Development of the vertebral column Flashcards
1
Q
How many true vertebrae are there?
A
- PRESACRAL VERTEBRAE
- 24 in total
- 7 cervical
- 12 thoracic
- 5 lumbar
2
Q
How many false vertebrae are there?
A
- 9 in total
- 5 sacral
- ~4 coccygeal
3
Q
Why are presacral vertebrae named ‘true’ vertebrae?
A
Because they are unfused
4
Q
What happens to coccygeal vertebrae with advancing age?
A
They fuse, therefore there is a variable number of them
5
Q
Identify the curvature
A
Cervical curvature
(Secondary)
6
Q
Identify the curvature
A
Thoracic curvature
(Primary)
7
Q
Identify the curvature
A
Lumbar curvature
(Secondary)
8
Q
Identify the curvature
A
Sacral / coccygeal curvature
(Primary)
9
Q
What shape is the vertebral column in the fetus?
A
C-shaped
10
Q
When do the primary curvatures develop?
A
During fetal development
11
Q
When do the secondary curvatures develop?
A
During infancy
12
Q
When, specifically, does the cervical curvature form and what is it in response to?
A
- At 2-3 months
- When child can hold head up (postural muscles in neck develop)
- compensatory secondary cervical curvature forms
13
Q
When, specifically, does the lumbar curvature form and what is it in response to?
A
- At 6-8 months
- When the child sits up unaided, there is a change in the loading regime acting on the vertebral column
- compensatory secondary lumbar curvature forms
14
Q
How are the primary curvatures maintained?
A
By the shape of the vertebra
15
Q
How do the secondary curvatures arise?
A
Arise from a modification in shape of the intervertebral disc.
There is a difference in thickness between anterior and posterior parts of the IV disc.
16
Q
What is caused by degeneration of the IV disc in the elderly?
A
More pronounced primary curvature
17
Q
What is kyphosis?
A
Hunchback deformity
18
Q
What is lordosis?
A
Swayback deformity
19
Q
Who is susceptible to lordisis and what does it cause?
A
- Common in pregnancy
- Causes forward pelvic tilt
20
Q
What is scoliosis?
A
Lateral deviation of the spine greater than 10°.
Often accompanied by a rotational defect.
Can be idiopathic or secondary to a primary neuromuscular condition.
21
Q
What is the adult vertebral body derived from?
A
The juvenile centrum plus a small portion of the neural arch.
22
Q
Name the structure indicated by the red arrow
A
Neurocentral junction
23
Q
Name the structure indicated by the red arrow
A
Bouton of the pedicle
24
Q
Name the structure indicated by the red arrow
A
Posterior synchondrosis
25
Name the structure indicated by the red arrow
Left half of the neural arch
26
Name the structure indicated by the red arrow
Centrum
27
Where is ossification of the centra initiated?
Dorsal to the notochord.
It represents true endochondral ossification.
28
Where is the first endochondral ossification of the centra and when does it occur?
* First appears in lower thoracic and upper lumbar regions (T10-L1).
* Occurs between 9 and 10 fetal weeks.
* Continues in bidirectional progression.
29
Where does endochondral ossification of the centra reach by the **3rd fetal month**?
L5 by the **3rd fetal month**
30
Where does endochondral ossification of the centra reach by the **end of the 4th fetal month**?
C2 by the **end of the 4th fetal month**
31
Describe the vascular penetration into the centra
* Notochord cells contain angiogenic inhibiting factor which delays vascular penetration.
* Vertebral centra from the first trimester display an axial avascular area around the notochord region.
* Results in ring-shaped ossification
32
Where does ossification of the neural arches begin?
On the inner surface of each hemi-arch
33
What kind of ossification do the neural arches undergo?
Intramembranous ossification, followed by endochondral ossification.
34
What do neural arches form bone from?
Directly from a mesenchymal membrane
35
When and where do the neural arches ossify?
* First, in lower cervical and upper thoracic regions in the second fetal month.
* Subsequently spreads upwards and downwards.
36
What is ossification of the neural arches initiated by?
* Initiated in response to the gasp reflex
* Lower limb movement (muscle contraction) - kicking during pregnancy.
* The muscle used during kicking is anchored to the vertebral column and twitching sets off bone formation via ENDOCHONRDAL OSSIFICATION.
37
Where does neural arch fusion commence?
Posteriorly at the spinous process.
38
When and in which region does neural arch fusion occur?
* Occurs **first** in **lower thoracic and upper lumbar** regions in the latter part of the **first year.**
* Progresses systematically in a cranial and caudal direction.
* **Cervical arches** may not fuse until the beginning of the **2nd year**.
* **Lowest lumbar arches** may not fuse until the end of the end of the **5th year.**
39
What are the first and last fusion points of the neural arches?
* First fusion point - posterior synchondrosis
* Last fusion point - sacral area
40
What is neurocentral fusion?
Fusion between the **neural arches** and the **centra**
41
Where does neurocentral fusion occur?
Ventral to the pedicles at the neurocentral junction
42
When does neurocentral fusion occur?
Between **2 and 5 years**
43
With what does the head of the costal process articulate?
The boutons of the pedicles.
NEVER with the centrum.
44
In what order do the regions of the vertebral column undergo neurocentral fusion?
* First in the lumbar region
* Followed by cervical segment
* Lastly, thoracic vertebrae are the last to fuse
45
Which structure takes the place of the centrum in C1?
Anterior bar or anterior arch.
THERE IS NO CENTRUM.
46
What forms first in C1?
Neural arch
| (converse to other vertebrae)
47
Describe the superior and inferior articular surfaces of C1
* Superior - very large articular surfaces for articulation with the occipital condyles.
* Inferior - much smaller articular surfaces.
48
When and how does the anterior bar in C1 form?
* Forms late - first or second year of life.
* Forms as a single piece but from 2 centres (bilateral ossification).
49
Where and when does the centre for the lateral masses of C1 appear?
* Posterior to the articular pillar
* In the 7th week
50
Describe C1 at birth
* Two bony masses
* Larger concave articular facets anteriorly on the superior surface
* Smaller, flatter articular facets on the inferior surface
* Morphology remains unchanged throughout the first year after birth
51
When does the posterior arch of the atlas fuse?
4-5 years
Can remain open into adulthood (1% incidence)
52
When do the anterior neurocentral junctions close?
5-6 years
53
When is the adult size of C1 reached?
4-6 years
54
How would you differentiate between spina bifida atlantis and fusion which hasn't happened yet?
* Pointed ends which taper off towards one another are true spina bifida atlantis.
* Flared appearance are just posterior arches which have not yet fused.
55
How does the axis (C2) ossify?
* From 5 primary ossification centres:
* 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
56
When do the centres of ossification in the neural arches of C2 appear?
* At 7-8 fetal weeks
* This is before the centra
57
Ossification of the centrum of the axis
* Commences ossification from a single centre
* 4-5 months intra-uterine life
58
What appears in the odontoid process at 4-5 months intra-uterine life?
* 2 laterally placed ossification centres
* These rapidly coalesce so that the intra-dental synchondrosis fuses by birth
* this forms the forked appearance of the juvenile dens
59
When does the posterior synchndrosis between the neural arches of the axis (C2) fuse?
3-4 years
60
When and how does the dens fuse?
* Fuses laterally to the neural arches at the **dentoneural synchondrosis**
* At **3-4 years**
61
What is the superior articular facet of the axis (C2) comprised of?
* Medial 1/3 by the dens (odontoid process)
* Lateral 2/3 by the neural arch
62
What is the inferior articular facet of the axis (C2) comprised of?
* Formed entirely of the neural arch
63
When does complete fusion of the foramen transversarium in the axis (C2) occur?
3-5 years
64
When do the dentocentral junction and the paired neurocentral junctions in the axis (C2) fuse?
4-6 years
65
When do all lines of fusion disappear by?
* 9-10 years
* A small horizontal crevice may remain in the region of the posterior dentocentral junction - this is a site of fracture weakness
66
What happens to the axis (C2) at ~2 years?
* Small ossific nodule - 'ossiculum terminale' - appears in the cartilage plug that fills the apical cleft.
67
When does the ossiculum terminale fuse with the dens?
~12 years
68
What kind of ossification centre is the ossiculum terminale?
Can be referred to as primary or secondary - secondary because it forms so late (start of puberty).
69
What are the secondary ossification centres of the axis (C2)?
* FIVE secondary ossification centres.
* 2 flake-like epiphyses for the transverse processes
* 2 flake-like epiphyses for the bifid spinous processes
* Inferior annular ring
* Rises to 6 if os terminale is considered epiphyseal
70
What happens at the inferior annular ring?
* A recognisable secondary centre of ossification appears.
* A small tongue of bone progresses up the posterior surface of the dens, infilling the interdental groove.
71
What is the interdental sulcus?
The groove between the fused right and left halves of the odontoid process
72
How many ossification centres form a typical cervical vertebra?
3
73
When and where do the laminae of typical cervical vertebrae unite?
Unite posteriorly within the 2nd year of life
74
When is neurocentral fusion complete in the cervical segment?
**3-4 years**
75
What happens once neurocentral fusion has taken place in typical cervical vertebrae?
Synovial uncovertebral joints of Luschka form on the sloping and elevated articular sides of the neural elements of the vertebral body.
76
Describe the secondary ossification centres of a typical cervical vertebra.
* SIX CENTRES
* 2 transverse processes
* 2 spinous processes
* 1 superior annular ring
* 1 inferior annular ring
77
When do the secondary ossification centres appear in typical cervical vertebrae?
At the beginning of puberty
78
When do the secondary ossification centres of a typical cervical vertebra begin to fuse?
End of puberty (18+)
79
When is fusion of a typical cervical vertebrae complete?
~24 years
80
When are the **three primary ossification centres** present by in the thoracic and lumbar vertebrae?
All **3 primary centres** present by the **end of the** **3rd intra-uterine month,** and identifiable by the 4th intrauterine month.
81
Describe the ossification pattern of the sacrum
* Complex - 21 centres of ossification
* Each vertebrae has the typical centres:
* 1 centrum
* 2 neural arches
* S1-S3 - incorporated paired lateral elements
* These form the ventral aspect of the alae and are the site of sacroiliac articulation
* Cranial to caudal ossification pattern
* By birth, all 21 ossification centres are represented, but are not identifiable
82
What is formed in the 3rd intra-uterine month in the sacrum?
* S1 centrum
* S2 centrum
83
What is formed in the 4th intra-uterine month in the sacrum?
* S3 centrum
* S4 centrum
* S1-S3 neural arches
84
What is formed in the 5th intra-uterine month in the sacrum?
* S5 centrum
* S4-S5 neural arches
85
What is formed in the 6th-8th intra-uterine months in the sacrum?
* S1-S3 paired costal elements
86
When does the neural arch unite with the lateral elements in a sacral vertebrae?
2-5 years
87
When does the united component (neural arch + lateral elements) fuse with the centrum in the sacrum?
2-6 years
88
Describe the state of fusion of the sacrum in a 6 year old
All the primary centres have fused except posteriorly at the spinous process
89
When does posterior fusion at the spinous process occur in the sacrum?
7-15 years
90
What is the last thing to fuse in the sacrum?
Posterior synchondrosis
91
What are the directions of appearance and fusion in the sacrum?
* Appearance is craniocaudal
* Fusion is caudocranial
92
Describe the secondary ossification centres in the sacrum
* Not consistent, varies between individuals
* 14 constant centres
* 10 annular rings
* 2 auricular epiphyses
* 2 lateral margin epiphyses
* Flake-like epiphyses
93
When does fusion of the secondary centres in the sacrum occur?
~12 years when the lateral elements are fusing, the annular epiphyses commence fusion in a caudocranial direction.
94
What age is an individual if spaces can be seen between the vertebral bodies?
\<20 years
95
What age is an individual is a space can be seen only between S1 and S2?
\<27 years
96
Describe the epiphyses for the sacroiliac joint
* Several ossific nodules which coalesce
* Appears at 15-16 years
* Fuses by ~18 years
* Lateral margin epiphyses follows the same pattern
97
When does the sacroiliac joint form?
2nd intra-uterine month
98
When is the sacroiliac joint complete?
7th intra-uterine month
99
What is the form of the sacroiliac joint at birth?
* Straight
* Parallel to vertebral column
* this reflects quadrupedal form
100
What forces the sacroiliac joint to curve **caudodorsally** into the adult morphology?
Mechanical forces associated with growth and bipedalism
101
Describe the ossification centres in the coccyx
Each coccygeal vertebrae forms its own ossification centre.
Co1 may form multiple
102
When does the ossification centre in Co1 appear?
Late fetal period and first year of life
103
When does ossification centre of Co2 appear?
3-6 years
104
When does ossificaition centre of Co3 appear?
10 years
105
When does ossification centre of Co4 appear?
Puberty
