Part-time Abduction Bracing in Infants With Residual Acetabular Dysplasia: Does Compliance Monitoring Support a Dose-dependent Relationship?

INTRODUCTION Residual acetabular dysplasia is often seen after successful Pavlik treatment or during follow-up for infants with risk factors for developmental dysplasia of the hip. A previous study supported the effectiveness of part-time abduction bracing for treating this residual dysplasia. However, the relationship between time in the brace and acetabular improvement was not established given the lack of compliance data. The purpose of this prospective study was to validate the effect of part-time bracing on acetabular dysplasia and determine if a dose-dependent relationship exists. METHODS Eligibility criteria included infants ~6 months of age with an AP pelvic radiograph demonstrating acetabular dysplasia, defined as an acetabular index (AI) ≥30 degrees. After obtaining informed consent, a rigid abduction orthosis was prescribed with a thermal compliance sensor. Patients were instructed to wear the brace for nights/naps and follow-up at 1 year of age for repeat radiograph. AIs were measured by the senior author who was blinded to the compliance data. Hours of wear were compared with changes in AI over the study period using descriptive statistics and a generalized estimating equation model. RESULTS Our series consisted of 26 infants (36 hips) with a mean age at enrollment of 5.9 months (range, 4.9 to 7.9); 84.6% were female individuals. At a mean follow-up of 6 months (range, 5.1 to 8.2), average wear time/day was 11.5 hours (range, 1.3 to 21.7), and total time in brace averaged 1698 hours (range, 218 to 3244 hours). The mean improvement in AI over the study period was 4.8 degrees (95% confidence interval, 3.9-5.5 degrees). The authors found a significant correlation between average hours of brace wear per day and improvement in AI (r=0.36, P<0.05), a relationship that remained significant in our multivariate model after adjusting for confounders. CONCLUSIONS Part-time abduction bracing is effective for treating residual dysplasia, with the degree of improvement in AI correlating with hours of brace wear per day. Given this dose-dependent relationship, the optimal hours of wear may depend on the severity of residual dysplasia and the tolerance of the child and family to bracing.