Osteology of Skull and Cervical Spine Flashcards
What are the categories of cervical vertebrae?
- Typical
- Atypical
What does wether a cervical vertebrae is typical or atypical depend on?
Their osteological features
What are the atypical cervical vertebrae?
C1, C2, and C7
What is C1 known as?
Atlas
What shape is C1?
Ring shaped
What is the function of the atlas?
Supports the skull at the atlanto-occipital joint
What does the atlas articulate with inferiorly?
The second cervical vertebrae
What is C2 known as?
Axis
How does the strength of the axis compare to other cervical vertebrae?
It is the strongest of all cervical vertebrae
Why is the axis need to be the strongest cervical vertebrae?
Because C1, carrying the skull, rotates on it
What feature does C2 have?
Odontoid process (the dens)
Where does the odotoid process project?
Superiorly from its body
How is the odontoid process held in position?
By strong transverse ligament of atlas
What is the function of the transverse ligament of the atlas?
Prevents horizontal displacement of the atlas, thus stabilises the atlanto-axial joint
What is the bony skeleton of the neck formed by?
The 7 cervical vertebrae
Where do the cervical vertebae lie?
Between the skull and the thorax
What is found between each vertebrae?
An intervertebral disc
What is the exception to there being an intervertebral disc between vertebrae?
There is no vertebral disc between C1/2
Why is there no intervertebral disc between C1/2?
Because C1 has no vertebral body
How do the cervical vertebrae differ in function to other vertebrae in the body functionally?
- They bear less weight than vertebrae in other regions of the body
- Convey a much greater degree of mobility
How do cervical vertebrae differ from other vertebrae in the body structurally?
- Much smaller
- Have a foramen in each of their transverse processes
- Vertebral foramen is much larger
- Articular surfaces are more horizontally orientated
Why do cervical vertebrae have a foramen in each of their transverse processes?
Transmit vertebral arteries on their way to supply the back of the brain
Which cervical vertebrae doesn’t have transverse foramen?
C7
Why is the vertebral foramen of cervical vertebrae much larger than other vertebrae in the body?
Accommodate much thicker cervical spinal cord
What happens to the vertebral foramen the more caudal it goes?
It gets smaller
Why does the vertebral foramen get smaller as it runs more caudally?
Because the spinal cord it transmits gets thinner, as more and more nerves leave the spinal cord to innervate various structures
What is the result of the articular surfaces of cervical vertebrae being more horizontally orientated than in other vertebrae?
They can dislocate or ‘slip off’ at much less force than is required for them to fracture
What is the skull?
The collective term referring to the complete skeleton of the head
What does the skull include?
- Cranium
- Mandible
What can the cranium be further subdivided into?
- Neurocranium
- Viscerocranium
What is the neurocranium?
The bones forming a protective box around the brain
What is the viscerocranium?
Bones forming facial skeleton
What does the neurocranium consist of?
- Calvaria
- Cranial floor
What is the calvaria?
The skull, or cranial, cap
What is the lower limit of the calvaria?
It has no lower limit to it as such
What do the bones of the calvaria consist of?
Two layers of bones, seperated by a layer of spongy bone
What is the layer of spongy bone in the calvaria known as?
Diploe
What is true of the innermost layer of the calvaria in adults?
It is particularly brittle
What is the purpose of the trilaminar arrangement of bone in the calvaria?
It conveys protective stength, without adding significant weight
What is the thinnest part of the calvaria?
The pterion
Where does the pterion lie?
On the lateral aspect of the skull
What is between the large, flat bones forming the calvaria?
Sutures
What are sutures?
Serrated, immobile joints of strong fibrous tissue
What are the names of the sutures?
- Coronal
- Sagittal
- Lamboid
What is the clinical relevance of sutures?
- Interlocking nature of these joints makes it very different or bones forming the joint to dislocate
- As we age, suture lines begin to ossify
What is the cranial floor divided into?
Three areas, or fossa
What are the areas of the cranial floor?
- Anterior
- Middle
- Posterior
What is found in the cranial floor?
A number of foramina (holes)
What is the function of the holes in the cranial floor?
Allow for passage of anatomical structures between extra- and intra-cranial compartments
What structures pass through the foramen in the cranial floor?
- Cranial nerves
- Blood vessels
What is the clinical relevance of the large number of foramina in the cranial floor?
Make the cranial floor vulnerable to fracture
When can the vertebral floor fracture?
When significant force is transmitted through the skull base
What is the viscerocranium formed by?
- Bones enclosing the orbits
- Nasal cavity
- Oral cavity
- Paranasal sinuses
- Maxillae
- Mandible
What is the maxillae?
The upper jaw
What is the mandible?
The lower jaw
What does the jaw house?
The teeth
What are the main features of the anterior aspect of the skull?
- Frontal bones
- Zygomatic bones
- Orbits
- Nasal region
- Maxillae
- Mandible
What do the frontal bones form?
Skeleton of forehead
What does the frontal bone articulate with?
- Nasal bones
- Zygomatic bones
- Lacrimal bones
- Ethmoid bones
- Sphenoid bones
What do the frontal bones form?
- Roof of orbit
- Part of floor of cranial cavity
What are the zygomatic bones?
Cheek bones
Where do the zygomatic bones lie?
On the inferolateral sides of orbits
What do the zygomatic bones articulate with?
- Frontal bone
- Sphenoidal bone
- Temporal bone
- Maxillae
What does the maxillae constitute?
The greater part of the upper facial skeleton
What is the maxillae fixed to?
Cranial base
Why is the mandible moveable?
Because it articulates with the cranial base at the temporomandibular joint
Why is the temporomandibular joint special?
It is the only moveable joint of the skull
What is found just above the orbital margin?
Supraciliary arch
What is the supraciliary arch?
A sharp bony ridge
Will slight dislocation of the cervical vertebrae damage the spinal cord?
It may or may not
Why may slight dislocation of the cervical vertebrae not damage the spinal cord?
Due to large vertebral canal in cervical region
What may significant dislocation of the cervical vertebrae cause?
Serious injuries to the spinal cord
What serious injuries to the spinal cord can be caused by significant dislocation of the cervical vertebrae?
- Partial paralysis
- Complete paralysis
- Death
What are the most common sites of cervical spine injuries?
- C1/2
- C6
- C7
Where do most severe (often fatal) spinal injuries occur?
In the upper part of the spine (C1-4)
What does damage to the upper part of the spine lead to?
- Quadriplegia
- Cessation of respiratory movements
When may a hyperflexion of the cervical spine injury occur?
During head on collision
What do hyperflexion injuries of cervical spine tend to involve?
Lower part of cervical spine
What can hyperflexion injuries of the cervical spine lead to?
- Crush factors of the vertebral body
- Rupture of supraspinous ligament
- Rupture of lower cervical intervertebral discs
Give an example of a crush fracture of the cervical spine?
Cervical wedge fracture
Is a cervical wedge fracture stable?
May be, if just one vertebra is involved
How will a cervical wedge fracture present on x-ray?
Loss of height of vertebral body
What are crush fractures of the vertebral body associated with?
Spinal degenerative disease
Give an example of a spinal degenerative disease?
Osteoporosis
What is the effect of the rupture of the supraspinous ligament?
Makes bony spine unstable
What cervical intervertebral discs can rupture?
- C5/6
- C6/7
What complication can rupture of the lower cervical spinal discs cause?
May cause compression of spinal nerve roots C6 and C7
What are hyperextension injuries of the neck associated with?
Rear-end vehile collision
What do hyperextension injuries of the neck most commonly affect?
Upper cervical spine
What can hyperextension injuries of the neck result in?
- Vertebral fracture
- Disc prolapse
- Cervical spinous process or odontoid process fracture
- Tearing of anterior longitudinal ligament
- Kinking of posterior longitudinal ligament
Where may hyperextension injuries of the neck cause kinking of the posterior longitudinal ligament?
In the degenerative spine
What is the protective function of car seat head rests?
They act to minimise the range of hyperextension that can occur at the neck
What is a Hangmans Fracture?
A type of injury that can occur caused by hyperextension of the neck
When may a Hangmans Fracture occur?
During judicial hanging, not suicidal hanging
What is the cause of death in suicidal hanging?
Asphyxiation
What happens in a Hangmans Fracture?
Bilateral fracture of posterior arch of C2, and disruption of C2-3 junction
Is a hangmans fracture stable?
No
What is the result of a Hangmans Fracture being unstable?
There is a risk of C2 displacement and spinal cord damage
What needs to be done when someone presents with a Hangmans Fracture?
MRA
Give an example of how an axial load injury through the head and neck may occur?
Falling onto head from height
What may an axial load injury through the head and neck cause?
Jeffersons fracture
What is a Jeffersons fracture?
A burst fracture of C1
What happens in a Jeffersons fracture?
Combination of anterior and posterior arch fractures
Is a Jeffersons fracture unstable?
It can be
What may be neccessary if a Jeffersons fracture is unstable?
External fixation
Why must patients presenting with a suspected neck injury be managed carefully?
Avoid (further) damage to the cervical spinal cord
Do all neck injuries or cervical fractures cause damage to the spinal cord?
No
What should happen to any patient with significant mechanism for neck injury?
They should have full in-line spinal immobilisation
Why should all patients with significant mechanism for spinal injury have full in-line spinal immobilisation?
Due to the potentially catastrophic neurological consequences should spinal injury occur
What does full in-line spinal immobilisation include?
Immobilisation of the cervical spine with;
- Appropriately sized semi-rigid collar
- Head blocks
- Tape
And rest of patients spine immoblised on a spinal board
When is immobilisation no longer required following a spinal injury?
When the cervical spine has been ‘cleared’
When can the cervical spine be ‘cleared’ after injury?
When the patient is determined to be at minimal risk for spinal injury
What does the clearing of a C-spine follow?
Thorough clinical examination
What is the clearing of a C-spine based on?
Specific criteria, e.g. Canadian C-spine rules
What should be done if any doubt remains about possibility of spinal injury, or risk to spine, and the C-spine cannot be cleared confidently by clinical examination?
Radiological examinations undertaken
What radiological examinations can be undetaken to clear a C-spine?
- Plain radiography, involving 3 views of the cervical spine
- CT
When is an x-ray used as the radiological examination to clear C-spine?
In paediatrics
Why are x-rays used to clear the C-spine in paediatrics?
Because don’t want radiation around structures of the neck, e.g. the thymus
What would happen if a fracture or other injury was identified on radiological imaging of the C-spine?
Further management would depend on the type of injury found
What are the facet joints of the vertebral arches (zygopophyseal joints) close to?
Intervertebral foramina
What emerges through the intervertebral foramina?
Spinal nerves
What happens if the zygapophyseal joints are affected by osteoarthritis?
Intervertebral foramen can narrow
What can age related changes in intervertebral discs cause?
Cause the discs to bulge, narrowing the intervertebral foramen
What can narrowing of the intervertebral foramen cause?
Compression of the spinal nerve exiting at that vertebral level
Give two pathologies resulting from narrowing of the intervertebral foramen?
- Cervical spondylotic myelopathy
- Cervical spondylotic radiculopathy
What happens in cervical spondylotic myelopathy?
Spinal cord compression
What does cervical spondylotic myelopathy lead to?
- Loss of function
- Often loss of fine motor skills in upper limbs
What happens in cervical spondylotic radiuclopathy?
Nerve root impingement
What does cervical spondylotic radiculopathy lead to?
Dermatomal arm pain, with or without mild weakness and sensory loss
What can osteoarthritis of the C-spine lead to?
Cervical spondylosis
In laymans terms, what is cervical spondylosis?
‘Wear-and-tear’ of C-spine vertebrae
Who does cervical spondylosis affect?
Older population
How common is cervical spondylosis?
Very common
What are the features of cervical spondylosis?
- Osteophytes
- Facet joint hypertrophy
- Disc herniation
- Disc space narrowing
- Sclerosis of end plates
What are osteopytes?
Bony spurs
What may severe blows to the skull result in?
- Local depression and splintering of bone
- Series of linear fractures radiating away from the initial point of injury
What severe trauma to the skull may result in fractures?
Impact injuries or blows
What complications can arise from skull fractures?
Can damage underlying brain and/or blood vessels
What does bleeding into the cranial cavity cause?
Haematoma
What are the types of intracranial haematoma?
- Epidural
- Extradural
- Subdural
Where does an extradural haematoma occur?
Between skull periosteum and outermost meningeal layer
What is the outermost meningeal layer?
Dura mater
What happens in an extradural haematoma?
It bleeds into the skull at high pressure, which can press on the brain, causing abnormal neurology
Wha is an extradural haematoma associated with?
Trauma and skull fracture
What is it important to do when a patient presents with a head injury?
- Examine head and any wounds thoroughly
- Undertake neurological assessment
What should be determined in a neurological assessment?
If there is evidence, or risk of, brain injury
What should be done when there is clinical suspicion of intracranial haemorrhage?
- CT imaging of head
- Consideration to possibility of C-spine injury
What is a basilar skull fracture?
Fracture through cranial floor
When can a basilar skull fracture occur?
If significant force is transmitted through the vertebral column
Why can a basilar skull fracture occur if significant force is transmitted through vertebral column?
Because base of skull is connected to vertebral column
How does a basilar skull fracture present?
- Battle’s sign
- ‘Raccoon’ eyes
- Haemotympanum
- Meningeal tears
- Cranial nerve palsies
What is Battle’s sign?
Bruising over mastoid process
What is ‘Raccoon’ eyes?
Bruising around both eyes
What is haemotympanum?
Blood behind ear drum
What results from meningeal tears?
Bleeding and/or CSF leakage from;
- Ear
- Nose
What is is called when CSF leaks from the ears?
CSF otorrhea
What is it called when CSF leaks from the nose?
CSF rhinorrhea
Why may a basilar skull fracture lead to cranial nerve palsies?
As cranial nerves run along base of skull in many cases
What is there a risk of in basilar skull fractures?
- Meningtis
- Need for neurosurgical intervention
How common are basilar skull fractures?
Uncommon, less than 5% of skull fractures
What does a fracture at the pterion risk?
Injuring the middle meningeal artery (anterior branch)
Why does a fracture at the pterion risk damaging the middle mengingeal artery?
As it lies immediately beneath the bone
What will bleeding from the anterior branch of the middle meningeal artery cause?
Extradural haematoma
What happens in an extradural haematoma from the anterior branch of the middle meningeal artery?
Blood accumulates between the periosteal layer of dura mater and the bone, exerting pressure on underlying brain
How are injuries to the facial skeleton caused?
- Road traffic collisions
- Fights
- Falls
What do the most common facial fractures involve?
- Nose
- Zygomatic bone
- Mandible
Why are fractures of the nasal bone common?
Because of the prominence of the nose
What does a hard blow to the lower jaw often result in?
Fracture of the neck of the mandible and its body
What may fracture of the mandible be associated with?
Dislocation of the temporomandibular joint
What is required to fracture the maxillary and frontal bones?
Significant force
