3-dimensional Morphological Analysis Of Anterior And Posterior Acetabular Notch In Developmental Dysplasia Of The Hip

Objective: Inappropriate acetabular cup orientation significantly increases the rate of perioperative complication following total hip arthroplasty(THA).However,there is a current controversy over which intraoperative landmark is better in guiding the anteversion placement of the acetabular cup during THA for developmental dysplasia of the hip(DDH).In this study,we analyzed the morphological characteristics of the anterior and posterior acetabular notches(APANs)using three-dimensional(3D)computed tomography(CT)and assessed its potential as a safe reference landmark for anteversion cup placement in THA for DDH.Methods: Database was searched retrospectively for patients with plain radiograph and high-definition CT of pelvis,then patients with clinical diagnosis of DDH were included.Through age/gender matching,patients who underwent a pelvis high-definition CT but with normal hips were set as a control group.After CT 3D-reconstruction using Mimics 20.0,the APANs recognition rate of hips was analyzed.Those hips with detectable APANs were included for future calculation.Three anteversion angles defined by surgery,anatomy and radiology were measured based on the line connecting the APANs,and their relationships with respective cup“safe zone” were explored.LCE angle,Sharp angle,Tonnis angle,lateral subluxation and acetabulum-head index were calculated on plain radiograph of DDH hips.X-rays of DDH hips with “non-safe” APAN anteversion angle were analyzed,and correlation between plainradiographic parameter and APAN anteversion angle were explored.Data was analyzed with SPSS 23.0.Results: 66 DDH patients(117 hips: Hartofilakidis type A,72;type B,41;type C,4)and 22 patients for control group(44 normal hips)were included.The recognition rate of APANs on CT is respectively: 100% for normal hips,100% for Hartofilikidis A hips,90.2% for Hartofilikidis B hips,0% Hartofilikidis C hips.After measurement of anteversion angle formed by detectable hips’ APANs,only average SAAN was within the cup safe zone,whereas average RAAN and AAAN were significantly smaller than their respective cup safe range.Safety ratio for SAAN is:100%(normal hips),88.9%(Hartofilikidis A hips),70.3%(Hartofilikidis B hips).Compared with DDH hips with safe SAAN,those with unsafe SAAN had smaller lateral center-edge angle(5.6° ± 12.3° vs-2.3° ± 13.0°,P=0.013),greater lateral subluxation(15.9 mm vs 20.9 mm,P=0.006),and greater Tonnis angle(30.8° vs.35.4°,P=0.005).Three measurements above were all correlated with SAAN(Correlation coefficient:-0.28,P=0.004;0.31,P=0.001;0.29,P=0.002).Conclusions: APANs can be easily identified by CT in healthy controls and Hartofilakidis A DDH patients,and may thereby serve as a good anatomical reference landmark for anteversion cup placement in sagittal view of the pelvis.SAAN-guided anteversion cup placement should be avoided in DDH hips with greatly reduced LCE angle,increased lateral subluxation,and increased Tonnis angle indicated by plain radiograph.