Quadriceps Fat Pad Edema Is Associated with Quadriceps Tendon Alteration in MR Imaging

Purpose: Edema of the quadriceps fat pad (QFP) has been shown to be associated with anterior knee pain and QFP mass effect. However, the etiology of QFP edema is still being debated, and a clear association with extensor tendinopathy has not yet been established. The aim of our study was to investigate a possible relationship between QFP edema and quadriceps tendon (QT) alterations. In addition, other possibly related parameters of anterior knee structures were determined.

Methods and Materials: In a retrospective study, 800 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 IW 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, moderate; and 3, strong). In addition, QFP signal intensity was measured and set in reference to signal intensity of Hoffa’s fat pad, popliteal fat tissue, and gastrocnemius muscle. Alterations of QT were classified into five grades (1, normal; 2, mild; 3, intermediate; 4, high-grade tendinopathy; and 5, partial tear). Furthermore, QT thickness and both tibial-tuberosity to trochlear groove (TT-TG) distance and Insall-Salvati ratio as established patellar parameters were determined. Statistical analysis was performed using the Kruskal-Wallis test or one-way analysis of variance.

Results: A total of 151 of the 800 (19%) patients but none of the asymptomatic controls showed various degrees of QFP edema. In controls, QTs were classified as grade 1 or 2. In 77 patients (9.6%) with moderate QFP edema, QT alterations ranged between grade 2 and 4 (mean, 2.8), and in 16 patients (2.0%) with strong QFP edema, tendon alterations were found to be grade 3 or 4 (mean, 3.6). Analysis showed significantly higher grades of QT alterations in patients with intermediate and intense QFP edema as compared with controls, and also significantly different grades of QT alterations of patients with mild and intermediate compared with those with high grades of QFP edema (p < 0.01). In addition, a mildly but not significantly increased average QT thickness was found in individuals with all grades of QFP edema compared with controls (controls, 7.5 mm; grade1, 7.6 mm; grade 2, 8.0 mm; grade 3, 8.6 mm; p > 0.05).

Conclusion: Our study shows that QFP edema is related to quadriceps tendinopathy in an intensity-dependent manner. Patients with intensive QFP edema display significantly higher grades of QT tendinopathy than controls and patients with lower grades of QFP edema. This is accompanied by a mild but not significant increase in QT thickness.

Publication History

Article published online:
17 December 2020