Week 6 Medical Imaging: Joints Flashcards
What is lipohaemoarthrosis?
What is it indicative of?
Collection 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 - tibial plateau fracture whereby fracture of the tibia breaks into the knee joint itself - often leads lipohaemoarthroses.
What causes lipohaemarthrosis?
How does it appear on X ray?
Liphaemarthrosis results from an intra articular fracture with escape of fat and blood from the bone marrow into the joint.
Most frequently seen in the knee, associated with tibial plateau fracture or distal femoral fracture, rarely a patellar fracture.
Radiographic features:
- Fat floats on water as it is less dense - fatty marrow separates from the water based blood and layers above it forming a fat fluid level - known as the FBI sign - straight line on xray.
- FBI sign seen on all modalities - less commonly on USS
What types of imaging can be used when a higher sensitivity is needed to image a joint?
What can they identify?
CT and MRI have much higher sensitivity to density differences, not only identify intraarticular fat but also the haematocrit effect.
Can identify haematocrit effect - which is where there are fluid- fluid levels as a result of layering of heavier cellular elements of blood located dependant to a liquid supernatant:
Fat above, serum/synovial fluid in the middle, rbc below.
USS –> not widely usses in ax post trauma in the knee, but fat fluid level can be identified as echogenic layer above hypo-anechoic blood fluid level.
Name 3 common joint emergencies seen on imaging
Lipohaemarthrosis
C-spine injury:
atlanto-occipital dislocation
atlanto-axial dislocation
C1 & C2 fractures
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
Nuclear imaging –> involves injection of radioactive substance into bones, which will highlight hyperactive regions of bone. Combining nuclear medicine with SPECT (single photon emission CT) or CT scan enables us to locate area of abnormal activity highlighted on a bone scan. Note a bone scan is just taken in planar (straight on) format.
Describe the method of interpreting a C-spine x-ray
Classic - correct patient, correct radiograph with patient details and date and time radiograph taken.
Typically there are three views provided in C spine Xray: 1) lateral 2) antero-posterior 3) odontoid/open mouth view
Interpretation:
Adequecy (all cervical vertebrae visible - should be able to see from C1 down to C7/T1 junction).
Alignment: multiple lines need to assess across each area of the three radiographs - should run uninterupted in healthy individuals. Are the lines smooth? Are there any bony prominences outside of the lines?
In lateral view:
- Anterior vertebral line (runs anterior surface of all vertebral bodies)
- Posterior vertebral line (runs posterior surface all vertebral bodies)
- Spino-laminar line (runs along anterior edge of spinous processes at junction of spinous process and laminae)
- Posterior spinous line –> runs down the back of the spinous processes
In AP view:
- Two lateral lines of the AP view run down either side of the vertebral bodies
- Middle line through all the spinous processes from C1-C7
Odontoid view: (open mouth view)
- Need to assess alignment of lateral masses of C1 and C2, and assess the odontoid peg, making sure it is aligned with lateral masses of C1.
Bones: are the borders of the cortex (outer white edge) of each bone smooth?
Cartilage: IV discs should be roughly similar in height thoughout the cervical spine w no obvious loss of height at any point in the disc, are the spaces between the vertebrae uniform?
Soft tissue: assess the prevertebral soft tissue width for evidence of swelling
When imaging joints, why would a CT spine be used over x-ray?
What can CT scan not exclude in terms of joints?
Higher sensitivity than X rays
used in trauma situations where x-ray appears normal and there is ongoing clinical concern.
If x-ray shows an abnormality, to further investigate
Limitations of CT spine –> 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.
How is atlanto-occipital dislocation diagnosed?
Usually results from trauma
CT
If either BAI (basion axial interval - between base of skull and posterior axial line of the spine) or BDI (basion - dens interval - between base of skull to dens) >12mm usually suggests AO dislocation.
Wackenheim line: straight line extending from posterior clivus of skull 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 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 is a Jefferson fracture?
How is it caused?
Is it a stable or unstable fracture?
Jefferson fracture = C1 burst fracture
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?
Hangman’s fracture = C2 pedicle fracture
Unstable injury where the cervicocranium is extremely hyperextended
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 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/depression fracture, resulting from impaction with the anterior glenoid rim - indicative of an anterior glemohumeral dislocation. Typically secondary to recurrent anterior shoulder dislocations, as the humeral head comes to rest against the anteroinferior part of the glenoid. Often associated with bankart lesion (first pic on L small depression in humeral head)
Bankart lesion: injuries specifically at the anteroinferior aspect of the glenoid labral complex, and represent a common complication of anterior shoulder dislocation (small region of overhang underneath inferior aspect of glenohumeral joint).
