Magnetic resonance imaging evaluation of the labrum to predict acetabular development in developmental dysplasia of the hip: A STROBE compliant study

Abstract

Recently, more attention has been paid to the role of the acetabular labrum. Therefore, we designed a retrospective cohort study of patients with residual hip dysplasia (RHD) who underwent magnetic resonance imaging (MRI). The objective of this study was to investigate an association between the MRI appearance of the labrum before school age and the natural history of RHD.We retrospectively investigated 45 hips of 40 patients who underwent MRI at about 3 and 4 years of age for RHD and were conservatively followed up with until 6 years of age or older. We evaluated the extent of eversion with a new method that measures the β angle (MRI β angle) using landmarks of the Graf method on MRI T2*-weighted images. The outcome measure was the Severin classification at the final follow-up. We compared the radiographic and MRI parameters at approximately 3 and 4 years of age between the good and poor outcome groups. The Student t test or one-way analysis of variance was used to compare the quantitative variables between groups. The Chi-square test was used to perform a ratio comparison.Although there was a significant difference in the center-edge (CE) angle, there was no significant difference in the acetabular index and the ratio of the presence of femoral head necrosis and the break in Shenton line between the good and poor groups. The MRI β angle was significantly greater in the poor outcome group than in the normal and good outcome groups. The cut-off value of the MRI β angle to differentiate the good and poor outcome groups was 65°, and its specificity and sensitivity were 92% and 53%, respectively.There was labral eversion on MRI scans in patients with RHD. Acetabular development before adolescence was poorer with greater labral eversion on MRI scans. The specificity for poor acetabular development was high when the MRI β angle was 65° or more. The MRI β angle has the potential to predict acetabular development.

Figure 1

Measurement of the β angle on magnetic resonance imaging (MRI) scans. On the basis of landmarks in the Graf method, the baseline (dotted line) and cartilage roofline (white line) are drawn to measure the β angle on MRI scans. The baseline is defined as the tangent line with the lateral edge of the iliac wing (low signal area; black arrow). The cartilaginous acetabular line is defined as the line between the acetabular bony rim (low signal area; white arrow) and the center of the labrum (low signal area; dotted arrow). The acetabular bony rim is defined as the point on the lateral acetabular edge (low signal area) at which the curvature switches from concave to convex. Furthermore, the center of the labrum is defined as the center of the triangle (low signal area).

Figure 2

Comparison of β angles on magnetic resonance imaging (MRI) scans among the normal control, good outcome, and poor outcome groups. Error bars indicate the average and standard deviation.

Figure 3

Receiver operating characteristic (ROC) curve based on each value of β angles on magnetic resonance imaging (MRI) scans. Left: We consider the data point of 65° (arrow) on the ROC curve as the cut-off value to differentiate the good and poor outcome groups. Right: The scatter plots show the data for each group. The line indicates the cut-off line.