Ultrasonographic Evaluation of Morphological Changes in the Infrapatellar Fat Pad During Knee Extension

Abstract

Purpose: To investigate morphological changes in the infrapatellar fat pad (IPFP) during active knee extension using ultrasonography. Methods: IPFP deformity from 30∘ knee flexion to full extension was recorded using ultrasonography. IPFP thickness and patellar tendon-tibial angle were evaluated on 26 healthy knees in the first session and nine knees in the second session. Intra-rater and inter-rate reliability were evaluated using coefficient of variation (CV) and intraclass correlation coefficient (ICC) of types (1, 3) and (2, 3), respectively. Absolute reliability was assessed using the standard error of measurement (SEM). Changes in the patellar tendon-tibial angle and IPFP thickness were analyzed using paired [Formula: see text]-test. Results: At each knee angle, ICC (1, 3) was [Formula: see text] for the patellar tendon-tibial angle and IPFP thickness (CV [Formula: see text]). Compared to 30∘ knee flexion, the patellar tendon-tibial angle increased significantly from 33.3∘ to 38.9∘ ([Formula: see text]). The IPFP thickness significantly increased from 4.4[Formula: see text]mm to 5.3[Formula: see text]mm with active knee extension ([Formula: see text]), without overlap of the 95% CI of SEM. For inter-rater reliability, ICC (2, 3) was [Formula: see text] for each variable (CV [Formula: see text]). Conclusions: Increased IPFP thickness during active knee extension indicates IPFP deformity in the anterior interval. Ultrasonography may help evaluate morphological changes and estimate IPFP scarring.