The Consistency Between Measurements Of The Femoral Neck Anteversion Angle In DDH On MRI And Three-Dimensional CT

1. BackgroundFemoral neck anteversion is the angle of anterior projection of the femoral neck relative to the femoral shaft when the femur is viewed along its long axis from above. FNA is very important to maintain the stability of Hip, FNA is one of the important pathological changes in Developmental Dislocation of the Hip (DDH).Accurate and reproducible measurement of femoral anteversion is indispensable for the evaluation of rotational disorders of the lower limbs, as well as in the preoperative planning of femoral neck derotation osteotomies.There are multiple methods for the quantification of the FNA angle, and the most used methods of imaging include fluoroscopic measurement methods, US evaluation, X-ray methods,2D CT,3D CT, and MR1.Relative to the 2D-CT,3D-CT can simulate anatomy method, reconstruction of the three-dimensional structure of the femur, so relatively more accurate and more reliable. Three-dimensional computed tomography (3D-CT) has been regarded by some investigators as the gold standard for measurements of the femoral neck anteversion angle (FNA) in developmental dysplasia of the hip (DDH). Because the femoral condyle of infants has not completely ossified, epiphyseal cartilage is not well visualized on CT and the condyle plane cannot be confirmed accurately using 3D CT, which affects the accuracy of FNA. Very young children are three to four times more sensitive to ionizing radiation than adults. Radiation has oncogenic effects in newborn babies and young children that can remain dormant for many years. Therefore, we develop and use simple and reliable imaging methods using nonionizing techniques for hip examination in these individuals. A simple and reliable imaging method using a nonionizing technique is needed.Ultrasonic measurement is economic, convenient and no radiation, and now it has been widely applied to clinical about diagnosis of newborn (<6 months) in DDH, and guidance of clinical treatment of infantile DDH; But the accuracy of diagnosis relies heavily on the experience of operator; Inspectors of the experience, operation technology and skilled degree is different, the consistency of the Graf method is used to check the result is also different, which can make the diagnosis of false positives, lead to excessive treatment. The results of ultrasonic measurement of FNA are related with experience of inspectors and the measurement method, relatively poor stability and repeatability.In 1997, the scholars Reinhard j. Tomczak proposed MRI measurement method of FNA, and made correlation research, compared with 2 d-CT; and considered that MRI is consistent with 2D-CT in the accuracy, reliability and repeatability. Since then, MRI measurement has been gradually applied in clinical for its accuracy, reliability and no radiation. But there is almost no study on consistency between measurements of the femoral neck anteversion angle in DDH on 3D-CT and MRI.2. PurposeOur purpose is to determine the consistency between measurements of the FNA in DDH using 3D-CT and magnetic resonance imaging (MRI) and to estimate the precision, reliability, and reproducibility of MRI for the measurement of the FNA and assess whether MRI could replace 3D-CT.3. Material and MethodsFrom June 2013 to April 2015, a total of 22 patients with a primary diagnosis of DDH clinically, were enrolled in the study. MRI was performed after CT examination within 24 hours.Cases included in the standards:the clinicians in the diagnosis of high qualification, in line with the developmental dislocation of the hip clinical manifestations and imaging features.The 3D CT scans were performed using a Toshiba Aquilion ONE 320 slice volume CT (Toshiba Medical Systems, Tokyo, Japan). Workstation adopts Toshiba Aquilion One medical image workstation Vitrea fx version 2.0. All of the MR images were obtained with a 3.0-T unit (Philips Achieva 3.0 T:Philips Medical Systems Nederland B.V., Amsterdam, Netherlands).For younger, unable to sleep, can’t cooperate with children who recommended the suitable amount of sedatives,30 min before scanning give chloral hydrate orally, after half an hour, if the children cannot sleep, can double the dose, waiting for the children to sleep after CT or MRI scan.MRI scan, indoor children observe MRI.The patients were placed in the supine position with the hips extended and the thighs horizontal and parallel. Feet slightly inward turning, heels slightly apart, place a cushion between ankles, and to tie the knee and ankle with the belt. Wear protective clothing to cover the scanning area.Scanning range:from the upper rim of the acetabulum to the lower rim of femoral condyle.The images were reconstructed at a CT workstation (Toshiba Aquilion One medical imaging workstation, Vitrea fx, version 2.0, Tokyo, Japan) to produce 3D images that could be observed and measured from any angle. We connected the posterior aspect of the epiphysis of the femoral condyles (Fig.2a) to a tangent to the femoral greater trochanter (Fig.2b) to form a plane called the condyle plane, which consisted of a straight line (Fig.2c) on the axis of an image. The FNA was the angle formed by the condyle plane and a line (Fig.2d) connecting the center of the femoral head to the midpoint of the narrowest femoral neckAfter the patient was properly positioned in the MR scanner, a triplane localizing sequence was performed with a hip coil to obtain the coronal section of the pelvis and femur (six slices with a thickness of 10 mm), and then sagittal to oblique axial sections could be placed parallel to the femoral neck axis. Oblique sagittal T2_TSE (TR,12.4 s; TE,120ms; matrix,256 X 256) non-fat-saturated images were obtained through the femoral neck, with each slice 3 mm in thickness with a 3 mm inter-slice gap. A single image was selected that showed the true neck axis connecting the center of the head and the midpoint of the narrowest femoral neck. The alpha angle between the axis and a horizontal reference line was calculated (Fig.3a). Then, T1_TSE (TR,600ms; TE,25ms; matrix,256 X 256) images of the knee were obtained, with each slice 2.5 mm in thickness with a 2.5 mm inter-slice gap, and the image that best demonstrated the convexities of the posterior aspects of the femoral condyles was chosen. The beta angle between the posterior border of the epiphysis cartilage on thefemoral condyle and the horizontal reference line could then be determined (Fig.3b).The FNA could be calculated from these two angles. Relative to the horizontal reference line, if the distal femur was externally rotated, the beta angle was subtracted from the alpha angle; alternatively, if the distal femur was internally rotated, the beta angle was added to the alpha angle.To determine the intra-and inter-rater variations in the measurements using each technique, the angles in all of the 3D CT and MRI images were measured independently by two radiologists (A, B). This exercise was repeated 2 weeks later by one (A) of the radiologists. Then, the data were tabulated, and statistical analysis was performed.According to our objective and the type of samples, the intra-class correlation coefficient (ICC) statistic was calculated using SPSS software (version 22, IBM, Armonk, NY, USA). The two-way mixed mode was used because our observers were measuring identical images and were not selected randomly. In this study, we chose an ICC of 0.7 as the cutoff point between unacceptable and acceptable agreement, and P <0.05 was regarded as significant.4. ResultsThese patients included 18 girls and four boys with a mean age of 3 years (age range,1-7 years). Because of the requirement for accurate estimation, the FNA was measured using 3D CT and MRI in 23 hips of 22 children, consisting of 15 left hips and eight right hips.On 3D CT, the mean angle was 48.82. On MRI, the mean angle was 46.47.The ICC values for the measurements of the FNA using 3D CT and MRI by two independent observers (A and B) at different times are listed in Tables 1-3 (A1 said observer A’s measurement for the first time, A2 said observer A’s measurement for the second time)The results showed the reliability of 3D-CT intra-observer (ICC=0.966), and MRI (ICC=0.964). The results showed the reliability of 3D-CT inter-observer (ICC=0.942), and MRI(ICC=0.948). The results showed the consistency of MRI and 3D-CT (ICC=0.906).The ICC values for all of the measurements were higher.5. ConclusionIn imaging diagnosis of developmental dislocation of the hip, MRI and 3D-CT have high consistency in measurements of FNA; with no ionizing radiation and the high resolution to the cartilage and the soft tissue around; can replace 3D-CT, measuring FNA accurately and reliably, provide adequate imaging basis for the diagnosis of developmental dislocation of the hip as well.