Why all newborn hip screening programs have same results—a mini review

All newborns are screened for developmental dysplasia of the hip (DDH), but countries have varying screening practices. The aim of this narrative mini review is to discuss the controversies of the screening and why it seems that all screening programs are likely to have same outcome. Different screening strategies are discussed alongside with other factors influencing DDH in this review. Universal ultrasound (US) has been praised as it finds more immature hips than clinical examination, but it has not been proven to reduce the rates of late-detected DDH or surgical management. Universal US screening increases initial treatment rates, while selective US and clinical screening have similar outcomes regarding late detection rates than universal US. This can be explained by the extrinsic factor affecting the development of the hip joint after birth and thus initial screening during the early weeks cannot find these cases. Conclusion: It seems that DDH screening strategies have strengths and limitations without notable differences in the most severe outcomes (late-detected cases requiring operative treatment). Thus, it is important to acknowledge that the used screening policy is a combination of values and available resources rather than a decision based on clear evidence.


Developmental dysplasia of the hip
Developmental dysplasia of the hip (DDH) is an umbrella term used in the literature to describe several newborn hip conditions [1].It includes early congenital dislocations, subluxations, loose hips, and in some cases clicky hips [1].The total pooled incidence estimates for early detected DDH were 23.0 per 1000 newborns among those with universal ultrasonographic screening, 4.4 per 1000 among those with selective ultrasonographic screening, and 8.4 per 1000 newborns with clinical screening [2].Typically, the newborn hips have been examined before discharge from the delivery hospital [3], yet there are many different screening strategies, and practices vary nationally and globally.In literature, the DDH is typically divided into early cases and late-detected cases [4].The typical cutoff for late detected has varied between 3 and 6 months [4,5].The late-detected cases require more intensive treatment than early cases, i.e., closed reduction and longer splinting or harness treatment is needed and late-detected cases are more often treated operatively in open reductions or osteotomies [6,7].
Untreated DDH leads to difficulties with moving and later promotes functional disability and early osteoarthritis [8].Therefore, the commonly accepted goal has been to recognize the DDH cases as early as possible [9,10].The aim of screening practice is to be effective in terms of clinical findings and economically.However, with DDH this has not been the case, as the universal ultrasonography (US) screening programs have not been shown more effective or cost-effective than selective or clinical screening programs [11][12][13].
In this narrative mini review, we aim to synthesize and describe why newborn DDH screening programs are unlikely to succeed perfectly in practice.

How are the newborn hips examined?
Clinical examination of the hip is performed by Ortolani and Barlow maneuvers which then are combined with clinical inspection of the asymmetry in the thighs and Galeazzi sign [14].The most used US methods for hip evaluation are dynamic US and Graf US [15].In the dynamic US, a posterior force is applied on the hip and the movement of the hip within the acetabulum or the change in the percentage cover can be measured.In the Graf US, the hip angles are measured, and the finding is then classified according to the scale (Table 1).The association between clinical screening findings and US findings has been weak [16].Different countries have varying patterns on how many times the hips are clinically examined, what ages the possible US examinations are performed, and what are the criteria for selective US.

Natural progression of DDH
As stated earlier, the term DDH has been used to describe a variety of hip conditions.Traditionally, it has been assumed that the development of prenatally dysplastic or luxated hip joint may be directed towards a normal hip joint development with early diagnosis and appropriate interventions after birth.The need of interventions is determined according to the initial hip joint condition assessed using clinical and/or ultrasound examination.This developmental model assumes that early started treatment leads to normalizing of pathological hips while normal hips at the beginning continue normal development.In reality, this would mean that universal US screening programs detect abnormal cases most efficiently and, thereby, have the lowest late-detection rates.However, according to previous literature, it seems that this is not the case.Indeed, the incidence of DDH has been found to be up to 69.5 per 1000 newborns at the US screening while only 4.8 per 1000 newborns requiring treatment, yielding that a majority of ultrasound-examined hips diagnosed as pathological will mature towards normal during the first weeks of life [17].Initially normal hips developed into normal hips, and no additional instances of DDH were found on follow-up [17].Thus, universal screening results into overtreatment of hips which would mature normally without any treatment.On the other hand, it has also been shown that some hips seem normal in the initial US examination but later require operative treatment despite the universal ultrasound screening [18].These findings challenge the traditional linear pathophysiological model of hip joint development.Instead, these findings suggest that also extrinsic factors have an effect on hip development after birth [19].

Factors associated to DDH
There are numerous factors which are found to be associated with DDH in previous literature.Breech presentation, female sex, a positive family history, oligohydramnios, postmaturity, high birthweight, and older maternal age, and swaddling of the baby are known to be associated to DDH [20][21][22][23].Other, less widely accepted risk factors are found to be multiple pregnancy, foot deformities, and torticollis [24,25].On the contrary, back-carrying has been connected to a lower incidence of DDH [26].In addition, it has been found that cold weather is a possible risk factor for DDH [27].The exact reason for this remains unknown, but tighter clothing or increased swaddling to protect the baby from the cold resulting in extension and adduction of the hips has been hypothesized as an explanation [27].

Costs, effectiveness and health care resources
In relation to clinical screening, US screening is an expensive process [28,29].However with the limited benefit of US screening of DDH, it could be used in high-risk areas or in areas with sufficient resources in health care but should not be globally recommendable.Before implementation of universal US to wider use, a more rigorous investigation of its benefits is required, as currently, the evidence does not promote the use of it.This can be explained by the extrinsic factor affecting the development of the hip joint after birth and thus initial screening during the early weeks cannot find these cases [17,18].Also, the late detection and operative treatment rates with universal screening were similar to those among selectively and clinically screened newborns [2].In addition, previous literature suggests, that the performance of DDH US screening examiners is highly related to the examiners' experience, the US screeners should be highly trained to gain the potential benefit from the screening [30], which is a challenging combination within countries with limited resources in the health care and education.

Conclusions
Hip screening strategies that focus on the first week or first month of life are likely to miss those cases that would develop into pathological hips due to extrinsic factors.Therefore, universal screening of DDH, especially using highly resource-consuming US, is a problematic concept in health care with limited resources.The possible US screening of DDH should only be focused on high-risk areas.The clinical examination and further examination with US could be addressed to newborns with known clinical risk factors.
As the universal screening of DDH appears to be a truly challenging concept, future studies should focus on better recognizing the risk factors and creating universal guidelines for the optimal targeted screening of newborns at high risk for DDH (Table 2).Presenting the causal pathways for potential risk factors in the analyses by for example using directed acyclic graphs.

Costs
Typically, the studies have not reported the cost of ultrasound screening in their setting.
Exact reporting of the costs of the screening programs per individual newborn.

Table 1
Simplified classification scale of developmental dysplasia of the hip (DDH) based on the alpha-angle, which is a measurement of the bony roof of the acetabulum in the Graf ultrasonography

Table 2
Considerations and recommendations on future studies More use of continuous age reporting at the time of the DDH diagnosis to provide a better estimation of variation in age.Study setting Too vague description of the screening process and how the screening results are handled.Exact description of the screening protocol and clear definitions of treatments were given.Risk factor studies Implementing risk factors without possible causality to DDH diagnosis to models and adjustments causes bias in estimations.