A follow up study of children with instability of the hip joint at birth. Clinical and radiological investigations with special reference to the anteversion of the femoral neck

Abstract

Among 6509 neonates, instability of the hip joint was found in 146 (22.4 per thousand liveborns). All of them were treated with Frejkas cushion splint usually for three months. Eleven patients required additional treatment with a plaster cast, and in four a derotational osteotomy was performed. During infancy the children showed several deviations from the normal motor development, the most important being an increased abduction and an increased external rotation capacity of the hip joint. A small group of infants showed a gradual increase of the passive internal rotation from 40-50 degrees to 80-90 degrees. In 129 patients a detailed clinical and radiological follow-up study was performed at the age of four to six years and the results were compared with those of 100 healthy children and 17 children with unstable hips at birth left untreated. Clinical examination at the age of four to six years showed that about 20 per cent of the girls and about 10 per cent of the boys with unstable hips treated with abduction had abnormal function of the hip. The most important findings were increased internal rotation and decreased external rotation in girls and increased abduction in boys. Radiological examination of the treated group of affected children showed pathological values of the angles measured in 30 per cent of the girls and in 10 per cent of the boys. In girls pathological mean values were demonstrated for all angles measured (AC, CE, CCD and AV), whereas the boys displayed pathological values of the AV-angle only. The mean angle values of the untreated children with unstable hips at birth showed no significant deviation from the values of the control group. A positive correlation was demonstrated between the values of the AC-angle and the CE-angle, but no correlation could be demonstrated between the AV-angle and the other angles. Slender children showed significantly higher values for the AV-angle than children with a low height/weight ratio. Seven of eleven children who received prolonged treatment with a plaster cast showed pronounced anteversion of the femoral neck. Increased anteversion of the femoral neck was also demonstrated in three patients with concomitant muscular abnormalities. It is suggested that increased anteversion of the femoral neck is a secondary phenomenon in CDH, possibly because of relative muscular inactivity, and that abduction splintage may be a causative factor.