Biochemical MRI With dGEMRIC Corresponds to 3D-CT Based Impingement Location for Detection of Acetabular Cartilage Damage in FAI Patients

Abstract

Background: Anterior femoroacetabular impingement (FAI) is associated with labral tears and acetabular cartilage damage in athletic and young patients. Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) is an imaging method for detecting early damage to cartilage.

Purpose: We evaluated the following questions: (1) What is the sensitivity and specificity of morphological magnetic resonance imaging (MRI) and dGEMRIC for detecting cartilage damage? Do the mean acetabular and femoral dGEMRIC indices differ between (2) superior acetabular clock positions with and without impingement and (3) between cam- and pincer-type FAI?

Study design: Cohort study (diagnosis); Level of evidence, 2.

Methods: This was a retrospective comparative study of 21 hips (20 patients with symptomatic anterior FAI) without osteoarthritis on anteroposterior radiographs. Morphological MRI and dGEMRIC (3.0-T, 3-dimensional [3D] T1 maps, dual-flip angle technique) of the same hip joint were compared. Intraoperative acetabular cartilage damage was assessed in patients who underwent surgical treatment. Computed tomography (CT)-based 3D bone models of the same hip joint were used as the gold standard for the detection of impingement, and dGEMRIC indices and zones of morphologic damage were compared with the CT-based impingement zones.

Results: Of the 21 hips, 10 had cam-type FAI and 8 had pincer-type FAI according to radiographs. The mean age was 30 ± 9 years (range, 17-48 years), 71% were female, and surgical treatment was performed in 52%. We found a significantly higher sensitivity (69%) for dGEMRIC compared with morphological MRI (42%) in the detection of cartilage damage (P < .001). The specificity of dGEMRIC was 83% and accuracy was 78%. The mean peripheral acetabular and femoral dGEMRIC indices for clock positions with impingement (485 ± 141 and 440 ± 121 ms) were significantly lower compared with clock positions without impingement (596 ± 183 and 534 ± 129 ms) (P < .001). Hips with cam-type FAI had significantly lower acetabular dGEMRIC indices compared with hips with pincer-type FAI on the anterosuperior clock positions (1 to 3 o'clock) (P = .018).

Conclusion: MRI with dGEMRIC was more sensitive than morphological MRI, and lower dGEMRIC values were found for clock positions with impingement as detected on 3D-CT. This could aid in patient-specific diagnosis of FAI, preoperative patient selection, and surgical decision making to identify patients with cartilage damage who are at risk for inferior outcomes after hip arthroscopy.

Keywords: 3D-CT; FAI; dGEMRIC; femoroacetabular impingement; hip arthroscopy; hip preservation surgery; hip preserving surgery.

Figure 1.

(A) T1 dGEMRIC map of a 32-year-old woman with symptomatic cam femoroacetabular impingement is shown with lower T1 indices from 1 to 3 o’clock (orange). Red and orange colors indicate low T1 index (cartilage damage), and blue indicates high T1 index (intact cartilage). (B) Bony impingement simulation using CT-based 3D models of the same patient, with the red line indicating impingement zones from 1 to 3 o’clock. The 3 o’clock position represents anterior and 9 o’clock indicates posterior. (C) Intraoperative image of the acetabulum during surgical hip dislocation of the same patient. The white arrows show cartilage damage. (Figure 1C from Schmaranzer et al. Reprinted with permission from Wolters Kluwer Health.)

Figure 2.

Mean dGEMRIC index (ms) and osseous impingement zone (%) based on CT-based collision detection software for each (A) acetabular and (B) femoral clock position (9 to 3 o’clock) for all hips. *Statistically significant difference between clock positions.

Figure 3.

Mean dGEMRIC indices for (A) acetabular and (B) femoral clock positions with and without osseous impingement. Subgroup analysis of hips with cam and pincer was performed. *Statistically significant difference between clock positions.

Figure 4.

The results of the mean dGEMRIC indices for hips with (A) cam-type FAI, (B) pincer-type FAI, (C) mixed-type, and (D) all hips. Blue indicates healthy cartilage, while red indicates cartilage damage. FAI, femoroacetabular impingement.

Figure 5.

Intraoperative view of a 33-year-old male patient who underwent surgical hip dislocation. A cartilage flap anterosuperiorly was detected using the surgical probe. The peripheral acetabular dGEMRIC index was 435 ms for 1 o’clock, 450 ms for 2 o’clock, and 440 ms for 3 o’clock.