Epidemiology and Screening of Developmental Dysplasia of the Hip in Europe: A Scoping Review

: Developmental hip dysplasia or developmental dysplasia of the hip (DDH) includes a wide range of deformities of the hip, such as congenital dysplasia, subluxation, and dislocation. It is usually identified through neonatal screening during the first 6–8 weeks of life. The incidence of DDH ranges from 1–7% in neonates among some populations, but this may vary among different ethnicities and countries. A consensus about the ideal age for screening has not been reached to date. The aim of this study is to summarize the existing data regarding the incidence of congenital hip dysplasia and screening tests among European countries. The authors conducted a systematic search in PubMed/Medline and Scopus and collected original studies published in English, French or German. The incidence of DDH presents fluctuations, not only among European countries, but also within the same country. There is no unanimity regarding the screening methods of DDH; in some countries, universal ultrasound is proposed as the basic screening method for neonates for DDH; in other countries screening is performed only in high-risk cases. More robust data are needed to conclude which screening approach is associated with improved long-term outcomes.


Introduction
Developmental dysplasia of the hip (DDH) describes a spectrum of conditions associated with the development of the hip in neonates and children.Laxity of the hip and immaturity of the acetabulum during the first few weeks of life is a normal finding; the laxity resolves, and the acetabulum develops normally.DDH encompasses numerous persisting alterations of the hip joint, ranging from dysplasia to real dislocation of the hip.The manifestations of DDH are variable; the femoral head can be within the acetabulum (enlocated), partially displaced (subluxated), or fully displaced from the acetabulum (dislocated) [1].
The differential diagnosis of DDH includes teratologic and neuromuscular hip dysplasia as well as other conditions such as proximal femoral deficiency [2].Typical DDH generally refers to otherwise healthy infants; however, hip dysplasia and instability may be related to other conditions.Teratologic hip dysplasia refers to hip dysplasia occurring in association with various conditions or syndromes such as arthrogryposis, etc. Neuromuscular hip dysplasia refers to hip instability and dysplasia occurring in association with conditions such as spina bifida or cerebral palsy, characterized by weakness or spasticity in some of the hip girdle muscles.A careful review of the infant's medical and family history helps to exclude other congenital or neuromuscular causes of hip instability, which is very important Reports 2024, 7, 10 2 of 19 since the management of the different forms of dysplasia in infants differs significantly [2,3].Important risk factors for DDH include female sex, family history of DDH, tight lower extremity swaddling, and breech presentation at ≥34 weeks of gestation regardless of the mode of delivery or a successful external cephalic version [4].Torticollis, plagiocephaly, metatarsus adductus, clubfoot, being the firstborn, oligohydramnios, birthweight > 4 kg, and multiple gestation pregnancy are also thought to be risk factors even though there is a lack of evidence to support these associations [5].Overall, breech presentation appears to be the most important risk factor, with the incidence of DDH reported up to 27% [6].
Timely diagnosis through the assessment of risk factors, physical examination, and the correct use of imaging techniques can lead to appropriate early treatment and therefore to the prevention of certain complications of DDH long-term sequelae, such as dislocation of the hip, avascular necrosis of the femoral head, and degenerative osteoarthritis.To date, a consensus regarding the ideal approach for screening has not been reached [3].
Across the globe and particularly in Europe, there are different screening programs at national level.This can be explained by the lack of universal instructions regarding the screening methods for DDH.Screening recommendations for DDH vary significantly from country to country.Some bodies recommend screening of all infants, whereas others recommend screening of high-risk children [7].
The age at which screening is performed as well as the screening approach (clinical examination, ultrasonography, risk stratification) also vary between different countries.For example, in the German-speaking countries and Italy, screening with ultrasound is performed at an early age, usually at 6-8 weeks of life.Of note, in German-speaking countries, Graf's practice is part of new-born screening for DDH.In more detail, the hip is evaluated by measuring two angles, the alpha angle (α) and the beta (β) angle.They are made by three lines, drawn from the acetabular lateral edge, the bottom of the acetabulum, and the acetabular labrum.These lines have to be noted down in order to determine the bony roof angle (known as the α angle) and the cartilage roof angle (known as the β angle).In a centered hip, an angle is normally more than 60 • , and the beta angle less than 55 • [1].In The Netherlands, screening with ultrasound is recommended for infants at the age of three months when risk factors have been reported, or earlier if clinical instability of the hips is ascertained during physical examination, which is performed at one week, one month, and three months of age.Generally, it is preferable not to perform ultrasound before six weeks of life unless there is clinical instability in the hips, due to the laxity of neonatal hips, which resolves by six weeks of age [3,4].The literature is limited regarding the epidemiology of DDH in certain parts of Europe, particularly in Greece, the Balkans, as well as in eastern and southern Europe.It is reasonable to assume that the lack of evidence, partially, stems from the discrepancies between national screening programs and relevant diagnostic criteria and tools [7].
In the absence of consensus regarding screening programs for DDH among European countries, a systematic review summarizing the existing evidence and highlighting the knowledge and practice gaps in the field is relevant.Commissions consisting of orthopedics, pediatricians, and obstetricians from different European countries could benefit from such results to design guidelines for DDH screening programs for Europe.The objectives of our study were to summarize the existing knowledge regarding the epidemiology and the screening programs in the region of Europe and indicate relevant knowledge gaps.

Materials and Methods
To identify relevant peer-reviewed publications and gray literature, the authors searched PubMed/Medline, Embase, and the Cochrane Library/Cochrane Central Register of Controlled Trials (CENTRAL) up until 15 October 2022.The reference lists of the selected sources and relevant systematic reviews were also manually searched to identify potentially relevant resources.The search terms "Developmental Dysplasia of the Hip" [MeSH], "Screening" [MeSH], "epidemiology [Subheading]", "Europe" [MeSH], and "Europe Eastern" [MeSH] were used in combination with Boolean operators (AND, OR), when appropriate.Studies were included if they fulfilled all of the following eligibility criteria: (1) ongoing or published clinical studies reporting on DDH epidemiology and/or screening methods and programs in the WHO Europe region and/or the European Union, and (2) epidemiological analyses and reports.A study was excluded if it met at least one of the following criteria: (1) non-English, French, or German publication language in order to be more familiar with the used language (members of the research team can speak all three languages), (2) opinion article, perspective, or letter to the editor, (3) focuses on different region(s), and (4) no "Congenital Dislocation of the Hip" was used in the search terms, since it is an older definition.No sample size restriction was applied when screening for eligible studies.Disputes in the selection of relevant studies were discussed between the two primary authors and a senior author until a consensus was reached.The literature was searched and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) extension for Scoping Reviews (PRISMASc) (Figure 1) [8].2) epidemiological analyses and reports.A study was excluded if it met at least one of the following criteria: (1) non-English, French, or German publication language in order to be more familiar with the used language (members of the research team can speak all three languages), (2) opinion article, perspective, or letter to the editor, (3) focuses on different region(s), and (4) no "Congenital Dislocation of the Hip" was used in the search terms, since it is an older definition.No sample size restriction was applied when screening for eligible studies.Disputes in the selection of relevant studies were discussed between the two primary authors and a senior author until a consensus was reached.The literature was searched and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) extension for Scoping Reviews (PRIS-MASc) (Figure 1) [8].

Results
During the initial review of the literature, 343 studies were identified, and 271 studies were excluded.From the remaining ones, 26 concerned the epidemiology of DDH, 21 focused on DDH screening and 25 concerned both the epidemiological and screening aspects of DDH in the European region.The oldest study was conducted back in 1964, and the most recent was conducted in 2020.A detailed overview of the included studies and their key outcomes is presented in Table 1.

Epidemiological Studies
The incidence of DDH in Europe ranged from 0.59 per 1000 live births to 27.53 per 1000 live births, which was the maximum limit of incidence of DDH in Europe, observed in Hungary.Furthermore, incidence also ranged significantly in Greece, especially in Crete, as it was reported to be 10.83 per 1000 live births [9][10][11].Differences in the rates of DDH can be observed not only among different countries in Europe, but also between different areas in the same country; for example, the incidence of DDH diagnosed in newborns varied between three hospitals in Northern Sweeden.The incidence was 10.0, 7.1, and 3.5 per 1000 live births in different hospitals [12].Unfortunately, very few epidemiological studies have examined the incidence of DDH, and due to the insufficient data, we cannot draw general conclusions regarding the incidence of DDH in Europe [7].
The effects of certain risk factors were also studied regarding their association with the development of DDH, namely, multiple pregnancies, increased gestational age, birthweight, and experience/competence of the physician in performing the neonatal screening tests for DDH.Rühmann et al. observed a correlation between heredity and breech presentation and the need for open procedures for DDH [13].
Rosendahl et al. concluded that breech presentation during birth appeared to be a significant risk factor affecting females only and having a sibling or a parent with DDH was a more significant risk factor for the appearance of DDH than having a second-or third-degree relative with DDH [14].

DDH Screening
There is no consensus regarding the appropriate screening methods for DDH in Europe or the age at which screening should be performed.Most studies recommend sonographic and/or clinical assessment as a screening tool.Krikler et al. conducted a comparative study at the Royal Orthopedic Hospital in the UK and concluded that screening can be effective, provided that all newborns are screened at birth and cases with risk factors are followed up by a trained team with an appropriate follow-up protocol and supervised by an orthopedic surgeon [15].A study from Norway that aimed to examine the impact of adding an ultrasound examination to the screening strategy showed that the treatment rate was doubled (non-operative) without influencing the already low numbers of latediagnosed cases [16].Laborie et al. conducted a randomized trial regarding the use of universal ultrasound; ultrasound use increased the early diagnosis of DDH to a nonstatistically significant level; however, in the long-term this was not clinically significant as it did not influence the frequency of chronic complications of the disease [17].A study by Čustović et al. also appears to be in favor of a simple clinical examination; it was shown that unilateral limited hip abduction could a valuable clinical sign of DDH (positive predictive value = 40.3%and negative predictive value = 80.4%), which could be used for diagnostic purposes [18] There has been, however, contradictory evidence regarding the effectiveness of DDH screening with a simple clinical examination, as many cases of DDH still remain undiagnosed when using this approach [7].Reidy et al. investigated the screening effectiveness of the hip examination at 6-8 weeks, performed by a general practitioner, and found that the sensitivity of examination was only 19.4%, as well as that four of five children with DDH remained undiagnosed [19].Two studies from Germany and one from Wales concluded that the universal use of ultrasound for screening purposes reduced the rate of open surgery for DDH [20][21][22].Günther et al. also confirmed the effectiveness of universal ultrasound screening for DDH in Germany [23].
Engesaeter et al. pointed out that only a small percentage, 8% of those who underwent total hip arthroplasty due to hip dysplasia, were reported to have it at birth, concluding that clinical testing for neonatal hip dysplasia is insufficient by itself as a screening method for dysplastic hips that require total hip arthroplasty in young adulthood [24].In this context, Elbourne et al. recruited infants with clinical hip instability from 33 centers in the UK and Ireland and randomized them to undergo either ultrasonographic hip examination or clinical assessment alone.They showed that the use of ultrasonography reduced abduction splinting rates and was not associated with higher rates of surgical treatment by 2 years of age or significantly higher health-service costs [25].
The use of ultrasound in selected groups has also been proposed.Salut et al. suggested the use of ultrasound for a high-risk group, namely 30-day-old female neonates [26].However, ultrasonography can also present certain limitations; Muresan et al. found that the most frequent stage of DDH detected through ultrasound was type IA, and the rarest stage was III.The incidence of hip dysplasia stage III diagnosed through ultrasound examinations in the central region of Romania was 0.2% [27].
As far as radiography is concerned, it seems not to be preferred as a screening tool.Nevertheless, it could be used in the context of screening at four months of age for babies at increased risk of DDH who had been normal at birth [28].Wenger et al. examined the radiographic outcomes at 1 year of life in newborns undergoing early treatment for neonatal hip instability.It was found that even in newborns who are diagnosed and treated, the radiographic differences may remain after 1 year of life [29].
The above results reflect the reality that exists in Europe regarding DDH epidemiology and screening.The incidence of DDH in Europe presents fluctuations in different countries [7].As mentioned above, the incidence of DDH in Europe ranged from 0.80 per 1000 live births to 27.53 per 1000 live births.The incidence of late diagnosis was low, probably due to raised awareness regarding the timely diagnosis of DDH.For instance, the incidence of late diagnosis was 1.28 per 1000 live births in Southampton, during the period 1990-2016 [30].Multigravidae and similarly multiparous women had a statistically significantly reduced risk of having a baby with CDH.Babies born by Caesarean section or in breech position had an increased risk of CDH (statistically significant).Cases were more likely to have a family history of CDH than subjects who were screened but found to be normal

Discussion
In this systematic review, the authors examined the available literature regarding the incidence and screening of DDH, focusing on the European region.However, the current situation in other continents appears to be similar.
There is no agreement regarding the optimal timing for ultrasound screening for DDH among European countries [7,75].This results in a wide variation of screening practices in the European area, due to different healthcare systems as well as the difference in DDH incidence amongst European countries.Ultrasound screening is performed for all neonates in Italy, Germany, and Austria.On the other hand, in The Netherlands, ultrasound screening is selective and is performed at the age of three months in case of risk factors, or earlier in case of instability of the hips during the clinical examination performed at the age of one week, one month, or three months [76].
Kilsdonk et al. presented in summary different screening programs throughout Europe for the detection of DDH in neonates.It was found that a selective ultrasound screening program is performed in The Netherlands, Belgium, France, Sweden, Norway, Hungary, the United Kingdom, Ireland, and Portugal.Ultrasounds are conducted as early as one week of life, for example, in the Scandinavian countries, or later until four weeks of life, for example, in France [76].In the UK, the NIPE guidelines recommend a clinical examination of the hip for all neonates, followed by a clinical examination at 6-8 weeks of life and referral for an US only in the case of risk factors [77].
A universal screening program is performed in Italy, Germany, Austria, Switzerland, Slovenia, and Slovakia.In Italy, an US is performed between four and twelve weeks of life, whereas in Germany and Slovenia, the timing depends on the presence of risk factors; in case of them, an US is performed as early as two weeks of life; otherwise, it is performed between four and five weeks of life.In Slovakia, an US is performed between one to twelve weeks of life [76].In reviewing the existing literature, it can be assumed that the method of screening for DDH depends on neonatal age; for example, hips that are Barlow-positive at birth, may become stable in the first weeks of life, as the normal laxity of the hips due to maternal estrogens will be reducing [78].
The incidence of DDH in Europe seems to be much higher than in Africa and Israel and similar to that in Native Americans.In Africa, the incidence of DDH ranges from zero in Malawi to 0.15% in Ethiopia, generally lower than in Europe.A lower incidence may be attributed to the lack of diagnostic means or to limited access to healthcare facilities.Nevertheless, biological and environmental factors should also be considered; Graham et al. (2015) found out that DDH is rarely found among the Sub-Saharan African population [79].Most mothers in Malawi back carry their babies during the first two years of life, in a position that is similar to that of the Pavlik harness.This could also contribute to the very low incidence of DDH in this country.Eidleman et al. conducted a 7-year prospective study (34,048 newborns were examined clinically and with US, 768 of whom were Ethiopian) and concluded that the incidence of DDH was 5.5% among the total Israeli population and 1.24% in Ethiopian Jews [80].
The incidence of DDH was found to be lower in Asia than in Europe.Den et al. estimated the incidence of DDH in Japan at 0.076%.In Hong Kong, the prevalence of DDH was also at a low level: 0.87/1000 live births [81,82].
The incidence of DDH was found to be quite high in Native Americans, likely due to genetic factors.In Arizona Fort Apache Indians, the incidence was 31 per 1000 live births, probably due to endogamy and therefore a very limited variety of genes.In Fort Defiance, Arizona and Gallup, New Mexico, the incidence was estimated to be 67 per 1000 live births [83].
Certainly, the differences in DDH prevalence can also be attributed to a difference in diagnostic protocols across countries and continents.The American Academy of Pediatrics (AAP) and the DDH Task Force of Canada suggest clinical examination of newborns as a screening method for the detection of DDH mainly using the Ortolani test, and generally, the AAP does not recommend universal ultrasonographic screening [3,84].Ultrasound is recommended for the ages of 6 weeks and 6 months for newborns with risk factors, including breech presentation, a positive family history, and female sex.The AAP suggests that most minor abnormalities of the hip, which are observed with ultrasonography at 6 weeks until 4 months, will retreat.The same approach regarding DDH screening is implemented in Asia.For example, in Hong Kong, universal physical examinations and selective ultrasounds are performed [82].
More awareness regarding DDH screening should be raised as it can lead to impaired functional outcomes in both children and adults.However, there is no direct proof that screening enhances functional outcomes, and the evidence supporting this is generally insufficient.According to expert opinion, early intervention is believed to be beneficial, although the evidence is mixed.Delayed diagnosis is associated with a higher likelihood of requiring surgical intervention and a higher rate of complications [7].Despite the lack of strong evidence supporting its effectiveness in improving outcomes, universal screening for DDH is a well-established approach to addressing the disorder.However, the specific methods of screening vary significantly.Alongside physical examination techniques like the Barlow and Ortolani techniques and assessments of the hip abduction range of motion, static and dynamic ultrasound can be utilized to identify anatomical abnormalities and assess hip stability [7].
Some experts have suggested using risk stratification to guide the selective use of ultrasound in diagnosing DDH.It has been observed that females in breech positioning during delivery have the highest rate of clinical hip instability [1,2].However, the effectiveness of ultrasound as a diagnostic tool for those with risk factors becomes less certain.Some healthcare systems have opted for universal ultrasound screening to reduce instances of late DDH diagnosis [7].Utilizing ultrasound to further evaluate hips that exhibit instability during clinical examination may decrease the need for unnecessary treatment.However, it may also lead to a higher number of follow-up appointments for hips that ultimately normalize on their own.The reliability of ultrasound in classifying DDH is uncertain.There are potential drawbacks to screening for DDH, including the possibility of examiner-induced hip problems due to vigorous testing, increased risk of certain cancers from radiation exposure during follow-up radiographic tests, and parental psychosocial stress caused by the diagnosis and treatment [7].However, none of these potential harms have been accurately quantified.
To our knowledge, this is the second study that has systematically reviewed the epidemiology and screening of DDH, and the first that specifically refers to the situation in Europe.The adaptation of a broad search and reference-screening strategy are strengths of this literature review.The limitations include that a language criterion was applied, resulting in the exclusion of potentially relevant papers as well as a significant heterogeneity of the studies that were included in our review.Furthermore, no "Congenital Dislocation of the Hip" was used in the search terms, since it is an older definition and there is no other in use.This could be a limitation to our study, but the literature with the term DDH is more recent.

Conclusions
The incidence of DDH presents fluctuations, not only among European countries, but also between different regions within the same country.Despite certain limitations in the existing body of literature, recent studies have offered valuable data regarding DDH screening.To establish an evidence-based approach for screening at the most appropriate time, a deeper understanding of the natural progression of hip instability and dysplasia, including spontaneous resolution, is necessary.Given the rarity of DDH, it is essential to conduct multicenter studies that evaluate interventions and measure functional outcomes in a standardized manner.It would be beneficial to conduct studies specifically aiming to identify reliable radiologic markers that accurately predict functional outcomes.In any case, the sensibilization of obstetric care specialists is essential.Identifying pre-and perinatal risk factors for DDH and referral to a multidisciplinary team comprised of a neonatologist

Figure 1 .
Figure 1.Flow diagram showing the numbers of titles and abstracts identified and screened and the full-text research papers assessed for eligibility and included in the qualitative synthesis.The

Figure 1 .
Figure 1.Flow diagram showing the numbers of titles and abstracts identified and screened and the full-text research papers assessed for eligibility and included in the qualitative synthesis.The included databases were (*) PubMed/Medline, Embase, the Cochrane Library/Cochrane Central Register of Controlled Trials (CENTRAL).

Table 1 .
Studies concerning the epidemiology and screening of DDH that were included in the systematic review.