A hip ultrasound can detect a wide range of conditions, from fluid buildup inside the joint to tendon tears, bursitis, and developmental problems in infants. It is one of the most versatile imaging tools for the hip because it captures soft tissue detail in real time, costs less than an MRI, and involves no radiation. What it finds depends largely on whether the patient is an adult with hip pain or an infant being screened for a joint abnormality.
Joint Effusion and Fluid Buildup
One of the most common reasons for a hip ultrasound is to check for excess fluid inside the joint capsule. In a healthy adult hip, the distance between the joint capsule and the femur bone averages about 5 mm. A measurement of 7 mm or more, or a difference of 1 mm or more between the two hips, suggests abnormal fluid accumulation. This fluid can signal infection, inflammation, or an inflammatory condition like rheumatoid arthritis. Ultrasound picks up this excess fluid quickly and reliably, which is why it is often the first imaging step when a swollen, painful hip needs evaluation.
Tendon Damage and Tendinosis
Ultrasound is especially good at revealing problems in the tendons surrounding the hip. On the screen, a healthy tendon has a characteristic striped pattern of fibers. When a tendon is degenerating, a condition called tendinosis, it appears thickened and darker than normal, with that organized fiber pattern partially lost. This type of wear is common in middle-aged adults, both active and sedentary, and affects women more often than men.
The tendons most frequently assessed include the gluteus medius and gluteus minimus (the main hip abductors on the outer hip), the iliopsoas (a deep hip flexor at the front), and the hamstring tendons at the back. Calcific tendinitis, where calcium deposits form within a tendon, also shows up clearly as a bright white spot on ultrasound. This is a frequent finding in the gluteus medius tendon and can be a significant source of lateral hip pain.
Beyond degeneration, ultrasound can distinguish between partial and complete tendon tears. A partial tear appears as a dark, fluid-filled gap within the tendon fibers, while a complete tear shows a full separation of the tendon from its attachment point on the bone. Gluteal tendon tears can result from chronic degeneration, trauma, or as a complication of hip replacement surgery. Iliopsoas tendon tears tend to occur in athletes, though spontaneous ruptures have been reported in older adults, particularly those on long-term steroids.
Bursitis
Several bursae, small fluid-filled sacs that reduce friction, surround the hip joint. When these become inflamed and swollen, ultrasound can detect the distension clearly. The most commonly assessed include:
- Greater trochanteric bursa: Located on the outer hip between the gluteus medius tendon and the gluteus maximus muscle. Inflammation here is a classic cause of lateral hip pain, often linked to underlying abductor tendon problems.
- Iliopsoas bursa: Situated at the front of the hip near the iliopsoas tendon. It is best seen on ultrasound when it is expanded with fluid.
- Ischiogluteal bursa: Found between the sit bone and the gluteus maximus. This bursa can become inflamed from prolonged sitting or exercise, and its irritation often accompanies hamstring problems.
Muscle and Myotendinous Junction Injuries
The junction where a muscle transitions into its tendon is a vulnerable spot for injury, especially during sports. Ultrasound is effective at identifying tears at the proximal rectus femoris (the front thigh muscle near the hip), which is one of the most commonly injured structures in the hip region among athletes. Because ultrasound captures images in real time, the examiner can ask you to contract or stretch the muscle during the scan, which can reveal injuries that might look normal at rest.
Labral Tears and Paralabral Cysts
The labrum is a ring of cartilage lining the hip socket. Tears in this structure are a well-known cause of deep hip and groin pain, particularly in younger, active adults. Ultrasound can detect anterosuperior labral tears (the most common type) with a sensitivity of about 69% and a specificity of 82%. By comparison, standard MRI has higher sensitivity at roughly 85% but lower specificity at 64%. This means ultrasound is less likely to catch every labral tear but more reliable when it does flag one as positive. For this reason, MRI or MR arthrography remains the preferred test when a labral tear is strongly suspected, but ultrasound can serve as a useful initial screen.
Ultrasound can also detect paralabral cysts, which are fluid-filled pockets that form next to a damaged labrum. These appear as well-defined dark regions adjacent to the socket wall and often connect directly to the torn labrum.
Developmental Dysplasia in Infants
Perhaps the most widespread use of hip ultrasound globally is screening newborns and young infants for developmental dysplasia of the hip (DDH), a condition where the hip socket does not fully cover the ball of the femur. Physical examination alone catches only severe cases, primarily hips that are already dislocated or unstable, and misses subtler forms of dysplasia.
Ultrasound fills that gap. In countries like Germany and Austria, universal screening programs use hip ultrasound at four to six weeks of age. Infants with specific risk factors, such as breech presentation at birth or a family history of DDH, are often scanned within the first ten days of life, since earlier detection allows the hip more time to mature with treatment. The scan measures two key angles formed by the hip socket and surrounding cartilage. An alpha angle below 60 degrees indicates an abnormal hip, and below 50 degrees points to true dysplasia. Catching these early, before a child starts walking, dramatically improves outcomes and can often be treated with a simple harness rather than surgery.
Ultrasound-Guided Injections
Beyond diagnosis, hip ultrasound plays an important role in guiding treatment. When a corticosteroid or other injection needs to reach the hip joint or a specific bursa, ultrasound guidance achieves 100% accuracy in needle placement. Without imaging guidance, relying on surface landmarks alone, accuracy drops to about 72%. That difference matters because a misplaced injection means the medication does not reach the inflamed tissue, reducing both pain relief and diagnostic value.
What to Expect During the Exam
A hip ultrasound typically takes about 20 minutes, though it can run longer depending on how many structures need evaluation. No special preparation is required. You will be asked to wear loose clothing or change into a gown, and to remove any jewelry near the hip. The technologist applies gel to the skin and moves a handheld probe over the area, pressing gently to capture images from different angles. The exam is painless for most people. For infant screening, feeding the baby just before the appointment can help keep them calm, though it is worth confirming this with the facility beforehand.
Where Ultrasound Falls Short
Ultrasound excels at evaluating superficial soft tissues like tendons, muscles, and bursae, but it has limitations. It cannot see deep into bone the way an X-ray or CT scan can, so it will not detect fractures. It also has difficulty imaging structures that sit very deep within the joint, such as the posterior labrum or internal cartilage surfaces. For complex intra-articular problems, MRI provides a more complete picture. Ultrasound’s accuracy is also more operator-dependent than other imaging methods, meaning the skill and experience of the person performing the scan directly affects what gets found.