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Knee morphology and patella malalignment in neglected developmental dysplasia of the hip: a systematic review and meta-analysis

Journal of Orthopaedic Surgery and Research volume 20, Article number: 489 (2025) Cite this article

Abstract

Purpose

To quantitatively analyze the structural changes of the knee in patients with neglected developmental dysplasia of the hip (DDH).

Methods

PubMed, Embase, Web of Science, and Cochrane Library databases were searched to identify studies comparing the morphological parameters of the knee between DDH patients and healthy individuals. Data on rotational and mechanical parameters of the lower limb, rate of occasional anterior knee pain (AKP), and knee morphological parameters, were extracted. Review Manager and R statistic software were used to perform the statistical analysis.

Results

Nine studies with a total of 790 legs in 521 neglected DDH patients and 431 legs in 303 health subjects were included. Patients were predominantly female (88.3%). The Crowe classification is most commonly used to assess the severity of DDH. The total incidence of occasional AKP ranged from 8.6 to 20.6%, with an overall pooled rate of 14.4% (95%CI = 9.8–19.8%). In patients with neglected DDH, significant increases (P < 0.0001) were observed in femoral anteversion (weighted mean: 39.1° vs. 17.7°), knee torsion (weighted mean: 9.0° vs. 1.6°), and the vertical dimension of the medial femoral condyle (weighted mean: 13.8 mm vs. 11.6 mm), along with a significant decrease in the lateral distal femoral angle (weighted mean: 82.1° vs. 84.8°), which can lead to torsion deformity of the lower limb and valgus inclination of the distal femoral articular surface. Compared with the intact subjects, DDH knees demonstrated an increased sulcus angle (weighted mean: 144.9° vs. 137.5°; P < 0.0001), decreased trochlear depth (weighted mean: 3.1 mm vs. 4.5 mm; P < 0.0001), increased lateral shift of the patella (5.1 mm vs. 3.8 mm, P = 0.06), and increased patellar tilt angle (weighted mean: 18.2° vs. 13.2°; P < 0.0001). These findings were associated with developmental dysplasia of femoral trochlear and patellar instability.

Conclusion

Developmental dysplasia of the hip leads to patellar malalignment and developmental changes in the bony anatomy of the knee joint, including the development of a valgus deformity of the lower extremity and trochlear dysplasia. These findings may be associated with patellar instability.

Level of evidence

III, systematic review.

Registration

This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42025640292).

Introduction

The impact of developmental dysplasia of the hip (DDH) ranges from acetabular dysplasia to complete dislocation of the hip. Situated at the junction of the axial and appendicular skeletons, the hip joint undergoes structural changes due to DDH, potentially affecting parameters of the axial skeleton [1]. Previous studies investigating the natural history of DDH from infancy to adulthood have demonstrated its association with valgus deformity of the knee and femoral trochlear dysplasia [1, 2]. Quantitative research by Kandemir et al. [3] revealed that DDH increases the vertical dimension of the medial femoral condyle and mechanical axis deviation, which may explain valgus malalignment. Other studies suggest that hip adduction contracture could lead to dysplasia of the distal femoral epiphyseal plate, resulting in mechanical malalignment in the coronal plane of the knee joint [3, 4]. Recent finding indicates a strong association between dysplasia of the distal femoral epiphyseal plate and trochlear dysplasia [5]. Additionally, quantitative studies have identified knee torsion deformity [6, 7] and patellar alignment abnormalities [8] in patients with hip dysplasia. These morphological changes in the knee are critically important for surgical decision-making in knee interventions.

Previous studies [3, 9, 10] suggested that some patients with neglected DDH are prone to symptomatic patellofemoral joint (PFJ) disease, including occasional anterior knee pain (AKP), damage to cartilage and soft tissue stabilizing structures, patellar instability, or osteoarthritis. Moreover, most of these patients exhibit altered morphological parameters of the distal femur, patellofemoral joint, and patella, which may explain these symptoms. Importantly, for such patients undergoing knee surgery, additional evaluation of osseous morphological parameters is essential, particularly in cases involving knee soft tissue reconstruction or joint replacement. To the best of our knowledge, no systematic review or meta-analysis has been conducted to assess the morphological changes in the knee joint among patients with neglected DDH.

This systematic review and meta-analysis aims to quantitatively analyze the structural changes of the knee joint and investigate the pooled rate of occasional AKP in patients with neglected DDH.

Methods

This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42025640292). This work was conducted in line with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and AMSTAR (Assessing the Methodological Quality of Systematic Reviews) Guidelines [11].

Search strategy and eligibility criteria

The search strategy was used to identify all publications eligible for inclusion in the review. PubMed, Embase, Web of Science, and Cochrane Library databases were searched in December 2024 (updated in January 2025). The search terms are listed in Supplementary Table 1. Specific search strategies were developed for each database and references of the identified studies were checked for potential eligibility.

The following inclusion criteria were used to identify eligible studies: comparing the morphological parameters of the knee between DDH patients and healthy individuals. Furthermore, this study excluded non-English language reports, case reports, conference abstracts/posters, or reviews. After the removal of duplicates, two orthopedic surgeons independently reviewed the titles and abstracts to screen for potentially eligible studies. Full texts were then assessed independently by the same two reviewers to identify the final list of publications suitable for inclusion in the current study. If disagreement occurred, a third senior orthopedic surgeon was consulted for final assessment and consensus.

Data extraction

Each included article was abstracted regarding study features, patient characteristics, physical examination information, and outcome measures. Study characteristics included author name, publication date, study design, level of evidence, and number of patients/hips/knees. Patient data included sex, age, and DDH classifications. Physical examination information primarily includes the incidence of occasional anterior knee pain (AKP), patellar instability, and dislocation. Outcome measures consisted of (1) rotational and mechanical parameters of the lower limb, such as femoral anteversion angle (FAA), knee torsion, tibial torsion, anatomic lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and mechanical axis deviation; (2) knee morphological parameters, such as dimensions of the medial and lateral femoral condyles (MFC and LFC), sulcus angle (SA), femoral trochlear depth (FTD), patellar tilt angle (PTA), lateral shift of the patella (LSP), etc. The data extraction of the included studies was conducted independently by two reviewers.

Quality assessment

The quality of the included studies was assessed independently by two reviewers. In this regard, the Methodological Index for Non-Randomized Study (MINORS) [12] for cohort studies was used. Items on the questionnaire were scored as follows: 0 if not reported, 1 if reported but inadequate, and 2 if reported and adequate. The maximum score for non-comparative studies was 16, with a score of 13 to 16 being considered the low risk of bias. The maximum score for comparative studies was 24, with scores of 21 to 23 considered to be at low risk of bias. Otherwise, studies were considered to have a high risk of bias. When disagreement occurred, a third senior orthopedic surgeon was consulted for final consensus. The intraclass correlation coefficient was calculated in SPSS software (version 26.0, IBM, Armonk, NY, USA) and used to evaluate the reliability of the publication bias assessment [13].

Statistical analysis

Review Manager (version 5.3 from Cochrane Collaboration) and R statistic software were used to perform the statistical analysis, with P < 0.05 as a threshold of statistical significance. In this study, the mean-variance estimation method described by Lou et al. [14] and Wan et al. [15] was used to estimate means (standard deviations) from median and interquartile ranges in some studies. For continuous data with standard deviation, meta-analysis was performed to calculate the weighted mean difference (WMD) with 95% confidence intervals (CIs) using the inverse variance (IV) method. When comparing the incidence of dichotomous data, such as residual J-sign, the Odds Ratio (OR) was calculated using the Mantel-Haenszel (M-H) method. The I2 statistic and Q test were used to measure heterogeneity. If I2 < 50% and the p-value for the Q test > 0.05, the studies were interpreted as minimally heterogeneous, and a fixed-effects model was applied for the meta-analysis. A random-effects model was applied when I2 > 50% or the p-value for the Q test < 0.05, which indicated that the data were of high heterogeneity. R statistic software was used to calculate the rate of occasional anterior knee pain. Other results were presented as a descriptive summary.

Results

Literature search and quality assessment

A total of 2064 studies were identified in the initial search and 9 articles were finally included for analysis (Fig. 1). All studies were comparative articles. The median MINORS scores of the two reviewers were 21 (range: 21 to 22) and 22 (range: 21 to 23) for all studies, respectively. The study features are summarized in Table 1.

Fig. 1
figure 1

Flow diagram of the selection of studies

Full size image

Patient characteristics

A total of 790 legs in 521 neglected DDH patients and 431 legs in 303 health subjects were included. In patients with developmental dysplasia of the hip, the reported cases of unilateral DDH are comparable to those of bilateral DDH (162 vs. 166). Females were more likely to develop DDH than males (88.3% [394/446] vs. 21.7% [52/446]). The mean age of patients ranged from 21.6 to 56 years. The Crowe classification is most commonly used to assess the severity of DDH [3, 6, 7, 10, 16], followed by the Hartofilakidis classification [17,18,19]. Only one study utilized the combined lateral center-edge angle (LCE) and femoral anteversion angle (FAA) for evaluating DDH [8]. The characteristics of the patients are summarized in Table 1.

Table 1 Study characteristics
Full size table

Occasional anterior knee pain

Four studies reported the rate of occasional AKP in patients with neglected DDH [3, 16, 18, 19]. The total incidence of AKP ranged from 8.6 to 20.6%, with an overall pooled rate of 14.4% (common effect model, 95%CI = 9.8–19.8%) (Fig. 2). One study was excluded from this analysis because it included AKP as an inclusion criterion (with an AKP incidence of 100%) [10].

Fig. 2
figure 2

Occasional anterior knee pain rate. Data pooled with a common effect model

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Rotational deformity and knee malalignment

Five studies compared the differences in FAA between DDH and control groups [3, 6, 8, 17]. The pooled analysis showed that the FAA increased significantly in patients with neglected DDH (weighted mean: 39.1° vs. 17.7°; WMD = 21.4°; P < 0.0001). Two similiar studies assessed knee torsion in patients with hip dysplasia and found that this deformity was greatly higher in the DDH group (DDH vs. control knees, 9.0° vs. 1.6°, P < 0.001) [6, 7]. In addition, the current study has not found any differences in tibial torsion between the two sample groups [3]. Regarding knee alignment, the pooled results indicated that patients with DDH exhibit a significant valgus knee deformity, characterized by a decrease in the LDFA (weighted mean: 82.1° vs. 84.8°; WMD = -2.8°; P < 0.0001) and an increase in the mechanical axis deviation (Table 2 and Fig. 3).

Fig. 3
figure 3

The differences in femoral anteversion and lateral distal femoral angle between the developmental dysplasia of the hip and control groups

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Table 2 Measurement methods and changes in DDH knees of the significant knee parameters
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Morphology of femoral condyles

Four studies evaluated the morphology of the distal femoral condyles in patients with DDH. The pooled analysis showed that the patients with DDH had significantly decreased horizontal dimension of the lateral femoral condyle (HDLFC) (weighted mean: 38.4 mm vs. 41.8 mm; WMD = -3.4 mm; P < 0.0001) and increased vertical dimension of the medial femoral condyle (VDMFC) (weighted mean: 13.8 mm vs. 11.6 mm; WMD = 2.2 mm; P < 0.0001) (Fig. 4). This finding was associated with the increased valgus inclination of the distal femoral articular surface.

Furthermore, pooled results also showed that DDH knees had a smaller anteroposterior diameter of MFC (weighted mean: 52.5 mm vs. 57.1 mm; WMD = -4.6 mm; P < 0.0001), while the differences in anteroposterior diameter of LFC and condyle asymmetry were not significant (P > 0.05) (Fig. 5).

Fig. 4
figure 4

The differences in the coronal plane dimension of the femoral condyles between the developmental dysplasia of the hip and control groups

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Fig. 5
figure 5

The differences in the transverse plane dimension of the femoral condyles between the developmental dysplasia of the hip and control groups

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Trochlear dysplasia and patella malalignment

Five studies reported the morphology of femoral trochlear and patellar alignment in patients with DDH. The pooled analysis showed that the patients with DDH demonstrated an increased sulcus angle (weighted mean: 144.9° vs. 137.5°; WMD = 7.4°; P < 0.0001), decreased trochlear depth (weighted mean: 3.1 mm vs. 4.5 mm; WMD = -1.4 mm; P < 0.0001), and increased patellar tilt angle (weighted mean: 18.2° vs. 13.2°; WMD = 5.0°; P < 0.0001) (Fig. 6). Furthermore, one study indicated that the mean lateral shift of the patella (LSP) increased by approximately 2 mm in patients compared to the control group (5.1 mm vs. 3.8 mm, P = 0.06) [18], while another study found a significant increase in the proportion of patients with LSP > 5 mm (75/196 [38.3%] vs. 2/34 [5.9%], P < 0.001) [8].

Fig. 6
figure 6

The differences in bony structures of the trochlear and patella between the developmental dysplasia of the hip and control groups

Full size image

Discussion

The most important finding of this meta-analysis and systematic review is that the developmental dysplasia of the hip leads to patellar malalignment and developmental changes in the bony anatomy of the knee joint, including the development of a valgus deformity of the lower extremity and trochlear dysplasia. These findings may be associated with patellar instability. In addition, the pooled rate of occasional anterior knee pain (AKP) was 14.4% in patients with neglected DDH.

The morphology of the patellofemoral joint (PFJ) is a critical factor influencing patellar tracking and stability [17, 20, 21]. Patellofemoral malalignment can result from three primary factors: ligamentous laxity, asymmetric chondral destruction, and structural osseous deformity [3]. Compared to the control group, patients with neglected DDH exhibited no significant differences in knee stability [3, 16, 18, 19], which may suggested similar soft tissue conditions between two populations. In the absence of soft tissue abnormalities, abnormal bony development of the knee joint is the primary cause of osseous malalignment. This meta-analysis found that DDH patients demonstrate a reduced LDFA, hypoplasia in the horizontal dimension of the LFC, and a reduced anteroposterior diameter of the MFC, but with a significant increase in vertical dimension of the MFC. In addition to influencing osteotomy planning during total knee arthroplasty [6, 22], these bony abnormalities have been shown to lead to valgus malalignment of the lower limb, which in turn affects patellofemoral congruence [3, 10] and patellar positioning [17, 23]. Furthermore, this study also revealed that patients with neglected DDH exhibit more pronounced torsional deformities of the lower limbs compared to controls, specifically with increased femoral torsion and knee torsion, while tibial torsion showed no significant changes. These torsional deformities have been shown to be closely associated with patellar instability [24,25,26,27,28].

The pathogenic factors and mechanisms of femoral trochlear dysplasia remain controversial. Genetic associations with DDH [29,30,31,32] and emerging genomic technologies [33] inform our understanding of musculoskeletal development. In addition to genetic factors, some studies proposed that mechanical stress in the PFJ is a direct determinant of normal trochlear development. Animal model studies have shown that abnormal PFJ mechanical stress caused by patellar dislocation can contribute to trochlear dysplasia [34,35,36]. Tardieu and Dupont observed that as children begin to walk, the femoral obliquity angle gradually forms, leading to secondary valgus of the knee extensor mechanism. This process deepens the trochlear groove and promotes the development of the lateral femoral condyle. However, this phenomenon was not observed in children who were unable to walk normally [37]. Recent studies [5] have identified the morphology of the medial epiphyseal plate and the trochlea-epiphysis distance as significant risk factors for trochlear dysplasia, both of which are associated with clinical outcomes.They also found that correcting abnormal PFJ stress in immature patients can significantly improve both epiphyseal plate and trochlear development. These findings underscore the close relationship between epiphyseal plate stress and trochlear development. Importantly, previous studies have suggested that hip adduction contracture caused by DDH may impair the development of the distal femoral epiphyseal plate [3]. This could explain the findings in the present study, where patients with neglected DDH exhibited increased sulcus angles and decreased trochlear depth, both of which are characteristic features of trochlear dysplasia.

Patellar instability is a common cause of anterior knee discomfort associated with patellofemoral osteoarthritis or chondromalacia patellae [38]. Patellar malalignment impair the balance of the surrounding soft tissue structures, making the patella prone to subluxation or dislocation even during daily sports activity. Fulkerson et al. [39] identified abnormal patellar tilt as one type of patellar instability. The findings of this meta-analysis indicated that in patients with neglected DDH, the patellar tilt angle and lateral shift of the patella were significantly higher than those in the control group, which may ultimately lead to patellar instability. These results highlight the importance for surgeons to pay additional attention to the developmental status of the hip joint when managing patellar instability.

This study has limitations. First, the search strategy contained bias due to the possibly unavoidable missing of relevant studies. However, four main databases were searched to include all the relative studies comparing the morphological parameters of the knee between DDH patients and healthy individuals. Second, significant heterogeneities were found in the comparison of structural variables between groups. This may be related to differences in the measurements, ethnicity of the subjects, the classification of DDH, and the affected side. The results of the analysis were carefully interpreted. Third, the participants included in these studies were limited, and the analysis was restricted to comparisons of a finite set of bony structural parameters, which may not fully elucidate the overall knee morphology. Future studies could leverage advanced image processing methods to analyze the comprehensive knee morphology.

Conclusion

Developmental dysplasia of the hip leads to patellar malalignment and developmental changes in the bony anatomy of the knee joint, including the development of a valgus deformity of the lower extremity and trochlear dysplasia. These findings may be associated with patellar instability. In the clinical management of patellar instability, hip morphology should be evaluated to assess the condition and guide treatment.

Data availability

No datasets were generated or analysed during the current study.

Abbreviations

DDH:

developmental dysplasia of the hip

AKP:

Anterior knee pain

PFJ:

Patellofemoral joint

MFC:

Medial femoral condyle

LFC:

Lateral femoral condyle

SA:

Sulcus angle

FTD:

Femoral trochlear depth

PTA:

Patellar tilt angle

FAA:

Femoral anteversion angle

LDFA:

Lateral distal femoral angle

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Acknowledgements

No.

Funding

This study was supported by the National Natural Science Foundation of China (82472527), and Beijing Municipal Science & Technology Commission (No. Z211100002921043 and No. Z221100007422004). We declare that no funds, grants, or other support were received during the preparation of this manuscript.

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Author notes

  1. Daofeng Wang, Jianzhong Sun and Yang Liu contributed equally to this work.

Authors and Affiliations

  1. Sports Medicine Service, Beijing Jishuitan Hospital, Capital Medical University, No. 31, Xinjiekou East Street, Beijing, 100035, China

    Daofeng Wang, Jianzhong Sun, Zhengjie Tang & Hui Zhang

  2. Beijing Research Institute of Traumatology and Orthopaedics, No. 31, Xinjiekou East Street, Beijing, 100035, China

    Daofeng Wang, Jianzhong Sun, Yang Liu, Zhengjie Tang & Hui Zhang

  3. Sports Medicine Service, The Fourth Clinical Medical College of Peking University, No. 31, Xinjiekou East Street, Beijing, 100035, China

    Yang Liu

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Hui Zhang: Conceptualization and study design; Daofeng Wang: data collection, analysis; and original manuscript writing; Jianzhong Sun and Yang Liu: data analysis and manuscript revision; Zhengjie Tang and Jianzhong Sun: Language check, review & editing. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Hui Zhang.

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Wang, D., Sun, J., Liu, Y. et al. Knee morphology and patella malalignment in neglected developmental dysplasia of the hip: a systematic review and meta-analysis. J Orthop Surg Res 20, 489 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13018-025-05877-y

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  • DOI: https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13018-025-05877-y

Keywords

Journal of Orthopaedic Surgery and Research

ISSN: 1749-799X