Comparison of MRI, CT, Dunn 45° and Dunn 90° alpha angle measurements in femoroacetabular impingement

Abstract

The Dunn 45° radiograph yielded a significantly higher alpha angle than Dunn 90°, axial oblique MRI, and CT imaging modalities. Use of the Dunn 90° or axial oblique MRI or CT as the threshold for cam osteoplasty may result in untreated symptomatic cam FAI. The authors recommend the Dunn 45° radiograph as the most sensitive evaluation of cam morphology.

Imaging Methodology for Hip Preservation: Techniques, Parameters, and Thresholds

“…With respect to combinations of lateral radiographic projections, some authors have demonstrated that the use of a three-view or two-view series provides the best approach for the evaluation of a cam morphology. [12][13][14] However, it is notable that the α angle and head-neck offset measurements from these and other XR views were reported to describe no more than 50% of the overall variation of the proximal femur shape. 13 In addition, less radiation exposure and affordable care have to be taken into account.…”

“…Nonetheless, relying on XR for the characterization of complex hip pathomorphologies, such as in femoroacetabular impingement (FAI), faces considerable constraints mainly related to inconsistencies in techniques, positioning, imaging quality, and reliability of reports. [9][10][11] With regard to femoral morphology, some authors have demonstrated that the use of a three-view series (AP pelvis, Dunn 45-degree view, and frog-lateral radiographs), 12 a twoview series (Meyer lateral and Dunn 90-degree views), 13 or even a one-view series (Dunn 45-degree view) 14 is adequately sensitive for the evaluation of a cam deformity. 14 In fact, the two-view series just described was reported to provide the most effective predictions of the three-dimensional (3D) shape of the proximal femur.…”

“…[9][10][11] With regard to femoral morphology, some authors have demonstrated that the use of a three-view series (AP pelvis, Dunn 45-degree view, and frog-lateral radiographs), 12 a twoview series (Meyer lateral and Dunn 90-degree views), 13 or even a one-view series (Dunn 45-degree view) 14 is adequately sensitive for the evaluation of a cam deformity. 14 In fact, the two-view series just described was reported to provide the most effective predictions of the three-dimensional (3D) shape of the proximal femur. 4,13 Conceptually, given that the hip is a 3D anatomical structure, fundamental radiologic parameters currently used to diagnose prearthritic hip conditions (i.e., two-dimensional [2D] parameters) would be increasingly facilitated with MRI and CT volumetric imaging (i.e., assessing both 2D and 3D parameters).…”

Editorial Commentary: Modified False-Profile View—Two Birds With One Stone?

“…This is because this image more consistently captures the area most commonly affected by cam morphology, which allows the practitioner to more consistently visualize the area of maximal deformity. 7 The modified false-profile view with the leg internally rotated 35 has consistently shown that it, too, looks at the area of the femoral neck between the 1-and 2-o'clock positions, 2 which is this area where cam lesions are most consistently located. 8 Up to 20% of patients will complain of hip pain on the contralateral side; the Dunn view has the advantage of showing the cam lesion in both hips, whereas the modified false-profile view will look at only 1 hip.…”

Editorial Commentary: What Exactly Is Impingement—Can Dynamic Magnetic Resonance Imaging “See” Impingement in Femoroacetabular Impingement?

“…Although providers should not routinely rely on advanced imaging to diagnose FAI syndrome, in select challenging clinical situations, MRI should obtain radial series to optimally evaluate the labrum and the proximal femoral morphology. 16,17 Sphericity morphology is a conceptually appealing theory to form the basis of a "normal" hip. This permits dichotomization with arbitrary choices of "abnormal" imaging findingsdelevated alpha angles, lateral centeredge angles, and version, among a few dozen others.…”