gms | German Medical Science

Objectives: Appropriate three-dimensional imaging of the hip joint is a substantial prerequisite for planning and performing surgical correction of clinically relevant deformities. Although most surgeons still use CT investigations, modern and fast acquisition techniques of volumetric imaging using MRI for pelvic measurements enable similar resolution. It is unclear, however, if commonly used measures of acetabular morphology are comparable in both techniques and if assessment can be performed with equal intra- and inter-observer reliability.

Methods: In a prospective study 32 hips (16 patients) were examined with a pelvic CT (0.6 mm slice thickness) and a MRI with 3 Tesla (3D isotropic VIBE sequence, 0.8 mm slice thickness). Pelvic orientation was standardized by each observer for correct coronal, axial, and sagittal rotation. Acetabular version as well as 7 acetabular sector angles in 30° steps were measured by two observers twice with a minimum of 4 weeks between sessions (Figure 1 [Fig. 1]).

Intra- and interobserver, as well as intermethod comparisons were evaluated with Intraclass Correlation Coefficients, Two one sided t-Test, Bland-Altman plots, and linear regression analysis.

Results and conclusion: Interrater reliability showed excellent results for intra- and interobserver comparison for CT (0.977-0.999) and MRI (0.969-0.998) measuring acetabular version and sector angles [Table 1]. Evaluating the reliability of CT and MRI for each observer revealed equal good results (0.972-0.998) [Table 1]. Evaluating the Bland-Altman plots for intraobserver reliability showed an equal distribution of the angles, within acceptable 95% confidence intervals, which were similar for each observer. Same results were observed for interobserver reliability evaluating CT and MRI as well as intermethod reliability evaluating both observers. A linear regression analysis showed no significant proportional bias for all plots. No significant occurrence of deviations of 2° or more for all comparisons were found.

Modern MRI scans are equally applicable to assess the bony pelvis as CT scans. In addition MRI enables the examination of soft tissues like chondrolabral structures and muscle in the same examination. Since hip preserving surgery is mostly conducted in younger patients the reduction of radiation exposure is a valuable benefit.