Hi Linh,
I keep these pretty simple.
I scan in the long axis of the TMJ in the long length of the mandibular condyle.
The TMJ looks a bit like a baby version of a long axis hip joint image.
The joint capsule passes along the condyle and attaches in a similar way to the anterior hip joint.
Compare both sides.
Like the hip joint when you see a concave joint capsule relative to the underlying bone it is pathological.
You may see an effusion or synovial proliferation.
I then ask them to open and close the mouth slowly and observe the range of movement and compare with the other side.
You can also use ultrasound to inject the joint with steroid.
There are some old published papers on looking for disk tears with ultrasound, but I have never had any luck with this !
Steve