In silico multibody analysis of a hinged total knee replacement under different daily loading conditions

Total knee replacements (TKRs) represent the gold standard for treating knee osteoarthritis. Nowadays, a variety of TKR designs are available on the market, differing mainly in geometrical features, degrees of freedom (DoFs) allowed to the implanted knee, and degree of tissue resection in order to adapt to various patient needs. Despite the significant evolution of this type of implant over the last 50 years, especially specific prosthesis designs still exhibit mechanical and structural limitations. Among the hinged total knee prostheses, generally characterized by one or three DoFs, the PANTHEON prosthesis (Adler Ortho SpA) features a particular design allowing for two DoFs. This prosthesis is indicated for revision surgery, due to infection, fracture, or failed TKR causing severe bone loss, but also in primary surgery for clinical cases involving major bone defects in the proximity of the knee joint, such as bone tumors. In the past, this specific design has reported a structural failure of the hinge element during higher-than-normal load cases, namely, higher body weight and/or critical motion tasks. In this context, this thesis was conceived to elucidate the biomechanical reasons behind the observed failure by analyzing the loads acting in the hinge element of the prosthesis, as a function of the body weight (BW) and daily activity performed. Using the geometry of the prosthesis components (femoral and tibial components), a multibody computational model was created in the Adams View software, with kinematics constraints, contact pairs, and BW-dependent loading conditions properly defined. A series of simulations were then carried out by varying both BW and motion tasks. Specifically, three explanatory BWs were chosen ("low weight" of 50 kg, "medium-high weight" of 100 kg, and "high weight" of 200 kg) together with four different daily living activities: walking, stair ascent, stair descent, and sit-to-stand-to-sit motion. The applied boundary conditions, i.e., kinematics and loads, were defined according to ASTM Standard F3141-23. Finally, the relative displacements with respect to the tibia and the reaction forces experienced by the hinge element of the prosthesis during all simulated activities were computed and compared. In accordance with the allowed DoFs, results revealed negligible hinge displacements along the transverse plane, regardless of the considered BWs. Conversely, as expected, the reaction forces at the hinge appeared to be strongly dependent on the applied BW. Indeed, higher BWs led to higher resulting forces at the hinge. Overall, walking was the demanding activity in terms of observed force magnitude at the hinge element. However, looking at the anterior-posterior direction, the highest reaction force was observed during the stair descent activity. In conclusion, the conducted analysis of the PANTHEON total knee prosthesis, based on an international standard for the biomechanical assessment of knee prostheses, has yielded valuable insights into its response to reaction forces related to BWs and daily activities. Additionally, the implemented model can be easily generalized, constituting an in silico framework for the performance evaluation of different prosthesis designs. The presented findings offer a clear perspective for enhancing the prosthesis design and provide significant indications regarding the suitable patient population with respect to BW and lifestyle.