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Developmental dysplasia of the hip (DDH) is the most common hip pathology in infants. Although its exact pathophysiology remains incompletely understood, its long-term prognosis depends not only on the severity of the dysphasia, but also on the timely implementation of appropriate treatment. Unrecognized and untreated hip subluxations and dislocations inevitably lead to early joint degeneration while overtreatment can produce iatrogenic complications, including avascular necrosis of the femoral head. In the past two decades, imaging has become an integral part of the clinical screening, diagnosis, and monitoring of children with DDH. Optimal timing for imaging and appropriate use of imaging can reduce the incidence of late diagnoses and prevent iatrogenic complications. In general, ultrasound of the hips is recommended in infants under the age of 4 months while pelvic radiography is recommended in older infants due to the fact that the femoral head ossific nucleus typically is not formed until 4 to 6 months of age.

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Background: Following open or closed reduction for children with developmental dysplasia of the hip, there remains a significant risk of residual acetabular dysplasia which can compromise the long-term health of the hip joint. The purpose of this study was to use postoperative in-spica magnetic resonance imaging (MRI) data to determine factors predictive of residual acetabular dysplasia at short-term follow-up. Methods: We retrospectively reviewed 63 hips in 48 patients which underwent closed or open reduction and spica casting for developmental dysplasia of the hip. MRI performed in-spica at ∼3-week follow-up were used to assess 11 validated metrics and 2 subjective factors. Acetabular index (AI) was measured on anteroposterior pelvic radiographs at 2-year postoperative followup. Binary logistic regression was then used to identify variables predictive of residual dysplasia, defined as an AI greater than the 90th percentile for age based on historic normative data. Results: Average age at surgical reduction was 9.3 ± 3.2 months. 58.7% (37/63) of reductions were open. A total of 43 (68.3%) hips demonstrated residual acetabular dysplasia at 2 years postoperatively based on normative values. In those with persistent dysplasia, patients were on average older at the time of reduction (10.0 mo ± 3.2 vs. 8.0 mo ± 2.8, P = 0.010) and more likely female (88.4% vs. 60.0%, P = 0.010). Patients with residual dysplasia were more likely to have mild subluxation on postoperative MRI (40.0% vs. 10.5%, P = 0.022). Hips with a cartilaginous acetabular index (CAI) of > 23 degrees were 7.6 times more likely to develop residual dysplasia. Type of reduction (ie, closed vs. open) did not appear to influence the rate of residual dysplasia (P = 0.682). Conclusion:In this series, the rate of residual dysplasia after surgical reduction was higher than most previous reports, with no appreciable difference between closed and open reductions. Older age, female sex, and a higher CAI were associated with a greater risk of persistent radiographic dysplasia. In particular, hips with a CAI > 23 degrees were 7.6 times more likely to be dysplastic at 2-year follow-up.