Can radiographic morphometric parameters for the hip be assessed on MRI?

Background: Although morphometric hip parameters measured on radiographs are valuable tools guiding diagnosis and therapy in patients with hip disorders, some clinicians use MRI for such measurements, although it is unclear whether the parameters assessed on MRI differ from those assessed on radiographs.

Questions/purposes: We asked whether the lateral center-edge angle (LCE), Tönnis angle, extrusion index, and anterior center-edge angle (ACE) are similar on MRI and radiography.

Methods: We retrospectively reviewed the imaging data of 103 hips from 103 patients: 46 with femoroacetabular impingement and 57 with hip dysplasia. We manually measured the LCE, Tönnis angle, extrusion index, and ACE from radiographs and MRI in all 103 hips. Four straight coronal (Ant-10 mm, Ant-5 mm, Center, and Post-5 mm), three straight sagittal (S-Med-5 mm, S-Center, S-Lat-5 mm), and three 25º oblique sagittal (OS-Med-5 mm, OS-Center, OS-Lat-5 mm) reformats were reconstructed from a three-dimensional isotropic morphologic MRI sequence. MRI measurements were compared against the gold standard radiographic measurements.

Results: We found good agreement for the LCE angle, Tönnis angle, and extrusion index between radiographic and coronal slice MRI measurements. The mean differences between radiographic and MRI measurements were 5º or less or 5% or less (for the extrusion index) in all coronal MRI slices. However, the differences between ACE angles on sagittal MRI slices and radiographs ranged from 5° to 28º.

Conclusions: LCE, Tönnis angle, and extrusion index can be measured on MRI with comparable results to radiography. The ACE angle on radiographs cannot be estimated reliably from MRI.

Clinical Relevance: MRI provides similar morphometric measurements as radiography for most hip parameters, except for the ACE angle.