Imaging Flashcards
What is the differences in what x-ray; CT and MRI are able to see anatomically?
x-rays only show bony outlines; CT shows bone outlines in more detail and some soft tissue structures; MRI shows bone outlines in less detail but shows all soft tissue structures
How should consecutive vertebrae appear in contrast to each other?
have similar size
When is a CT used to image spinal trauma?
when x-ray shows # but more detail is required or wonder if there are more# or if x-ray is noram but there is a high clinical suspicion of #
What is the function of ligaments in the spine?
ligaments tether vertebrae together and are responsible for spinal stability
How can you know if there are intact ligaments on x-ray and CT if they cannot be seen?
seeing normal vertbral alignments implies this
How do normal and damaged ligaments appear on MRI?
normal appear black whereas if damaged they appear white
When would MRI be used to image spinal traume?
if a pt has neuro which isnt explained by x-ray or CT
What might be seen on x-ray and CT with a bone tumour of the spine?
bone destruction; vertebral collapse (pathological #); bone sclerosis
What may be seen on MRI in a bony tumour?
early- bone marrow infiltration
late- extradural mass and spinal cord compression
What is the only mode of imaging that adequately shows the spinal cord?
MRI
What can cause spinal cord disease?
trauma; demyelination; tumour; ischaemia
What type of pattern of joints affected is seen in OA
asymmetrical
What joints are infected in primary OA?
weight bearing or active joints- spine, hip, knee, thumb base , DIP
what is secondary OA?
when unexpected joints are affected by OA because there is overuse, previous injury or previous arthritis
Why is there sclerosis of subchondral bone in OA?
increased subchondral bone cellulairty and vascularity which excites bone turnover leading to sclerosis
What leads to osteophyte formation?
increased vascularity stimulates the periosteum to increase the joint SA to share the load
What results in joint deformity in OA?
weakened bone caves in
What is the distribution of affecgted joints in RA?
symmetrical- MCP;MTP; IP; wrists; hips; knees; hsoulders; atlanto-axial
What causes soft tissue swelling in RA?
synovial prolferation and reactive joint effusion
What else is seen on x-ray in RA?
periarticular osteoporosis; destroyed bone-marginal erosions
what destroys the bone in RA?
inflammatory pannus- inflamed thicked synovium
What are the hallmark lesions of RA?
marginal erosions
What causes joint subluxation and deformity in RA?
the bones become eroded and shorter which makes the ligaments and capsules lax and inflam also softens the ligamnets which stretch further leading ot increased subluxation and joint deformity
Why might ankylosis be seen in RA?
if the eroded bones become exposed to each otehr and then fuse
What joints tend to be affected in psoriatic arthritis?
small joints of hands and feet; DIP joints; Ip joint of hallux
what joints are affected in AS?
scattered lwoer limb large joints- (and sacro-iliac joints
What is Reiters syndrom?
Reactive arthritis with uveitis and urethritis/cervicitis
What might be shown on an isotope bone scan?
increased vascularity around joints which accompanies synovitiis- i.e showing inflam
What is the use of US in arthritis?
thickening of synovium and increased blood flow
Why is an MRI useful in early disease?
shows bone marrow oedema which often precedes significant joint erosion/damage
Why do you need more than one x-ray view?
fractures may be invisible on one view and alignment cannot be seen
What circumstances do you need more than 2 views?
cervical spine and scaphoid
What does a bone fracture ususally look like?
lucency crossing bone
How does an impaction fracture appear?
dense as opposed to lucent
What is an avulsion fracture?
when part of a bone is pulling away by a tendon or ligament
What features help differentiate an avulsion fracture from their mimics?
all avulsion fracture mimics have a completely corticated contour
What are examples of avulsion fracture mimics?
seasmoid bones; accessory ossification centres; old non-united fractures
How do you assess bony alignment at the radio-capitellar joint?
draw a line alone radius and it should interst the capitulum
How can you assess the bony alignment of the humero-capitella joint?
draw a line down the humerus and it should bisect the capitulum
Why is it important to asses the humero-capitellar alignment?
supra-condylar fractures are common and easy to miss
What causes the posterior fat pad sign?
an elbow effusion which displaces fat posterior to the distal humerus
What does the posterior fat pad indicate?
it is always abnormal and an effusion is usually caused by trauma-so tells you there was trauma in that area
What happens to childrens bones in repsonse to trauma in comparison to adults bones?
bend or bow rather than snap and spinter, can have incomplete fractures
What is seen in a buckle fracture?
the metaphyses isn’t smooth- it has a bump
What is seen with a greenstick fracture?
the fracture only transverses a portion of the bone
Why are avulsion fractures common in children?
the bones are soft so it is fairly easy for ligamnets or tendons to avulse their soft bony attachments
What is the growth plate on imaging?
a lucency between the epiphysis and metaphysis that may simulate a fracture
Why is the growth plate prone to injury?
it is the weakest part of a developing bone
What is a Salter-Harris fracture?
when the epiphysis is not centred on the metaphysis due to a fracture invovling the growth plate
What are examples of bony rings in the body?
spinal canal; pelvis; forearm and lower leg
What is important in assessing injuries to bony rings?
you should expect to see 2 or more disruptions because it is difficult to disrupt a ring in only one place
What is the point of a bony ring?
to help share the transmission of force and increase strength
What must be present if the radius is displaced?
there must be an ulnar injury because otherwise the ulnar would splint the radius in place
What foreign bodies are invisible on x-ray?
plastic and wood
What may cause focal skeletal weakening?
metastatic deposits
What may cause diffuse skeletal weaknening?
osteoprosis or other metabolic bone disease
What is a Colles fracture?
a fracture of the radius in the wrist, with a characteristic backward displacement of the hand.
What view should be obtained if a posterior shoulder disolcation is suspected?
an oblique view
What artery can be damaged in a supracondylar fracture?
brachial artery
Why are scaphoid fractures important to diagnose?
blood supply can be disrupted leading to non-union or AVN leading to early wrist OA
What is Bennett’s fracture?
a fracture involving the articular surface of the first metacarpal base, tendons pulling on the thumb distal to the fracture cause displacement and if this is missed leads to defomrity, dysfunction and arthritis
What can result from immobility through lower limb injury?
dehydration adn starvation; DVT/PE; pneumonia
What is the benefit of MRI over US?
MRI can show soft tissues deep inside the body whereas US is only useful for superficial structures
What are the typical sites of impacted fractures?
femoral neck; tibial plateau; calcaneus
Why do many lower limb fractures appear sclerotic?
often involve axial force with bone impaction
What typically causes high energy pelvic ring fractures?
RTA or fall from a height
What imaging modality is used in patients with polytrauma?
CT
What is acute pelvic soft tissue injury typically caused by?
muscle tear or tendon avulsion
What causes hip disolcation?
RTA or contact sports where the hip is flexed
What tends to occur with hip dislocation?
tends to be posterior with an acetabular rim fracture
What are risks with femoral shaft fractures?
risk of blood loss, fat embolus
What can small avulsed bone fragments sometimes indicate in the knee?
significant soft tissue injury
What ususally accompanies a significant soft tissue injury in the knee?
an effusion which fills the suprapatellar space
What does a lipohaemarthrosis in the suprapatellar recess indicate?
it is a specific sign of an intra-articular fracture
Why is it important to check the bony alignment at the knee carefully?
dislocation are often largely reduced by the time of the x-ray due to the action of tendons adn ligaments
What artery can be damaged in a knee dislocation?
popliteal artery
Which tibial plateau is most commonly fractured?
80%- lateral condyle
What injury causes a lateral condyle fracture?
valgus force with foot planted
What mode of imaging is useful in assesing extendor mechanism injuries?
US
What type of injury causes mensical tears?
twisting injuries
What will patients whose torn meniscus has displaced present with?
a locked knee
What is the injury mechanism with ankle fractures?
inversion or eversion
What may indicate the site of injury?
soft tissue swelling
What indicates instability (often with accompanying ligamentous damage) on x-ray?
non-unifrom joint spcae
What creates the posterior malleolus?
posterioinferior tibia
What injuries are imaged using an MRI?
scaphoid; pelvic ring injuries; femoral head/neck; knee
What can 5th MT base fractures be confused with in adolescents?
ossification centres
How can 5th MT base fractures be differentiated from normal ossification centres?
fractures in the 5th MT base are transverse whereas the ossification is longitidunial
What type of injury usually causes a calcaneal fracture?
usually follows axial compression- falling from height onto the heel
How does a calcaneal fracture appear?
loss of the calcaneal central peak and increased bone density; often comminuted- multiple pieces
What is often seen at slong the posterior calcaneus in children?
a fragmented accessory ossification centre
What can be seen in some people posterior to teh distal femur?
the fabella- a seasmoid within the lateral head of gastrocnemius
What is os trigonum?
an accessaory ossification centre see posterior to the talus
What can be seen on the medial and lateral plantar aspects of the 1st metatarsal head?
rounded sesamoid bones
What can predispose to tendon rupture?
diabetes; RA and steroid use
How are ankle tendon injuries assessed?
US or MRI
What is key to diagnosing TMT joint injury?
alignment
What are TMT joint injuries also known as?
Lisfranc
What is seen on x-ray with a Lisfranc fracture?
the TMTs a misaligned- there shouldnt be a step, it whould be smooth and the joint space should be equal
