snapping can have intra-articlar causes such as osteo-arthritis, labral tears or cysts. these may not be visible on ultrasound.
the 2 most likely forms of snapping hip encountered with ultrasound are:
- lateral snapping hip syndrome.
this involves the ilio-tibial band catching on the greater trochanter or gluteal tendon insertions. to evaluate this, roll the patient onto the unaffected side and scan transversely over the greater trochanter. with the leg flexed, ask the patent to lift their feet apart, whilst keeping their knees together. watch the itb. it should slide smoothly over the trochanter and gluteals. (see normal video here)
- anterior snapping hip syndrome.
this occurs less commonly. it involves the ilio-psoas musculo-tendinous junction catching on ilio-pectineal ridge. this occurs during movement from hip flexion to extension.
with the patient supine, ask the patient to flex, then abduct the hip (frog-leg position). then return to full extension so the feet are side-by-side. it is on this return to extension that the click will occur.
to observe this on ultrasound, scan the iliopsoas tendon in transverse at the level of the pubis.