Femoral Head Sphericity in Untreated Developmental Dislocation of the Hip

Background Although many studies have discussed acetabular changes in walking aged children with developmental dysplasia of the hip (DDH), almost no data exists in the literature regarding dysplasia of the femoral head. The purpose of our study was to quantify the sphericity of the femoral head in a large, consecutive series of walking aged children with DDH. Methods We conducted a prospective study on 37 consecutive hips (30 patients) that were undergoing surgical procedures for DDH. After induction with general anesthesia (before the planned procedure), hip arthrograms were conducted. An AP radiograph was then taken with the patient positioned supine and the knee-flexed 90 degrees over the end of the operating table and the leg held perpendicular to the plane of the table. The limb was then rotated 90 degrees for the lateral radiograph. Radii were measured from the center of the femoral head to the edge of the head in line with the longest diameter, and then at 45, 90, and 135 degree angles. We created a femoral head sphericity score that was based primarily on the largest difference between these four radii (for each view). Results The mean age of the children in our series was 33.5 months (range 6 to 79 mo). There were 4 males and 26 females; 7 patients had bilateral involvement. The mean femoral head sphericity score was 85.2±5.5. There was significant variability in the “roundness” of the femoral head: the lowest score was 72.2 and the highest was 97.3. We did not find a relationship between age and femoral head sphericity. Conclusions In walking aged patients with DDH, the femoral head is dysplastic and usually aspherical. Our results suggest that developmental hip dislocation results not only in morphologic changes to the acetabulum but also the femoral head. The asphericity of the femoral head in DDH may affect outcomes following treatment. Level of Evidence Anatomic study.