Evaluation of the mechanical response of osteoarthritic articular cartilage by indentation tests [English translation]

In the context of various health conditions affecting the global population, musculoskeletal disorders hold significant importance. Extensive research in the literature has revealed that these disorders are among the most prevalent in Europe.
This thesis focuses on human knee osteoarthritis (OA), which alone affects 7% of the global population. Due to its high frequency and degenerative nature, its impact cannot be overlooked, both in terms of the population's quality of life and its socio-economic implications. Additionally, the limited literature available, although few studies are specifically conducted on human knee OA, suggests that this condition predominantly affects the elderly population, particularly females.
Microstructural and biochemical changes in joint cartilage tissues, in the presence of a degenerative disease like OA, influence their mechanical behavior. Any alteration in mechanical properties leads to a change in the functional characteristics of the tissue, affecting the surrounding tissues.
While there are studies in the literature that have examined how the mechanical properties of articular cartilage change in the presence of degenerative diseases like OA, these studies often rely on animal models due to the difficulty in obtaining human samples, or the tests conducted are limited.
Therefore, the objective of this thesis is to evaluate and quantify how the mechanical and morphological properties of OA-affected cartilage change. Indentation tests were performed, mapping six human tibial plates from individuals with different genders and ages who have osteoarthritis. After creating a point map on the tibial plates, an innovative automated procedure was used to evaluate the instantaneous elastic modulus and cartilage thickness through two experimental tests: normal indentation at the surface and needle penetration.
The indentation tests were conducted using the Mach-1TM Biomomentum at the Laboratory of Biological Tissue Mechanics at the University of Padua. The experimental values provide a method for assessing the mechanical properties of cartilage, offering an opportunity to understand how this tissue behaves in response to variations in parameters, such as the severity of osteoarthritic pathology, the specific region of the tibial plate involved, and the body mass index (BMI).
From the analysis of the results, it was found that the mean instantaneous elastic modulus is 2.55 ± 2.56 MPa. Additionally, the lateral region exhibited greater rigidity with an instantaneous elastic modulus value of 2.76 ± 2.54 MPa compared to the medial region, which had a value of 2.15 ± 2.55 MPa. The thickness was also greater in the lateral region, with an average value of 1.73 ± 0.74 mm.
Two main conclusions emerged when examining factors influencing the behavior of the elastic modulus and cartilage thickness. Firstly, it was observed that the degree of osteoarthritic pathology has a greater impact on the loss of cartilage tissue rigidity. Secondly, the body mass index (BMI) affects the thickness of articular cartilage. Specifically, an increase in the severity of OA results in decreased cartilage tissue rigidity, while the presence of an overweight BMI leads to a reduction in articular cartilage thickness.