Retrospective observational study comparing the international hip dysplasia institute classification with the Tonnis classification of developmental dysplasia of the hip

Abstract

The Tonnis radiographic classification of developmental dysplasia of the hip (DDH) has been widely used. The International Hip Dysplasia Institute (IHDI) classification, a new classification system recently developed by the IHDI, is beginning to be applied to evaluate DDH with the absence of an ossification center. This study aimed to validate its reliability in evaluating DDH with an ossification center and compared the 2 classifications in evaluating all DDH hips. In addition, the prediction values of the 2 classifications on clinical management selection were compared.In total, the pelvic radiographs of 212 DDH patients (318 hips) between the ages of 6 and 48 months admitted to Shanghai Children's Medical Center between 2007 and 2014 were assessed by 3 observers retrospectively using the 2 classifications. Intraobserver and interobserver agreements were evaluated using the kappa method. We also assessed the correlation of the 2 radiographic classifications in terms of treatment selection.In total, 216 hips received closed reduction, 61 hips received open reduction, and 41 hips received pelvic osteotomy. Both classifications showed excellent intraobserver and interobserver reliability. However, the IHDI demonstrated more interobserver reliability, especially for evaluating DDH without an ossification center. Both classifications were found to be relevant in detecting the DDH treatment type (P < 0.01). The Tonnis classification was also relevant, especially for evaluating DDH with 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. Like the Tonnis classification, the IHDI classification can predict treatment plans. Therefore, the IHDI classification seems to be the upgraded version of the Tonnis classification.

Figure 1

Anteroposterior pelvic radiograph of an infant with right DDH. (A) The right hip was classified as a Tonnis grade III hip and the left hip was classified as a Tonnis grade I hip. The yellow point represented the center in ossific nucleus of femoral head. The right yellow point is located in the lower part of external upper rim of acetabulum but near with the SMA-line, whereas the left yellow point is medial to the P-line. (B) The right hip was classified as an IHDI grade III and the left hip was classified as an IHDI grade I. The yellow point represents the H-point which is defined as the midpoint of the superior margin of proximal femoral metaphysis. The horizontal/vertical/oblique purple lines respectively represent the H-line/P-line/D-line. DDH = developmental dysplasia of the hip, D-line = diagonal line, H-line = Hilgenreiner's line, IHDI = International Hip Dysplasia Institute, P-line = Perkin's line, SMA-line = superolateral margin of the acetabulum lines.

Figure 2

Anteroposterior pelvic radiograph of an infant with bilateral DDH. (A) The right hip was classified as a Tonnis grade II hip and the left hip was classified as a Tonnis grade IV hip. The yellow point represents the center in ossific nucleus of femoral head. The right yellow point is lateral to the P-line but below the SMA-line, whereas the left yellow point is above the SMA-line. (B) The right hip was classified as an IHDI grade III and the left hip was classified as an IHDI grade IV. The yellow point represents the H-point. The horizontal/vertical/oblique purple lines respectively represent the H-line/P-line/D-line. DDH = developmental dysplasia of the hip, D-line = diagonal line, H-line = Hilgenreiner's line, IHDI = International Hip Dysplasia Institute, P-line = Perkin's line, SMA-line = superolateral margin of the acetabulum lines.