A cluster-based study on the epidemiology of developmental dysplasia of the hip (DDH) and implication of ultrasonography findings of capsular laxity

Introduction Developmental dysplasia of hip (DDH) is a major paediatric musculoskeletal problem that can cause lifelong disability if left untreated. Hong Kong currently adopts universal clinical assessment and selective ultrasound screening. This study aims to obtain a cluster-based epidemiology of DDH and to evaluate the effectiveness of the current screening system. It is also aimed to look for implication of capsular laxity and to propose optimal timing for first ultrasound. Methods Records of children referred to orthopaedics clinic in a major regional hospital for suspected DDH with ultrasound hips performed in 2017–2019 were reviewed. Patient demographics, ultrasound results, treatment and outcome of DDH were reviewed. Results Totally, 929 patients were referred with ultrasound hips done. Twelve of them were diagnosed with DDH. Another 2 patients presented late. The incidence of DDH in 2017–2019 was 0.89/1000 live births and delay diagnosis was 0.13/1000 live births. The open reduction rate was 0.19/1000 live births. Ninety-one patients had capsular laxity and normal follow-up ultrasound. Patients with capsular laxity were significantly younger than those without capsular laxity by Mann–Whitney U test. A statistically significant higher proportion of patients was found to have capsular laxity if first ultrasound was done before 6 weeks old ( p < 0.001). Conclusion The incidence of DDH in the studied cluster is comparable to local study published a decade ago. The current system is justified given the comparable results of late diagnosis and open reduction rate to other developed countries. Purely capsular laxity is benign ultrasonographic finding and 6weeks old is a reasonable time to perform the first ultrasound to prevent overdiagnosis of it.