Changes of the Patellar Tendon Moment Arm Length in Different Knee Angles: A Biomechanical in Vivo Study

Abstract

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