Regional Differences in Infrapatellar Fat Pad Stiffness With Changes in Knee Flexion Angle: A Quantitative Analysis Using Shear Wave Elastography

Purpose This study aimed to quantitatively evaluate regional variations in infrapatellar fat pad (IPFP) stiffness at different knee flexion angles using shear wave elastography in healthy young adults and examined the effects of region and flexion angle. Methods Thirty-four healthy young adults participated in this study. IPFP stiffness was measured at four knee flexion angles (0°, 45°, 90°, and 135°) in four regions: subpatellar, central, lateral, and medial. Each condition was measured five times, and the mean value was used for analysis. Two-way repeated measures analysis of variance was performed to assess the effects of knee flexion angle and measurement site. Results IPFP stiffness differed significantly by flexion angle (p = 0.010) and region (p = 0.03). A significant interaction between flexion angle and site was also found (p < 0.001). Post-hoc Bonferroni analysis showed no significant pairwise differences among simple main effects. Conclusion IPFP stiffness demonstrated angle- and region-dependent patterns in healthy young adults, with significant main effects of knee flexion angle and measurement region as well as their interaction. However, Bonferroni-adjusted post-hoc analyses did not reveal significant pairwise differences between specific conditions. These findings suggest that the IPFP is a structurally complex tissue whose mechanical behavior varies with knee position and interactions with surrounding patellofemoral structures and provide clinically relevant baseline information for physiotherapeutic assessment of knees presenting with anterior knee pain.