MRI hip morphology is abnormal in unilateral DDH and increased lateral limbus thickness is associated with residual DDH at minimum 10-year follow-up

Abstract

Purpose: The purpose of the study was to compare the post-reduction magnetic resonance imaging morphology for hips that developed residual acetabular dysplasia, hips without residual dysplasia, and uninvolved contralateral hips in patients with unilateral developmental dysplasia of the hip undergoing closed or open reduction and had a minimum 10-year follow-up.

Methods: Retrospective study of patients with unilateral dysplasia of the hip who underwent open/closed hip reduction followed by post-reduction magnetic resonance imaging. Twenty-eight patients with a mean follow-up of 13 ± 3 years were included. In the treated hips, residual dysplasia was defined as subsequent surgery for residual acetabular dysplasia or for Severin grade > 2 at latest follow-up. On post-reduction, magnetic resonance imaging measurements were performed by two readers and compared between the hips with/without residual dysplasia and the contralateral uninvolved side. Magnetic resonance imaging measurements included acetabular version, coronal/ axial femoroacetabular distance, acetabular depth-width ratio, osseous/cartilaginous acetabular indices, and medial/lateral (limbus) cartilage thickness.

Results: Fifteen (54%) and 13 (46%) hips were allocated to the "no residual dysplasia" group and to the "residual dysplasia" group, respectively. All eight magnetic resonance imaging parameters differed between hips with residual dysplasia and contralateral uninvolved hips (all p < 0.05). Six of eight parameters differed (all p < 0.05) between hips with and without residual dysplasia. Among these, increased limbus thickness had the largest effect (odds ratio = 12.5; p < 0.001) for increased likelihood of residual dysplasia.

Conclusions: We identified acetabular morphology and reduction quality parameters that can be reliably measured on the post-reduction magnetic resonance imaging to facilitate the differentiation between hips that develop with/without residual acetabular dysplasia at 10 years postoperatively.

Level of evidence: level III, prognostic case-control study.

Keywords: Post-reduction MRI; developmental dysplasia of the hip; hip; hip MRI; surgical hip reduction.

Figure 1.

Flowchart of the study population is shown.

Figure 2.

Bilateral MRI measurements are shown in a hip undergoing closed reduction and in the untreated contralateral side. Differences in quantitative parameters are demonstrated with the treated hip showing a greater degree of morphologic instability. (a and b) Axial measurements: (a) Acetabular version is measured as a line connecting anterior and posterior acetabular cartilage perpendicular to a line connecting the posterior acetabular columns (dashed line). (b) Axial femoroacetabular distance corresponds to the perpendicular line between the rotation center and a line connecting anterior and posterior acetabular cartilage (dashed line). (c-g) Coronal measurements are shown. (c) Coronal femoroacetabular distance corresponds to the perpendicular line between the rotation center and a reference line (dashed line) connecting the teardrop with the lateral cartilage space. (d) Depth–width ratio. “Width” (gray line) corresponds to the distance between teardrop and the lateral cartilage space. “Depth” (white line) corresponds to the perpendicular distance between the halfway point of the acetabular width and the triradiate cartilage. (e) Osseous/(f) cartilaginous acetabular index corresponds to the angle between the lateral aspect of the osseus/cartilaginous acetabular edge relative to the Hilgenreiner line (dashed line). (g) Limbus thickness corresponds to a vertical line drawn along the lateral joint space at the transition between labrum and cartilage. (h) Medial cartilage thickness corresponds to a line drawn perpendicular to the osseous acetabulum along the medial cartilage space just above the level of the triradiate cartilage.