Computationally efficient model of the implanted knee for time-sensitive applications

Objectives To design and analyze orthopaedic devices, finite element (FE) models represent a cost-effective alternative to in vitro experiments. The main problem of such simulations is their extremely long time required to reach a solution; this limitation make this approach not compatible with time-sensitive applications, such as real-time surgery-planning or intra-operative setting. On the contrary, Multibody (MB) simulations are faster than FE simulations, as they consider each component rigid and not deformable. Therefore, the goal of this study was to demonstrate the equivalence in terms of kinematic, contact force, and ligament strain results between a FE and a MB model of the knee under the same boundary conditions.

Methods The numerical model of the knee, both for the FE and for the MB analysis, consisted of femoral, tibial and patellar bone, obtained from CT scan of a cadaveric specimen. A cruciate retaining total knee replacement was used as TKA. After the calibration of the MB model (see [Figure 1]), a deep squat up to 120° of flexion was simulated in both models, similarly to what done in previous experimental activities,. Tibiofemoral (TF) and patellofemoral (PF) kinematics (in terms of anteroposterior translation, flexion-extension and internal-external rotation),together with contact forces on tibial plateaus and ligament strains, were obtained as output from both models and compared.

Figure 1

Results and Conclusion Computational time required by the FE and rigid body simulations was respectively 155 and 2 minutes. Pearson correlations between FE and MB simulations outcomes resulted to be above 0.93, thus these high correlation coefficients demonstrate a good agreement between the two methods for the knee squat simulation. The comparison between computational times indicate that 77 rigid MB simulations can be completed in the same time of one FE simulation. A fast simulation that is able to accurately estimate joint kinematics, contact interactions and ligament strain could represent a great tool to provide support in decision making process before or even during surgery.

Stichwörter Simulations, TKA, surgical pre-planning

Publication History

Article published online:
15 October 2020