Specimen-Specific Finite Element Analysis to Study Cruciate Ligament Mechanics

Katherine Stemmer, Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, The Ohio State University

Ahmet Erdemir, Computational Biomodeling (CoBi) Core and Department of Biomedical Engineering,Lerner Research Institute, Cleveland Clinic

-

Connecting the tibial and femoral bones in the lower limb are the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). These ligaments prevent the bones from sliding anteriorly and posteriorly relative to each other, therefore providing mechanical stabilization of the joint. Knowing the mechanical function of the ACL and PCL helps researchers and clinicians develop surgical devices and procedures to repair torn cruciate ligaments. Additionally, understanding these ligaments helps therapists create more effective exercises for patients with knee injuries to restore healthy mechanical function of the knee. The purpose of this project is to create a specimen-specific finite element representation of the cruciate complex of the knee joint in order to study the mechanics of the ACL and PCL under prescribed tibiofemoral joint movements. By creating a computer model, users may discover the stresses, strains, and displacements of the cruciate ligaments under varying conditions which may not be acquired in vivo or in vitro. In a clinical setting, this will allow surgeons to learn the specific mechanical behavior of these ligaments in the patient rather than gross measurements of joint function. This knowledge will be particularly beneficial during ACL reconstruction when the surgeon must decide which muscle tendon to use as a graft, the appropriate thickness of the graft, and placement of the graft. The specific components of the knee joint analyzed for the model were the ACL, PCL, femur, and tibia. Starting with magnetic resonance images1 in the axial, sagittal, and coronal planes of the knee joint obtained from CoBiCore2 at the Cleveland Clinic Lerner Research Institute, the components were manually segmented using the open source software program, Slicer 3D3, to apply color labels to the different tissues in the magnetic resonance images. Moreover, volumes were generated using the model maker option in Slicer 3D3. Next, geometries were reconstructed using the open source program Meshlab4 by smoothing and remeshing the surface models. Finally, using the open source program Salome5, three-dimensional volume meshes of different densities were created in order to allow finding the optimal mesh density which balances between accuracy and speed of computation. The mechanical properties of the different tissues will then be applied to the meshes to complete the model development. Simulations prescribing knee joint movements, which are collected experimentally, will predict deformations, stresses, and forces within cruciate ligaments under varying motions of the human knee.

1Chokhandre, S., Bennetts, C., Halloran, J., Colbrunn, R., Bonner, T., Jones, M. H., & Erdemir, A.

(n.d.). Comprehensive identification of tibiofemoral joint anatomy and mechanical response:

Pathway to multiscale characterization. In ASME 2012 Summer Bioengineering Conference (pp.

1089-1090). http://dx.doi.org/10.1115/SBC2012-80200

2CoBiCore at the Cleveland Clinic Lerner Research Institute http://cobicore.lerner.ccf.org/

3Slicer 3D open source software http://www.slicer.org/

4Meshlab open source software http://meshlab.sourceforge.net/

5Salome open source software www.salome-platform.org