###### Abstract  
Just like menisci, articular cartilage is exposed to constant and varying stresses. Injuries to the meniscus are associated with the development of gonarthritis. Both the articular cartilage and the menisci are subject to structural changes under gonarthritis. The aim of this study was to investigate biomechanical alterations in articular cartilage and the menisci under gonarthritis by applying an indentation method. The study assessed 11 menisci from body donors as controls and 21 menisci from patients with severe gonarthritis. For the simultaneous examination of the articular cartilage and the menisci, we only tested the joint surfaces of the tibial plateau covered by the corresponding menisci. Over the posterior horn of the meniscus, the maximum applied load--the highest load registered by the load cell--of the arthritic samples of \(0.02\pm 0.02\) N was significantly greater (\(p=0.04\)) than the maximum applied load of the arthritis-free samples of \(0.01\pm 0.01\) N. The instantaneous modulus (IM) at the center of the arthritic cartilage covered by the meniscus with \(3.5\pm 2.02\) MPa was significantly smaller than the IM of the arthritis-free samples with \(5.17\pm 1.88\) MPa (\(p=0.04\)). No significant difference was found in the thickness of the meniscus-covered articular cartilage between the arthritic and arthritis-free samples. Significant correlations between the articular cartilage and the corresponding menisci were not observed at any point. In this study, the biomechanical changes associated with gonarthritis affected the posterior horn of the meniscus and the mid region of the meniscus-covered articular cartilage. The assessment of cartilage thickness as a structural characteristic of osteoarthritis may be misleading with regard to the interpretation of articular cartilage's biomechanical properties. Keywords:gonarthritis; meniscus; articular cartilage; biomechanical testing; mapping; indentation; instantaneous modulus; tissue biomechanics +
Footnote †: journal: Applied Soft  
Degenerative changes are manifested in a softening and continuous thinning of the joint cartilage, potentially leading to the complete loss of cartilage [4]. The meniscus improves weight distribution in the knee joint by increasing the contact surface between the femoral condyles and the tibial plateau [5], serving as shock absorption [5; 6] and protecting the joint cartilage beneath it [7]. Consequently, meniscus displacement or meniscus extrusion is a strong predictive factor for the loss of cartilage tissue, indicating that the biomechanical properties of the meniscus have failed [8; 9]. This results in the current approaches that aim to preserve as much meniscus tissue as possible [10]. There exist a variety of forms of meniscus replacement, such as autogenous replacement, but also artificial implants. However, in contrast to articular cartilage replacement [11], a widely applicable meniscus replacement with clear scientifically proven efficacy is not yet available [12]. Given this gap in research, a deeper understanding of the biomechanical behavior of meniscus and cartilage tissue appears vital. Thus far, for both menisci and joint cartilage, animal samples have predominantly been studied [13; 14; 15; 16; 17; 18]. Previous biomechanical examination of the articular cartilage, as well as for the meniscus, included both unconfined compression tests [19; 20; 16] and confined compression tests [21; 22]. However, a complete mapping of the biomechanical properties of the tissue with a large number of measurement points was only possible to a limited extent [23; 24], with exception of [PERSON] et al. [25], who examined the articular cartilage with a complete mapping of biomechanical properties. This was possible by using an indentation test. The main objective of the indentation test is to determine the instantaneous modulus (IM) and hardness of a sample. IM thus describes the ability of an elastic material to resist deformation under applied mechanical stress. The work from [PERSON] et al.