Imaging lower limb guide Flashcards
What are the relevant imaging modalities for upper limb?
- XR -including angiogram
- US
- CT
- MRI
Nuclear medicine to rule out cancer.
Describe how to report images for lower limb
There are several features that should always be mentioned when reporting images of the lower limb:
- XR: projection (frontal: AP/PA, lateral, oblique]); plane; region imaged; patient details: rotation, quality, exposure, artefacts; identify normal and abnormal structure
- US: x; plane; region imaged; patient details: quality and exposure, artefacts; normal and abnormal structures
- MRI: imaging modality (PD fluid-weighted/fat saturated); plane; region imaged; contrast vs no contrast ^[i.e. unenhanced]; patient details: quality and exposure, artefacts; normal and abnormal structures
Describe the role of X-rays in lower limb imaging
X-rays are used as first line investigation in the emergency department for diagnosis of fractures.
When looking at an x-ray:
- First observe overall alignment.
- Next trace the white cortical line around each bone and look for a step or discontinuity.
Describe the appearance of structures on XR
- air is black (radiolucent), as are cysts ^[OA], as are fat-fluid level consistent with lipohaemarthosis
- fat is dark grey
- soft tissue is grey
- bone is off white, as are osteophytes, sclerosis
- metal is white (radioopaque), as are effusions, sclerosis
List the structures to identify
- iliac crest
- ASIS
- AIIS
- PIIS
- inferior pubic ramus
- superior pubic ramus
- sacroiliac joint
- symphysis
- ischial tuberosity
- greater trochanter
- lesser trochanter
- intertrochanteric crest
- obturator foramen
- acetabulum
- femoral head
- femoral neck
- coccyx
![[Pasted image 20240228175313.png]]
- femur shaft
- tibia head and shaft
- fibula head and shaft
- patella
- medial femoral epicondyle
- lateral femoral epicondyle
- medial condyle
- lateral condyle
- medial condyle of tibia
- lateral condyle tibia
- medial tibial plateau and lateral tibial plateau
- intercondylar eminence
- medial and lateral tibial spines
-
![[Pasted image 20240228175548.png]]
- femur
- tibia and fibula head and shaft
- patella
- quadriceps tendon
- lateral condyle
- intercondylar eminence
- tibial tuberosity
![[ankle-ap.webp]]
- medial malleolus
- lateral malleolus
- syndesmosis
- tibia and fibula shaft
- talus
![[lateralv-1.jpg]]
- tibia
- fibula
- lateral/medial malleolus
- talus
- calcaneum
- cuboid
- navicular
- 5th MT base
![[unnamed 1.jpg]]
- phalanges
- metatarsals
- cuneiforms: lateral, intermediate, middle
- cuboid
- navicular
- talus
- calcaneus
- tibia
- fibula
![[unnamed-1.jpg]]
- phalanges
- metatarsals
- cuneiforms
- navicular
- cuboid
- talus
- calcaneus
Describe the role of ultrasound in the lower limb
Ultrasound is the imaging modality of choice when investigating lower limb or upper limb venous thrombosis. When the thrombus is present in the deep venous system, it is termed a DVT.
In the lower limb, we want to know whether these are above knee or below knee as this will guide treatment decisions.
Thrombus/clot in the lower limbs can break off and migrate (“embolise”) to the lungs. When this occurs, the fragment that is lodged in the pulmonary arteries is called a pulmonary embolus.
Ultrasound can also be used to detect joint effusions. It can also be used to measure flow in case of stenosis suspicion.
Describe the appearance of structures in lower limb
Recall that structures may be hyperechoic (light grey) or hypoechoic (dark grey or black).
- bone - hypoechoic with defined margins
- fat - hyperechoic
- muscles- hypoechoic with “hyper-echoic speckles” : starry night appearance
- tendons - hyperechoic and fibrillar : hypoechoic when torn
- fluid - anechoic/hypoechoic
- skin- hyperechoic, faded grey
- vessels - black: veins should be compressible. Clots will appear grey
- effusions: black, typically above structures e.g. femoral neck
Describe the role of MRI in the lower limb
MRI is a fantastic tool for imaging most lower limb conditions. It is particularly used for subtle/occult fractures and imaging sports conditions. Note again that T1w and T2w are substituted for PD fluid-weighted and fat-saturated imaging.
Pros
* Superb contrastresolution
* No ionisingradiation
Cons
* Expensive
* Longer examinations than CT
* Not readily tolerated by some patients
* Not possible in some patients
* Subtle calcifications or small bonefragments might be missed
Describe the appearance of structures on lower limb MRI
Fluid weighted, non-fat saturated:
- fluid appears white
- fat appears light grey
- muscles are grey
- bones are white
- ligaments are dark/grey
Fat saturated:
- fat appears dark
- fluid still appears white
- muscles are grey
- bones are black
- ligaments are dark/grey
List structures to identify
- lateral meniscus
- medial meniscus
- anterior cruciate ligament
- posterior cruciate ligament
- medial collateral ligament
- lateral collateral ligament
- tibia
- femur
- medial condyle
- lateral condyle
![[Pasted image 20240228182227.png]]
![[Pasted image 20240228182335.png]] - lateral meniscus
- medial meniscus
- anterior cruciate ligament
- posterior cruciate ligament
- medial collateral ligament
- lateral collateral ligament
- tibia
- femur
- lateral condyle
- patella tendon
- quadriceps tendon
- patella
- supra- and infra- patellar fat pad
![[Pasted image 20240228182422.png]]
![[Pasted image 20240228182449.png]] - tibia
- tibiotalar joint
- talus body and neck
- calcaneus
- cuboid
- navicular
- 5th MT if possible
What are considerations for a differential diagnosis?
- Arthritis
- Infection
- Tumours
- Trauma
- Muscle/tendon tear
- Vascular
- Neurological
List and describe some clincially relevant patholgoies
Gout
![[Pasted image 20240228182956.png]]
note: right hand side image shows calcific arteriopathy.
- Dense soft tissue swelling
- Erosions with sclerotic margins distant to the joint space
- Incidental calcific arteriopathy
- Bone density preserved on either side of the joint
Septic arthritis or osteomyelitis
![[Pasted image 20240228183356.png]]
- Bony rarefaction on either side of the 5th MTP joint
- Ill-definition of opposing articular surfaces
- Thinning cortex
- Erosion of 5th MT head
- Erosion of base of 5th proximal phalanx
- Midfoot arthropathy
- Localised soft tissue swelling
- Incidental calcific arteriopathy
- Dorsal soft tissue swelling
Charcot foot
![[Pasted image 20240228183444.png]]
- Incidental calcific arteriopathy
- Destroyed mid-foot articulations and mid-foot arch collapse
DVT
![[Pasted image 20240228183531.png]]
- non-compressible veins + greyish structure in lumen = DVT
Lipo-haemarthrosis
![[UJc9cJdydOoBM9XU2RIRwg93531.jpeg]]
- indicative of fracture, even if not visible on imaging
Knee OA
![[Pasted image 20240228183743.png]]
- Non-uniform joint space narrowing
- Implies the arthritis is destroying the medial meniscus»_space; lateral
- Which implies that this is a cartilage-based arthropathy
- Development of osteophytes, usually on the medial side
List some other clinically relevant conditions
- NoF
- diastasis
- left protrusion acetaulum
- metastasis (Sclerosis)
