Title: Derivation and internal validation of a clinical decision rule to predict in newborns clinically important hip dysplasia at a minimum age of two years
Funder: Department of Health (England)

Abstract: Background: DDH is the most common congenital musculoskeletal disorder and may be responsible for as much as 25% of all osteoarthritis of the hip. Several risk factors for the development of DDH have been postulated but these have never been validated from basic principles, and their true clinical importance, as well as their interrelationship, remain uncertain. Consequently, the interpretation of risk factors differs by surgeon and centre with different protocols applied in defining cases subjected to ultrasound screening, followup and even treatment. There is a need to elicit robust risk factors, their interrelationship, and how these should be used in clinical practice. We commenced in 2010 a prospective cohort study to address these questions. In this research, we established a cohort of 2220 newborns and ascertained candidate risk factors and an intermediate imaging test, ultrasound at the age of 8 weeks. Because ultrasound is not considered as a definitive diagnostic test for this condition, we are seeking further funding to ascertain a robust, widely-accepted outcome, i.e. radiographic dysplasia at a minimum age of 2 years. Experts regard 2 years as adequate to establish the presenc­­­­­e of clinically important dysplasia, and the likelihood of a normal hip becoming abnormal beyond this age is remote. Aims: In infants less than 12 weeks old, identified at risk of DDH and varying in a number of characteristics, we will establish the incidence of clinically important dysplasia at ≥2 years. We will develop a clinical prediction rule to identify newborns at high risk of DDH at a minimum age of 2 years. Plan of investigation: 2220 children who have been recruited in a cohort study will be asked to return to hospital for a single appointment in a research clinic. The caregivers of 1889 newborns have already given written consent to be contacted for such research. Each participant will have 1 low-dose standardized pelvic radiograph taken to ascertain the primary outcome, acetabular index. Age-based cutoffs exist for this continuous outcome. We will define clinically important hip dysplasia as an acetabular index >20° at age ≥2 years because, in routine care, such a finding prompts clinical followup (or treatment if the index is higher) of the patient. Using a multivariable model we will examine potential risk factors (these have already been ascertained in each participant prospectively and in standardized fashion from 2010-2012) and develop a clinical decision rule to identify infants at risk of this particular outcome. We will internally validate the rule using bootstrapping techniques. The prediction rule that will be developed from this study will be externally validated and tested for its impact on patient care in a randomized trial performed at UCH and Royal Free NHS Trust. Potential benefits for patients: A clinical decision rule will allow clinicians of maternity and orthopaedic units to delineate high risk groups for DDH with a meaningful outcome, i.e. DDH at ≥2 years. Early identification of this group will potentially enable earlier-than-usual treatment or radiographic surveillance of high risk children, with the potential to preserve normal adult hip function. Valid and robust risk factors will be of particular importance in counselling parents by quantifying the risk of DDH given a certain combination of risk factors. This information will enable parents to make more informed decisions about possible management options, such as “wait & see” or early splinting.


Research activity codes: 4.2 EVALUATION OF MARKERS AND TECHNOLOGIES
Health categories: MUSCULOSKELETAL;REPRODUCTIVE HEALTH AND CHILDBIRTH