Preliminary study of vacuum phenomenon in pediatric hip joint / 国际儿科学杂志

ABSTRACT

Objective To find the accurate incidence of vacuum phenomenon in the hip and the best projection position produced the vacuum phenomenon on plain radiograph of hip in children.Methods All pediatric anteroposterior view and frog-leg position plain radiographs of hip joints were retrieved in our hospital between January 2003 and March 2013.All subjects was between 0 and 14 years old (mean age,4.2 years old).All the plain radiographs showing the crescent,linear,and irregular lucency between the femoral head and acetabulum were included in the present study.Results A total of 16 749 cases,including 12 422 cases (5 912 boys and 6 510 girls) only taken AP view plain radiographs and 4 327 cases (1 537 boys and 2 790 girls) taken both AP view and frog-leg position plain radiographs,were taken in our hospital between January 2003 and March 2013.None of AP view plain radiographs of hips could find the vacuum phenomenon.Two hundred and fifty-eight cases (321 hips) with vacuum phenomenon of the hips were found only in the frog-leg position plain radiographs of 4 327 cases,and the constituent ratio of vacuum phenomenon in the hip joint is 5.96％ in frog-leg position plain radiographs.One thousand seven hundred and thirty-eight normal children were included in 4 327 frog-leg position radiographs,and 150 cases of vacuum phenomenon were included in 1 738 normal children,and incidence of vacuum phenomenon in normal children is 8.63％.Two thousand three hundred and sixty children with developmental dysplasia of the hip (DDH) were included in 4 327 frog-leg position radiographs,and 98 cases of vacuum phenomenon were included in 2 360 children with DDH,and incidence of vacuum phenomenon in children with DDH is 4.15％.258 cases with vacuum phenomenon included 150 cases of normal hips (58.14％),98 cases of developmental dysplasia of the hip (37.98％),5 cases of Legg-Calvé-Perthes disease (1.94％),and 1 each in solitary eosinophilic granuloma of ischium,polyostotic fibrous dysplasia of the bilateral proximal femur,hereditary multiple exostoses,congenital coxa vara and fracture of femoral neck after surgery.Three hundred and twenty-one hips in 258 cases were classified into complete type (121 hips,37.69％) and partial type (200 hips,62.31％) according to the proportion of lucency area in the hip joints and linear (159 hips,49.53％),crescent (151 hips,47.04％) and irregular (11 hips,3.43％) lucency according to the shape of lucency area in the hips.Conclusion Vacuum phenomenon of the hip in children is not very rare in frog-leg position plain radiograph.It is easier to find the vacuum phenomenon in normal hip compared to that of developmental dysplasia of the hip.The frog-leg position plain radiograph is a better projection position to obtain the vacuum phenomenon of the hip in children compared to the anteroposterior view plain radiograph.