Body Mass Index as a Predictor of Medial Knee Subcutaneous Fat on MRI: A Retrospective Study of 100 Knees

Obesity is characterized by excess adiposity. Magnetic resonance imaging (MRI) is used for quantifying and evaluating adiposity by precisely delineating soft tissues. It is widely used for assessing the visceral fat, but its use in evaluating subcutaneous fat (SCF) deposition in the lower body is scarce. This study aims to determine whether body mass index (BMI) predicts regional adiposity around the knee joint. In this retrospective study, 100 patients who had an MRI of the knee were enrolled. Based on the BMI, the patients were categorized into healthy, overweight, and obese groups. Landmark-based representative coronal sections of a proton density (PD) MRI sequence were used, and two experienced musculoskeletal radiologists calculated the medial fat measurement (MFM). The one-way analysis of variance (ANOVA) method was used for statistical analysis. 27, 41, and 32 patients were enrolled in the healthy, overweight, and obese groups, respectively. There was a clinically significant difference between the groups (F-ratio = 7.70, p-value = 0.00079) for the MFM. There was good intra- and interobserver reliability, with kappa coefficients of 0.8 and 0.9, respectively. BMI is a strong predictor of MFMs, indicating a direct relationship with knee regional adiposity. Landmark-based and straightforward measurements allow for reproducible and replicable assessment of SCF deposition.