Background: Patellar tendon moment arm length changes at different knee flexion angles have not been determined in in vivo studies.We aimed to determine patellar tendon moment arm lengths in four different knee angles using Magnetic Resonance Imaging (MRI) to predict in vivo changes in the moment arm length from different knee angles during running.
Methods: The moment-arm length of patellar tendon was measured as the perpendicular distance from muscle–tendon line of action to the knee joint axis of rotation at 0 (full extension), 20, 40 and 60 degrees flexion of knee by using MRI method. A repeated measure ANOVA method was applied to compare the moment arms length among four degrees of knee flexion (p<0.05). A regression analysis was used to predict the patellar tendon moment arm’s length during different knee joint angles.
Results: Mean and standard deviation of patellar tendon moment arm lengths in the four angles at 0, 20, 40 and 60 degrees of knee flexion were observed 42.55±4.20, 39.91±2.98, 37.73±2.87 and 36.18±2.90 mm, respectively (p<0.05). A regression analysis provided an equation to predict the patellar tendon moment arm’s length from different knee joint angles during running.
Conclusion: patellar tendon moment arm lengths values decreased from knee extension to flexion in a linear manner. These findings have important implications for estimating patellar tendon moment arm lengths using a regression equation model from different knee joint angles.