Suprapatellar fat-pad mass effect: MRI findings and correlation with anterior knee pain. 
The purpose of this study was to evaluate the MRI characteristics of the suprapatellar fat-pad, determine the prevalence and pattern of suprapatellar fat-pad edema, and correlate the findings with the presence of anterior knee pain, patellofemoral malalignment, and patellofemoral joint osteoarthritis.  We retrospectively reviewed 879 consecutive knee MRI examinations of 843 patients for the presence of a suprapatellar fat-pad mass effect on the suprapatellar joint recess.  The relative signal intensity and the maximum anteroposterior, craniocaudal, and oblique diameters of the suprapatellar fat-pad on sagittal fat-suppressed intermediate-weighted turbo spin-echo images were measured.  Findings of anterior knee pain, patellofemoral malalignment, and patellofemoral joint osteoarthritis were also recorded.  The Fisher exact, Mann-Whitney, and independent samples Student t tests and Spearman rank correlation coefficient were used for statistical analysis.  The prevalence of suprapatellar fat-pad mass effect on the suprapatellar joint recess in our study population was 13.8%.  The relative signal intensity (p < 0.0001) and maximum anteroposterior (p < 0.0001), craniocaudal (p = 0.0017), and oblique (p < 0.0001) diameters of the pad were significantly greater in patients with a mass effect.  Significant correlation was found between the relative signal intensity and the maximum anteroposterior (ρ = 0.0986, p = 0.0053), craniocaudal (ρ = 0.0968, p = 0.0062), and oblique (ρ = 0.123, p = 0.0005) diameters.  Mass effect was not significantly associated with anterior knee pain, patellofemoral malalignment, or patellofemoral joint osteoarthritis.  Six patients with suprapatellar fat-pad edema had anterior knee pain.  Suprapatellar fat-pad edema with a mass effect on the suprapatellar joint recess is a common finding at MRI examinations of the knee that is rarely associated with anterior knee pain.