Relation between changes in knee flexion angle and patellar tendon-tibial angle:

prediction of infrapatellar fat pad’s movement by ultrasonography

Abstract

Purpose: It has been reported that the range of movement of the infrapatellar fat pad (IFP) is reflected by the measurement of the patellar tendon-anterior tibial angle (PTTA). In this study, we examined the reliability and reproducibility of the measurement of PTTA using ultrasonography in healthy subjects.

Method: PTTA was measured bilaterally using ultrasonography of the knee flexion angle at 0 degree, 45 degree, and 90 degree in 25 healthy subjects (50 knees). The probe was placed on the anterior knee and the angle between the patellar tendon and the anterior tibia was measured at each flexion angle. The difference in PTTA at each knee flexion angle was compared. Intra-rater reliability also was evaluated.

Result: PTTA was significantly different among all knee flexion angles (p < 0.001). The PTTA decreased as knee flexion increased. The intra-rater reliability evaluated by the ICC (1.3) was 0.97–0.98 for all PTTAs, indicating good reproducibility.

Conclusion: The evaluation by PTTA is highly reproducible. Therefore, the amount of IFP movement can be measured based on the PTTA measurement using ultrasonography.