Biomechanics and Motion Analysis

Validated Subject-Specific Model of Knee Joint Contact Force Distribution

Principal Investigator: Kenton R. Kaufman, Ph.D.

Biomechanical analysis of joints can be an important indicator of joint health. Improper loading may cause degenerative changes. Few models exist to predict articular surface loads during dynamic activities. Therefore, the purpose of this study was to develop a analytical model which predicts the tibial plateau load distribution based on an individual's joint geometry and dynamic loading pattern.

The tibiofemoral joint was modeled as two rigid bodies with spring elements representing the articular cartilage and collateral ligaments. The model used subject-specific joint geometry and loads for predicting joint contact pressure distribution. Joint geometry was obtained from fluoroscopy-guided, weight-bearing radiographs analyzed with a Canny edge detection algorithm (Mathworks, Natick, MA). The spring elements were assumed to have linear deformation and the model initially assumed that the cartilage to be loaded in compression and ligaments in tension.

After the model was loaded, elements that experience an incorrect load was subtracted from the stiffness matrix and displacements recalculated until equilibrium was reached. The joint space was modeled with 46 cartilage springs having a compressive modulus of 15Mpa in the normal direction and 2.6MPa in the shear direction. The medial and lateral collateral ligaments were each modeled as individual springs with stiffness of 1290N/mm in the normal and shear direction. The model was then validated using data from a cadaver knee.