CT And MRI Study Of The Children’s Hip Center Of Rotation And Hip Sphericity In DDH

Part ⅠCT and MRI study of the children’s hip center of rotationBackgroundDevelopmental dysplasia of the hip(DDH)is a common lower limb deformity in orthopedics.It is a common and frequently-occurring disease in pediatric orthopedics.The incidence rate is 0.1%to 0.2%,and women are about 5 times as many as men.The hip joint is a ball and socket joint of the human body.The acetabulum and the femoral head are concentric sphere structure.The hip center of rotation,the center of the acetabular sphere,and the center of the femoral head are the same center.The growth and development of the normal hip depends on the concentric sphere relationship between the acetabulum and the femoral head.When the concentric sphere relationship of hip joint is destroyed,a series of changes occur in the shape,size and compatible relation of the acetabulum and the femoral head,resulting in the appearance of DDH.The diagnosis of DDH depends on physical examination and imaging examination,in which imaging data are important objective basis.The main examination methods include ultrasound,X-ray,CT,MRI and joint angiography.At present,ultrasound and X-ray examination are the common clinical examination methods for the diagnosis of DDH in infants and young children.Ultrasound is suitable for infants within 6 months.At this stage,the femoral head is almost all cartilage components,which is of great value for screening and early diagnosis of DDH.Ordinary X-ray examination can not directly display the uncalcified femoral head of infants and young children,only the ossification center of femoral head can be displayed.The diagnosis of DDH can only be judged by some indirect signs or parameters,such as the central edge angle,etc.There are many parameters related to the center of the femoral head,which is an important reference mark.In the past,there were literatures describing how to position the center of the femoral head on the X-ray film,However the steps are cumbersome,the measurement and positioning are quite different,and the requirements for the the children’s posture and plain film quality are very high.CT and MRI can display the three-dimensional anatomy of the hip joint in multiple directions,and the pathological changes of hip joint diseases such as DDH are also three-dimensional.Therefore,CT and MRI are more and more widely used for the examination of hip joint.MRI has an excellent soft tissue resolution and can clearly show the bone,cartilage and soft tissue structure of intra and extra the hip joint,which is not available in any other imaging methods.Since the hip anatomy can be clearly displayed on a multidirectional tomographic image,whether the childen’s hip center of rotation can be accurately positioned on the tomographic image is rarely involved in the prior literature.ObjectiveBased on the concentric sphere structure of normal children’s hip joints,the hip center of rotation is attempted to be positioned on CT and MR images,and a simple and accurate clinical positioning method is proposed.Materials and Methods1.Research objectCT and MRI data of 54 normal children’s hip joints were collected in Shandong Provincial Hospital from June 2015 to June 2018.All 54 chilren underwent MSCT and MRI,1-12 years,mean age 6.5 years;there were 31 males and 23 females.Exclusive criteria:1.History of hip trauma,inflammation,tumor,etc;2.Diseses such as hip dysplasia or other low limb deformities;3.Cerebral palsy,spinal cord injury or other neuromuscular diseases.2.Equipment and technology,methods2.1 PreparationFor children less than 5 years old who cannot cooperate with imaging examination,30 minutes before the examination,and oral 10%chloral hydrate solution at a dose of 0.5 ml/kg was performed for sedation.During MSCT and MR examination,the child uses a supine posture and the head enters firstly,both lower limbs are naturally straight and the toes are up,and the sandbags are fixed between the ankle joints and the lateral sides to prevent the position of the lower limbs change during the scanning process.At the time of MSCT scanning,the radiation sensitive parts of the examinee are protected by lead clothing.2.2 CT scanning and image post-processingVolume scanning was performed using the Discovery CT 750HD produced by American GE Company.The scan range was from the level of the iliac crest to the proximal part of the femur.After the scan was completed,thin layer thick reconstruction of raw data was carried out by soft tissue algorithm.The data was reformationed in multiple directions by the ADW4.6 post-processing workstation of CT.The post-processing workstation was used to draw a circle tool on the central slice image of the femoral head in oblique-coronal,oblique-sagittal,and conventional coronal position,on the middle window image.The fitted circle coincides with the edge of the femoral head and the center of the circle is automatically generated.On the oblique-coronal image,draw a parallel line along the direction of the epiphyseal cartilage plate through the center,intersect with the fitted circle,and draw the vertical line of the epiphyseal plate to the edge of the femoral head,toward the acetabular apex.Two other vertical lines were obtained by performing the same operation on the central slice images of the oblique-sagittal and conventional coronal position.2.3 MR scanning and image post-processingThe hip joint scan was performed using Verio 3.0T magnetic resonance produced by SIEMENS,Germany.The transverse and coronal scans of the bilateral hip joints were performed.The "Y" cartilage of the acetabulum on both sides serves as a reference marker,adjusting the scanning plane to pass through the center of the femoral head.The TSE sequence,the axial position T1WI,the T2WI,the coronal T1WI,and the short TI inversion recovery sequency(STIR)coronal image scanning were performed using a multi-channel body coil.The scan range was from the level of the iliac crest to the proximal part of the femur.The layer thickness is 2.5 to 3 mm and the layer space is 0.5 to 0.6 mm.The same operation of the CT coronal image was performed on the central slice image of the femoral head in coronal STIR sequence.3.Data processingAccording to the developmental rules and characteristics of children femoral head cartilage,children were divided into groups of 1-4 years old and 4-12 years old according to age.Using the blind method,the three high-grade imaging specialists measured vertical line length on the central slice image in the oblique-coronal,oblique-sagittal,and conventional coronal position of the bilateral femoral head MSCT;On the central slice of the femoral head of the hip joint MR coronal STIR sequence,the length of the parallel line of the epiphyseal cartilage plate and the vertical line were measured;The radius of femoral head on oblique-coronal,oblique-sagittal and conventional coronal CT images,the diameter and radius of femoral head on MRI were obtained in normal children.4.Statistical analysisData statistical analysis was performed using SPSS(Statistical Product and Service Solutions)22.0 software.The samples were tested for homogeneity by variance using the Levene test.One-Way ANOVA was used to compare the differences in the measured values of the bilateral femoral head radii in different age groups on different orientation CT images and coronal MR images,P<0.05 difference was statistically significant.Using independent sample T test,vertical line length of epiphyseal cartilage plate and 1/2 value of the length of a parallel line of epiphyseal cartilage plate was compared on central slice image on the coronal MRI of the bilateral femoral head,P<0.05 was statistically significant.Results1.Radius values were measured of femoral head on multidirectional CT and MRI(i.e.vertical line length of femoral head on oblique-coronal,oblique-sagittal,coronal CT and coronal MRI)in 54 children(108 hips).P value>0.05,sample variance was uniform and in accordance with normal distribution.Coronal MRI of hip joint are superior to CT images in displaying the shape,bony and cartilaginous structure of femoral head in children,and can clearly distinguish epiphysis and epiphyseal cartilage of femoral head.2.In 1-4 year old group,the mean radius of the femoral head in the oblique-coronal,oblique-sagittal,coronal CT image and coronal MRI of 17 normal children was:9.51 ± 1.72、8.76±1.68、8.82±1.61、3.11 ± 1.38(mm)on the left,9.44±1.80、8.76± 1.77、8.88± 1.80、2.96±1.46(mm)on the right.About the measurements,bilateral P value<0.05,there was significant difference between multidirectional CT and the coronal MRI.3.In 4～12 years old group,the mean radius of the femoral head in the oblique-coronal,oblique-sagittal,coronal CT and coronal MRI of 37 normal children was:18.33±2.52、18.01 ± 2.39、18.41±2.45、18.41 ± 2.40(mm)on the left,18.14±2.54、17.86±2.41、18.18±2.54、18.16±2.44(mm)on the right.About the measurements,Bilateral P value>0.05,there was no significant difference between multidirectional CT image and the coronal MRI.The centers of a circle of oblique-coronal,oblique-sagittal,coronal CT and coronal MRI are the same center.There was no significant difference in the center location between multidirectional CT and coronal MRI.4.On coronal MRI,the measurement of femoral head radius and 1/2 value of the length of parallel line of epiphyseal cartilage plate was:16.74±3.26、16.39 ± 3.6(mm)on the left,16.52±3.26、16.30±3.60(mm)on the right.Using independent sample T test,the left side:P = 0.368,the right side:P = 0.335,the difference was not statistically significant.That is,the epiphyseal cartilage plate parallel 1/2 point was consistent with the center of the femoral head.5.During the measurement,we observed that the morphology of epiphyseal cartilage plate of femoral head in infants was slightly thicker and straighter;while in older children,the morphology of epiphyseal cartilage plate was relatively thinner and slightly wavy.On multidirectional CT and coronal MRI of the femoral head in children,the fitting center is located in the traveling area of epiphyseal cartilage plate,which is the center of the femoral head and the hip center of rotation.Conclusion1.On the central slice image of the femoral head in normal children,the midpoint of the epiphyseal cartilage plate can be used as the center of the femoral head.The radius of the femoral head is equal to 1/2 of the parallel line length of the epiphyseal cartilage plate.The fitting center is located in the walk region of epiphyseal cartilage plate;That is,the hip center of rotation can be accurately located on CT and MRI.2.The epiphyseal cartilage of femoral head in children is different with age.The epiphyseal cartilage of femoral head in children of 1-4 year old group is thicker and the ossification center is smaller.MRI is superior to CT in displaying the shape of acetabulum and femoral head in children,and it is more accurate in locating the hip center of rotation.However,MSCT has limited resolution to femoral head cartilage,at this time the center of femoral head can be located at the 1/2 midpoint in the upper border of the femoral metaphysis.3.In children of 4-12 years old group,the thickness of epiphyseal cartilage of femoral head became thinner obviously.MSCT and MRI showed betterly the shape of femoral head,and the edge of femoral head was clearly distinguished.There was no significant difference in the measurement of femoral head radius and the location of hip center of rotation.Part IICorrelation study between DDH hip sphericity on MRI and IHDI typeBackgroundBecause of the high disability rate of DDH,it seriously affects the physical and mental health of children,and brings enormous negative impact on families.The etiology of DDH is still uncertain.The age of DDH child,the degree of deformity of acetabulum and proximal femur,and the condition of adjacent muscles and ligaments and soft tissues of the hip directly affect the choice of treatment options and long-term efficacy.The basic pathological changes of DDH hip joint are the destruction of theconcentric sphere relationship between acetabulum and femoral head,and other pathological changes occur on this basis.The best therapeutic effect of DDH is to restore the stable concentric spherical reduction of acetabulum and femoral head.For children with DDH less than 6 months old,pediatric orthopedic surgeons routinely use orthopedic brace.If the brace treatment failure or the patient is more than 6 months or less than 12 months old,the surgeon usually uses closed reduction under anesthesia and external fixation with plaster.Over 12 months old,only open reduction and orthopaedic surgery can achieve a stable restore of the hip joint in children who have failed in closed reduction and plaster external fixation.Therefore,early diagnosis and early treatment of DDH are very important.Clinical judgment of DDH is based on medical imaging,especially X-ray plain film,there are a variety of measurement parameters to judge hip dysplasia or dislocation,and a variety of grades,type methods to determine the severity of the disease.But there is hardly a definite index in the classical parameters of X-ray,which can be used to intuitively and quantitatively evaluate the morphological changes of spherical and curved hip joint surface.MRI can visually display acetabular cartilage,labrum of hip joint and non-ossified femoral head in children,and can accurately show the morphological changes of the articular surface;however there is a lack of quantitative indicators for assessing changes in articular surface morphology.ObjectiveTo explore the quantitative evaluation value of sphericity in the changes of the articular surface of acetabulum in children with DDH and normal children.According to the MRI features of DDH hip joint,the sphericity of the diseased hip joint surface was compared with the International Hip Dysplasia Institute(IHDI)type,providing a new basis for making clinical treatment,judging the restore degree of hip joint and predicting the long term therapeutic effect.Materials and Methods1.Research objectFrom June 2015 to June 2018 in Shandong Provincial Hospital,MRI of hip joint were collected include 49 cases of DDH were confirmed by imaging and clinical examination,there were 34 cases of left hip and 15 cases of right hip,the age ranged from 1 to 12 years,mean age of 8.1 years,there were 15 males and 34 females;And 54 normal children aged 1-12 years,mean age 6.5 years,there were 31 males and 23 females,exclusive criteria:1.History of hip trauma,inflammation,tumor,etc;2.Diseases such as hip dysplasia or other lower limb deformities;3.Cerebral palsy,spinal cord injury or other neuromuscular diseases.2.Equipment and technology,methods2.1 Preparation:Same as the section I2.2 MR scanning and image post-processingSIEMENS Verio 3.0T MRI was used to scan the hip joints.(1)Transverse T1WI,T2WI and coronal T1WI,STIR sequences of bilateral hip joints were performed.The"Y" shaped cartilage of the acetabulum was taken as the reference marker,and the scanning plane was adjusted through the center of the femoral head when positioning;(2)For DDH children,the healthy side and the affected side were performed respectively,the coronal PDWI sequence of the single hip joint was scanned.3.Data processing3.1 Measurement method:In the center slice image of the femoral head on the hip coronal MRI,three straight lines were drawn from the center of the femoral head to the labrum of the upper edge of the acetabulum,the top of the acetabulum and the upper edge of the "Y" cartilage respectively.The sphericity score of the acetabulum surface was calculated by the difference between maximum radius and minimum radius in three straight lines3.2 The sphericity score is used to evaluate the similarity between the shape of the hip joint surface and the sphere.The formula is as follows:sphericity score = 1-Dmax,Dmax = maximum radius-minimum radius;for standard sphere,Dmax = 0,sphericity score is 1.0<sphericity score<1,when the sphericity score is closer to 1,the difference between the maximum radius and the minimum radius is smaller,the joint surface shape is closer to the sphere;when the sphericity score is closer to 0,the difference between the maximum radius and the minimum radius is bigger,the difference between the joint surface shape and the sphere is bigger.The sphericity depends on the shape of the object and has no correlation with the size of the object.According to the IHDI criteria,49 cases of DDH were classified,and the sphericity of the diseased hip joint was measured.The correlation between the sphericity of DDH and IHDI type was analyzed.4.Statistical analysisSPSS 22.0 software was used to analyze the data,and the measurement results were expressed as X±S.The sphericity scores of left and right hip joints in normal children were tested by independent sample T test,and P value<0.05,there was statistical difference between them.Normal children were divided into 1-4 years old group and 4-12 years old group according to their age,the sphericity scores of the two groups were statistically analyzed by independent sample T test,P value<0.05 the difference was statistically significant.One-way ANOVA was used to compare the sphericity scores between normal children and different types of DDH,and P value<0.05 the difference was statistically significant.Results1.MRI of the hip joints in 54 normal children showed that the articular surface of cartilage in both hips was generally round and spherical.The sphericity scores of the hip joint was 0.95 ± 0.03 on the left side,0.93 ± 0.03 on the right side,and the sphericity scores of both hip joints was close to 1.The results of the T test on the left side and right side showed P value =0.388,and the difference was not statistically significant.2.In this study,independent sample T test results of hip sphericity score in normal children of different age groups(1-4 years group and 4-12 years group):the right P value = 0.657,the left P value = 0.559,the difference was not statistically significant.3.According to IHDI criteria,49 DDH children were classified into four types.17 cases of type Ⅰ,11 cases of type Ⅱ,11 cases of type Ⅲ,and 10 cases of type Ⅳ.The sphericity scre of type I to IV were 0.77±0.08,0.72±0.13,0.46±0.21,0.39±0.15,One-way ANOVA results:P value=0.000,the difference was statistically significant.Conclusion1.In normal children,the morphology of the articular surface of the hip joint is basically round and spherical;there was no significant correlation between hip sphericity with age and side.2.The sphericity of DDH was negatively correlated with IHDI type,and the sphericity of DDH decreased with the IHDI type upgrade.With the sphericity of DDH decreases,histopathological changes of MRI in DDH hip joint were aggravated.3.Sphericity can directly and accurately reflect the morphology changes of hip joint surface.Combined with IHDI type is of great significance in guiding the treatment of DDH,judging the degree of joint reduction and predicting the long-term therapeutic effect.