![]() They are often unable to walk, and they may exhibit shortening and external rotation of the affected limb. 27.8).Patients with hip fracture typically present to the emergency department or their physician's office after a fall. When DDH is advanced or untreated, the typical AP radiographic findings are a shallow acetabulum with an index exceeding 30 degrees and superolateral subluxation of the femoral head with delayed ossification ( Fig. Finally, the Shenton line should smoothly arc along the lesser trochanter, medial femoral neck, and lower margin of the superior pubic When the femoral head is not ossified, the Perkin line should intersect the middle third of the proximal femoral metaphysis. The ossified femoral head is normally located medial and inferior to the intersection of the Hilgenreiner and Perkin lines. The Perkin line is drawn vertically from the superolateral acetabular margin to intersect Hilgenreiner line ( perpendicular to the horizontal line) ( Fig. The maximum normal acetabular angle is 30 degrees after age 12-16 weeks, and decreases to 25 degrees in children up to 2 years. The acetabular angle or index is formed between this second line and the Hilgenreiner line ( Fig. Another line is drawn connecting the inferomedial and superolateral aspects of the acetabular roof. The lucent triradiate cartilage forms the medial acetabular wall. ![]() The Hilgenreiner line passes horizontally between the superior aspects of bilateral triradiate cartilages ( Fig. 4 On the AP projection, it is helpful to draw several lines to evaluate hip position, in addition to globally assessing the pelvis. 1, 2, 3, 4, 5, 6 and 7įor children older than 4 months, pelvic radiographs are performed instead of US because the femoral head typically has begun ossifying by that time. If there is joint laxity, then the femoral head subluxes or dislocates posterolaterally with stress. Stress is applied to the hip with the transducer in the transverse plane. Dynamic hip imaging includes stress maneuvers that simulate Ortolani and Barlow tests. Additional gray-scale findings of DDH include blunting of the acetabular corner and hypertrophy of the echogenic These measurements often spontaneously normalize by 12 weeks of age upon repeat evaluation. The term “functional immaturity” is often applied when femoral head coverage is 40% to 50% or the alpha angle is 50 to 60 degrees in an infant less than 12 weeks of age. Normal alpha angles are greater than 60 degrees. The alpha angle is the slope of the acetabular roof with respect to the ilium on the coronal image. Normal femoral head coverage exceeds 50%, with smaller percentages indicating lateral subluxation until acetabulofemoral contact is lost (dislocation) ( Figs. The ilium appears as a horizontal echogenic line and should normally bisect the cartilaginous femoral head, which has a speckled hypoechoic echotexture. The static hip images are acquired in the coronal plane, simulating an AP pelvic radiograph tilted 90 degrees ( Fig. The examination consists of both static (anatomic) and dynamic (physiologic stress) components. Because there is physiologic neonatal ligamentous laxity related to maternal hormones, it is best to start screening hips with ultrasound (US) at 4 to 6 weeks of age. Ultrasound with a high-frequency linear transducer is used to evaluate for DDH in infants younger than 4 to 6 months.
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