Reliability of a New Radiographic Classification System for Developmental Dysplasia of the Hip

The Tonnis radiographic classification for developmental dysplasia of the hip (DDH) has been widely used for grading the severity of the disease. By definition, this method requires the presence of an ossification centre, which can be delayed in appearance and eccentric in location at times. The International Hip Dysplasia Institute (IHDI) classification, a new classification system recently developed by the IHDI, answers the scenario unanswered by the Tonnis classification. This study aimed to validate its reliability in evaluating DDH with an ossification center and to compare the 2 classifications in evaluating all DDH hips. In total, the pelvic radiographs of 92 DDH patients (115 hips) between the ages
of 6 and 48 months between 2014 and 2017 were assessed by 3 observers retrospectively using the 2 classifications. Intraobserver and interobserver variations were evaluated using Cohen’s kappa method and graded with Munro’s correlation strength categories. Both classifications showed excellent intraobserver and interobserver reliability. However, the IHDI demonstrated more interobserver reliability,
especially for evaluating DDH without an ossification center. The IHDI classification exhibited good practicability in classifying the radiographic severity of DDH compared to the Tonnis classification, particularly in hips without an ossification center. Therefore, the IHDI classification seems to be the expanded version of the Tonnis classification and can be used as a reliable tool in the management of the early
stages of DDH to stage the disease and plan treatment accordingly. Keywords:Tonnis classification, IHDI classification, DDH