The Application Of MRI In The Infantile Developmental Dislocation Of The Hip

Objective: Developmental dislocation of the hip (DDH) is a common disease in the pediatric orthopaedics. Acetabular morphology in DDH can be delineated by Magnetic resonance imaging (MRI) more accurately than by previously available imaging methods. To study the utility of MRI in the diagnosis and treatment of infantile DDH, we evaluated the morphous of the acetabulum and measured the degree of acetabular anteversion including bony and cartilaginous components.Methods: Unilateral DDH in 30 cases which were 25 females and 5 males, ranging in age from 12 to 36 months old (average 18.5 months) were examined with MRI at 3. 0T to perform the structure of the affected pelvis before the operations. All the cases were evaluated with coronal and transverse sections of T1-weighted images (T,WI) ,T2-weighted images (T₂WI) and fat-suppressed 3D spoiled gradient-echo (FS 3D SPGR). Both the bony acetabular anteversion and cartilaginous acetabular anteversion of the bilateral acetabulum were measured on the transverse section image passing the center of the normal femoral head.Results: (1)On the base of morphological observations, the images of the hips with dislocation can be divided into three types: I type: the picture in the affected acetabulum is uniform without strong singal ; II type:only a small piece of strong signal is on the margin of the acetabulum roof ;III type:more than half of the accetabulum is filled with strong signal. The positive rate to predict the interposition of the accetabulum with MRI is 93. 3% with the comparion of the findings during the operation. (2) The average values of BAA and CAA of the normal sides were respectively (11.5 ±4.5) (13.3 ± 4.2) ; those of the dislocated hips were (19.8±4.6) (22.2 ± 4.4) . The correlation coefficient between the average values of BAA and CAA of the normal hips was r=0.853, t: 8.54, p<0.05; and on the affected sides the correlation coefficient was r=0.928, t: 8.52, p<0. 05. All the cases were divided into two parts on the age of 18 months. The values of BAA of the normal side of the junior and senior parts were respectively (9. 17 ± 4.3) .. (12.2 ± 4.9) , the difference between the two values was not significant p>0. 05. The values of CAA of normal side of the two parts were respectively (11.3±1.2) , (13.9 ± 4.1) , the difference between the two values was also without significance p>0. 05. The values of the BAA of the dislocated sides of junior and senior parts were (16.4 ± 4. 5) (20.8 ± 4.3) respectively and the difference of the values was significant p<0. 05. The values of the CAA of the dislocated sides of junior and senior part were (18.3 ± 4.4) , (23.4 ± 4.6) respectively and the difference of the values was significant p<0. 05. Conclusions : (1) MRI is a useful method which could truly reflect the total morphologic changes of the soft tissue in the dislocated hips, so MRI can be used to predict the necessity of the cleaning of the accetabulum during the operation. (2) The BAA and CAA of the dislocated side are larger than those of the normal side respectively .There is no significant difference between the BAA and CAA of child' s normal side during developmental process. Both the bony and cartilaginous degrees of the accetabular anteversion of the affected side are increasing with age.