Hi Charith,
Good question!
The anterior hip in these patients is an untidy place on ultrasound.
There is no labrum and the acetabulum and femoral head / neck are now all prosthetic. So with the exception of a post op collection there is no real role for ultrasound.
BUT there is one structure that is very important and that is the iliopsoas apparatus.
These post THR patients often present with hip flexion pain and the cause is iliopsoas tendinopathy and associated iliopsoas bursitis.
It is caused by either a change in the biomechanics of the hip following the replacement or my the iliopsoas tendon rubbing against the anterior lip of the prosthetic acetabular anterior margin (which is really the same thing as the iliopectineal eminence). If the prosthetic cup is slightly proud it can cheese grater the iliopsoas tendon leading to tendinosis and bursitis.
This is a cause of post op hip pain.
I would also look at the rectus femoris direct head origin as well looking for tendinosis or hydroxyapatite (calcific tendinosis) changes.
Steve