Mechanical characterization of knee articular cartilage: indentation tests on healthy and osteoarthritic subjects [English translation]

Introduction There are many studies on osteoarthritis, but only a few studies focus on human osteoarthritis of the knee, comparing the mechanical properties of healthy and pathological specimens. Furthermore, in most cases only isolated areas of the tibia are investigated. The aim of this study is to evaluate and quantify how the morphological and mechanical properties of cartilage change as a result of a degenerative pathology such as OA, through the complete mapping of tibial plateaus by indentation tests and evaluation of the thickness of the cartilage. Case study Five tibial plateaus and respective condyles (grade 3 and 4 of osteoarthritis) and one healthy control were analysed. The biomechanical characterization of the cartilage tissue was carried out through an innovative automated procedure which, through a map of xy points previously created to define the measurement points, allowed to evaluate the spatial distribution of the instantaneous elastic modulus and the thickness of the cartilage by two experimental tests: normal indentation and needle penetration. Modeling Obtained the experimental values from the analysis of the instantaneous elastic modulus (IM, mechanical property of the material) and of the thickness of the cartilage, we wanted to reproduce a 3D model of the healthy tibial plateau with photogrammetry techniques in order to simulate the experimental indentation test. The patient-specific model was created using Zephyr 3DF photogrammetric software and Abaqus Explicit 2018. Results A significant difference (p < 0.05) was observed in the measured IM of the tibial plateaus between the control with 3.95 ± 2.66 MPa and the samples with 3.22 ± 2.49 MPa. In addition, there is also a significant difference in the measured thickness between the control with 3.05 ± 0.89 MPa and the samples with 2.32 ± 0.98 MPa. An interesting result is the mapping of the mechanical properties that reveals the spatial variation of thickness and elastic modulus for both tibial plateaus and condyles. Conclusions The obtained experimental values allowed to quantify the mechanical properties of the tibial plateaus and condyles, highlighting properties that are not uniform, but variable from point to point. These results not only provide a method of evaluating cartilage properties, a better understanding of tissue behavior and the pathology, but also provide information for the development of more accurate predictive 3D cartilage models and/or surgical evaluation models in the future. The biomechanical characterization could lead to more efficient and less invasive diagnostic and treatment strategies than the replacement of the entire joint.