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Applied Bionics and Biomechanics
Volume 5, Issue 2, Pages 59-63

In vivo Evaluation of Patellar Tendon Stiffness in Individuals with Patellofemoral Pain Syndrome

Hsin-Yi Liu,1,2,3 Michelle Boling,2 Darin Padua,2 R. Alexander Creighton,1 and Paul Weinhold1,2

1Department of Orthopaedics, University of North Carolina, Chapel Hill, NC 27599, USA
2Sports Medicine Laboratory, University of North Carolina, Chapel Hill, NC 27599, USA
3Department of Physical Education and Recreation, North Carolina Central University, Durham, NC27707, USA

Received 29 October 2008

Copyright © 2008 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The objective of this study was to utilise an ultrasonic technique to assess the effect of patellofemoral pain syndrome (PFPS) on the mechanical properties of the patellar tendon. Seven subjects with PFPS and seven matched control subjects volunteered to participate in this study. Subjects were asked to perform isometric maximal voluntary contractions of the knee extensors while their knee extension torque was monitored and the displacement of the patellar tendon was recorded with an ultrasonic system. Our results showed significantly lower tendon stiffness (by ∼30%) in the PFPS subjects. Although tendon secant modulus was lower by 34% in the PFPS subjects, the difference was not statistically significant. Therefore, we conclude that the ultrasonic technique was able to detect a decrease in the structural stiffness of the patellar tendon associated with PFPS. The decrease in tendon stiffness was moderately correlated with the length of symptoms in these individuals.