Title: In-vivo detection of patellar tendon creep using a fibre-optic sensor

Authors: J.H. Muller, Cornie Scheffer, Alex Elvin

Addresses: Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa. ' Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa. ' Department of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg, South Africa

Abstract: Tendon creep causes an increase in longitudinal and negative transverse strain (Poisson effect), resulting in a pressure increase on an implanted optic fibre. An optic fibre was inserted through a volunteer|s right patellar tendon, after hysteresis and measurement sensitivity were characterised. The volunteer performed three isokinetic knee-extensions and one isometric knee-extension on a dynamometer. In-vivo calibrations of quadriceps torque versus sensor output were obtained and used to predict the torque delivered during the isometric exercise. Optic fibre hysteresis induced an 18% full-scale root mean square error, and in-vivo calibrations were less dependent on loading rate than in-vitro calibrations. Dynamometer isometric torque readings decreased by 3.7% over 180 seconds while sensor predictions indicated a 5.9% rise. This rise can be ascribed to the increase in transverse strain (resulting from creep). The fibre-optic sensor was influenced by tendon creep. Knowledge of tendons| time dependent behaviour are essential in medical engineering modelling studies.

Keywords: fibre optic sensors; patellar tendon; tendon creep; transverse strain; Poisson effect; isokinetic dynamometer; medical engineering; knee extensions; optic fibre hysteresis; modelling.

DOI: 10.1504/IJMEI.2008.020747

International Journal of Medical Engineering and Informatics, 2008 Vol.1 No.2, pp.155 - 173

Published online: 13 Oct 2008 *

Full-text access for editors Full-text access for subscribers Purchase this article Comment on this article