Hip effusion is the accumulation of fluid within the hip joint capsule. On ultrasound, the hip is typically examined with the patient lying on their back and the transducer placed along the anterior aspect of the hip. An effusion appears as a hypoechoic or anechoic collection of fluid between the femoral neck and the joint capsule, with the capsule displaced away from the bone. In children, a hip effusion may indicate transient synovitis, septic arthritis, or other conditions, and ultrasound is the first imaging study performed because it can quickly detect fluid and guide aspiration if needed. In adults, hip effusion can occur with arthritis, trauma, or infection.
Sonography Term