MRI Predictors of Residual Dysplasia in Developmental Dysplasia of the Hip Following Open and Closed Reduction

Background: Following open or closed reduction for children with developmental dysplasia of the hip (DDH), 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 MRI data to determine factors predictive of residual acetabular dysplasia at medium-term follow-up.

Methods: We retrospectively reviewed 63 hips in 48 patients which underwent closed or open reduction and spica casting for DDH. MRI performed in-spica at approximately 3-week follow-up were used to assess 11 validated metrics and 2 subjective factors. Key metrics are demonstrated in Figure 1. Acetabular index (AI) was measured on AP pelvic radiographs at 2 year follow-up. Binary logistic regression was then used to identify variables predictive of residual dysplasia, defined as an acetabular index 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 months ± 3.2 vs. 8.0 months ± 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). Regression analysis demonstrated factors predictive of residual dysplasia (Table 1). Hips with a cartilaginous acetabular index (CAI) of greater than 23° were 7.6 times more likely to develop residual dysplasia. Type of reduction (i.e. closed vs. open) did not seem 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 gender, and a higher CAI were associated with a greater risk of persistent radiographic dysplasia. In particular, hips with a CAI > 23° were 7.6 times more likely to be dysplastic at 2-year follow-up.