Computational analisys of the Anterior Cruciate Ligament when climbing a step

Resumo

The human body is a complex mechanic structure and the knee joint (KJ) is one of the most complex and
demanded joint due to it has to carry very high loads and his structure must to enable triaxial movements without
lose both, the stability and the control motor. In addition, the Anterior Cruciate Ligament (LCA) deficiency is
one of the most common injuries of the KJ and affect about one of 3000 people in US every year. Moreover, a
LCA deficiency commonly leads to more than one causes that produces articular surfaces damage or osteoarthritis.
Many studies about the KJ had been carried out in both in-vivo and in-vitro and it showed a high variability by
both person and age.
The aim of this work is to take a first step towards developing a procedure to quantify the subject specific
LCA health with a non-invasive technique. This procedure is based on two steps, the motion capture and then the
numeric simulation with the finite element method. For the motion capture we designed an experiment of climbing
a step, to record the movements of the KJ with stereophotogrammetry using the well-known protocol Plug-in Gait
developed by Vicon Motions Systems. We record the trajectories of the markers placed over the skin of the patient

lower limb and extracted the curves of the knee kinematics. This data was transform to extract both, the flexion-
extension an internal-external rotation curves, to use as boundary condition for the finite element model of the

patient’s tibiofemoral joint.
On the second part, we developed a 3D finite element model of the KJ starting from the model released by
the OpenKnee project to run on FEBio. With this model we analyze the resulting joint kinematics and its changes
when using, another constitutive models for the ligaments or different the mesh densities for de ACL. Moreover,
we determine the kinematics of the LCA and the stress and strain distribution on this complex structure when
climbing a step. The obtained results were compared against available data from literature and showed a good
agreement. Furthermore, this procedure enable to work on the study of specific mechanic properties of soft tissues
for each patient with this protocol as starting point in order to obtain more reliable results.