Medical Imaging: Joints Flashcards
What is lipohaemoarthrosis?
What is it indicative of?
Fat and blood in a joint
Indicative of an intra-articular fracture
What does this xray indicate?
Lipohaemoarthrosis:
- Effusion beneath patella - straight line above femur
- ‘FBI’ sign: fat-blood interface sign
Fracture to tibial head
What causes lipohaemarthrosis?
Fatty marrow separates from the blood (water based) which gives the characteristic fat-fluid level indicated by the straight line on the xray.
What types of imaging can be used when a higher sensitivity is needed to image a joint?
What can they identify?
CT and MRI
Can identify haematocrit effect:
- Fat
- Synovial fluid
- Blood
Name 3 common joint emergencies seen on imaging
Lipohaemarthrosis
C-spine injury
Joint dislocation
What indications may there be for spinal imaging?
Trauma
Malignancy
Infection: TB, discitis, abscess
Disc prolapses
Degenerative changes
Limb pain (neuropathic)
What imaging modalities may be used for a suspected c-spine injury?
X-ray
CT
What is the first line imaging used for suspected cauda equina syndrome?
MRI
What imaging modality should be used for suspected discitis?
MRI
In what circumstances may nuclear imaging of the spine be indicated?
Malignancy
Describe the method of interpreting a C-spine x-ray
Adequecy (all cervical vertebrae visible? and ideally top of T1)
Alignment: are the lines smooth? Are there any bony prominences outside of the lines?
- Anterior vertebral line
- Posterior vertebral line
- Spino-laminar line
- Posterior spinous line
Bones: are the borders of the cortex of each bone smooth?
Cartilage: are the spaces between the vertebrae uniform?
When imaging joints, why would a CT scan be used over x-ray?
What can CT scan not exclude in terms of joints?
Higher sensitivity
In trauma situations where x-ray appears normal
If x-ray shows an abnormality, to further investigate
Cannot exclude ligamentous injury
What are the benefits of using MRI?
What type of tissue can they show?
Higher sensitivity
Can see ligaments, nerves and soft tissue
Can look closely at individual nerves: demyelination
No radiation compared to CT and MRI
WHat type of imaging can be used to investigate suspected demyelination?
MRI
What does this MRI show?
Prolapse of lumbar vertebral disc causing spinal cord compression
What does the MRI show?
Discitis causing obliteration of the disc and damage to the vertebral bodies above and below.
Why might neck positioning for intubation in a patient with RA be potentially fatal?
What should be performed before intubation for RA patients?
Asymptomatic C1/C2 disease in rheumatoid arthritis patients
Routine radiographic evaluation should be performed for patients with RA going for procedures that involve neck manipulation.
Where is the most common site of spinal injuries?
Why is this?
C-spine (particularly C1 and C2)
Flexible, exposed part of the spine
What is atlanto-occipital dislocation?
What damage does it cause?
= Ligamentous separation of the spinal column to the skull base
Pure flexion injury: usually results in instant death, also known as ‘internal decapitation’.
- Damage to brain stem and spinal cord
- Dissections of carotid and vertebral arteries
Survivors usually have irreversible tetraplegia
How is atlanto-occipital dislocation diagnosed?
CT
If either BAI or BDI >12mm usually suggests AO dislocation.
Wackenheim line: straight line extending from posterior clivus through the dens (normal situations should not intersect the dens)
What is an atlanto-axial dislocation?
What are the degenerative and traumatic causes?
Dislocation of C1 from C2
Degenerative:
- Rheumatoid arthritis (c-spine third most common place for RA to affect)
- Down’s syndrome
Traumatic:
- C1/C2 fractures
- Transverse ligament injuries
What are the potential symptoms of c-spine damage in a person with RA?
Quadriparesis
Altered consciousness/drop attacks
Lhermitte’s phenomenon
Neck pain
Respiratory dysfunction
Dysphagia
When may plain radiographs be used for C1/C2 imaging?
Which 2 views can be used?
Non-trauma cases only
Open-mouth odontoid view
Flexion and extension views (should only be done after open-mouth odontoid views have excluded odontoid fracture or severe subluxation)
What should be calculated in an open-mouth odontoid radiograph?
Sum of lateral mass displacement, if >6mm combined may indicate lateral ligament injury
What should be measured in flexion and extension views of C1/C2 radiographs?
ADI: atlanto-dens interval: distance between odontoid process and the posterior border of the anterior arch of atlas.
- >3.5mm = unstable
SAC: space available for cord: distance from the posterior surface of dens to anterior surface of posterior arch of atlas.
- In RA, >14mm = high risk of cord injury
What distance between the odontoid process and posterior border of the anterior arch of atlas is considered unstable?
>3.5mm
What is a Jefferson fracture?
How is it caused?
Is it a stable or unstable fracture?
C1 burst
Due to vertical compression force through the occipital condyles into the lateral mass of atlas. Caused by inferiorly directed forces on top of head (e.g. diving into swimming pool)
Forces drive the lateral masses of C1 outwards causing fractures of the anterior and posterior arches +/- disruption of the transverse ligament.
Highly unstable
What is a hangman’s fracture?
How is it caused?
Stable or unstable?
C2 pedicle fracture
Hyperextension injury
Unstable
How is a C2 odontoid fracture caused?
What are type I and type II odontoid fractures?
How is it best seen on x-ray?
Forceful flexion or hyperextension
Type I: occurs above the transverse ligaments
Type II: occurs below the transverse ligaments, at the base of the peg. Most common.
Best seen on open-mouth odontoid view
According to the Canadian C-spine rules, when is imaging of the C-spine required?
Age 65 or above
Dangerous mechanism
Paraesthesias in extremities
Inability to rotate neck 45°
What imaging modality should be used in children <16 if there is a strong suspicion of:
Cervical spinal cord injury
Cervical spinal column injury
MRI
When should plain x-ray be used in children under 16 for c-spine imaging?
When they do not fulfil criteria for MRI (strong suspicion of cervical spinal cord or column injury based on Canadian C-spine rules and clinical assessment) but there is still clinical suspicion after assessment.
When should CT be used for suspected spinal injury in adults?
When should MRI be used?
When imaging is recommended by Canadian C-spine rules
Strong suspicion of thoracic or lumbosacral spinal injury associated with abnormal neurological symptoms.
MRI should be used after CT if there is neurological abnormalities which could be attributable to spinal cord injury
Define joint dislocation
Abnormal seperation in the joint where 2 or more bones meet
Which imaging modality is usually used for suspected dislocations?
Which views are required?
Plain radiograph
Anterior view and lateral view
What type of dislocations are the most common?
What should also be considered when looking at this type of dislocation?
Shoulder- particular anterior dislocations
Hill-Sachs and Bankart lesions, AC joint disruption and acromioclavicular fracture should also be looked for.
What type of shoulder dislocation is this?
What other imaging should be used to confirm this?
Anterior shoulder dislocation
Side view radiograph should be used to confirm as could be posterior dislocation
What type of shoulder dislocation is this?
Why?
Posterior
Humeral head is to the left of the normal position
What type of shoulder fracture is this?
Why?
Anterior dislocation
Humeral head is to the right of the normal position
What are Hill-Sachs and Bankart’s lesions?
What are they caused by?
Hill-Sachs: posterolateral humeral head compression fracture, typically secondary to recurrent anterior shoulder dislocations, as the humeral head comes to rest against the anteroinferior part of the glenoid.
Bankarts: injuries specifically at the anteroinferior aspect of the glenoid labral complex, and represent a common complication of anterior shoulder dislocation
What is ultrasound useful for identifying?
What do bilateral findings suggest?
Effusions
Bilateral: may indicate systemic arthritis disorder or transient synovitis.
What are the advantages and disadvantages of using MRI in children?
Advantages:
- Highest resolution
- Good for muscular and ligamentous injuries
Disadvantages:
- Degraded by motion: most children will need sedation
