Correlation between Subcutaneous Knee Fat Thickness and Chondromalacia Patellae on Magnetic Resonance Imaging of the Knee

PURPOSE: Chondromalacia patellae is a common cause of anterior knee pain in young patients and can be detected noninvasively with magnetic resonance imaging (MRI). The purpose of our study was to evaluate the correlation between subcutaneous fat thickness around the knee joint on axial MRIs as a surrogate marker of obesity, with the presence or absence of chondromalacia patellae. METHODS: A retrospective review was conducted of knee MRIs in 170 patients who satisfied the inclusion criteria. Imaging was performed over a 12-month period on a 1.5T MRI system with a dedicated extremity coil. Two radiologists experienced in musculoskeletal imaging assessed each examination in consensus for the presence or absence of chondromalacia patellae and graded positive studies from 0 (absent) to 3 (full cartilage thickness defect). Measurement of subcutaneous knee fat thickness was obtained on the medial aspect of the knee. RESULTS: MRI findings of chondromalacia patellae were present in 33 patients (19.4%), of which, there were 11 grade 1 lesions (33.3%), 9 grade 2 lesions (27.3%), and 13 grade 3 lesions (39.4%). The mean subcutaneous knee fat thickness was significantly higher in the chondromalacia patellae group for all grades compared with the normal group (P < .001), and there was a significant correlation between subcutaneous knee fat thickness and grades of chondromalacia patellae (R = 0.48 [95% confidence interval, 0.38-0.68]; P < .001). Female patients had thicker subcutaneous knee fat and more severe grades of chondromalacia patellae. CONCLUSION: Subcutaneous knee fat thickness as a surrogate marker of obesity was positively associated with the presence and severity of chondromalacia patellae on MRI.