Hip ultrasound in newborns

Certain skills and abilities are required to perform ultrasound examinations of the hip joints of newborns to exclude congenital hip dislocations. With the appropriate skill, it is possible to visualize the lower part of the ilium, the acetabulum, especially the upper part of the hip joint and the acetabular rim. The exact position of the femoral head can be determined, and any abnormalities in the shape or size of the hip joint are detected.

If there is any doubt or if even minor ultrasound signs of hip dislocation are detected in a newborn, repeat the examination at 4-6 weeks. By this time, most joints become normal.

Anatomy of the hip joint of a newborn

The hip joint is formed by the articular surfaces of the head of the femur and the acetabulum of the pelvic bone. The head of the femur, the neck and most of the acetabulum in a newborn consist of cartilaginous tissue. Cartilaginous tissue before ossification appears hypoechoic during ultrasound examination. Three bones participate in the formation of the acetabulum: the ilium, ischium and pubis, which are connected by cartilage in a newborn. The acetabulum is attached to the free edge of the acetabulum, which increases the depth of the acetabulum and covers the head of the femur.

Ultrasound examination of the hip joint in children

Congenital hip dysplasia occurs in approximately 10 cases per 1000 healthy infants. This pathology is usually called an anomaly of the hip joint, detected at birth, when the head of the femur is completely or partially displaced from the acetabulum. There are different degrees of dysplasia: from subluxation of the hip, incomplete dislocation of the hip, to complete dislocation of the hip with displacement and with varying degrees of underdevelopment of the acetabulum. The use of X-ray examination in newborns to diagnose this anomaly is inappropriate, since the X-ray method does not fully reflect the changes occurring in the cartilaginous tissues of newborns. In contrast, ultrasound reliably displays the cartilaginous structures. Therefore, the ultrasound method is considered a generally accepted method of choice in diagnostics and monitoring the treatment of hip dysplasia in newborns. The research methodology includes stress and dynamic tests to assess the position, stability of the hip joint and the development of the acetabulum, based on the relationship between the femoral head and the acetabulum.

Ultrasound examination technique

Standard ultrasound examination of the hip joint of newborns, according to published data of the American College of Radiologists, should include three stages. In the first stage, the ultrasound examination evaluates the position of the femoral head in relation to the acetabulum. In the second stage, the stability of the hip joint is examined. Changes in the position of the femoral head during movement and stress testing (after the Barlow and Ortolani tests) are assessed. The Barlow test involves pressing on the knee of the adducted and bent leg of the infant.

In this test, the femoral head is displaced from the acetabulum. In the Ortolani test, the femoral head is independently reduced into the acetabulum when the leg bent at the knee joint is abducted. It should be taken into account that these tests can normally be positive for up to 2 months. In the case of subluxation (subluxation) of the femoral head, its incomplete immersion into the acetabulum is noted. In the case of incomplete dislocation, the femoral head is displaced from the acetabulum only during a dynamic test or stress test. In the case of complete dislocation, the head is completely outside the acetabulum before the tests are performed. At the third stage, morphological abnormalities in the formation of bone and cartilage tissues of the acetabulum are detected. Quantitative indicators: development of the acetabulum angle and the angle of immersion of the femoral head into the acetabulum reflect the degree of dysplasia. The study is carried out with the baby lying on his back or on his side. To examine this joint and surrounding soft tissues, a 7.5 MHz sensor with a linear or convex working surface is used; in a 3-month-old infant, it is more appropriate to use a 5 MHz sensor.

The sensor is installed longitudinally in the projection of the acetabulum. The bone landmarks are: the ilium line, the transition of the ilium into the acetabulum, the femoral head with the joint capsule. Normally, the ilium line will be a horizontal straight line, and when passing into the cartilaginous part of the acetabulum, it forms a bend. In this projection, the angles are measured according to Graf. The bend and the horizontal straight line form angle a - the degree of development of the acetabulum, the second angle is the angle of immersion of the femoral head - b. Angle a has less error and variability than b. Normally, angle a is more than 60 °, with subluxation, angle a decreases to 43-49 °, with dislocation, angle a is less than 43 °. Angle b with subluxation is less than 77, with dislocation - more than 77.

Not all clinics use angle measurements. In some cases, they limit themselves to describing the acetabulum curvature, the configuration of the lateral edge of the ilium, and the structure of the acetabulum. It is also possible to calculate the degree of immersion of the femoral head into the acetabulum (Morin et al.). Normally, more than 58% of the femoral head should be immersed in the acetabulum.

When performing a dynamic test: abduction - adduction, flexion - extension of the limb, the position of the femoral head should not change. When performing a stress test, the femoral head should also not shift from the acetabulum. The femoral head can shift laterally, upward, backward - depending on the degree of dysplasia. To identify the direction of displacement, the sensor is moved in the anteroposterior direction, and transverse sections of the hip joint are obtained.

In a cross-sectional examination, the infant's legs are bent at approximately 90°. The sensor is placed in the projection of the acetabulum. A section of the femur metaphysis, femoral head, and ischium is obtained. The femoral head in this section is normally completely immersed between the metaphysis and the ilium, which form a U-shape. In this position, an abduction-adduction test is also performed to exclude subluxation. If there is a displacement, the femoral head is displaced and the femoral metaphysis approaches the ilium, schematically forming a V-shape.