Hoffa's Test-Positive Knees Exhibit Increased Stiffness in the Lateral Region of the Infrapatellar Fat Pad: A Shear Wave Elastography Study.

Objective This study aimed to quantitatively evaluate the region-specific stiffness of the infrapatellar fat pad (IPFP) using shear wave elastography (SWE) in healthy young adults and to determine whether differences could be detected between individuals with positive and negative results on Hoffa's test. Methods Forty-four healthy young adults participated in this study. IPFP stiffness was measured using SWE with participants in the supine position with the knee fully extended. Measurements were obtained from four regions of the IPFP: subpatellar, central, lateral, and medial. Each region was measured five times, and five regions of interest were set within each area. The mean shear wave velocity (m/s) was calculated and used as the stiffness index. Hoffa's test was subsequently performed on all participants, who were then classified into Hoffa-positive and Hoffa-negative groups. After confirming normality using the Shapiro-Wilk test, between-group comparisons were conducted using independent samples t-tests. Effect sizes were calculated using Cohen's d. Results Seventeen participants were classified as Hoffa-positive and 27 as Hoffa-negative. The Hoffa-positive group demonstrated significantly greater stiffness in the lateral region of the IPFP than the Hoffa-negative group (p < 0.01, Cohen's d = 1.31). No significant between-group differences were observed in the other regions. Conclusions In healthy young adults, a positive Hoffa's test was associated with increased stiffness in the lateral region of the IPFP rather than generalized stiffness changes across the entire fat pad. Because this study was cross-sectional and conducted in asymptomatic individuals, these findings should be interpreted as an association rather than as evidence of a causal or pathological relationship. Regional stiffness assessment using SWE may provide quantitative information about localized mechanical characteristics of the IPFP and may complement the conventional clinical examination. Further longitudinal studies, including studies involving symptomatic populations, are required to clarify the clinical relevance of this approach.