Imaging

Question 1

What are the three X-Ray views commonly used in foot and ankle surgery?

Answer 1

Weightbearing:
-Dorsoplantar

-Oblique

-Lateral

Question 2

Why is it important to get weightbearing views in foot and ankle surgery?

Answer 2

Weight-bearing views provide a more accurate picture of foot function, as inter-metatarsal and hallux valgus angles change are different when weight-bearing and not weight-bearing

Question 3

What hallux valgus and inter-metatarsal angles constitute a mild deformity?

Answer 3

HVA - 15-30°

IM - 9-11°

Question 4

What HVA and IMA values constitute a moderate deformity?

Answer 4

HVA - 30-40°

IM - 11-14°

Question 5

What HVA and IMA constitute a severe deformity?

Answer 5

HVA - >40°

IM - >14°

Question 6

Why is post-operative imaging obtained in foot and ankle surgery?

Answer 6

To check the alignment, normal healing, position of metalwork and any complications

Post-op imaging can be taken immediately in theatre or several weeks later

Question 7

What are the four main radiological features of arthritis in a joint visible on X-Ray?

Answer 7

Sclerosis of the joint margins

Osteophyte formation

Joint space narrowing

Subchondral cyst formation

Question 8

Name some vascular imaging studies that can be used to assess peripheral arterial disease

Answer 8

Duplex Ultrasound - Recommended by NICE as 1st line

Conventional Angiography

Digital Subtraction Angiography - Gold standard for assessing PAD and Critical Limb Ischaemia

Magnetic Resonance Angiography

CT Angiography

Question 9

What does conventional angiography involve?

Answer 9

Plain X-Ray or fluoroscopy of vessels following the injection of contrast dye

It is useful to guide procedures, but can be difficult to interpret to determine a diagnosis

Question 10

What does digital subtraction angiography involve?

Answer 10

Live fluoroscopy based imaging where iodine (ICM) or carbon dioxide based contrast material is used to show the vessels. Images are taken before contrast and then the bones and tissues are masked so that in subsequent images the vessels are clear.

Considered the gold standard for imaging in Critical Limb Ischaemia

Question 11

What are the risks associated with digital subtraction angiography using iodine contrast medium and why would CO2 contrast medium potentially be used as an alternative?

Answer 11

Iodine contrast material presents risk of nephrotoxicity and allergy, so should not be used in patients in kidney failure (eGFR <15mg/mmol)

CO2 can be used in patients with an eGFR of less than 15mg/mmol as it is not nephrotoxic

Question 12

What are the advantages and disadvantages of using contrast enhanced magnetic resonance angiography to assess PAD?

Answer 12

Advantages:
- Produces good quality images
- Useful for visualising arterial calcification (for bypass graft site)

Disadvantages:
- Cannot be used in patients with an eGFR of less than 30mg/mmol due to nephrotoxicity of contrast medium

Question 13

What are the advantages and disadvantages of using computed tomography angiography to assess PAD?

Answer 13

Advantages:
- Higher spatial resolution than MRA
- Created a map of the bodies vascular supply from hundreds of axial images: is detailed and can detect a number of pathologies
- Less susceptible to motion artefact than MRA

Disadvantages:
-Requires iodine based contrast: increased risk of nephrotoxicity, so should not be used in patients with an eGFR of less than 30mg/mmol
- Exposure to ionising radiation
- Should be avoided if there is significant vessel calcification present