B. Moyen¹, J.P Picon¹, J. Dimnet¹

1 Laboratory of Motion Biomechanics, University of Lyon I

The laboratory of Motion Biomechanics is specialized in the identification of the kinematics and dynamics of in vivo joints from the trajectories of external markers and the treatments of force signals (1)(2)(3). The goal of this paper is to present coupled information relative to the synchronized kinematics and dynamics of the loaded knee joint during the stance phase of gait. Normal joints were compared with knees with anterior cruciate ligament deficiency.

In vivo knees were studied. Reflective markers were placed next to the knee joint and observed during motion through the use of an optoelectronic system (six cameras, 180 Hz). External forces were recorded using an AMTI force platform. The knee axis is represented by a straight line connecting the markers placed on the lateral and medial epicondyles. During motion the knee axis moves with respect to the tibia, assumed to be fixed. The set of knee axes is included in a plane. This plane is roughly parallel to the tibial plateau. A local anatomical tibial frame is based upon this plane. The kinematic and dynamic results describing the knee behaviour during the stance phase of gait are related to this anatomical tibial frame. There are both angles and moment components of flexion, abduction and axial rotation. Angles were expressed in degrees, while moment components were related to the product height x weight of the studied subjects. Curves were drawn. They describe the changes in both kinematic and dynamic values with respect to the percentage of stance phase duration.

In the same subject, the results are very reproducible. In a series of normal subjects, the curves show comparable patterns. Patients with ACL deficiency have significant differences in the pattern of kinematic and dynamic curves when compared with the series of normal subjects. Corresponding results are presented and discussed. For each degree of freedom (flexion, abduction and axial rotation) related to the anatomical tibial frame and for each instant of time, the dynamic and kinematic gradients dM and df were calculated. The corresponding ratios dM/df were subsequently obtained. They made it possible to obtain the matrix of stiffness of in vivo knee joints under certain conditions. The results are presented and discussed.

Each subject was submitted to ten different tests. The mean curves and corresponding dispersions (± 1 SD) were drawn. The results were not greatly altered when the subject was asked to undergo twenty separate different tests. Knees with ACL deficiency show significant differences in comparison with normal knees. The results must be extended to a larger sample of subjects and to other knee pathologies.

This paper presents clinical applications of biomechanical studies. They were carried out in strong collaboration with orthopaedic surgeons. Other studies are in progress.

1. DIMNET J. et al.., J. of Biomech, 17, 387-394, 1984. 2. CHEZE L.,et al., J. of Biomechanics, 28, 879-884, 1995. 3. JIED A.,et al. Proc. of 4^th ISAHM, 1996.

Bernard MOYEN

Laboratoire de Biomécanique du Mouvement, Groupe de Biomécanique Clinique, Centre Hospitalier Lyon Sud – Bât 3A, Service de Chirurgie Orthopédique, 165 chemin du Grand Revoyet, 69495 PIERRE BENITE CEDEX

Tel : 04 78 86 14 31, Fax : 04 78 86 59 34, Email : eric@mecaflu.univ-lyon1.fr