Infrapatellar fat pad stiffness is associated with knee symptoms in patients with knee osteoarthritis.

Objective: To clarify the association between infrapatellar fat pad (IFP) stiffness and size with knee osteoarthritis (OA) severity and knee symptoms.

Method: This study included 93 participants: 66 with symptomatic medial knee OA (Kellgren-Lawrence grade [KL] ≥ 2) and 27 healthy controls (KL grade 0 or 1) with asymptomatic knees. Shear modulus (stiffness) and thickness (size) of the IFP were measured using ultrasonography. The Knee Society Score (KSS) was used to assess knee symptoms. Maximum knee extension strength and external knee adduction moment during walking, both related to the symptoms of knee OA, were measured. The shear modulus and thickness of the IFP were compared among three groups: control, mild OA (KL grade 2), and severe OA (KL grades 3 and 4). Multiple regression analysis was performed to determine the association of IFP shear modulus and thickness with knee symptoms.

Results: The IFP shear modulus was higher in the severe OA group than that in the control group, with no significant differences among the other groups. There were no significant differences in thickness between the groups. The shear modulus was significantly associated with the KSS symptom scores, indicating that a stiffer IFP correlated with more severe knee OA symptoms. Conversely, the IFP thickness was not associated with the KSS symptom scores.

Conclusions: Infrapatellar fat pad stiffness was higher in severe knee OA, and greater stiffness was associated with more severe symptoms, suggesting that IFP stiffness may serve as both an assessment marker and therapeutic target in knee OA management.