Predictors of residual hip dysplasia in 12-18-month-old vs. over 18-month-old DDH patients after closed reduction and the reliability of one residual hip dysplasia criterion: a retrospective cohort study

Background: The diagnostic and prediction criteria of residual hip dysplasia (RHD) remains controversial. There were no studies that focused on the risk factors of RHD after closed reduction (CR) in children with developmental dislocation of the hips (DDH) over 12 months of age. In this study, we assessed the percentage of RHD in DDH patients aged 12 to 18 months vs. that in DDH patients aged over 18 months after CR and determine the predictors of RHD. Meanwhile, we tested the reliability of our RHD criteria compared with Harcke standard. Methods: Patients over 12 months of age who underwent successful CR from October 2011 to November 2017 and followed up for at least 2 years were enrolled. Gender, affected side, age at CR and follow-up time were recorded. Acetabular index (AI), horizontal acetabular width (AWh), center-to-edge angle (CEA), and femoral head coverage (FHC) were measured. The cases were divided into two groups according to whether older than 18 months. RHD was determined according to our criteria. Results: A total of 82 patients (107 hips) were included, including 69 females (84.1%), 13 males (15.9%), 25 patients (30.5%) with bilateral DDH, 33 patients (40.2%) with left side, 24 patients (29.3%) with right side, 40 patients (49 hips) with age 12-18 months, and 42 patients (58 hips) with age >18 months. At a mean follow-up of 47.8 [24-92] months, the percentage of RHD was higher in patients >18 months of age (58.6%) than patients 12-18 months of age (40.8%), but the difference was not statistically significant. Binary logistic regression analysis showed that pre-AI, pre-AWh, and improvement in AI and AWh (P=0.025, 0.016, 0.001, 0.003, respectively) had significant difference. The sensitivity and specialty of our RHD criteria were 81.82% and 82.69%, respectively. Conclusions: For patients with DDH over 18 months, CR is still a choice. We documented four predictors of RHD, suggesting that we should focus on the developmental potential of an individual's acetabulum. Our RHD criteria may be one of the reliable and useful tools in clinical practice to help determine whether to perform continuous observation or surgery, but further research is needed due to limited sample size and follow-up time.