Residual Acetabular Dysplasia at Walking Age: A Study of 470 Hips Treated With Pavlik Harness

Background: This study aims to report on the acetabular indices of walking age children following successful DDH treatment with Pavlik harness and investigate risk factors for residual acetabular dysplasia (RAD). Methods: We retrospectively reviewed the data for children treated for DDH at a single centre between 2015 and 2020. Acetabular indices (AI) measured on pelvic radiographs taken at 2- and 4-year follow-up visits were referenced against age-matched and sex-matched normal data. Values ≥90th percentile were considered to represent RAD. Results: A total of 305 children with 470 hips were suitable for inclusion. The mean age at treatment initiation was 7.0±4.5 weeks and mean treatment duration was 15.9±4.3 weeks. Overall, 27% and 19% of hips were found to have RAD at 2- (n=448) and 4-year (n=206) follow-up, respectively. The χ 2 test for independence demonstrated that the difference in the proportion of hips with RAD at both time points was significant ( P =0.032). Patients with RAD at 2 years were found to have been treated for longer ( P =0.028) and had lower alpha angles on final ultrasound assessment ( P <0.001). Patients with RAD at 4 years were older at initiation of treatment ( P =0.041), had lower alpha angles on final ultrasound assessment ( P <0.001) and were more likely to have had RAD at 2 years ( P <0.001). Multivariate analysis identified lower alpha angles on final ultrasound to be predictive for RAD at 2 years ( P =0.011), and presence of RAD at 2 years to be predictive for RAD at 4 years ( P <0.001). Conclusions: The risk of RAD beyond walking age in children successfully treated with Pavlik harness is not negligible. However, we observed that a significant proportion of children with RAD at 2-year follow-up had spontaneously improved without any intervention. This data suggests that routine long-term radiologic follow-up of children treated with Pavlik harness is necessary, and surgical intervention to address RAD should be delayed until at least 4 years of age. Level of Evidence: Level III—case-control study.