Hi Leszek,
Indeed these are a challenge, but don’t dispair ultrasound can make a useful contribution.
Patients that have a THR in situ get a variety of problems ultrasound can help with.
Firstly the iliopsoas tendon and bursa can become symptomatic at the point where the tendon passes over the iliopectineal eminence (in other words where it passes over the new prosthetic acetabular cup anterior margin). Sometimes the cup is left slightly proud and this leads to a progressive abrasion injury of the iliopsoas tendon. Sometimes it is just the altered biodynamics that lead to the damage to the iliopsoas tendon.
So look for evidence of tendinosis in the iliopsoas tendon where the tendon is swollen and hypo echoic with a loss of normal fibrillar architecture. You can also log for evidence of iliopsoas bursitis by assessing the distance between the iliopsoas tendon and the underlying bony iliopectineal eminence. If there is a significant gap between the tendon and the bone this is evidence of bursae thickening and hence bursitis. The gap should be really small (less than 2mm say) and you can also compare with the other side.
The next thing to consider is the lateral hip. If the THR was put in from a lateral approach the G-min and G-Med tendons are separated and then reconstituted during the surgery. Look for tendinosis of the G-min and med tendons as well as any evidence of a tear in the area of the MTJ of each tendons. If there is a tear you will see fluid in the trochanteric bursa. You can test the MTJ of each tendon by having the patient lying decubitus with the hips and knees slightly flexed . Ashk the patient to keep their knees together and then lift the uppermost ankle off of the other one towards the ceiling. This activated G-min and med and if there is an MTJ tear it will be easily seen. Patients may also suffer from trochanteric bursitis initiated from the gluteal tendinopathy or the operative trauma. Remember that there i always a catalyst for trochanteric bursitis (tendinosis, enthesopathy, operative trauma ) and the concept of pure bursitis with normal tendons is not really a thing.
The next thing is the “pseudo tumour” from some of the metal hip prosthesis that were used a few years ago where the metal breaks down and forms a collection in the posterior hip joint area. You will see a fluid collection with debris in the poster-lateral part of the hip joint just being the super-posterior facet attachment of the G-med tendon.
Other that that also consider all of the usual suspects with hip ultrasound. The rectus femoris origins, LFCN, TFL origin, ITB origin, etc.
That should be enough to get you going,
Cheers
Steve.