Hi Sonjjay,
This is well covered in a couple of presentations.
If you watch the fundamentals of the wrist it is covered there as well as in a couple of other wrist presentations on the website.
To assess the radiotriquetral ligament you first need to scan axial and locate the Listers tubercle on the dorsal radius.
Then scan distally,
When you drop off the radius you will see the scaphoid, lunate and triquetrum in a row.
Keep the triquetral end of the transducer stationary and rotate the scaphoid (radial) end of the transducer proximally, back to the radius.
Now you have the radius and triquetrum lined up.
You can see extensor compartment 4 (EDC) and beneath that is the radiotriquetral ligament.
Ask the patient to move the wrist into radial deviation and the ligament will tighten and you have perfect image of it all the way from the radius to the triquetrum.
You can see schematics I have made as well as live scanning demonstrations on the website wrist material.
Look at :
SMUG wrist presentation
Advanced wrist ultrasound
Fundamentals of wrist ultrasound
They all have material on this topic.
Happy scanning,
Steve Bird