Developmental dysplasia of the hip: Role of pelvic radiograph in patients with normal ultrasonography

Abstract

Developmental dysplasia of the hip (DDH) is an abnormal development of the components of the pediatric hip joint. Various screening programs are used, including physical examination, ultra-sound, pelvic X-ray, or a combination of them. Objective: To evaluate the risk of abnormal findings on pelvic X-ray in infants with a normal early hip ultrasound. Patients and Method: Retrospective diagnostic test study. Infants born between 2018 and 2021 with at least one risk factor for DDH were included. All patients had a normal hip ultrasound performed between the 2nd and 12th week of life and a pelvic X-ray obtained at or after 3 months of age. Demographic data, risk factors, ultrasound results (alpha angle according to Graf classification), and radiographic findings (acetabular index at 3 months) were collected. Data were analyzed to identify factors associated with abnormal radiographic findings. Results: A total of 232 hips from 116 infants were included. Of these, 55.2% (n = 128) were male. At 3 months, 20.3% of the hips showed an abnormal pelvic X-ray. The main risk factors for this condition were a smaller alpha angle and female sex. An alpha angle < 65 degrees was associated with an odds ratio (OR) of 5.8 (95% CI: 2.0–11.6) for presenting an abnormal X-ray. Conclusion: Infants with a normal ultrasound before 3 months of age with an alpha angle < 65° are at high risk of an abnormal pelvic X-ray; therefore, follow-up is recommended.