The Study On MRI'S Imaging Change In Infantile DDH Using Ferguson's Medial Approach Open Reduction

Objective:To study the clinical value of MRI during infantile DDH treatment through analysising MRI and X-ray which were obtained pre-operation and after operation with three～five months interval.Materials and Methods:Twelve untreated patients (3 boys and 9 girls;Age range from 11 months to 24 months;mean age 16.6 months ) ware diagnosed DDH by clinical characters.Those patients include unilateral hip dislocation 8 and bilateral hip dislocation 4;right was 6 and left was 10;in total was 16 ;and normal hip 8, dislocation hip which was caused by CP or joint contracture or injury etc was excluded.MRI studies were performed with a 0.35T MRI scanner and in a body coil.Axial and coronal images were obtained with a T1-weighted spin-echo(SE) pulse sequence,a repetition time (TR) of msec,and echo time (TE) of msec (TR/TE=350～450ms/14～18ms),a T2-weighted fast spin-echo (FSE) pulse sequence (TR/TE=2500～3000ms/118ms),and 2～3 excitations,slice thickness=4mm.X-ray pelvis films were performed with a(PHILIPS)IEC-60601-1 DR scanner,voltage is 66KV, electric current is 4mAs, exposure time is 13.3ms.All dislocation hip was classified three types according to the standard of Ogden and Dunn based on the position of femoral head on coronal layer,the femoral head removed lateral and located in acetabulum in TypeⅠ;the head center situated acetabular lateral rim in TypeⅡ;the head removed out completely from acetabulum and form a false acetabulum in TypeⅢ. All patients were measured with X-ray Acetabular Index(AI),X-ray Acetabular Quotient(AQ) on pelvis films ;the bony acetabular index (BAI) , cartilaginous acetabular index ( CAI) , bony acetabular quotient (BAQ) , and cartilaginous acetabular quotient (CAQ) on the coronal view passing femoral head center according to the method described by Fisher etc,and,to observe the dislocation hip by MRI.Results: The average value and standerd deviation of AI, AQ, BAI, BAQ, CAI ,and CAQ of the dislocation hip before operation and after operation with three～five months interval were respectively (29.25°±2.28°→25.97°±2.01°),( 0 . 21±0 . 03→0 . 23±0 . 03 ),( 29 . 06°±2 . 93°→25 . 34°±2 . 79°),( 0 . 17±0 . 03→0 . 19±0 . 03 ),( 17 . 06°±3 . 38°→12 . 56°±3 . 72°),(0.19±0.02→0.22±0.03);The difference between before operation and after operation with three～five months interval were (3.28°±0.75°),(0.018±0.014),(3.72°±1.47°),(0.019±0.027),(4.5°±1.81°),(0.03±0.028) .The difference of the normal hips on the same times were (2.06°±1.18°),(0.019±0.015),(1.5°±0.46°),(0.013±0.009),(1.13°±0.64°),(0.017±0.014) .We performed the statistical analysis about the measurement results of all dates.⑴T here were significant differences between pre-operation and after operation with three～five months interval of dislocation hip about AI,BAI,CAI and CAQ.⑵There were significant differences of dislocation hip between AQ and BAQ , AI and CAI , BAI and CAI pre-operation and after operation with three～five months interval respectively.⑶There were significant differences of dislocated hips between the difference of AI and CAI,AQ and CAQ, BAI and CAI,BAQ and CAQ.⑷There were significant differences between dislocation hip and normal hip of the difference of AI,BAI,CAI and CAQ.The MRI manifestations of DDH include:①Bony changes:In all dislocated hips,the femoral head became thin and flat. The epiphysis were smaller than that in normal hips.The development after reposition about the femoral head was faster than mormal hips.Severe developmental dysplasia of acetabulum were observed . Acetabulum was shallowed more and more as a triangle.The rotation of upward and forward about acetabulum could be observed on axial view.The neck of femur became short and flat,and the anteversion angle was increased with the development of dislocation.②Cartilaginous changes:The femoral head cartilage lacked smooth in most of dislocated hips.The normal shape of acetabular cartilage was disappeared.The changes of acetabular cartilage were various with different types. The acetabular cartilage was moved outward and proliferated unobviously in typeⅠ.The acetabular cartilage was displaced outward and thickened more visibly in typeⅡ. The acetabular cartilage was proliferated gibbously and its signal was uneven while labrum was inverted in typeⅢ.③Other changes: High signal in T1WI and T2WI about hyperplastic Fatty tissue inside joint were observed before operation in 14 dislocated hips.Low signal in T1WI and T2WI about ligamentum teres and transverse acetabular ligament were observed before operation in 9 dislocated hips while they were hyperplastic visibly. Moderately signal in T1WI and T2WI about Labrum and hyaline cartilage could be obtained ,and Labrum were inverted in 7 dislocated hips.A few effusion of articular cavity were presented in 11 dislocated hips which was low signals in T1WI and high signals in T2WI. Iliopsoas muscle and adductor muscles were presented in coronal position in all patients.Conclusions:①MRI can be used for diagnosing DDH accurately,evaluating pathologic changes of dislocated hips detailedly and individualy choosing reasonable treatment.②cartilaginous acetabular index ( CAI) and cartilaginous acetabular quotient (CAQ) were more accurate and sensitive than X-ray Acetabular Index(AI),X-ray Acetabular Quotient(AQ),bony acetabular index (BAI),bony acetabular quotient (BAQ) in describing the development of total hip joint after reposition,especially the development of cartilage and the globular acetabulum.③The Ferguson's operation was a ripe procedure which has significant therapeutic efficacy.It was more scientific to observe the development of cartilage than ossific structure after reposition by operation.The development of cartilage which were described by MRI provided a developmental tendency of total acetabulum within some times in the future. Some patients will avoid from osteotomy.④Compared to normal hips ,after reposition and achieve cocenric citcle standard,the development of total acetabulum in dislocated hips was faster than normal hips,and the dislocated hips has more powerful capability of growth and moulding.