of posterior dentocentral junction:
- Fracture weakness
64
When does the ossiculum terminale appear?
~2 years
65
What is the ossiculum terminale?
A small ossific nodule
66
Where does the ossiculum terminale appear?
In cartilage plug that fills apical cleft of dens
67
When does the ossiculum terminale fuse with the dens?
~12 years
68
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
69
What does a small tongue of bone progressing up posterior surface of dens fill?
Interdental groove
70
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
71
When do the cervical laminae unite posteriorly?
In 2nd year
72
When is cervical neurocentral fusion complete?
3-4 years
73
What structures form following neurocentral fusion of the cervical vertebrae?
Synovial uncovertebral joints of Luschka
74
When is a typical cervical vertebra fully fused?
~4 years
75
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
76
When do the secondary ossification centres appear in the typical cervical vertebrae?
Beginning of puberty
77
When do the secondary ossification centres of cervical vertebrae begin and finish fusing?
Begin at end of puberty (18+ years)
| Complete by 24 years
78
When do all 3 ossification centres in the thoracic and lumbar vertebrae appear?
By end of 3rd foetal month
| Identifiable by 4th foetal month
79
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
```
80
What are the 6th and 7th secondary ossification centres of thoracic vertebrae?
A costal articular surface on each transverse process
81
What are the 6th and 7th secondary ossification centres of lumbar vertebrae?
Mamillary processes:
| - Part of superior articular surface
82
How many primary ossification centres does the sacrum have?
21
83
What is each sacral vertebra represented by in regards to primary ossification centres?
3 typical primary ossification centres:
- 1x centrum
- 2x neural arches
84
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
85
What sacral primary ossification centres appear in the 3rd foetal month?
S1 and S2 centra
86
What sacral primary ossification centres appear in the 4th foetal month?
S3 and S4 centra
| S1-S3 neural arches
87
What sacral primary ossification centres appear in the 5th foetal month?
S5 centrum
| S4-S5 neural arches
88
What sacral primary ossification centres appear in the 6th-8th foetal months?
S1-S3 paired costal elements
89
When do the neural arches fuse to the lateral elements in the sacrum?
2-5 years
90
When does each united neural arch-lateral element component fuse to the centrum in the sacrum?
2-6 years
91
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
92
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
93
How many constant secondary ossification centres are there in the sacrum?
14:
- 10x annular rings
- 2x auricular epiphyses
- 2x lateral margin epiphyses
94
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
95
What age is a skeleton if there are still spaces between sacral vertebral bodies?
<20 years
96
What age is a skeleton if there is still a space between S1-S2 vertebral bodies?
<27 years
97
When is there complete union of the sacrum?
25+ years
98
When do the several ossific nodules for the SIJ appear?
15-16 years
99
When do the ossific nodules of the SIJ fuse?
18 years
100
What epiphyses of the sacrum follow the same pattern as the SIJ secondary ossification nodules?
Lateral margin epiphyses
101
When does the SIJ form and by what action?
2nd fetal month
| Cavitating
102
When is the SIJ joint complete?
7th fetal month
103
What is the shape of the SIJ at birth?
Straight
Parallel to vertebral column:
- Reflects quadripedal form
104
What do mechanical forces due to growth and bipedalism cause the SIJ to do?
Curve caudodorsally:
105
How does the surface area of the SIJ change with milestones?
Increases
106
How do we know that the SIJ is non-weight bearing?
No dense lines in trabeculae to indicate stress
107
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
108
Which coccygeal element may appear from multiple primary centres instead of a single centre as they usually do?
Co1
109
When does the Co1 primary ossification centre appear?
Late foetal period to early life
110
When does the Co2 primary ossification centre appear?
3-6 years
111
When does the Co3 primary ossification centre appear?
10 years
112
When does the Co4 primary ossification centre appear?
Puberty
113
When is the coccyx fully recognisable?
By puberty
