Medical Imaging: Joints

Question 1

What is lipohaemoarthrosis?

What is it indicative of?

Answer 1

Fat and blood in a joint

Indicative of an intra-articular fracture

Question 2

What does this xray indicate?

Answer 2

Lipohaemoarthrosis:

• Effusion beneath patella - straight line above femur
• ‘FBI’ sign: fat-blood interface sign

Fracture to tibial head

Question 3

What causes lipohaemarthrosis?

Answer 3

Fatty marrow separates from the blood (water based) which gives the characteristic fat-fluid level indicated by the straight line on the xray.

Question 4

What types of imaging can be used when a higher sensitivity is needed to image a joint?

What can they identify?

Answer 4

CT and MRI

Can identify haematocrit effect:

• Fat
• Synovial fluid
• Blood

Question 5

Name 3 common joint emergencies seen on imaging

Answer 5

Lipohaemarthrosis

C-spine injury

Joint dislocation

Question 6

What indications may there be for spinal imaging?

Answer 6

Trauma

Malignancy

Infection: TB, discitis, abscess

Disc prolapses

Degenerative changes

Limb pain (neuropathic)

Question 7

What imaging modalities may be used for a suspected c-spine injury?

Answer 7

X-ray

CT

Question 8

What is the first line imaging used for suspected cauda equina syndrome?

Answer 8

MRI

Question 9

What imaging modality should be used for suspected discitis?

Answer 9

MRI

Question 10

In what circumstances may nuclear imaging of the spine be indicated?

Answer 10

Malignancy

Question 11

Describe the method of interpreting a C-spine x-ray

Answer 11

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?

Question 12

When imaging joints, why would a CT scan be used over x-ray?

What can CT scan not exclude in terms of joints?

Answer 12

Higher sensitivity

In trauma situations where x-ray appears normal

If x-ray shows an abnormality, to further investigate

Cannot exclude ligamentous injury

Question 13

What are the benefits of using MRI?

What type of tissue can they show?

Answer 13

Higher sensitivity

Can see ligaments, nerves and soft tissue

Can look closely at individual nerves: demyelination

No radiation compared to CT and MRI

Question 14

WHat type of imaging can be used to investigate suspected demyelination?

Answer 14

MRI

Question 15

What does this MRI show?

Answer 15

Prolapse of lumbar vertebral disc causing spinal cord compression

Question 16

What does the MRI show?

Answer 16

Discitis causing obliteration of the disc and damage to the vertebral bodies above and below.

Question 17

Why might neck positioning for intubation in a patient with RA be potentially fatal?

What should be performed before intubation for RA patients?

Answer 17

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.

Question 18

Where is the most common site of spinal injuries?

Why is this?

Answer 18

C-spine (particularly C1 and C2)

Flexible, exposed part of the spine

Question 19

What is atlanto-occipital dislocation?

What damage does it cause?

Answer 19

= 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

Question 20

How is atlanto-occipital dislocation diagnosed?

Answer 20

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)

Question 21

What is an atlanto-axial dislocation?

What are the degenerative and traumatic causes?

Answer 21

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

Question 22

What are the potential symptoms of c-spine damage in a person with RA?

Answer 22

Quadriparesis

Altered consciousness/drop attacks

Lhermitte’s phenomenon

Neck pain

Respiratory dysfunction

Dysphagia

Question 23

When may plain radiographs be used for C1/C2 imaging?

Which 2 views can be used?

Answer 23

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)

Question 24

What should be calculated in an open-mouth odontoid radiograph?

Answer 24

Sum of lateral mass displacement, if >6mm combined may indicate lateral ligament injury

Question 25

What should be measured in flexion and extension views of C1/C2 radiographs?

Answer 25

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

Question 26

What distance between the odontoid process and posterior border of the anterior arch of atlas is considered unstable?

Answer 26

\>3.5mm

Question 27

What is a Jefferson fracture? How is it caused? Is it a stable or unstable fracture?

Answer 27

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

Question 28

What is a hangman's fracture? How is it caused? Stable or unstable?

Answer 28

C2 pedicle fracture Hyperextension injury Unstable

Question 29

How is a C2 odontoid fracture caused? What are type I and type II odontoid fractures? How is it best seen on x-ray?

Answer 29

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

Question 30

According to the Canadian C-spine rules, when is imaging of the C-spine required?

Answer 30

Age 65 or above Dangerous mechanism Paraesthesias in extremities Inability to rotate neck 45°

Question 31

What imaging modality should be used in children \<16 if there is a strong suspicion of: Cervical spinal cord injury Cervical spinal column injury

Answer 31

MRI

Question 32

When should plain x-ray be used in children under 16 for c-spine imaging?

Answer 32

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.

Question 33

When should CT be used for suspected spinal injury in adults? When should MRI be used?

Answer 33

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

Question 34

Define joint dislocation

Answer 34

Abnormal seperation in the joint where 2 or more bones meet

Question 35

Which imaging modality is usually used for suspected dislocations? Which views are required?

Answer 35

Plain radiograph Anterior view and lateral view

Question 36

What type of dislocations are the most common? What should also be considered when looking at this type of dislocation?

Answer 36

Shoulder- particular anterior dislocations Hill-Sachs and Bankart lesions, AC joint disruption and acromioclavicular fracture should also be looked for.

Question 37

What type of shoulder dislocation is this? What other imaging should be used to confirm this?

Answer 37

Anterior shoulder dislocation Side view radiograph should be used to confirm as could be posterior dislocation

Question 38

What type of shoulder dislocation is this? Why?

Answer 38

Posterior Humeral head is to the left of the normal position

Question 39

What type of shoulder fracture is this? Why?

Answer 39

Anterior dislocation Humeral head is to the right of the normal position

Question 40

What are Hill-Sachs and Bankart's lesions? What are they caused by?

Answer 40

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

Question 41

What is ultrasound useful for identifying? What do bilateral findings suggest?

Answer 41

Effusions Bilateral: may indicate systemic arthritis disorder or transient synovitis.

Question 42

What are the advantages and disadvantages of using MRI in children?

Answer 42

Advantages: * Highest resolution * Good for muscular and ligamentous injuries Disadvantages: * Degraded by motion: most children will need sedation