Correlation of the pathologic morphology on magnetic resonance imaging with Tönnis and International Hip Dysplasia Institute classification in developmental dysplasia of the hip.

Abstract

Background: The Tönnis classification is widely used to quantify the severity of developmental dysplasia of the hip (DDH) based on the epiphyseal ossification center, while the International Hip Dysplasia Institute (IHDI) has proposed an alternative system. However, the pathological morphology associated with these classifications remains inadequately defined.

Objective: This study aimed to elucidate the correlation between the Tönnis classification and the IHDI classification with the pathological morphology of cartilage and soft tissues in DDH.

Materials and methods: A retrospective analysis was performed on preoperative imaging data from 170 DDH children (210 hips). The degree of dislocation was classified according to the Tönnis and IHDI classifications. Magnetic resonance imaging (MRI) was utilized to observe limbus morphology, the relationship between the femoral head and acetabulum, and the coverage of the cartilaginous femoral head.

Results: In the Tönnis classification, all limbus in grade I were everted, whereas inverted or mixed grades comprised 95.1% in grade II and were 100% in grades III and IV. The IHDI classification showed similar trends. For the Tönnis classification, grade I exhibited joint formation in acetabular structures, while joint formation was noted in only 27.5% of grade II, 3.2% of grade III, and 6.3% of grade IV. In the IHDI classification, joint formation was complete in grades I and II, observed in 27.3% of acetabular structures in grade III and 3.6% in grade IV.

Conclusion: Both classifications significantly correlate with pathological morphology in DDH, with the IHDI outperforming the Tönnis classification in distinguishing these morphologies as dislocation severity increases.