Screening program for neonates at risk for developmental dysplasia of the hip: comparing first radiographic evaluation at five months with the standard twelve week ultrasound. A prospective cross-sectional cohort study.

To assess whether delayed radiological hip screening at five months (versus ultrasound at 3 months) results in a higher incidence of persistent developmental dysplasia of the hip (DDH) at 18 months. We analyzed 3536 screened neonates (2009-2013) at age two to three weeks. In the case of risk factors for DDH, 460 infants were assigned to a pelvic radiograph at five months between 2009 and 2010 and 651 infants were assigned to an ultrasound at three months (2011-2013). In the case of DDH, appropriate treatment was started and radiological follow-up occurred at eight, ten, 12, and 18 months. We compared incidence and severity of persistent DDH at 18 months. Analysis was performed using linear regression. Both groups were comparable for risk factors (breech, gender, twins, family history). Eighty-nine patients (2.5%) showed DDH (n = 43 (group 1), n = 46 (group 2)). At 18 months, ten patients showed persistent DDH (n = 8 (group 1), n = 2 (group 2) (7.7% vs. 0.3% respectively)). The mean acetabular index (AI) at 18 months in group 1 (left hip) is 22.4° (95% CI 20.6-24.3°) vs. group 2 at 22.3° (95% CI 21.2-23.4°) (p = 0.098). The mean AI in group 1 (right hip) is 21.9° (95% CI 18.9-24.9°) vs. 21.2° (95% CI 20.5-22.0°) in group 2 (p = 0.293). Adjusted for risk factors, there is no difference in incidence of persistent DDH between both groups after 18 months (OR 0.519; 0.07, 3.845). This study revealed no significant difference in incidence or severity of persistent DDH at 18 months between the two screening groups. These results suggest justification for delayed screening to prevent overtreatment of immature hips. In clinically stable hips, delayed ultrasound between three and five months is regarded as safe and could prevent for overtreatment of mild dysplastic hips.