Revisiting selected risk factors and their association with ultrasonographic hip types in developmental dysplasia of the hip: a multivariate regression analysis

Abstract

Background

Developmental dysplasia of the hip (DDH) presents a diagnostic challenge due to varying risk factors (RFs) and ultrasonographic (USG) classifications. This study aimed to identify independent RFs for DDH and evaluate their association with USG hip types in a large pediatric cohort.

Methods

A retrospective review was conducted on infants under six months of age from a tertiary DDH screening program (2008–2022). The study included 227 cases with DDH and 924 controls with normal hips. Univariate and multivariate logistic regression analyses were performed to assess the association of RFs with DDH and USG hip types (stable dysplastic vs. unstable hips).

Results

Female sex (OR: 2.518), breech presentation (OR: 1.817), oligohydramnios (OR: 2.762), and foot deformities (OR: 2.262) were identified as independent RFs for DDH. Firstborn girls were significantly more likely to exhibit unstable hips (OR: 1.889, p = 0.027), underscoring their predisposition to severe forms of DDH.

Conclusion

This study highlights the importance of early USG screening for infants with critical risk factors, including female sex, breech presentation, oligohydramnios, and foot deformities. Notably, firstborn girls with DDH exhibit a significantly higher risk of unstable hips, emphasizing the need for targeted screening in this high-risk subgroup.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-025-06426-6.

Introduction

Developmental dysplasia of the hip (DDH) is the most common neonatal musculoskeletal condition, characterized by a spectrum of abnormalities ranging from acetabular dysplasia to hip dislocation [1, 2]. The reported incidence of DDH varies considerably across different geographic regions, with studies documenting rates between 0.7 and 10.8 per 1,000 live births [3]. These variations are attributed to differences in diagnostic criteria, geographic factors, and screening strategies, as countries employing universal ultrasound screening tend to report higher detection rates compared to those utilizing selective screening protocols based on risk factors (RFs) [3, 4].

Hip ultrasonography (USG) has become the gold standard method for diagnosing and monitoring DDH in infants under six months of age. As an essential component of early orthopedic screening, it has gained widespread acceptance in routine clinical practice. While some countries perform hip USG for all infants in the context of a universal newborn hip screening program, others implement selective hip USG screening for children with RFs or suspicious clinical findings [4, 5]. Graf’s method for infant hip USG, the earliest and probably most commonly used technique, successfully addresses newborn hip problem when its protocol for examination, interpretation, and measurement protocols are rigorously followed [4].

Although the exact etiology remains unclear, several causative or coexisting conditions have been described as RFs in the DDH pathogenesis [1, 6–8]. A recent large-scale meta-analysis by Tirta et al. (2025) [9] confirmed female sex, breech presentation, oligohydramnios, family history, and high birth weight as significant RFs for DDH, reinforcing their relevance in current screening practices. However, despite these associations being well established, our literature review indicates that conflicting results persist regarding their relationship with DDH, likely due to heterogeneity in study designs and patient populations. This knowledge gap is particularly critical for healthcare systems that employ selective screening protocols, where accurate identification of high-risk infants is essential. Our study was therefore designed to revisit these selected causative and coexisting factors in a large cohort to clarify their association with DDH development and support evidence-based refinements in screening strategies.

Furthermore, infants diagnosed with sonographically dislocated hips face an increased failure risk of brace treatment, highlighting the critical importance of the initial USG type of DDH in predicting outcomes of conservative therapy. To our knowledge, only one study by Ömeroğlu et al. drew attention to this issue and analyzed the relationship between selected RFs and USG hip type in DDH [10]. This issue should be re-addressed to clarify the extent of correlation between USG hip types and RFs, potentially guiding improved screening and therapeutic strategies.

The primary aim of this retrospective case-control study was to reevaluate the relationship between previously identified RFs and the development of DDH through univariate and multivariate analyses in a large cohort series. The secondary aim was to investigate the relationship between Graf’s DDH types and selected RFs, which was classified as stable dysplastic and unstable decentralized hips in children with DDH. By bridging the gap between RFs and USG findings, this study aims to provide novel insights into DDH pathogenesis and guide more effective screening and therapeutic strategies.

Patients and methods

A retrospective analysis was performed on a single-centre database from the universal neonatal hip screening program administered by a tertiary referral university hospital’s Department of Orthopaedics and Traumatology during the study period (2008–2022). This retrospective study utilized anonymized data from the institutional universal neonatal hip screening program. Written informed consent for the use of anonymized clinical data in future research was routinely obtained from parents/legal guardians at the initial screening visit. Therefore, no additional prospective consent was required, and no patients declined participation. The study was conducted in accordance with the ethical standards of the Declaration of Helsinki and was approved by the institutional ethics committee (Istanbul University Istanbul Faculty of Medicine Clinical Research Ethics Committee; approval number: 2025/1182).

A comprehensive medical history for DDH was obtained from the infants’ parents by the residents specializing in orthopaedics and trauma surgery before the ultrasonographic hip examination. The following variables were defined and recorded as ‘’RFs associated with DDH’’: sex, firstborn girl, birth weight, multiparity, twin pregnancy, type of delivery (caesarean or vaginal), a family history of DDH in first or second-degree relatives, breech presentation in the third trimester, history of oligohydramnios (diagnosed by an obstetrician), history of postnatal traditional swaddling (wrapping the infant for a certain duration with the hips in adduction and extension and knees in extension), and foot deformities such as idiopathic or postural club foot, pes calcaneovalgus, and metatarsus adductus. Birth weight was categorized as low (< 2500 g), normal (2500–4000 g), and high (> 4000 g). Prematurity was defined as birth before 37 weeks’ gestation, and postmaturity as birth after 42 weeks’ gestation. Analyzed RFs were obtained from the standardized screening files of our DDH program. These factors were defined based on the existing literature and are routinely used in clinical practice.

All ultrasonographic hip examinations were performed on both hips of each child using a standardized protocol based on the Graf method [11] by experienced pediatric orthopaedics surgeons or under their supervision (Fig. 1). Alpha and beta angles were measured on ultrasonographic image printouts using the same specialized hip USG goniometer, and all the hips were then categorized as per the Graf’s hip ultrasonography classification system [11]. The methodology for this study included following two parts.

Fig. 1.

Representative ultrasonographic image showing measurement of alpha (α) and beta (β) angles according to Graf’s method [11]. The base line (1) originates from the uppermost point of the proximal perichondrium and runs caudally tangential to the iliac bone. The bony roof line (2) extends from the inferior border of the lower limb tangentially to the bony roof. The cartilage roof line (3) connects the bony rim to the center of the labrum. The α angle is measured between lines 1 and 2, and the β angle between lines 1 and 3

Part 1: comparison of risk factors between study and control groups

The control group included healthy consecutive infants with bilateral mature Graf type I (normal) hips under six months of age, whereas the study group was composed of consecutive infants who underwent any abduction brace treatment because of unilateral or bilateral DDH (Graf type IIa [-] and worse) under six months of age. The exclusion criteria were: (i) children over 6 months old, (ii) infants with neuromuscular or teratologic hip dislocation, or (iii) those who had received prior treatment for dysplasia or dislocation.

Part 2: comparison of risk factors between stable dysplastic and unstable decentralized groups

The abnormal hips on USG examination were categorized as “stable dysplastic hips” (Graf types IIa [-], IIb, IIc) and “unstable (decentralized) hips” (Graf types D, III, IV) [11]. Unilateral or bilateral stable dysplastic hips were included in the ‘stable dysplastic group’, while unilateral or bilateral unstable hips were included in the unstable group. Infants with bilateral DDH who had a stable hip on one side and an unstable hip on the other side were included in the unstable group Figure 2.

Fig. 2.

Shows the flowchart of the study

Statistical analysis

All statistical analyses were performed using SPSS software (version 29, Armonk, NY: IBM Corp.). Statistical significance was set at P < 0.05. Normality tests were conducted using the Shapiro–Wilk test and histogram graphics. Data are presented as “arithmetic mean” ± " standard deviation (SD)” and “range” from “minimum” to “maximum” or “median” (interquartile range) and “minimum” to “maximum” based on the data distributions. In univariate analysis, between-group comparisons of parametric data were conducted utilizing paired sample t-test for normally distributed variables and the Mann-Whitney U test for non-normally distributed ones. Comparisons of categorical data were undertaken using the Fisher exact test or the Chi-square test. A binary multivariate logistic regression analysis using the backward stepwise method was performed to identify the RFs significantly associated with DDH by systematically removing non-significant variables and minimizing overfitting in models with multiple predictors. Only variables that were statistically significant (p < 0.05) in univariate analysis were included in the multivariate logistic regression models. Additionally, a subgroup analysis was performed within the unstable hips (Graf D, III, IV) to compare the proportion of firstborn girls using Fisher’s exact test. Metatarsus adductus, pes equinovarus, and calcaneovalgus were collectively categorized as ‘foot deformities’ in the statistical analyses.

Results

Part 1: comparative analyses of RFs between study and control groups

Three cases of torticollis (2 in the control group and 1 in the study group) were excluded from the analysis due to their low frequency. The study group included 227 children with DDH, while the control group consisted of 924 children with normal bilateral hips. Female sex was strongly linked to DDH, with more girls in the study group (n = 178, 78%) compared to the control group (n = 558, 60%; p < 0.001). Conversely, boys were less represented in the study group (n = 49, 22%) compared to the control group (n = 366, 40%). Being a firstborn girl was also significantly related to DDH (p < 0.001). Breech presentation (p = 0.034) and oligohydramnios (p = 0.02) were found to be associated with the development of DDH. Foot deformities, such as clubfoot or metatarsus adductus, were more common in the study group than in the control group (10% vs. 6%, p = 0.015) (Table 1). Among the 23 infants with foot deformities, 9 had metatarsus adductus, 7 idiopathic clubfoot, and 6 pes calcaneovalgus, and 2 postural clubfoot. Additionally, the mean birth weight did not differ significantly between the stable and unstable groups (3109.50 ± 623.30 g vs. 3211.72 ± 680.84 g, p = 0.15). When categorized as low (< 2500 g), normal (2500–4000 g), and high (> 4000 g), no overall difference was observed among the groups (p = 0.245). Pairwise comparisons with Bonferroni correction likewise revealed no significant differences between specific subgroups (low vs. normal, p = 0.38; low vs. high, p = 0.62; normal vs. high, p = 0.47), indicating that birth weight was not associated with DDH severity.

Table 1.

Univariate analyses of the impact of risk factors on the development of DDH in the overall study population

Risk factors	Control group (n = 924)	Study group (n = 227)	P values
Age on DDH diagnosis (months, mean ± SD)	2.96 ± 1.50 (95% CI: 2.86–3.05)	2.92 ± 1.45 (95% CI: 2.73–3.11)	0.378
Sex (number, %)
Girl	558 (60%)	178 (78%)	< 0.001*
Boy	366 (40%)	49 (22%)
Firstborn girl (number, %)	244 (26%)	84 (37%)	< 0.001*
Gestation period at delivery (weeks, mean ± SD)	38.17 ± 2.39 (95% CI: 38.01–38.32)	38.27 ± 2.07 (95% CI: 38–38.54)	0.279
Maternal age (years, mean ± SD)	29.08 ± 5.23 (95% CI: 28.75–29.42)	28.70 ± 5.28 (95% CI: 28.01–29.39)	0.162
Birth weight (grams, mean ± SD)	3109.50 ± 623.30 (95% CI: 3069.26–3149.75)	3211.72 ± 680.84 (95% CI: 3122.67- 3300.76)	0.15
Birth weight category
Low (< 2500 g)	112 (12%)	20 (9%)	0.245
Normal (2500–4000 g)	787 (85%)	198 (87%)
High (> 4000 g)	25 (3%)	9 (4%)
Laterality (number, %)
Unilateral DDH		168 (77%)
Bilateral DDH		52 (23%)
Affected side of unilateral DDH (number, %)
Left		48 (21%)
Right		127 (51%)
Breech presentation (number, %)	55 (6%)	22 (10%)	0.034*
Family history (number, %)	28 (%3)	3 (%1)	0.249
Oligohydramnios (number, %)	14 (%2)	9 (%4)	0.02*
Prematurity (number, %)	117 (13%)	26 (12%)	0.357
Postmaturity (number, %)	11 (1%)	4 (2%)	0.513
Multiparity (number, %) Primipara Multipara	405 (44%) 519 (80%)	103 (45%) 124 (55%)	0.365
Twin pregnancy (number, %)	41 (4%)	5 (2%)	0.082
Type of delivery (number, %) C-section Vaginal	570 (62%) 354 (38%)	131 (58%) 96 (42%)	0.153
Foot deformities (number, %)	53 (6%)	23 (10%)	0.015*
Pathologic USG examination (number, %)
Stable dysplastic hips		138 (61%)
Unstable hips		89 (39%)

*Low birth weight: <2500 g; Normal birth weight: 2500–4000 g; High birth weight: >4000 g. Prematurity: <37 weeks’ gestation; Postmaturity: >42 weeks’ gestation

Variables found to be significantly associated with DDH in the univariate analysis were included in the multivariate logistic regression model. The analysis identified female sex (OR = 2.518, p < 0.001), breech presentation (OR = 1.817, p = 0.028), oligohydramnios (OR = 2.762, p = 0.023), and foot deformities (OR = 2.262, p = 0.003) as significant independent predictors of DDH (Table 2).

Table 2.

Multivariate binary logistic regression analysis of the predictive value of risk factors in the diagnosis of developmental dysplasia of the hip

	Parameter estimate β	OR (95% CI)	p value
Female sex	0.92	2.52 (1.78–3.57)	< 0.001*
Breech presentation	0.60	1.82 (1.07–3.10)	0.028*
Oligohydramnios	1.02	2.76 (1.15–6.64)	0.023*
Foot deformities	0.82	2.26 (1.33–3.84)	0.003*

^*Variables included in the multivariate analysis: Female sex, breech presentation, oligohydramnios, foot deformities, and firstborn girl OR, odds ratio; CI, confidence interval

*The statistically significant level was set at p < 0.05.

Part 2: comparative analyses of risk factors between stable dysplastic and unstable decentralized groups

In the univariate analysis, several RFs demonstrated statistically significant differences between the stable dysplastic and unstable decentralized groups. The proportion of firstborn girls was significantly higher in the unstable group (46%) compared to the stable dysplastic group (31%) (p = 0.033). Laterality also revealed significant differences, with bilateral DDH being more frequent in the unstable group (29%) than in the stable group (19%) (p = 0.049). In contrast, sex distribution did not differ significantly between the groups, as the proportion of girls was similar (78% vs. 79%, p = 0.95). Regarding the affected side in cases of unilateral DDH, right-sided involvement was more prevalent in the unstable group (61%) compared to the stable group (47%) (p < 0.001). Additionally, the presence of oligohydramnios was marginally more frequent in the unstable group (5%) compared to the stable group (4%), reaching statistical significance (p = 0.038). No statistically significant differences were found for other perinatal variables, including gestational age, maternal age, birth weight, or the presence of foot deformities (p > 0.05) (Table 3).

Table 3.

Univariate analyses of risk factors between stable dysplastic and unstable decentralized groups in children with developmental dysplasia of the hip

Risk factors	Stable dysplastic group (n = 138)	Unstable decentralized group (n = 89)	P values
Age on DDH diagnosis (months, mean ± SD)	3.02 ± 1.55 (95% CI: 2.76 − 3.29)	2.77 ± 1.29 (95% CI:2.49–3.04)	0.96
Sex (number, %)
Girl	108 (78%)	70 (79%)	0.95
Boy	30 (22%)	19 (21%)
Firstborn girl (number, %)
Present	43 (31%)	41 (46%)	0.033
Absent	95(69%)	48(54%)
Gestation period at delivery (weeks, mean ± SD)	38.32 ± 1.75 (95% CI: 38.02–38.61)	38.19 ± 2.50 (95% CI:37.66 − 38.72)	0.326
Maternal age (years, mean ± SD)	28.85 ± 5.19 (95% CI: 27.97–29.72)	28.47 ± 5.44 (95% CI:27.33 − 29.62)	0.301
Birth weight (grams, mean ± SD)	3240.80 ± 724.759 (95% CI: 3118.80 − 3362.80)	3166.63 ± 607.722 (95% CI:3038.61 −3294.65)	0.212
Laterality (number, %)
Unilateral DDH	112 (81%)	63 (71%)	0.049
Bilateral DDH	26 (19%)	26 (29%)
Affected side of unilateral DDH (number, %)
Left	47 (34%)	9 (10%)	< 0.001
Right	65 (47%)	54 (61%)
Breech presentation (number, %)	12 (8%)	9 (11%)	0.64
Family history (number, %)	3(2%)	0(0%)	0.28
Oligohydramnios (number, %)	5(4%)	4 (5%)	0.038
Prematurity (number, %)	16(12%)	10 (11%)	0.55
Postmaturity (number, %)	3(2%)	1(1%)	0.48
Multiparity (number, %) Primipara Multipara	56 (40%) 82(60%)	47 (53%) 42 (47%)	0.077
Twin pregnancy (number, %)	1 (1%)	4 (4%)	0.79
Type of delivery (number, %) C-section Vaginal	79 (57%) 59 (43%)	52 (58%) 37 (42%)	0.89
Foot deformities (number, %)	12(9%)	11 (12%)	0.37

The variables identified as significant in the univariate analysis—firstborn girl, and oligohydramnios—were included in the multivariate binary logistic regression model to assess their independent predictive value for unstable hips. In the final step (Step 2), only the variable “firstborn girl” remained statistically significant, with an odds ratio (OR) of 1.620 (95% CI: 1.065–3.3358, p = 0.045). This finding highlights the independent role of being a firstborn girl as a predictor for unstable hips (Table 4).

Table 4.

Multivariate binary logistic regression analysis of the predictive value of risk factors in the diagnosis of unstable hips

	Parameter estimate β	OR (95% CI)	p value
Firstborn girl	0.28	1.62 (1.07–3.36)	0.045*

^*Variables included in the multivariate analysis: firstborn girl and oligohydramnios SE, standard error; Sig, significance; OR, odds ratio; CI, confidence interval

*The statistically significant level was set at p < 0.05.

As firstborn girl remained the only independent predictor in the multivariate analysis, its distribution was further evaluated by Graf subtypes within the unstable group (n = 87): Graf D (n = 48, 55.2%), Graf III (n = 30, 34.5%), and Graf IV (n = 9, 10.3%). The proportions of firstborn girls were 38% (18/48) in Graf D, 53% (16/30) in Graf III, and 78% (7/9) in Graf IV. Although an increasing trend was observed, the overall difference among the subgroups was not statistically significant (p = 0.06).

Discussion

This study identified female sex, breech presentation, oligohydramnios, and foot deformities as significant risk factors for DDH in multivariate analysis. In contrast, family history and high birth weight, although well-recognized in the literature, were not significant in our cohort. Interestingly, firstborn girls emerged as the only independent predictor of unstable hip types, highlighting their potential clinical relevance. Despite numerous studies, the influence of risk factors on DDH development remains incompletely understood, with conflicting findings often attributed to heterogeneity in patient populations and methodological differences [1, 6–8]. This underscores the importance of re-examining both established and potential risk factors, particularly in large cohorts from regions with selective or universal newborn hip screening. The current retrospective case-control study leverages multivariate regression analysis to meticulously examine the impact of these risk factors on DDH and their relationship with ultrasonographic hip types.

The most recent meta-analysis by Tirta et al. (2025) [9] provided the strongest available evidence regarding the risk factors for DDH, identifying female sex (OR 2.50), breech presentation (OR 4.15), oligohydramnios (OR 3.76), family history (OR 3.83), and high birth weight (OR 2.0) as significant predictors. In our study, the associations observed for female sex (OR 2.518), breech presentation (OR 1.817), and oligohydramnios (OR 2.762) were consistent with this meta-analysis, reinforcing their role in DDH risk stratification. Notably, our analysis also identified foot deformities (OR 2.262) as an additional associated factor. However, family history and high birth weight were not significant in our cohort, possibly due to differences in population characteristics, universal screening practices, or retrospective data limitations such as underreporting.

Current literature identifies several well-established RFs for DDH, including female sex, breech presentation, positive family history, and birth order. Schams et al. (2017) [12], Woodacre et al. (2016) [7], and Talbot et al. (2013) [2] each highlighted these factors, contributing valuable insights into the debate on selective versus universal ultrasound screening. Ömeroğlu et al. (2019) [10] further identified breech presentation as a significant predictor of DDH (OR 1.87). Our study supports this, identifying female sex (OR 2.518) and breech presentation (OR 1.817) as risk factors, but also highlights oligohydramnios (OR 2.762) and foot deformities (OR 2.262) as additional predictors. Notably, our analysis provides narrower confidence intervals, offering a more precise estimation of these associations (Table 5).

Table 5.

Comparison of the existing literature on the risk factors for developmental dysplasia of the hip

Study	Risk Factor	OR (95% CI)	Notes
Woodacre et al. [7]	Female sex	7.2 (4.6–11.2)	Identified primary risk factors for DDH.
	Breech presentation	24.3 (13.1–44.9)
	Family history	15.9 (11.0–22.9)
	First or second child	1.8 (1.5–2.3)
Schams et al. [12]	Female sex	4.07 (3.01–5.51)	Increased risk especially with high birth weight.
	Breech presentation	4.98 (3.71–6.71)
	Family history	5.05 (3.49–7.31)
	Female sex + high birth weight	3.51 (2.45–5.03)
Talbot et al. [2]	Female sex	0.028 per 1000 live births (0.021–0.037)	Raises questions about the UK’s screening policy.
Ömeroğlu et al. [10]	Family history	2.42 (1.50–3.91)	Demonstrated effects of single and multiple risk factors.
	Breech presentation	1.87 (1.12–3.11)
	Swaddling	2.81 (1.72–4.59)
Tirta et al. [9]	Female sex	2.50 (1.74–3.59)	Provides robust pooled estimates of established RFs across diverse populations.
	Breech presentation	4.15 (2.62–6.57)
	Family history	3.83 (2.05–7.15)
	High birth weight	2.00 (1.60–2.49)
	Oligohydramnios	3.76 (1.66–8.53)
The current study	Female sex	2.518 (1.777–3.568)	Provides more precise estimates with narrower confidence intervals.
	Breech presentation	1.817 (1.065–3.101)
	Oligohydramnios	2.762 (1.149–6.639)	Highlights additional risk factors overlooked in previous studies.
	Foot deformities	2.262 (1.331–3.842)

Most studies in the existing literature focus on exploring the relationship between developmental dysplasia of the hip (DDH) and various RFs [1, 2, 6–8, 12]. In contrast, the present study uniquely investigates the association between specific ultrasonographic hip types and selected RFs, providing a more nuanced understanding of DDH pathogenesis. Ömeroğlu and colleagues [10] emphasized the significance of risk factors such as family history, swaddling, and oligohydramnios, reporting higher odds ratios and broader confidence intervals, thereby underlining their critical role in DDH development. Complementing these findings, the present study identifies “firstborn girl” as a statistically significant risk factor, offering a novel contribution to the literature. The association between firstborn girls and unstable hip types may be attributed to intrauterine crowding in primigravid pregnancies, which may limit fetal mobility and exert mechanical constraints on hip development. These constraints could be especially impactful for female fetuses, who may be predisposed to ligamentous laxity due to maternal relaxin exposure. This association could warrant closer monitoring of firstborn girls in selective screening programs, as early identification and intervention could potentially reduce the risk of late-presenting DDH and associated complications [11]. Furthermore, in our cohort, right-sided involvement was more common. This difference may reflect sampling variation inherent to the referral-based population of our tertiary center, which included both inborn and externally referred infants. Variations in breech presentation patterns or random distribution within the relatively limited unilateral subgroup might also have contributed to this asymmetry.

The differences in the relationship between RFs and DDH versus severe DDH (unstable/decentralized hips) may stem from several factors. First, population differences and diagnostic criteria play a role, as broader studies on DDH often include heterogeneous groups, whereas severe DDH analyses focus on specific subgroups. Second, certain RFs, like “firstborn girl,” may strongly correlate with the occurrence of DDH but show a weaker association with its severity, reflecting the multifactorial nature of severe DDH. Third, the interaction of multiple RFs, such as breech presentation combined with oligohydramnios, might be more critical in severe cases. Additionally, smaller sample sizes in severe DDH studies may limit statistical power, while variability in ultrasonographic classifications can further complicate comparisons. Lastly, the interplay of genetic, environmental, and mechanical factors, often overlooked in isolated RF analyses, likely influences severe DDH development. These differences highlight the need for tailored approaches and larger, more homogeneous samples in future research.

Several strengths of this study should be acknowledged. This investigation exhibits rigorous methodological precision by deploying comprehensive multivariate regression analysis to explore the complex associations between various RFs and DDH. Utilizing a large cohort enhances the statistical power and reliability of the findings, thereby contributing valuable insights into the epidemiological aspects of DDH. By focusing on ultrasonographic hip types in conjunction with risk factors, this research not only extends the current understanding of DDH pathogenesis but also refines diagnostic criteria within pediatric orthopedics. Moreover, incorporating a broad spectrum of demographic variables significantly bolsters the study’s ability to formulate detailed conclusions, which are instrumental in crafting precise screening and tailored intervention strategies.

Several limitations should be considered in interpretation of study results. Initially, the retrospective design of the study inherently limits our ability to establish causality between identified RFs and DDH, leading to potential biases due to variations in data recording and acquisition. This particularly may have affected the accuracy of USG classification and measurement, introducing biases in the assessment of hip types. Furthermore, although family history is a well-established risk factor for DDH [9], it was not found to be significant in our cohort. This may reflect underreporting by caregivers, incomplete data in retrospective records, or sample selection bias. Second, despite the use of a large cohort, the generalizability of the results may be constrained by the demographic and geographical characteristics of the sample. The study’s findings may not be entirely applicable to populations outside the examined region, particularly in countries with different healthcare systems or screening practices. The third limitation is the lack of a formal sample size analysis prior to the study’s commencement, which may affect the generalizability of the results. Additionally, the relatively small number of patients within the unstable decentralized hip subgroup has constrained our ability to draw robust statistical inferences about this category. Fourth, in our statistical analysis, metatarsus adductus, pes equinovarus, and calcaneovalgus were collectively categorized under ‘foot deformities’. This generalization may mask specific impacts of individual deformities on DDH risk assessment. Fifth, due to its rarity in the studied population, torticollis was not included in the statistical analysis, potentially omitting a relevant risk factor in DDH pathogenesis. Sixth, the mean USG age was about 3 months, which may have allowed spontaneous improvement in some mild cases, potentially affecting the observed association between risk factors and DDH severity. Seventh, a limitation of this study is the use of the composite variable “firstborn girl,” which combines sex and birth order and may reduce comparability with studies analyzing these factors separately. Finally, the spontaneous transition to universal newborn hip screening in our country may skew comparative analysis by introducing measurement biases that affect the prevalence of certain risk factors in the control group.

To advance the understanding of DDH related RFs, future studies should consider a prospective design to establish stronger causality links and incorporate a broader and more diverse patient cohort to enhance generalizability. Insights into the multifactorial nature of DDH could be more enhanced by incorporating detailed physical examination data alongside ultrasonographic findings. Additionally, longitudinal and cross-cultural studies could shed light on the long-term outcomes and global variations in DDH management. Moreover, future prospective research incorporating follow-up data and treatment outcomes, such as Pavlik harness success rates, could provide additional insights into the clinical relevance of ultrasonographic classifications.

Conclusion

The results of this study have revealed that it is crucial to refer newborns to ultrasonographic hip examinations when four critical risk factors are present: female sex, breech presentation, oligohydramnios, and the presence of foot deformities. This study uniquely identifies firstborn girls with DDH as having a higher risk of unstable hips, underscoring the need for targeted screening in this subgroup. However, as this study was conducted in a single tertiary referral center within a universal screening program, caution should be exercised when generalizing these findings to other populations or healthcare settings. Early identification and intervention for high-risk infants may help reduce delayed diagnoses and improve outcomes in managing DDH.

Abbreviations

DDH

Developmental dysplasia of the hip

RFs

risk factors

USG

ultrasonographic

SD

standard deviation

OR

odds ratio

Authors’ contributions

Authors’ contributions: Mehmet Demirel, MD (Contribution: study design, performed measurements, manuscript preparation, statistical analysis)Bedirhan Demir, MD (Contribution: study design, performed measurements, manuscript preparation, manuscript submission)Zeynep Elif Çalış, MD (Contribution: study design, performed measurements)Cem Yapar, MD (Contribution: study design, performed measurements)Yavuz Sağlam, Assoc. Prof, MD (Contribution: study design, performed measurements)Fuat Bilgili, Prof, MD (Contribution: study design, performed measurements).

Funding

We declare that we have gained no funding related to this study.

Data availability

The datasets generated and analyzed during the current study are not publicly available due to institutional and national regulations governing patient privacy and confidentiality. De-identified data may be made available from the corresponding author upon reasonable request and with appropriate ethical approval.

Declarations

Ethics approval and consent to participate

We received our ethics committee approval from Internal Review Board (IRB) of Istanbul University Istanbul Faculty of Medicine.

Consent for publication

All participants were informed about the objectives, methodology, and potential implications of the study, and provided their voluntary written consent prior to participation. Participation was entirely voluntary, and individuals were assured that they could withdraw from the study at any time without any negative consequences. The study was conducted in accordance with the ethical standards of the Declaration of Helsinki and approved by the relevant institutional ethics committee.

Competing interests

The authors declare no competing interests.