Modeling of the knee joint load in rehabilitative knee extension exercises under water

Authors: Biscarini A (1,2) , Cerulli G (3,4)
(1) Department of Physics, University of Perugia (2) LAMS Laboratory, University of Perugia (3) Department of Orthopedic Surgery, University Hospital of Perugia (4) Let People Move Biomechanics Laboratory
Source: J Biomech. 2007;40(2):345-55
DOI: 10.1016/j.jbiomech.2005.12.018 Publication date: 2007 E-Publication date: Feb. 20, 2006 Availability: abstract Copyright: © 2006 Elsevier Ltd. Published by Elsevier Inc. All rights reserved.
Language: English Countries: Not specified Location: Not specified Correspondence address: A. Biscarini : Department of Physics, University of Perugia, Via Pascoli, 06100 Perugia, Italy. Tel.: +390755852703; fax: +3907544666. Email :


Article abstract

A biomechanical and hydrodynamic theoretical model has been developed in order to calculate the knee joint load during underwater knee extension exercises. The hydrodynamic force has been evaluated within the framework of a strip-theory approach, when a blunt rectangular resistive device is applied proximally to the shank to increase its frontal area. Analytical expressions of the patellar tendon force (F(PT)), the axial (phi(n)) and the shear (phi(t)) component of the tibiofemoral joint load have been derived as a function of joint angle (theta), angular velocity (theta ), angular acceleration (theta ), resistive device density, length (L(x)), width (L(z)) and thickness, and average hydrodynamic drag and added mass coefficients. An inverse dynamic problem has been solved, assuming for theta and theta a dependence on theta consistent with the experimental kinematic data available in the literature. The results highlight that the characteristics of the resistive device and the level of muscular activation can be adjusted reciprocally in order to control the peak value of F(PT), phi(n) and phi(t), and the position of these peaks within the joint range of motion (ROM). No anterior cruciate ligament (ACL) stress is observed (phi(t)>0) over the whole ROM, independent of the level of muscular activation, for a light resistive device with L(x) < or = 0.3 m and L(z) < or = 0.4 m. This work highlights that aquatic exercises can be usefully and safely implemented in the rehabilitation program following ACL surgery, and whenever it is important to avoid excessive shear joint forces that constrain the tibial plateau anterior translation with respect to the femur.

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