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

Document Type : TECHNICAL NOTE


1 1 Faculty of Sports sciences, University of Mazandaran, Babolsar, Iran- 3 Mobility Impairment Research Center, Babol University of Medical Sciences, Iran

2 Department of Physical Education, Payame Noor University, Tehran, Iran

3 Mobility Impairment Research Center, Babol University of Medical Sciences, Iran

4 Clinical Research Department, Shahid Beheshti Hospital, Babol University of Medical Sciences, Babol, Iran


Patellar tendon moment arm length (PTma) changes at different knee flexion angles have not been determined in in
vivo studies. We aimed to determine PTma 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.
PTma 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° flexion of knee by using MRI method. Repeated measure ANOVA method was
applied to compare the moment arm length among four degrees of knee flexion (p <0.05). A regression analysis was
used to predict the PTma during different knee joint angles.
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
36.18±2.90 mm, respectively (p <0.05). The regression analysis provided an equation to predict the PTma from different
knee joint angles during running.
PTma values decreased from knee extension to flexion in a linear manner. These findings have important implications
for estimating PTma using a regression equation model from different knee joint angles.
Level of evidence: V


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Pages 641-645
  • Receive Date: 24 August 2019
  • Revise Date: 14 December 2019
  • Accept Date: 09 February 2020
  • First Publish Date: 01 September 2020