Dynamic feature of infrapatellar fat pad during walking in patients with knee osteoarthritis

The infrapatellar fat pad (IFP) absorbs mechanical stress in the knee joint owing to flexible morphological changes. The IFP is a key factor in knee osteoarthritis (OA); however, its dynamic feature during walking remains unknown. This study aimed to investigate whether the morphological changes in the IFP during walking involve specific features for patients with knee OA.

Twelve patients with knee OA, 12 healthy young volunteers, and 12 healthy elderly volunteers were recruited. The IFP was evaluated using ultrasonography, and dynamics were recorded in video mode during walking. The IFP value was identified as the thickness between the patellar tendon and proximal tibial line. The morphological change in the IFP (ΔIFP) was shown as the difference in IFP value between maximum and at initial contact on the waveform. Kinematics and kinetics data were evaluated using a three-dimensional motion analysis system synchronized with ultrasonography, and the knee flexion angle and its moment in the stance phase were evaluated.

In the patients with knee OA, the ΔIFP was lower than that in healthy volunteers, but there was no difference between control groups (knee OA: 1.4 ± 0.3 mm, elderly control: 1.8 ± 0.2 mm, young control: 2.1 ± 0.5 mm, p < 0.05). In all the groups, there was no significant correlation between the IFP values and kinetic parameters, including the range of knee flexion angles and gait speed.

Insufficient morphological changes in the IFP during walking could be a feature of knee OA.