Buttock/Hip

Hi Heath.
These patients are often poorly referred but if you get the correct type of patient ultrasound is useful. Lets start with Piriformis syndrome. The patient should present with sciatica and have a normal lumbosacral spine. So typically a young fit patient with sciatica. In these patient the possibility of an extra axial cause for sciatica is worth considering. If the patient is middle aged or older the likelihood is their sciatica is coming from lumbosacral nerve root compression and a search for piriformis syndrome as a cause is usually a waste of time. This works well for us as the target audience are acoustic friendly folk. Remember the sciatic nerve is two nerves, the tibial nerve and the common peroneal nerve running together in tandem. I find the sciatic nerve lateral to the ischial tuberosity and hamstring origin where it sits on the Quadratus Femoris muscle with Glut Max above it. I follow it up in long axis as it passes over the inferior gemellus, obturator interns and superior gemellus in that order heading cephalad. Then it passes under the muscle of piriformis. The piriformis will have the Glut max superficial to it and internal / external rotation of the hip will identify the piriformis muscle as it will be mobile. If the sciatic nerve passes entirely beneath piriformis this is a low risk patient. If the nerve passes through or superficial (posterior) to the piriformis or if the nerve divides and passes under and over / under and through etc this is a high risk patient. If the nerve is passing through or over the piriformis it will be irritated during muscle contraction and result in neuritis leading to sciatica. If the nerve passes beneath the piriformis it may still be compressed and irritated during strong deep lateral hip rotator compression. I like my C10 transducer rather than a linear array due to the extra penetration and ability co compress the G-Max comfortably. Look for oedema of the sciatic nerve as it passes under or enters the piriformis.
Steve

You can see the two gemelli and obturator interns on ultrasound as described above as the sciatic nerve passes over them . The gemelli are hypo-echoic as they are muscular and the OI is echogenic as it is a tendon at this level with the muscle being inside the pelvis. If you scan them in short axis (long axis of the sciatic nerve) they look like an Egyptian eye painting with an echogenic pupil being the OI surrounded by hypoechoig Gemellus muscle. I do look for tears or atrophy of these small deep lateral rotators, however I find it difficult and am not really convinced ultrasound has a great utility in diagnosing small tears. the clinical examination is very important and treatment may be guided by the clinical findings. The posterior hip and posterior labrum sit deep to thee muscles and again this is a difficult area for us to assess with the exception of obvious OA changes and paralabral cysts.