Modified International Hip Dysplasia Institute Classification And Its Correlation With The Pathologic Morphology Of The Hip On Magnetic Resonance Imaging In Developmental Dysplasia Of The Hip

Objective: Based on the T?nnis classification and International Hip Dysplasia Institution(IHDI)classification in developmental dysplasia of the hip(DDH),a new X-ray classification was defined as "modified IHDI classification",and the correlation was evaluated between the modified IHDI classification and the pathological morphology of the hip on magnetic resonance imaging(MRI).Methods: A retrospective review was conducted by analyzing the preoperative imaging data of DDH children who treated in the authors' institution from May 2010 to April2018.A total of 420 children(529 hips)with DDH met the inclusion criteria,including59 males and 361 females,105 involved in bilateral hips and 311 unilateral,303 left and226 right hips.The average age in surgery was 21.2 months(2.7-60.4 months).The radiographic severity was respectively graded by T?nnis,IHDI and modified IHDI classification methods and intra class correlation coefficient(ICC)was used to further evaluate the intra-observer and inter-observer consistency of the modified IHDI classification.Pathological changes of all hips in MRI were measured,including the morphology of the limbus,cartilaginous acetabular index(CAI),articular relationship between the femoral head and the acetabulum,and coverage of the femoral head.Results: The modified IHDI classification method revealed excellent intra-observer agreement(ICC = 0.985)and inter-observer agreement(ICC 0.955~0.984)across the three observers.The type III of IHDI classification coved three types of limbus,inverted type(70%),mixed type(17.7%)and everted type(12.3%);type IV demonstrated inverted(86.8%)and mixed shape(13.2%)of limbus(P < 0.001).The type III and IV of the modified IHDI classification all include mixed(15.7%,5.9%)or completely inverted limbus(84.3%,94.1%)(P=0.039).In the IHDI classification,articulated relationship was seen in 46.3% of type III hips and 7.5% type IV hips(P < 0.001);however,89.8% of the type III hips in modified IHDI classification,the femoral head did not form joint with the acetabulum.The CAI increased with the increased severity of dislocation in IHDI classification(ANOVA,P < 0.001);this changed trend was also seen in up to type III hips in modified IHDI,but the CAI was decreased in type IV hips(ANOVA,P < 0.001).There was a negative correlation between CAI and cartilage femoral head coverage(r =-0.389,P < 0.001).Conclusion: Related to the T?nnis and IHDI classification,the modified IHDI classification has a better capability to distinguish the pathological morphology of the hip among grades.With increased severity of modified IHDI,the limbus gradually tended to be more inverted and acetabular dysplasia was more serious while type IV was not serious;the modified IHDI classification enable to identify the frank dislocation from subluxated joints.The modified IHDI classification is helpful for the clinical diagnosis and treatment of DDH.