Ultrasound measurements in hips of children above 2 years of age. Normal variations in 232 hips.

In order to find the limits of normal variation of ultrasound measurements in children over 2 years of age, we examined 116 children and adolescents with normal hip joints. The children had been referred for various complaints from their lower extremities. Longitudinal ultrasound scanning from the lateral and anterior aspects was performed by the orthopedic surgeon as an integral part of the clinical examination. The most relevant parameters regarding hip dysplasia are those assessing the coverage of the femoral head: the lateral head distance (LHD, the distance from the lateral tangent of the bony epiphysis to the lateral bony acetabular rim) and the anterior head distance (AHD, measured as LHD, but from the anterior scan). The LHD increased with age; the upper normal limit (mean + 2 SD) increased from 4 mm at age 2-3 years to 7 mm at age 12-16 years. The AHD was larger in adolescents 12-16 years of age than in younger patients. The upper normal limit was 1 mm in the youngest and 2 mm in the oldest children. The mean (SD) differences (right minus left) in LHD and AHD were 0.3 (1.1) mm and 0.2 (1.0) mm, respectively. Radiographs were available in 15 of the patients and confirmed the ultrasound findings regarding femoral head coverage. Our findings should be of value in interpreting ultrasound measurements in older children.