Assessment and Quantitative Analysis of Hip Surrounding Muscles in Children with Developmental Dysplasia of the Hip via Magnetic Resonance Imaging

doi:10.21203/rs.3.rs-5312604/v1

Background

The muscles that encase the hip serve a crucial role in both joint stability and functional efficacy, and as developmental dysplasia of the hip (DDH) progresses, the surrounding musculature may undergo specific adaptations that reduce joint stability, thereby exacerbating dislocation. Yet, the exact nature of changes in muscle morphology and quality remains inadequately investigated. This study aims to compare magnetic resonance imaging (MRI) evaluations of the iliopsoas and other hip flexor and extensor muscles in children with unilateral DDH before and after treatment.

Methods

Children with unilateral DDH were included in this study and compared to a matched control group. Using T2-weighted MRI sequences, muscle cross-sectional area (CSA) and fat infiltration (FI) were measured for the iliopsoas, sartorius, rectus femoris, tensor fasciae latae, and gluteus maximus. The cross-sectional area ratio (CSAr) was calculated as the CSA of the affected side divided by the CSA of the healthy side, corresponding to the respective sides in normal controls. For long-term follow-up (≥ 5 years), data from DDH children were analyzed, categorized into groups based on treatment. Comparisons of muscle CSAr and FI at the final follow-up were made against preoperative levels.

Results

Preoperative median CSAr values for the iliopsoas, rectus femoris, and gluteus maximus in DDH children were significantly lower than those of the control group (P < 0.001). FI levels were also higher in the DDH group compared to controls. In the closed reduction group, iliopsoas CSAr increased and FI decreased at the final follow-up compared to preoperative measurements. Conversely, in the open reduction group, iliopsoas CSAr and FI decreased. In the Dega osteotomy group, both iliopsoas CSAr and FI decreased, while CSAr for the sartorius, rectus femoris, and gluteus maximus increased, with also reduced FI.

Conclusion

Children with DDH exhibit varying degrees of muscle atrophy and increased fat infiltration compared to their age-matched healthy counterparts. Aside from the iliopsoas, muscle morphology and fat infiltration in DDH children improved post-treatment compared to pre-treatment levels.

muscles

developmental dysplasia of the hip

magnetic resonance imaging

osteotomy

Developmental dysplasia of the hip (DDH) is a prevalent hip disorder in pediatric orthopedics characterized by morphological or positional abnormalities of the femoral head and acetabulum that may arise at birth or during developmental processes(1). The pathological anatomy of DDH involves both skeletal and soft tissue components. Skeletal alterations include modifications of the acetabulum, femoral head, neck, and shaft, while soft tissue changes encompass the morphological shifts of the cartilaginous acetabulum, cartilaginous femoral head, joint capsule, labrum, and surrounding muscles. The intricate muscular framework surrounding the hip is critical for maintaining joint stability and enabling flexion and extension movements. As DDH progresses, the dislocation of the femoral head and subsequent shortening of the affected limb may result in thickening of the joint capsule and outward and upward extension, leading to dysfunction of the iliopsoas and hip adductor and abductor muscles. This dysfunction can consequently precipitate unstable gait patterns and exacerbate dislocation(2-6). It is thus imperative to assess morphological and quality changes of hip surrounding muscles following treatment in children with DDH. Previous studies have predominantly addressed muscle morphological alterations post-surgery, with insufficient emphasis on comparative analyses of muscle parameters between pre-treatment DDH children and their normal counterparts.

Magnetic resonance imaging (MRI) offers superior soft tissue resolution, allowing for clear visualization of muscular morphology and signal alterations surrounding the hip joint. Its application for preoperative evaluation and postoperative monitoring in DDH is increasingly recognized(7, 8). This study aims to assess changes in hip flexor muscles, particularly the iliopsoas, prior to treatment and evaluate the associated morphological and quality changes post-treatment through CSA and FI measurements.

Study Population

Retrospective imaging data were collected from 738 children diagnosed and treated for unilateral DDH between January 2011 and December 2017. Exclusion criteria included children with comorbid hip disorders (108), bilateral dysplasia (295), neuromuscular or pathological hip dysplasia (126), prior treatments at other institutions (46), and those lacking accessible preoperative or final follow-up MRI data (67). Ultimately, 96 children met the inclusion criteria (15 males, 81 females; mean age 21.2 ± 13.8 months). Patients were classified according to IHDI grades I-IV, with an accompanying age- and sex-matched control group comprising 96 healthy children who underwent hip MRI.

Scanning Equipment and Methodology

MRI scans of the hip and surrounding structures were performed using a Philips 3.0 T imaging system, acquiring axial, coronal, and sagittal T1 and T2-weighted images with a slice thickness of 3 mm. T2 fast spin-echo parameters were set to TR 4500 ms and TE 120 ms; T1 fast spin-echo parameters were set to TR 450 ms and TE 12 ms, with a matrix size of 512 × 512. Children were placed in a calm and comfortable environment prior to the MRI examination, positioned supine with lower limbs extending naturally and toes externally rotated approximately 15 degrees to ensure proper alignment of knees and thighs.

Radiological Measurement Techniques

Measurement of Hip Muscle CSA

Muscle morphology was evaluated by measuring CSA from MRI images. CSA measurements for hip flexors (iliopsoas, tensor fasciae latae, rectus femoris, sartorius) and extensors (gluteus maximus) were performed on axial T2-weighted scans, employing region of interest (ROI) tools to exclude adjacent bony and soft tissue structures. Two specific slices were defined for standardization: measurements for the tensor fasciae latae, rectus femoris, sartorius, and gluteus maximus were taken at the upper margin of the pubic symphysis, and measurements for the iliopsoas were taken at a point 10 mm superior to this landmark. In the DDH group, the affected side CSA was divided by the healthy side CSA to calculate CSAr for each muscle. In the control group, results corresponded to the affected side of matched DDH children.

Measurement of Fat Infiltration in Hip Surrounding Muscles

On axial T2-weighted MRI scans, ROIs were delineated for muscle CSA and adjacent subcutaneous fat, collecting signal intensity values (A for muscle, B for fat) for each. The ratio of A to B was defined as the FI.

Postoperative Measurement of Hip Surrounding Muscle CSA and FI

From the 96 DDH patients included, a subset of 27 children with a follow-up duration of at least 5 years was analyzed, averaging 6.04 ± 1.69 years postoperatively. This cohort included 7 patients in the closed reduction group, 10 in the open reduction group, and 10 in the Dega osteotomy group. Muscle CSA and FI were measured at the final follow-up MRI. All patients exhibited favorable clinical outcomes, as determined by modified McKay criteria established by Barrett et al.(9), demonstrating stable, pain-free hips, negative Trendelenburg signs, and no restrictions in range of motion. Furthermore, all patients exhibited I-type hip joint attributes based on the Severin classification(10) at the last follow-up, with no cases requiring secondary surgeries for residual acetabular dysplasia.

Statistical Analysis

Data statistical analyses were performed using SPSS version 25.0. (1) Normality tests were conducted on continuous variables; those conforming to a normal distribution were expressed as mean ± standard deviation. Inter-group comparisons were analyzed via independent sample t-tests or one-way analysis of variance based on the number of groups. For data failing to meet normal distribution criteria, median and percentiles were expressed for descriptions, and non-parametric tests were utilized for inter-group comparisons. Categorical data were presented as frequencies and percentages, analyzed using chi-squared tests or Fisher’s exact tests based on data unit size. (2) For DDH patients with follow-up durations ≥5 years, paired t-tests or Wilcoxon signed-rank tests were employed to compare preoperative and final follow-up MRI hip surrounding muscle CSAr and FI. A significance threshold of 0.05 was established, with P < 0.05 indicating statistically significant differences.

Comparison Between Preoperative DDH Group and Control Group in CSAr and FI

In the DDH group, the median CSAr for the iliopsoas, rectus femoris, and gluteus maximus were 0.80, 0.65, and 0.91, respectively, all significantly lower than those seen in the control group (iliopsoas: 1.02, rectus femoris: 0.88, gluteus maximus: 0.97), with statistically significant differences (P < 0.001). No significant differences were noted between the two groups for the sartorius (P = 0.069) and tensor fasciae latae (P = 0.874) (Table 1).

The median FI values in the DDH group for the iliopsoas (P < 0.001), sartorius (P = 0.002), rectus femoris (P < 0.001), tensor fasciae latae (P < 0.001), and gluteus maximus (P < 0.001) were 0.14, 0.19, 0.17, 0.23, and 0.28, respectively, all demonstrating statistically significant increases compared to the respective values in the control group (iliopsoas: 0.07, sartorius: 0.13, rectus femoris: 0.12, tensor fasciae latae: 0.17, gluteus maximus: 0.23) (Table 1).

Additionally, this study compared CSAr and FI across IHDI types II, III, and IV within the DDH group. The findings indicated that the iliopsoas CSAr progressively declined with increasing severity of dislocation among types II, III, and IV, showing statistically significant differences between types II and III (P = 0.001) and between types II and IV (P < 0.001). No statistically significant differences were observed for other muscle CSAr and FI metrics (Table 2).

Comparative Analysis of Preoperative and Final Follow-Up CSAr and FI in DDH Group

In the closed reduction group, the iliopsoas CSAr at the final follow-up (0.86) significantly increased compared to the preoperative measurement (0.66, P = 0.043), while the FI decreased from 0.15 preoperatively to 0.06 at the final follow-up (P = 0.028), indicating statistically significant differences. No significant differences were observed for the CSAr and FI of other muscle groups (Table 3).

In the open reduction group, the iliopsoas CSAr at the final follow-up (0.62) showed a statistically significant decrease from the preoperative level (0.83, P = 0.017), alongside a substantial reduction in FI from 0.11 preoperatively to 0.07 at final follow-up (P = 0.037). The FI for the gluteus maximus similarly decreased from 0.27 preoperatively to 0.16 at the final follow-up (P = 0.009) (Table 4).

In the Dega osteotomy group, both iliopsoas CSAr (preoperative: 0.83, final follow-up: 0.72, P = 0.013) and FI (preoperative: 0.14, final follow-up: 0.08, P = 0.037) were significantly reduced at the final follow-up compared to preoperative values. Conversely, CSAr for the sartorius (preoperative: 1.05, final follow-up: 1.29, P = 0.013), rectus femoris (preoperative: 0.79, final follow-up: 0.90, P = 0.013), and gluteus maximus (preoperative: 0.73, final follow-up: 0.93, P = 0.028) increased significantly compared to their preoperative counterparts. Additionally, FI decreased for sartorius (preoperative: 0.19, final follow-up: 0.13, P = 0.013), rectus femoris (preoperative: 0.17, final follow-up: 0.07, P = 0.022), and gluteus maximus (preoperative: 0.25, final follow-up: 0.16, P = 0.037), with all differences being statistically significant (Table 5).

Research focusing on the skeletal pathological changes associated with DDH has matured significantly. In recent years, increasing attention has been directed towards alterations in both intra-articular and extra-articular soft tissues, particularly concerning the evaluation of the acetabular cartilage(11–13). However, investigations into the hip surrounding muscles remain sparse. The muscles that encase the hip serve a crucial role in both joint stability and functional efficacy, and as DDH progresses, the surrounding musculature may undergo specific adaptations that reduce joint stability, thereby exacerbating dislocation. Yet, the exact nature of changes in muscle morphology and quality remains inadequately investigated.

In clinical practice, the challenges associated with accurately measuring muscle morphology through imaging techniques often lead to the neglect of assessments regarding muscular alterations pre- and post-DDH treatment. Therefore, selecting a straightforward and reliable imaging assessment technique for evaluating hip surrounding muscles is essential for clinical practitioners. Methods for assessing muscle morphology typically involve measuring CSA at specified MRI slices(14–16), which, in contrast to three-dimensional reconstruction techniques, provide a more practical clinical utility. This study also incorporates the affected-to-healthy side ratio to enhance the applicability and interpretability of measurement outcomes. Degenerative changes in muscle often manifest as morphological atrophy and increased FI(17, 18); MRI has demonstrated advantages in assessing fat infiltration compared to alternative imaging modalities. This study specifically evaluates changes in CSA and FI of hip surrounding muscles by utilizing methods adapted from Hyun et al.(19) for assessing FI in paraspinal muscles affected by degeneration.

Given the potential for pathological changes in the contralateral hip surrounding muscles in patients with unilateral DDH, this study design included a corresponding age- and sex-matched cohort of healthy children to bolster result reliability. The findings indicate that DDH children presented with reduced iliopsoas, rectus femoris, and gluteus maximus CSA before surgery compared to their normal counterparts, while demonstrating significantly higher FI levels across the iliopsoas, sartorius, rectus femoris, tensor fasciae latae, and gluteus maximus. Among these, changes in both CSA and FI were most pronounced for the iliopsoas, followed by the rectus femoris, both of which are primary flexors significantly impacted by DDH. Conversely, the sartorius and tensor fasciae latae, as accessory flexors, exhibited less noticeable morphological changes despite increased FI. These results suggest that the degree of fat infiltration could serve as an early indicator of intrinsic muscle changes prior to apparent morphological alterations, thereby facilitating the early identification and intervention for muscle pathologies.

Existing studies utilizing MRI to evaluate hip surrounding muscle changes in DDH have primarily focused on postoperative assessments. For example, Basset et al.(14) found no significant CSA differences between affected and unaffected sides for the rectus femoris, sartorius, and gluteus maximus postoperatively. Yilmaz et al.(15) noted significantly smaller iliopsoas areas on the affected side in unilateral DDH patients, while no significant differences were observed for tensor fasciae latae, rectus femoris, sartorius, and gluteus maximus between affected and healthy sides. Yuksel et al.(16) quantified muscle CSA post-osteotomy in DDH patients, reporting significantly reduced areas for the iliopsoas, tensor fasciae latae, rectus femoris, and gluteus maximus on the surgical side compared to the healthy side.

These studies primarily emphasize the differences observed between affected and healthy sides after surgery without addressing the progression of pre- to post-treatment changes within the same muscle groups. Yuksel et al.(16) suggest the possibility of pre-existing differences that may have been intensified by surgical intervention. In our study involving 27 DDH patients with over five years of follow-up, it was indicated that in the closed reduction group, iliopsoas CSAr increased compared to preoperative measurements, while in the open reduction group, both iliopsoas CSA and FI showed reductions, and the FI for the gluteus maximus decreased as well. Conversely, the Dega osteotomy group exhibited diminished iliopsoas CSA and FI, yet demonstrated increased CSA and reduced FI for the sartorius, rectus femoris, and gluteus maximus. These results indicate that improvements in muscle morphology and quality were observed in DDH children post-treatment relative to their pre-treatment states.

A critical consideration in the open reduction and osteotomy groups is the complete detachment of the iliopsoas tendon. Such detachment may explain the further reduction in iliopsoas CSA observed postoperatively. In contrast, in the closed reduction group, where tendon preservation was practiced, these changes did not materialize. Thus, it may be prudent for orthopedic surgeons to contemplate surgical techniques that extend the iliopsoas tendon instead of executing complete detachment, which could mitigate postoperative atrophy while ensuring surgical efficacy. Early detection and timely intervention through closed reduction might minimize the damage inflicted on the iliopsoas during surgical procedures, culminating in significantly enhanced clinical outcomes. Furthermore, the early initiation of structured rehabilitation protocols following DDH treatment remains essential for optimizing recovery and improving clinical outcomes, emphasizing the necessity for targeted rehabilitation of the hip surrounding musculature.

This study does possess certain limitations. Firstly, as a retrospective analysis, the number of postoperative follow-up cases was limited, which may skew statistical results, underscoring the need for larger, prospective studies to validate the findings. Secondly, the phenomenon of “reattachment” of the iliopsoas tendon following complete detachment in certain patients requires further investigation to clarify similarities or differences in muscle changes. Additionally, while specific MRI slices were used for the measurement of CSA and FI, alternative comprehensive MRI examinations could yield more accurate results but were not employed due to practical clinical considerations and financial implications for patient families.

In conclusion, children with DDH demonstrate varying degrees of muscle atrophy and increased fat infiltration when compared to age-matched healthy children. Following treatment, except for the iliopsoas, the morphology and fat infiltration of the hip surrounding muscles showed improvement relative to pre-treatment evaluations. The complete detachment of the iliopsoas during open reduction and Dega osteotomy resulted in exacerbated atrophy of the iliopsoas, whereas no significant changes were noted in the closed reduction group post-treatment.

DDH: Developmental Dysplasia of the Hip

MRI: Magnetic Resonance Imaging

CSAr：cross-sectional area ratio,

FI：degree of fatty infiltration

I: iliopsoas muscle

S: sartorius muscle

R: rectus femoris muscle

T: tensor fascia lata muscle

G: gluteus maximus muscle

Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Ethics approval: This retrospective chart review study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The Human Investigation Committee (IRB) of Shengjing Hospital of China Medical University approved this study (2022PS995K).

Consent to participate: Informed consent was obtained from legal guardians.

Consent for publication: Informed consent was obtained from legal guardians.

Conflicting interests: The authors declare that there is no conflict of interest.

Availability of data and materials: No datasets were generated or analysed during the current study.

Authors' contributions: All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by LD, WZ, and LL. The first draft of the manuscript was written by LD and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Competing interests: The authors declare that they have no competing interests.

Acknowledgements: Not applicable.

Terjesen T. Special symposium issue: Developmental dysplasia and dislocation of the hip. J Child Orthop. 2018;12(4):294-5. https://doi.org/10.1302/1863-2548.12.180092
Harris MD, MacWilliams BA, Bo Foreman K, Peters CL, Weiss JA, Anderson AE. Higher medially-directed joint reaction forces are a characteristic of dysplastic hips: A comparative study using subject-specific musculoskeletal models. J Biomech. 2017;54:80-7. https://doi.org/10.1016/j.jbiomech.2017.01.040
Noble PC, Kamaric E, Sugano N, Matsubara M, Harada Y, Ohzono K, et al. Three-dimensional shape of the dysplastic femur: implications for THR. Clin Orthop Relat Res. 2003(417):27-40
Song K, Gaffney BMM, Shelburne KB, Pascual-Garrido C, Clohisy JC, Harris MD. Dysplastic hip anatomy alters muscle moment arm lengths, lines of action, and contributions to joint reaction forces during gait. J Biomech. 2020;110:109968. https://doi.org/10.1016/j.jbiomech.2020.109968
Tsukagoshi Y, Kamada H, Kamegaya M, Takeuchi R, Nakagawa S, Tomaru Y, et al. Three-dimensional MRI Analysis of Femoral Head Remodeling After Reduction in Patients With Developmental Dysplasia of the Hip. J Pediatr Orthop. 2018;38(7):e377-e81. https://doi.org/10.1097/BPO.0000000000001186
Wu X, Li SH, Lou LM, Cai ZD. The techniques of soft tissue release and true socket reconstruction in total hip arthroplasty for patients with severe developmental dysplasia of the hip. Int Orthop. 2012;36(9):1795-801. https://doi.org/10.1007/s00264-012-1622-6
Barkatali BM, Imalingat H, Childs J, Baumann A, Paton R. MRI versus computed tomography as an imaging modality for postreduction assessment of irreducible hips in developmental dysplasia of the hip: an interobserver and intraobserver reliability study. J Pediatr Orthop B. 2016;25(6):489-92. https://doi.org/10.1097/BPB.0000000000000326
Starr V, Ha BY. Imaging update on developmental dysplasia of the hip with the role of MRI. AJR Am J Roentgenol. 2014;203(6):1324-35. https://doi.org/10.2214/AJR.13.12449
Barrett WP, Staheli LT, Chew DE. The effectiveness of the Salter innominate osteotomy in the treatment of congenital dislocation of the hip. J Bone Joint Surg Am. 1986;68(1):79-87
Severin E. Congenital dislocation of the hip; development of the joint after closed reduction. J Bone Joint Surg Am. 1950;32-A(3):507-18
Li LY, Zhang LJ, Li QW, Zhao Q, Jia JY, Huang T. Development of the osseous and cartilaginous acetabular index in normal children and those with developmental dysplasia of the hip: a cross-sectional study using MRI. J Bone Joint Surg Br. 2012;94(12):1625-31. https://doi.org/10.1302/0301-620X.94B12.29958
Lu W, Li L, Zhang L, Li Q, Wang E. Development of acetabular anteversion in children with normal hips and those with developmental dysplasia of the hip: a cross-sectional study using magnetic resonance imaging. Acta Orthop. 2021;92(3):341-6. https://doi.org/10.1080/17453674.2020.1866928
Takeuchi R, Kamada H, Mishima H, Mukai N, Miyakawa S, Ochiai N. Evaluation of the cartilaginous acetabulum by magnetic resonance imaging in developmental dysplasia of the hip. J Pediatr Orthop B. 2014;23(3):237-43. https://doi.org/10.1097/BPB.0000000000000032
Bassett GS, Engsberg JR, McAlister WH, Gordon JE, Schoenecker PL. Fate of the psoas muscle after open reduction for developmental dislocation of the hip (DDH). J Pediatr Orthop. 1999;19(4):425-32. https://doi.org/10.1097/00004694-199907000-00002
Yilmaz S, Aksahin E, Duran S, Bicimoglu A. The Fate of Iliopsoas Muscle in the Long-term Follow-up After Open Reduction of Developmental Dysplasia of the Hip by Medial Approach. Part 1: MRI Evaluation. J Pediatr Orthop. 2017;37(6):392-7. https://doi.org/10.1097/BPO.0000000000000690
Yuksel HY, Yilmaz S, Aksahin E, Celebi L, Duran S, Muratli HH, et al. The evaluation of hip muscles in patients treated with one-stage combined procedure for unilateral developmental dysplasia of the hip: part I: MRI evaluation. J Pediatr Orthop. 2009;29(8):872-8. https://doi.org/10.1097/BPO.0b013e3181c29cc9
Engelken F, Wassilew GI, Kohlitz T, Brockhaus S, Hamm B, Perka C, et al. Assessment of fatty degeneration of the gluteal muscles in patients with THA using MRI: reliability and accuracy of the Goutallier and quartile classification systems. J Arthroplasty. 2014;29(1):149-53. https://doi.org/10.1016/j.arth.2013.04.045
Goutallier D, Postel JM, Bernageau J, Lavau L, Voisin MC. Fatty muscle degeneration in cuff ruptures. Pre- and postoperative evaluation by CT scan. Clin Orthop Relat Res. 1994(304):78-83
Hyun SJ, Bae CW, Lee SH, Rhim SC. Fatty Degeneration of the Paraspinal Muscle in Patients With Degenerative Lumbar Kyphosis: A New Evaluation Method of Quantitative Digital Analysis Using MRI and CT Scan. Clin Spine Surg. 2016;29(10):441-7. https://doi.org/10.1097/BSD.0b013e3182aa28b0

Table 1 Comparison of muscle cross-sectional area and degree of fat infiltration around the hip between normal and DDH groups

	CSAr					FI
	I	S	R	T	G	I	S	R	T	G
DDH group	0.80 （0.70,0.87）	1.08 （0.94,1.19）	0.65 （0.45,0.83）	0.97 （0.85,1.15）	0.91 （0.74,0.90）	0.14 （0.10,0.22）	0.19 （0.12,0.23）	0.17 （0.10,0.23）	0.23 （0.16,0.31）	0.28 （0.22,0.35）
Normal group	1.02 （0.96,1.07）	1.02 （0.93,1.13）	0.88 （0.69,1.21）	0.98 （0.86,1.13）	0.97 （0.91,1.08）	0.07 （0.06,0.14）	0.13 （0.09,0.20）	0.12 （0.07,0.18）	0.17 （0.11,0.23）	0.23 （0.20,0.29）
P value	＜0.001	0.069	＜0.001	0.874	＜0.001	＜0.001	0.002	＜0.001	＜0.001	＜0.001

I: iliopsoas muscle S: sartorius muscle R: rectus femoris muscle T: tensor fascia lata muscle

G: gluteus maximus muscle

CSAr：cross-sectional area ratio, FI：degree of fatty infiltration

Table 2 Differences in muscle cross-sectional area and degree of fat infiltration among the subtypes in the DDH group

CSAr

FI

I

S

R

T

G

I

S

R

T

G

IHDI-Ⅱ

0.93

（0.88,1.02）

1.17

（0.88,1.49）

0.88

（0.63,1.02）

0.94

（0.79,1.13）

0.90

（0.73,1.11）

0.12

（0.11，0.16）

0.17

（0.14,0.21）

0.17

（0.09,0.23）

0.21

（0.17,0.26）

0.32

（0.18,0.35）

IHDI-Ⅲ

0.80

（0.71,0.86）

1.11

（1.00,1.23）

1.06

（0.80,1.30）

1.01

（0.87,1.28）

1.07

（0.87,1.28）

0.14

（0.10,0.22）

0.19

（0.12,0.19）

0.18

（0.10,0.23）

0.25

（0.16,0.34）

0.29

（0.23,0.32）

IHDI-Ⅳ

0.76

（0.63,0.84）

1.07

（0.92,1.13）

0.96

（0.67,1.27）

0.95

（0.85,1.13）

1.04

（0.67,1.42）

0.15

（0.09,0.21）

0.18

（0.11,0.24）

0.17

（0.11,0.23）

0.24

（0.16,0.29）

0.27

（0.23,0.38）

P value

＜0.001

0.108

0.379

0.438

0.725

0.982

0.731

0.829

0.409

0.872

I: iliopsoas muscle S: sartorius muscle R: rectus femoris muscle T: tensor fascia lata muscle

G: gluteus maximus muscle

CSAr：cross-sectional area ratio, FI：degree of fatty infiltration

Table 3 Comparison of muscle cross-sectional area and degree of fat infiltration in closed reduction alone group before operation and at last follow-up

	CSAr					FI
	I	S	R	T	G	I	S	R	T	G
Pre-operation	0.66 （0.62,0.79）	1.09 （1.02,1.25）	1.12 （0.69,1.24）	0.87 （0.76,1.14）	0.85 （0.80,0.86）	0.15 （0.06,0.19）	0.18 （0.10,0.23）	0.13 （0.10,0.19）	0.17 （0.12,0.23）	0.24 （0.20,0.27）
Last follow-up	0.86 （0.80,1.02）	0.93 （0.87,1.04）	0.93 （0.74,1.09）	1.07 （0.90,1.67）	1.00 （0.82,1.02）	0.06 （0.05,0.11）	0.09 （0.06,0.17）	0.08 （0.05,0.14）	0.09 （0.08,0.15）	0.14 （0.09,0.16）
P value	0.043	0.237	0.866	0.128	0.176	0.028	0.310	0.237	0.128	0.176

I: iliopsoas muscle S: sartorius muscle R: rectus femoris muscle T: tensor fascia lata muscle

G: gluteus maximus muscle

CSAr：cross-sectional area ratio, FI：degree of fatty infiltration

Table 4 Comparison of muscle cross-sectional area and degree of fat infiltration in the open reduction alone group before operation and at the last follow-up

	CSAr					FI
	I	S	R	T	G	I	S	R	T	G
Pre-operation	0.83 （0.75,0.91）	1.07 （0.87,1.16）	0.75 （0.50,1.28）	0.93 （0.72,1.04）	0.91 （0.86,1.01）	0.11 （0.08,0.16）	0.09 （0.06,0.15）	0.08 （0.07,0.15）	0.18 （0.12,0.23）	0.27 （0.22，0.33）
Last follow-up	0.62 （0.56,0.77）	1.18 （1.02,1.31）	0.91 （0.70，1.01）	1.14 （1.00,1.23）	0.89 （0.82,0.94）	0.07 （0.06,0.11）	0.08 （0.06,0.13）	0.07 （0.06,0.09）	0.12 （0.10,0.14）	0.16 （0.13,0.17）
P value	0.017	0.139	0.878	0.093	0.445	0.037	0.959	0.445	0.333	0.009

I: iliopsoas muscle S: sartorius muscle R: rectus femoris muscle T: tensor fascia lata muscle

G: gluteus maximus muscle

CSAr：cross-sectional area ratio, FI：degree of fatty infiltration

Table 5 Comparison of muscle cross-sectional area and degree of fat infiltration in the osteotomy treatment group before operation and at the last follow-up

	CSAr					FI
	I	S	R	T	G	I	S	R	T	G
Pre-operation	0.83 （0.78,0.92）	1.05 （0.95,1.12）	0.79 （0.36,0.97）	0.97 （0.88,1.12）	0.73 （0.58,0.91）	0.14 （0.08,0.23）	0.19 （0.12,0.23）	0.17 （0.08,0.23）	0.20 （0.12,0.31）	0.25 （0.19,0.30）
Last follow-up	0.72 （0.54,0.76）	1.29 （1.20,1.36）	0.90 （0.79，1.48）	0.75 （0.53,1.15）	0.93 （0.82,1.00）	0.08 （0.06,0.12）	0.13 （0.06,0.15）	0.07 （0.06,0.13）	0.14 （0.09,0.25）	0.16 （0.14,0.24）
P value	0.013	0.013	0.013	0.169	0.028	0.037	0.013	0.022	0.508	0.037

I: iliopsoas muscle S: sartorius muscle R: rectus femoris muscle T: tensor fascia lata muscle

G: gluteus maximus muscle

CSAr：cross-sectional area ratio, FI：degree of fatty infiltration

No competing interests reported.

Assessment and Quantitative Analysis of Hip Surrounding Muscles in Children with Developmental Dysplasia of the Hip via Magnetic Resonance Imaging

Status:

Version 1

Abstract

Background

Methods

Results

Conclusion

Figures

Introduction

Materials and Methods

Results

Discussion

Abbreviations

Declarations

References

Tables

Additional Declarations

Status:

Version 1