MR Imaging of Quadriceps Fat Pad Edema and Associated Structures of the Anterior Knee Joint

Introduction Edema of the quadriceps fat pad (QFP) has been shown to be associated with anterior knee pain; however, its association with extensor tendinopathy is under debate. The aim of our study was to investigate a possible relationship between QFP edema and quadriceps tendon (QT) alterations.

Material and Methods In a retrospective study, 650 consecutive patients with clinically indicated magnetic resonance imaging (MRI) of the knee and 10 healthy individuals as controls were included. A 3-T MRI was performed using T1-weighted sagittal and intermediate-weighted sagittal, coronal, and axial sequences with 3-mm slice thickness. Absence or presence of QFP edema was determined visually by two readers; if present, QFP edema was classified into three grades (1, mild; 2, intermediate; and 3, intensive). In addition, QFP signal intensity was measured and referenced to Hoffa’s fat pad, popliteal fat tissue, and gastrocnemius muscle. Morphological alterations of QT were classified into five grades (1, normal; 2, mild, 3, intermediate, 4, high-grade tendinopathy; and 5, partial tear). Statistical analysis was performed using the Fisher exact test.

Results In none of the controls but in 136 of 650 patients (21%), various degrees of QFP edema were found. In controls, QTs were classified grade 1 or 2. Overall, 11 patients (1.7%) with intensive QFP edema displayed morphological alterations of QT grade 3 or 4 (mean grade: 3.6). In 77 patients with intermediate QFP edema, QT alterations ranged between grade 2 and 4 (mean: 2.8). Data show a significant difference in QT tendon alteration between controls and patients with intensive QFP edema (p < 0.01).

Conclusion Our study shows that QFP edema is related to QT alterations. Patients with intensive QFP edema displayed significantly higher grades of QT tendinopathy than controls.

No conflict of interest has been declared by the author(s).