Relationship between the deep flexion of the knee joint and the dynamics of the infrapatellar fat pad after anterior cruciate ligament reconstruction via ultrasonography

[Purpose] A sufficient flexion angle of the knee joint after knee surgery leads to higher quality of their life; therefore, here we investigated the relationship between the dynamics of the infrapatellar fat pad and seiza-style sitting via ultrasonography. [Participants and Methods] Twenty-eight patients were enrolled 3 months post-operatively after anterior cruciate reconstruction. They were divided into a “possible” group and “impossible” group, according to whether they could sit in the seiza style. The thickness of the superficial part of the infrapatellar fat pad was measured at 10° and 90° knee flexion on reconstructed knees in the sitting position via ultrasound evaluation. Images were taken to capture the patella apex and tibial tuberosity. The thickness of the superficial part of the infrapatellar fat pad was measured, and the thickness change ratio was calculated. The characteristics of each group were compared. [Results] The superficial part of the infrapatellar fat pad was significantly thinner in the possible group at a 10° knee flexion. The thickness change ratio of the infrapatellar fat pad was significantly greater in the possible group. [Conclusion] The thickness of the infrapatellar fat pad at a 10° knee flexion and the thickness change ratio of the infrapatellar fat pad could affect the possibility of sitting in the seiza style.