Objective:To evaluate the feasibility of high resolution MRI for the measurement of anterior cartilaginous acetabulum-head-index (A-CAHI) and the value of A-CAHI for predicting hip clinical function after treatment in developmental dysplasia of the hip (DDH).Methods:The imaging data of 92 hips from 61 children with treated DDH were retrospectively reviewed in Shandong Medical Imaging Research Institute from January 2019 to January 2020. All children underwent conservative treatments or surgical interventions 3 years ago. Hip function after treatment was evaluated clinically based on the modified MacKay criteria. The hips were divided into satisfactory clinical function group (McKay rating excellent or good, n=46) and unsatisfactory group (McKay rating fair or poor, n=46). All patients were imaged with conventional MRI, high resolution fat suppressed proton density weighted image (FS-PDWI) of the unilateral hip joint in oblique sagittal view, and anteroposterior hip radiographs. A-CAHI and lateral cartilaginous acetabulum-head-index (L-CAHI) were measured respectively on high-resolution oblique sagittal PDWI and conventional coronal T 1WI. Acetabulum head index (AHI) was also measured on anteroposterior hip radiograph. Mann-Whitney U test or independent-samples t test was used to compare the difference of A-CAHI, L-CAHI and AHI between satisfactory and unsatisfactory clinical function groups. The diagnostic value using A-CAHI, L-CAHI, AHI, or A-CAHI combined with L-CAHI for unsatisfactory clinical function were investigated by the ROC curve. The area under the curve (AUC) and the Z statistic were used to compare diagnostic performance. Results:The values of A-CAHI, L-CAHI and AHI were significantly higher in satisfactory clinical function group compared with the unsatisfactory group ( Z=-7.746, -7.735, t=-7.199, all P<0.001).A-CAHI combined with L-CAHI had the significant highest diagnostic accuracy compared with A-CAHI, L-CAHI and AHI (AUC were 0.994, 0.969, 0.968, 0.861, respectively), with significant differences ( Z=1.975, 2.006, 3.553, P=0.048, 0.051,<0.001). The sensitivity and specificity of A-CAHI combined with L-CAHI for the diagnosis of prognosis were 95.7% and 97.8%, respectively. Conclusions:A-CAHI measured by high resolution MRI was found to have the highest diagnostic accuracy for prediction of hip clinical function in the treated DDH, and combined with L-CAHI can improve the diagnostic accuracy significantly.